Interacting Agegraphic Dark Energy
Wei, Hao; Cai, Rong-Gen
2007-01-01
A new dark energy model, named "agegraphic dark energy", has been proposed recently, based on the so-called K\\'{a}rolyh\\'{a}zy uncertainty relation, which arises from quantum mechanics together with general relativity. In this note, we extend the original agegraphic dark energy model by including the interaction between agegraphic dark energy and pressureless (dark) matter. In the interacting agegraphic dark energy model, there are many interesting features different from the original agegrap...
Cosmological constraints on Agegraphic dark energy in DGP braneworld gravity
Farajollahi, H; Fadakar, G F
2016-01-01
A proposal to study the original and new agegraphic dark energy in DGP braneworld cosmology is presented in this work. To verify our model with the observational data, the model is constrained by a variety of independent measurements such as Hubble parameter, cosmic microwave background anisotropies, and baryon acoustic oscillation peaks. The best fitting procedure shows the effectiveness of agegraphic parameter $n$ in distinguishing between the original and new agegraphic dark energy scenarios and subsequent cosmological findings. In particular, the result shows that in both scenarios, our universe enters an agegraphic dark energy dominated phase.
Cosmological constraints on Agegraphic dark energy in DGP braneworld gravity
Farajollahi, H.; Ravanpak, A.; Fadakar, G. F.
2016-01-01
A proposal to study the original and new agegraphic dark energy in DGP braneworld cosmology is presented in this work. To verify our model with the observational data, the model is constrained by a variety of independent measurements such as Hubble parameter, cosmic microwave background anisotropies, and baryon acoustic oscillation peaks. The best fitting procedure shows the effectiveness of agegraphic parameter $n$ in distinguishing between the original and new agegraphic dark energy scenari...
Agegraphic dark energy: growth index and cosmological implications
Malekjani, M; Davari, Z; Mehrabi, A; Rezaei, M
2016-01-01
We study the main cosmological properties of the agegraphic dark energy model at the expansion and perturbation levels. Initially, using the latest cosmological data we implement a joint likelihood analysis in order to constrain the cosmological parameters. Then we test the performance of the agegraphic dark energy model at the perturbation level and we define its difference from the usual $\\Lambda$CDM model. Within this context, we verify that the growth index of matter fluctuations depends on the choice of the considered agegraphic dark energy (homogeneous or clustered). In particular, assuming a homogeneous agegraphic dark energy we find, for the first time, that the asymptotic value of the growth index is $\\gamma \\approx 5/9$, which is close to that of the usual $\\Lambda$ cosmology, $\\gamma^{(\\Lambda)} \\approx 6/11$. Finally, if the distribution of dark energy is clustered then we obtain $\\gamma \\approx 1/2$ which is $\\sim 8\\%$ smaller than that of the $\\Lambda$CDM model.
Evolution of spherical overdensities in new agegraphic dark energy model
Setare, M R; Darabi, F
2016-01-01
We study the structure formation by investigating the spherical collapse model in the context of new agegraphic dark energy model in flat FRW cosmology. We compute the perturbational quantities $g(a)$, $\\delta_{c}(z_{c})$, $\\lambda(z_{c})$, $\\xi(z_{c})$, $\\Delta_{vir}(z_{c})$, $\\log[\
On initial condition of the new agegraphic dark energy model
Li, Yun-He; Zhang, Xin
2012-01-01
The initial condition $\\Omega_{\\rm de}(z_{\\rm ini})=n^2(1+z_{\\rm ini})^{-2}/4$ at $z_{\\rm ini}=2000$ widely used to solve the differential equation of $\\Omega_{\\rm de}$, the density of the new agegraphic dark energy (NADE), makes the NADE model be a single-parameter dark-energy cosmological model. However, this initial condition, we find, is only applicable in a flat universe with only dark energy and pressureless matter. In fact, in order to obtain more information from current observational data, such as cosmic microwave background (CMB) and baryon acoustic oscillations (BAO), it often needs us to consider the contribution of radiation. For this situation, the initial condition mentioned above becomes invalid. To overcome this shortage, we deeply investigate the evolution of NADE in the matter-dominated and radiation-dominated epochs, and obtain a new initial condition $\\Omega_{\\rm de}(z_{\\rm ini}) = \\frac{n^2(1+z_{\\rm ini})^{-2}}{4} (1+\\sqrt{F(z_{\\rm ini})})^2$ at $z_{\\rm ini}=2000$. Here $F(z)\\equiv\\frac{...
New initial condition of the new agegraphic dark energy model
Institute of Scientific and Technical Information of China (English)
Li Yun-He; Zhang Jing-Fei; Zhang Xin
2013-01-01
The initial condition Ωde (zini) =n2(1 + Zini)-2/4 at Zini =2000,widely used to solve the differential equation of the density of the new agegraphic dark energy (NADE) Ωde,makes the NADE model a single-parameter dark-energy cosmological model.However,we find that this initial condition is only applicable in a fiat universe with only dark energy and pressureless matter.In fact,in order to obtain more information from current observational data,such as the cosmic microwave background (CMB) and the baryon acoustic oscillations (BAO),we need to consider the contribution of radiation.For this situation,the initial condition mentioned above becomes invalid.To overcome this shortcoming,we investigate the evolutions of dark energy in matter-dominated and radiation-dominated epochs,and obtain a new initial condition Ωde(Zini) =n2(1 + zini)-2(1+ √F(Zini))2/4 at zini =2000,where F(z) ≡ Ωr0(1+z)/[Ωm0 + Ωr0(1 +z)] with Ωr0 and Ωm0 being the current density parameters of radiation and pressureless matter,respectively.This revised initial condition is applicable for the differential equation of Ωde obtained in the standard Friedmann-Robertson-Walker (FRW) universe with dark energy,pressureless matter,radiation,and even spatial curvature,and can still keep the NADE model as a single-parameter model.With the revised initial condition and the observational data of type Ia supernova (SNIa),CMB,and BAO,we finally constrain the NADE model.The results show that the single free parameter n of the NADE model can be constrained tightly.
Bianchi type I Universe and instability of new agegraphic dark energy in Brans-Dicke theories
Fayaz, V.
2016-02-01
In this paper, we consider the new agegraphic dark energy (NADE) in a Bianchi type-I metric (which is a spatially homogeneous and anisotropic) in the framework of Brans-Dicke theory. For this purpose, we use the squared sound speed vs2 whose sign determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. The equation of state and the deceleration parameter of the new agegraphic dark energy in a anisotropic Universe is obtained. We show that the combination of Brans-Dicke field and new agegraphic dark energy can accommodate ω_{\\varLambda}=-1 crossing for the equation of state of noninteracting dark energy. When an interaction between dark energy and dark matter is taken into account, the transition of ω_{\\varLambda} to phantom regime can be more easily accounted when the Einstein field equations is being resort. In conclusion, we find evidences that the new agegraphic dark energy in BD theory can not lead to a stable Universe favored by observations at the present time. The anisotropy of the Universe decreases and the Universe transits to an isotropic flat FRW Universe accommodating the present acceleration.
Interacting agegraphic dark energy model in tachyon cosmology coupled to matter
Farajollahi, H.; Ravanpak, A.; Fadakar, G. F.
2012-01-01
Scalar-field dark energy models for tachyon fields are often regarded as an effective description of an underlying theory of dark energy. In this paper, we propose the agegraphic dark energy model in tachyon cosmology by interaction between the components of the dark sectors. In the formalism, the interaction term emerges from the tachyon field nonminimally coupled to the matter Lagrangian in the model rather than being inserted into the formalism as an external source. The model is constrain...
Interacting entropy-corrected new agegraphic dark energy in the non-flat universe
Energy Technology Data Exchange (ETDEWEB)
Karami, Kayoomars [Department of Physics, University of Kurdistan, Pasdaran Street, Sanandaj (Iran, Islamic Republic of); Sorouri, Arash, E-mail: KKarami@uok.ac.i [Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), Maragha (Iran, Islamic Republic of)
2010-08-15
Here, we consider the entropy-corrected version of the new agegraphic dark energy (NADE) model in the non-flat Friedmann-Robertson-Walker universe. We derive the exact differential equation that determines the evolution of the entropy-corrected NADE density parameter in the presence of interaction with dark matter. We also obtain the equation of state and deceleration parameters and present a necessary condition for the selected model to cross the phantom divide. Moreover, we reconstruct the potential and the dynamics of the phantom scalar field according to the evolutionary behavior of the interacting entropy-corrected new agegraphic model.
Setare, M R
2010-01-01
Recently one of us derived the action of modified gravity consistent with the holographic and new-agegraphic dark energy. In this paper, we investigate the stability of the Lagrangians of the modified gravity as discussed in [M. R. Setare, Int. J. Mod. Phys. D 17 (2008) 2219; M. R. Setare, Astrophys. Space Sci. 326 (2010) 27]. We also calculate the statefinder parameters which classify our dark energy model.
Thermodynamics of Interacting new Agegraphic Dark Energy and Dark Matter Due to Bianchi Type I Model
Hossienkhani, Hossien
2016-07-01
We study a thermodynamical description of the interaction between new agegraphic dark energy (NADE) and dark matter (DM) in an anisotropic universe. We find expressions for the entropy changes of these dark energy (DE) candidates. In addition, considering thermal fluctuations, thermodynamics of the DE component interacting with a DM sector is addressed. We also show that if one wants to solve the coincidence problem by using this mutual interaction, then the coupling constants of the interaction will be constrained. Finally, we obtain a physical expression for the interaction which is consistent with phenomenological descriptions and passes reasonably well the observational tests. Our study shows that, with the local equilibrium assumption, the generalized second law of thermodynamics is fulfilled in a region enclosed by the apparent horizon.
Karami, K.; Abdolmaleki, A.
2010-01-01
In the present work, we reconstruct different f(T)-gravity models corresponding to the original and entropy-corrected version of the holographic and new agegraphic dark energy models. We also obtain the equation of state parameters of the corresponding f(T)-gravity models. We conclude that the holographic and new agegraphic f(T)-gravity models behave like phantom or quintessence model. Whereas in the entropy-corrected models, the equation of state parameter can justify the transition from the...
Interacting entropy-corrected new agegraphic dark energy in Brans-Dicke cosmology
Karami, Kayoomars; Sheykhi, Ahmad; Jamil, Mubasher; Azarmi, Z.; Soltanzadeh, M. M.
2010-01-01
Motivated by a recent work of one of us [1], we extend it by using quantum (or entropy) corrected new agegraphic dark energy in the Brans-Dicke cosmology. The correction terms are motivated from the loop quantum gravity which is one of the competitive theories of quantum gravity. Taking the non-flat background spacetime along with the conformal age of the universe as the length scale, we derive the dynamical equation of state of dark energy and the deceleration parameter. An important consequ...
Li, Yun-He; Cui, Jing-Lei; Wang, Zhuo; Zhang, Xin
2010-01-01
Many dark energy models fail to pass the cosmic age test via the old quasar APM 08279+5255 at redshift $z=3.91$, even the $\\Lambda$CDM model and the holographic dark energy model are not exception. In this paper, we focus on the topic of age problem in the new agegraphic dark energy (NADE) model. We determine the age of the universe in the NADE model by using the fitting result of observational data including type Ia supernovae (SNIa), baryon acoustic oscillation (BAO) and cosmic microwave background (CMB). It is shown that the NADE model also faces the challenge of the age problem caused by the old quasar APM 08279+5255. In order to overcome such a difficulty, we consider the possible interaction between dark energy and matter. We show that the old quasar APM 08279+5255 at redshift $z=3.91$ can be successfully accommodated in the interacting new agegraphic dark energy (INADE) model at $2\\sigma$ level under the current observational constraints.
Karami, K
2010-01-01
Here we peruse cosmological usage of the most promising candidates of dark energy in the framework of $f(R)$-gravity. We reconstruct the $f(R)$ theory in the spatially-flat FRW universe according to the ordinary and entropy-corrected versions of the holographic and new agegraphic dark energy models, which describe accelerated expansion of the universe.
f(R) in Holographic and Agegraphic Dark Energy Models and the Generalized Uncertainty Principle
Majumder, Barun
2013-01-01
We studied a unified approach with the holographic, new agegraphic and the $f(R)$ dark energy model to construct the form of $f(R)$ which in general responsible for the curvature driven explanation of the very early inflation along with presently observed late time acceleration. We considered the generalized uncertainty principle in our approach which incorporated the corrections in the entropy area relation and thereby modified the energy densities for the cosmological dark energy models considered. We found that holographic and new agegraphic $f(R)$ gravity models can behave like phantom or quintessence models in the spatially flat FRW universe. We also found a distinct term in the form of $f(R)$ which goes as $R^{\\frac{3}{2}}$ due to the consideration of the GUP modified energy densities. Although the presence of this term in the action can have its importance in explaining the early inflationary scenario but Capozziello {\\it et.al.} recently showed that $f(R) \\sim R^{\\frac{3}{2}}$ leads to an accelerated ...
f(R in Holographic and Agegraphic Dark Energy Models and the Generalized Uncertainty Principle
Directory of Open Access Journals (Sweden)
Barun Majumder
2013-01-01
Full Text Available We studied a unified approach with the holographic, new agegraphic, and f(R dark energy model to construct the form of f(R which in general is responsible for the curvature driven explanation of the very early inflation along with presently observed late time acceleration. We considered the generalized uncertainty principle in our approach which incorporated the corrections in the entropy-area relation and thereby modified the energy densities for the cosmological dark energy models considered. We found that holographic and new agegraphic f(R gravity models can behave like phantom or quintessence models in the spatially flat FRW universe. We also found a distinct term in the form of f(R which goes as R 3 / 2 due to the consideration of the GUP modified energy densities. Although the presence of this term in the action can be important in explaining the early inflationary scenario, Capozziello et al. recently showed that f(R ~ R 3 / 2 leads to an accelerated expansion, that is, a negative value for the deceleration parameter q which fits well with SNeIa and WMAP data.
Energy Technology Data Exchange (ETDEWEB)
Karami, K., E-mail: KKarami@uok.ac.i [Department of Physics, University of Kurdistan, Pasdaran St., Sanandaj (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), Maragha (Iran, Islamic Republic of); Khaledian, M.S.; Felegary, F.; Azarmi, Z. [Department of Physics, University of Kurdistan, Pasdaran St., Sanandaj (Iran, Islamic Republic of)
2010-03-29
We study the correspondence between the tachyon, K-essence and dilaton scalar field models with the interacting new agegraphic dark energy model in the non-flat FRW universe. We reconstruct the potentials and the dynamics for these scalar field models, which describe accelerated expansion of the universe.
International Nuclear Information System (INIS)
In the present work, we reconstruct different f(T)-gravity models corresponding to the original and entropy-corrected versions of the holographic and new agegraphic dark energy models. We also obtain the equation of state parameters of the corresponding f(T)-gravity models. We conclude that the original holographic and new agegraphic f(T)-gravity models behave like the phantom or quintessence model, whereas in the entropy-corrected models, the equation of state parameter can justify the transition from the quintessence state to the phantom regime as indicated by the recent observations.
Karami, Kayoomars; Abdolmaleki, Asrin
2013-07-01
In the present work, we reconstruct different f(T)-gravity models corresponding to the original and entropy-corrected versions of the holographic and new agegraphic dark energy models. We also obtain the equation of state parameters of the corresponding f(T)-gravity models. We conclude that the original holographic and new agegraphic f(T)-gravity models behave like the phantom or quintessence model, whereas in the entropy-corrected models, the equation of state parameter can justify the transition from the quintessence state to the phantom regime as indicated by the recent observations.
Institute of Scientific and Technical Information of China (English)
Kayoomars Karami; Asrin Abdolmaleki
2013-01-01
In the present work,we reconstruct different f(T)-gravity models corresponding to the original and entropy-corrected versions of the holographic and new agegraphic dark energy models.We also obtain the equation of state parameters of the corresponding f(T)-gravity models.We conclude that the original holographic and new agegraphic f(T)-gravity models behave like the phantom or quintessence model,whereas in the entropy-corrected models,the equation of state parameter can justify the transition from the quintessence state to the phantom regime as indicated by the recent observations.
New agegraphic dark energy in Brans-Dicke theory with logarithmic form of scalar field
Kumar, Pankaj
2016-01-01
In a very recent paper, the current authors (arXiv:gr-qc/1609.01477) have proposed and analyzed in detail the logarithmic form of Brans-Dicke scalar field $\\phi$ as $\\phi \\propto ln(\\alpha+\\beta a)$, where $\\alpha$ and $\\beta$ are positive constants, to alleviate the problems of interacting holographic dark energy models in Brans-Dicke theory. In this paper, the cosmological evolution of a new agegraphic dark energy (NADE) model within the framework of Friedmann-Robertson-Walker Universe is analyzed with the same form of scalar field in Brans-Dicke theory. We derive the equation of state parameter $w_D$ and deceleration parameter $q$ of NADE model. It is observed that $w_D\\rightarrow -1$ when $a\\rightarrow \\infty$, i.e., the NADE mimics cosmological constant in the late time evolution. Indeed, due to the assumption of logarithmic form of Brans-Dicke scalar field the NADE in Brans-Dicke theory behaves like NADE in general relativity in the late time evolution. The NADE model shows a phase transition from matte...
Karami, K.; Khaledian, M. S.
2010-01-01
Here, we peruse cosmological usage of the most promising candidates of dark energy in the framework of f(R) theory. We reconstruct the different f(R) modified gravity models in the spatially flat FRW universe according to the ordinary and entropy-corrected versions of the holographic and new agegraphic dark energy models, which describe accelerated expansion of the universe. We also obtain the equation of state parameter of the corresponding f(R)-gravity models. We conclude that the holograph...
Karami, K.; Khaledian, M. S.
2011-03-01
Here, we peruse cosmological usage of the most promising candidates of dark energy in the framework of f( R) theory. We reconstruct the different f( R) modified gravity models in the spatially flat FRW universe according to the ordinary and entropy-corrected versions of the holographic and new agegraphic dark energy models, which describe accelerated expansion of the universe. We also obtain the equation of state parameter of the corresponding f( R)-gravity models. We conclude that the holographic and new agegraphic f( R)-gravity models can behave like phantom or quintessence models. Whereas the equation of state parameter of the entropy-corrected models can transit from quintessence state to phantom regime as indicated by recent observations.
Saha, Pameli
2016-01-01
Here, we peruse cosmological usage of the most promising candidates of dark energy in the framework of $f(T)$ gravity theory. We reconstruct the different $f(T)$ modifed gravity models in the spatially flat FRW universe according to entropy-corrected versions of the holographic and new agegraphic dark energy models in power-law and logarithmic corrections, which describe accelerated expansion history of the universe. We conclude that the equation of state parameter of the entropy-corrected models can transit from quintessence state to phantom regime as indicated by recent observations or can lie entirely in the phantom region. Also, using these models, we investigate the different erase of the stability with the help of the squared speed of sound.
Saha, Pameli; Debnath, Ujjal
2016-09-01
Here, we peruse cosmological usage of the most promising candidates of dark energy in the framework of f( T) gravity theory where T represents the torsion scalar teleparallel gravity. We reconstruct the different f( T) modified gravity models in the spatially flat Friedmann-Robertson-Walker universe according to entropy-corrected versions of the holographic and new agegraphic dark energy models in power-law and logarithmic corrections, which describe an accelerated expansion history of the universe. We conclude that the equation of state parameter of the entropy-corrected models can transit from the quintessence state to the phantom regime as indicated by recent observations or can lie entirely in the phantom region. Also, using these models, we investigate the different areas of the stability with the help of the squared speed of sound.
Debnath, Ujjal
2013-01-01
Here we briefly discuss the Einstein-Aether gravity theory by modification of Einstein-Hilbert action. We find the modified Friedmann equations and then from the equations we find the effective density and pressure for Einstein-Aether gravity sector. These can be treated as dark energy provided some restrictions on the free function $F(K)$, where $K$ is proportional to $H^{2}$. Assuming two types of the power law solutions of the scale factor, we have reconstructed the unknown function $F(K)$...
Debnath, Ujjal
2013-01-01
Here we briefly discuss the Einstein-Aether gravity theory by modification of Einstein-Hilbert action. We find the modified Friedmann equations and then from the equations we find the effective density and pressure for Einstein-Aether gravity sector. These can be treated as dark energy provided some restrictions on the free function $F(K)$, where $K$ is proportional to $H^{2}$. Assuming two types of the power law solutions of the scale factor, we have reconstructed the unknown function $F(K)$ from HDE and NADE and their entropy-corrected versions (ECHDE and ECNADE). We also obtain the EoS parameter for Einstein-Aether gravity dark energy. For HDE and NADE, we have shown that the type I scale factor generates the quintessence scenario only and type II scale factor generates phantom scenario. But for ECHDE and ECNADE, the both types of scale factors can accommodate the transition from quintessence to phantom stages i.e., phantom crossing is possible for entropy corrected terms of HDE and NADE models. Finally, w...
2014-01-01
Here we briefly discuss the Einstein-Aether gravity theory by modification of Einstein-Hilbert action. We find the modified Friedmann equations and then from the equations we find the effective density and pressure for Einstein-Aether gravity sector. These can be treated as if dark energy provided some restrictions on the free function F(K) where K is proportional to H2 . Assuming two types of the power law solutions of the scale factor, we have reconstructed the unknown function F(K) from HD...
Directory of Open Access Journals (Sweden)
Ujjal Debnath
2014-01-01
Full Text Available Here we briefly discuss the Einstein-Aether gravity theory by modification of Einstein-Hilbert action. We find the modified Friedmann equations and then from the equations we find the effective density and pressure for Einstein-Aether gravity sector. These can be treated as if dark energy provided some restrictions on the free function F(K, where K is proportional to H2. Assuming two types of the power law solutions of the scale factor, we have reconstructed the unknown function F(K from HDE and NADE and their entropy-corrected versions (ECHDE and ECNADE. We also obtain the EoS parameter for Einstein-Aether gravity dark energy. For HDE and NADE, we have shown that the type I scale factor generates the quintessence scenario only and type II scale factor generates phantom scenario. But for ECHDE and ECNADE, both types of scale factors can accommodate the transition from quintessence to phantom stages; that is, phantom crossing is possible for entropy-corrected terms of HDE and NADE models. Finally, we show that the models are classically unstable.
Variable G correction to statefinder parameters of dark energy
Jamil, Mubasher
2010-01-01
Motivated by several observational and theoretical developments concerning the variability of Newton's gravitational constant with time $G(t)$, we calculate the varying $G$ correction to the statefinder parameters for four models of dark energy namely interacting dark energy, holographic dark energy, new-agegraphic dark energy and generalized Chaplygin gas.
Variable G Corrections to Statefinder Parameters of Dark Energy
Jamil, Mubasher
2010-11-01
Motivated by several observational and theoretical developments concerning the variability of Newton’s gravitational constant with time G( t), we calculate the varying G correction to the statefinder parameters for four models of dark energy namely interacting dark energy holographic dark energy, new-agegraphic dark energy and generalized Chaplygin gas.
Loop Quantum Corrections to Statefinder Parameters of Dark Energy
Jamil, Mubasher; Momeni, D.; Myrzakulov, Ratbay
2013-09-01
In this paper, we have calculated the statefinder parameters for the Friedmann-Robertson-Walker (FRW) Universe in the gravitational framework of loop quantum cosmology (LQC). As examples, we study two types of dark energy models namely Holographic dark energy and New-Agegraphic dark energy.
Loop Quantum Corrections to Statefinder Parameters of Dark Energy
Jamil, Mubasher; Myrzakulov, Ratbay
2013-01-01
In this short letter, we presented the explicit forms of the statefinder parameters for the Friedmann-Robertson-Walker (FRW) Universe in the loop quantum cosmology (LQC) for Holographic dark energy and New-Agegraphic dark energy. Numerically we investigated cosmological implications of these parameters for models of dark energy.
Correspondence between Ricci and other dark energies
Chattopadhyay, Surajit
2010-01-01
Purpose of the present paper is to view the correspondence between Ricci and other dark energies. We have considered the Ricci dark energy in presence of dark matter in non-interacting situation. Subsequently, we have derived the pressure and energy density for Ricci dark energy. The equation of state parameter has been generated from these pressure and energy density. Next, we have considered the correspondence between Ricci and other dark energy models, namely tachyonic field, DBI-essence and new agegraphic dark energy without any interaction and investigated possible cosmological consequences.
Entropy-Corrected Holographic Dark Energy
Wei, Hao
2009-01-01
The holographic dark energy (HDE) is now an interesting candidate of dark energy, which has been studied extensively in the literature. In the derivation of HDE, the black hole entropy plays an important role. In fact, the entropy-area relation can be modified due to quantum gravity or other reason. With the modified entropy-area relation, we propose the so-called "entropy-corrected holographic dark energy" (ECHDE) in this note. We consider many aspects of ECHDE and find some interesting results. In addition, we also consider the so-called "entropy-corrected agegraphic dark energy" (ECADE) briefly.
Entropy-Corrected Holographic Dark Energy
International Nuclear Information System (INIS)
The holographic dark energy (HDE) is now an interesting candidate of dark energy, which has been studied extensively in the literature. In the derivation of HDE, the black hole entropy plays an important role. In fact, the entropy-area relation can be modified due to loop quantum gravity or other reasons. With the modified entropy-area relation, we propose the so-called 'entropy-corrected holographic dark energy' (ECHDE) in the present work. We consider many aspects of ECHDE and find some interesting results. In addition, we briefly consider the so-called 'entropy-corrected agegraphic dark energy' (ECADE). (geophysics, astronomy, and astrophysics)
Entropy-Corrected Holographic Dark Energy
Wei, Hao
2009-10-01
The holographic dark energy (HDE) is now an interesting candidate of dark energy, which has been studied extensively in the literature. In the derivation of HDE, the black hole entropy plays an important role. In fact, the entropy-area relation can be modified due to loop quantum gravity or other reasons. With the modified entropy-area relation, we propose the so-called “entropy-corrected holographic dark energy" (ECHDE) in the present work. We consider many aspects of ECHDE and find some interesting results. In addition, we briefly consider the so-called “entropy-corrected agegraphic dark energy" (ECADE).
Original and entropy-corrected versions of the holographic and new agegraphic f(T)-gravity models
Karami, K
2013-01-01
In the present work we obtain the different $f(T)$-gravity models corresponding to the original and entropy-corrected versions of the holographic and new agegraphic dark energy models. We conclude that the equation of state parameter of the holographic and new agegraphic $f(T)$-gravity models always crosses the phantom-divide line. Whereas for the entropy-corrected models, crossing the phantom-divide line depends on the constant parameters of the models.
Entropy In The Present And Early Universe: New Small Parameters And Dark Energy Problem
Alexander Shalyt-Margolin
2009-01-01
It is demonstrated that entropy and its density play a significant role in solving the problem of the vacuum energy density (cosmolog- ical constant) of the Universe and hence the dark energy problem. Taking this in mind, two most popular models for dark energy - Holo- graphic Dark Energy Model and Agegraphic Dark Energy Model - are analyzed. It is shown that the fundamental quantities in the first of these models may be expressed in terms of a new small dimensionless par...
Holographic and new agegraphic f(T)-gravity models with power-law entropy correction
Karami, K
2013-01-01
Using a correspondence between the f(T)-gravity with the power-law entropy corrected versions of the holographic and new agegraphic dark energy models, we reconstruct the holographic and new agegraphic f(T)-gravity models with power-law entropy correction. We also obtain the equation of state parameters of the selected models due to torsion contribution. Our results show that the equation of state parameters can accommodate the transition from the quintessence state to the phantom regime at recent stage.
Power-law entropy corrected holographic and new agegraphic f(R)-gravity models
Karami, K.; Khaledian, M. S.
2011-01-01
Motivated by the recent works of us [1], we establish a correspondence between f(R)-gravity with the power-law entropy corrected holographic dark energy (PLECHDE) and new agegraphic dark energy (PLECNADE) models. We reconstruct corresponding f(R)-gravities and obtain the equation of state parameters. We show that the selected f(R)-gravity models can accommodate the transition from the quintessence state to the phantom regime as indicated by the recent observations.
Chakraborty, Shuvendu; Jamil, Mubasher; Myrzakulov, Ratbay
2011-01-01
In this work, we have calculated the deceleration parameter, statefinder parameters and EoS parameters for different dark energy models with variable G correction in homogeneous, isotropic and non-flat universe for Kaluza-Klein Cosmology. The statefinder parameters have been obtained in terms of some observable parameters like dimensionless density parameter, EoS parameter and Hubble parameter for holographic dark energy, new agegraphic dark energy and generalized Chaplygin gas models.
Chakraborty, Shuvendu; Debnath, Ujjal; Jamil, Mubasher; Myrzakulov, Ratbay
2012-07-01
In this work, we have calculated the deceleration parameter, statefinder parameters and EoS parameters for different dark energy models with variable G correction in homogeneous, isotropic and non-flat universe for Kaluza-Klein Cosmology. The statefinder parameters have been obtained in terms of some observable parameters like dimensionless density parameter, EoS parameter and Hubble parameter for holographic dark energy, new agegraphic dark energy and generalized Chaplygin gas models.
Debnath, Ujjal
2015-12-01
In this work, we have studied accretion of the dark matter and dark energy onto of (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole. The mass and the rate of change of mass for (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole have been found. We have assumed some candidates of dark energy like holographic dark energy, new agegraphic dark energy, quintessence, tachyon, DBI-essence, etc. The black hole mass and the wormhole mass have been calculated in term of redshift when dark matter and above types of dark energies accrete onto them separately. We have shown that the black hole mass increases and wormhole mass decreases for holographic dark energy, new agegraphic dark energy, quintessence, tachyon accretion and the slope of increasing/decreasing of mass sensitively depends on the dimension. But for DBI-essence accretion, the black hole mass first increases and then decreases and the wormhole mass first decreases and then increases and the slope of increasing/decreasing of mass not sensitively depends on the dimension.
Caldwell, Robert
2009-01-01
"Observations continue to indicate that the Universe is dominated by invisible components - dark matter and dark energy. Shedding light on this cosmic darkness is a priority for astronomers and physicists" (3 pages)
Comparing holographic dark energy models with statefinder
International Nuclear Information System (INIS)
We apply the statefinder diagnostic to the holographic dark energy models, including the original holographic dark energy (HDE) model, the new holographic dark energy model, the new agegraphic dark energy (NADE) model, and the Ricci dark energy model. In the low-redshift region the holographic dark energy models are degenerate with each other and with the ΛCDM model in the H(z) and q(z) evolutions. In particular, the HDE model is highly degenerate with the ΛCDM model, and in the HDE model the cases with different parameter values are also in strong degeneracy. Since the observational data are mainly within the low-redshift region, it is very important to break this lowredshift degeneracy in the H(z) and q(z) diagnostics by using some quantities with higher order derivatives of the scale factor. It is shown that the statefinder diagnostic r(z) is very useful in breaking the low-redshift degeneracies. By employing the statefinder diagnostic the holographic dark energy models can be differentiated efficiently in the low-redshift region. The degeneracy between the holographic dark energy models and the ΛCDM model can also be broken by this method. Especially for the HDE model, all the previous strong degeneracies appearing in the H(z) and q(z) diagnostics are broken effectively. But for the NADE model, the degeneracy between the cases with different parameter values cannot be broken, even though the statefinder diagnostic is used. A direct comparison of the holographic dark energy models in the r-s plane is also made, in which the separations between the models (including the ΛCDM model) can be directly measured in the light of the current values {r0, s0} of the models. (orig.)
Power-Law Entropy Corrected Holographic Dark Energy
Sheykhi, Ahmad
2010-01-01
Among various scenarios to explain the acceleration of the universe expansion, the holographic dark energy (HDE) model has got a lot of enthusiasm recently. In the derivation of holographic energy density, the area relation of the black hole entropy plays a crucial role. Indeed, the power-law corrections to entropy appear in dealing with the entanglement of quantum fields in and out the horizon. Inspired by the power-law corrected entropy, we propose the so-called "power-law entropy-corrected holographic dark energy" (PLECHDE) in this Letter. We investigate the cosmological implications of this model and calculate some relevant cosmological parameters and their evolution. We also briefly study the so-called "power-law entropy-corrected agegraphic dark energy" (PLECADE).
Power-Law entropy corrected holographic dark energy model
Sheykhi, Ahmad; Jamil, Mubasher
2011-10-01
Among various scenarios to explain the acceleration of the universe expansion, the holographic dark energy (HDE) model has got a lot of enthusiasm recently. In the derivation of holographic energy density, the area relation of the black hole entropy plays a crucial role. Indeed, the power-law corrections to entropy appear in dealing with the entanglement of quantum fields in and out the horizon. Inspired by the power-law corrected entropy, we propose the so-called "power-law entropy-corrected holographic dark energy" (PLECHDE) in this Letter. We investigate the cosmological implications of this model and calculate some relevant cosmological parameters and their evolution. We also briefly study the so-called "power-law entropy-corrected agegraphic dark energy" (PLECADE).
Diagnosing holographic dark energy models with statefinder hierarchy
International Nuclear Information System (INIS)
We apply a series of null diagnostics based on the statefinder hierarchy to diagnose different holographic dark energy models including the original holographic dark energy, the new holographic dark energy, the new agegraphic dark energy, and the Ricci dark energy models. We plot the curves of statefinders S3(1) and S4(1) versus redshift z and the evolutionary trajectories of {S3(1), element of } and {S4(1), element of } for these models, where is the fractional growth parameter. Combining the evolution curves with the current values of S3(1), S4(1), and element of, we find that the statefinder S4(1) performs better than S3(1) for diagnosing the holographic dark energy models. In addition, the conjunction of the statefinder hierarchy and the fractional growth parameter is proven to be a useful method to diagnose the holographic dark energy models, especially for breaking the degeneracy of the newagegraphic dark energy model with different parameter values. (orig.)
Dark Energy Models and Cosmic Acceleration with Anisotropic Universe in f(T) Gravity
Sharif, M.; Sehrish, Azeem
2014-04-01
This paper is devoted to studing the accelerated expansion of the universe in context of f(T) theory of gravity. For this purpose, we construct different f(T) models and investigate their cosmological behavior through equation of state parameter by using holographic, new agegraphic and their power-law entropy corrected dark energy models. We discuss the graphical behavior of this parameter versus redshift for particular values of constant parameters in Bianchi type I universe model. It is shown that the universe lies in different forms of dark energy, namely quintessence, phantom, and quintom corresponding to the chosen scale factors, which depend upon the constant parameters of the models.
Dark Energy Models and Cosmic Acceleration with Anisotropic Universe in f(T) Gravity
International Nuclear Information System (INIS)
This paper is devoted to studing the accelerated expansion of the universe in context of f(T) theory of gravity. For this purpose, we construct different f(T) models and investigate their cosmological behavior through equation of state parameter by using holographic, new agegraphic and their power-law entropy corrected dark energy models. We discuss the graphical behavior of this parameter versus redshift for particular values of constant parameters in Bianchi type I universe model. It is shown that the universe lies in different forms of dark energy, namely quintessence, phantom, and quintom corresponding to the chosen scale factors, which depend upon the constant parameters of the models
On the stability of the dark energy based on generalized uncertainty principle
Pasqua, Antonio; Khomenko, Iuliia
2013-01-01
The new agegraphic Dark Energy (NADE) model (based on generalized uncertainty principle) interacting with Dark Matter (DM) is considered in this study via power-law form of the scale factor $a(t)$. The equation of state (EoS) parameter $\\omega_{G}$ is observed to have a phantom-like behaviour. The stability of this model is investigated through the squared speed of sound $v_{s}^{2}$: it is found that $v_{s}^{2}$ always stays at negative level, which indicates instability of the considered model.
Entropy In The Present And Early Universe, New Small Parameters And Dark Energy Problem
Shalyt-Margolin, A E
2009-01-01
It is demonstrated that entropy and its density play a significant role in solving the problem of the vacuum energy density (cosmological constant) of the Universe and hence the dark energy problem. Taking this in mind, two most popular models for dark energy - Holographic Dark Energy Model and Agegraphic Dark Energy Model - are analyzed. It is shown that the fundamental quantities in the first of these models may be expressed in terms of a new small dimensionless parameter. It is revealed that this parameter is naturally occurring in High Energy Gravitational Thermodynamics and Gravitational Holography (UV-limit). On this basis the possibility of a new approach to the problem of Quantum Gravity is discussed. Besides, the results obtained on the uncertainty relation of the pair "cosmological constant - volume of space-time", where the cosmological constant is a dynamic quantity, are reconsidered and generalized up to the Generalized Uncertainty Relation
Entropy in the Present and Early Universe: New Small Parameters and Dark Energy Problem
Directory of Open Access Journals (Sweden)
Alexander Shalyt-Margolin
2010-04-01
Full Text Available It is demonstrated that entropy and its density play a significant role in solving the problem of the vacuum energy density (cosmological constant of the Universe and hence the dark energy problem. Taking this in mind, two most popular models for dark energy—Holographic Dark Energy Model and Agegraphic Dark Energy Model—are analysed. It is shown that the fundamental quantities in the first of these models may be expressed in terms of a new small dimensionless parameter that is naturally occurring in High Energy Gravitational Thermodynamics and Gravitational Holography (UV-limit. On this basis, the possibility of a new approach to the problem of Quantum Gravity is discussed. Besides, the results obtained on the uncertainty relation of the pair “cosmological constant–volume of space-time”, where the cosmological constant is a dynamic quantity, are reconsidered and generalized up to the Generalized Uncertainty Relation.
Scott, Douglas; Frolop, Ali
2007-01-01
It is now well accepted that both Dark Matter and Dark Energy are required in any successful cosmological model. Although there is ample evidence that both Dark components are necessary, the conventional theories make no prediction for the contributions from each of them. Moreover, there is usually no intrinsic relationship between the two components, and no understanding of the nature of the mysteries of the Dark Sector. Here we suggest that if the Dark Side is so seductive then we should no...
Chamseddine, Ali H
2016-01-01
We modify Einstein General Relativity by adding non-dynamical scalar fields to account simultaneously for both dark matter and dark energy. The dark energy in this case can be distributed in-homogeneously even within horizon scales. Its inhomogeneities can contribute to the late time integrated Sachs-Wolfe effect, possibly removing some of the low multipole anomalies in the temperature fluctuations of the CMB spectrum. The presence of the inhomogeneous dark matter also influences structure formation in the universe.
Chamseddine, Ali H.; Mukhanov, Viatcheslav(Theoretical Physics, Ludwig Maxmillians University, Theresienstr. 37, 80333, Munich, Germany)
2016-01-01
We modify Einstein General Relativity by adding non-dynamical scalar fields to account simultaneously for both dark matter and dark energy. The dark energy in this case can be distributed in-homogeneously even within horizon scales. Its inhomogeneities can contribute to the late time integrated Sachs-Wolfe effect, possibly removing some of the low multipole anomalies in the temperature fluctuations of the CMB spectrum. The presence of the inhomogeneous dark matter also influences structure fo...
Kunz, Martin; Amendola, Luca; Sapone, Domenico
2008-01-01
We discuss the phenomenology of the dark energy in first order perturbation theory, demonstrating that the dark energy cannot be fully constrained unless the dark matter is found, and that there are two functions that characterise the observational properties of the dark sector for cosmological probes. We argue that measuring these two functions should be an important goal for observational cosmology in the next decades.
Weak lensing: Dark Matter, Dark Energy and Dark Gravity
Heavens, Alan
2009-01-01
In this non-specialist review I look at how weak lensing can provide information on the dark sector of the Universe. The review concentrates on what can be learned about Dark Matter, Dark Energy and Dark Gravity, and why. On Dark Matter, results on the confrontation of theoretical profiles with observation are reviewed, and measurements of neutrino masses discussed. On Dark Energy, the interest is whether this could be Einstein's cosmological constant, and prospects for high-precision studies...
Analysis of dark matter and dark energy
Yongquan, Han
2016-05-01
As the law of unity of opposites of the Philosophy tells us, the bright material exists, the dark matter also exists. Dark matter and dark energy should allow the law of unity of opposites. The Common attributes of the matter is radiation, then common attributes of dark matter must be absorb radiation. Only the rotation speed is lower than the speed of light radiation, can the matter radiate, since the speed of the matter is lower than the speed of light, so the matter is radiate; The rotate speed of the dark matter is faster than the light , so the dark matter doesn't radiate, it absorbs radiation. The energy that the dark matter absorb radiation produced (affect the measurement of time and space distribution of variations) is dark energy, so the dark matter produce dark energy only when it absorbs radiation. Dark matter does not radiate, two dark matters does not exist inevitably forces, and also no dark energy. Called the space-time ripples, the gravitational wave is bent radiation, radiation particles should be graviton, graviton is mainly refers to the radiation particles whose wavelength is small. Dark matter, dark energy also confirms the existence of the law of symmetry.
Liang, Shi-Dong; Harko, Tiberiu
2015-01-01
Based on the analogy with superconductor physics we consider a scalar-vector-tensor gravitational model, in which the dark energy action is described by a gauge invariant electromagnetic type functional. By assuming that the ground state of the dark energy is in a form of a condensate with the U(1) symmetry spontaneously broken, the gauge invariant electromagnetic dark energy can be described in terms of the combination of a vector and of a scalar field (corresponding to the Goldstone boson),...
Scott, Douglas
2007-01-01
It is now well accepted that both Dark Matter and Dark Energy are required in any successful cosmological model. Although there is ample evidence that both Dark components are necessary, the conventional theories make no prediction for the contributions from each of them. Moreover, there is usually no intrinsic relationship between the two components, and no understanding of the nature of the mysteries of the Dark Sector. Here we suggest that if the Dark Side is so seductive then we should not be restricted to just 2 components. We further suggest that the most natural model has 5 distinct forms of Dark Energy in addition to the usual Dark Matter, each contributing precisely equally to the cosmic energy density budget.
Landim, Ricardo G
2016-01-01
We build a model of metastable dark energy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable dark energy is also embedded into a model with $SU(2)_R$ symmetry. The dark energy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the dark energy particle into (cold and warm) dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and dark energy, and the model opens a new window to investigate the dark secto...
Weak lensing: Dark Matter, Dark Energy and Dark Gravity
Heavens, Alan
2009-01-01
In this non-specialist review I look at how weak lensing can provide information on the dark sector of the Universe. The review concentrates on what can be learned about Dark Matter, Dark Energy and Dark Gravity, and why. On Dark Matter, results on the confrontation of theoretical profiles with observation are reviewed, and measurements of neutrino masses discussed. On Dark Energy, the interest is whether this could be Einstein's cosmological constant, and prospects for high-precision studies of the equation of state are considered. On Dark Gravity, we consider the exciting prospects for future weak lensing surveys to distinguish General Relativity from extra-dimensional or other gravity theories.
International Nuclear Information System (INIS)
Though the concept of a dark energy driven accelerating universe was introduced by the author in 1997, to date dark energy itself, as described below has remained a paradigm. We quickly review these and find a second cosmological signature of the 1997 model, consistent with latest observations. (author)
Song, Yong-Seon; Knox, Lloyd
2003-01-01
We study how parameter error forecasts for tomographic cosmic shear observations are affected by sky coverage, density of source galaxies, inclusion of CMB experiments, simultaneou fitting of non--dark energy parameters, and the parametrization of the history of the dark energy equation-of-state parameter w(z). We find tomographic shear-shear power spectra on large angular scales (l
Extended Holographic dark energy
Gong, Yungui
2004-01-01
The idea of relating the infrared and ultraviolet cutoffs is applied to Brans-Dicke theory of gravitation. We find that extended holographic dark energy from the Hubble scale or the particle horizon as the infrared cutoff will not give accelerating expansion. The dynamical cosmological constant with the event horizon as the infrared cutoff is a viable dark energy model.
Liang, Shi-Dong
2015-01-01
Based on the analogy with superconductor physics we consider a scalar-vector-tensor gravitational model, in which the dark energy action is described by a gauge invariant electromagnetic type functional. By assuming that the ground state of the dark energy is in a form of a condensate with the U(1) symmetry spontaneously broken, the gauge invariant electromagnetic dark energy can be described in terms of the combination of a vector and of a scalar field (corresponding to the Goldstone boson), respectively. The gravitational field equations are obtained by also assuming the possibility of a non-minimal coupling between the cosmological mass current and the superconducting dark energy. The cosmological implications of the dark energy model are investigated for a Friedmann-Robertson-Walker homogeneous and isotropic geometry for two particular choices of the electromagnetic type potential, corresponding to a pure electric type field, and to a pure magnetic field, respectively. The time evolution of the scale fact...
Gibson, Carl H
2011-01-01
Is the accelerating expansion of the Universe true, inferred through observations of distant supernovae, and is the implied existence of an enormous amount of anti-gravitational dark energy material driving the accelerating expansion of the universe also true? To be physically useful these propositions must be falsifiable; that is, subject to observational tests that could render them false, and both fail when viscous, diffusive, astro-biological and turbulence effects are included in the interpretation of observations. A more plausible explanation of negative stresses producing the big bang is turbulence at Planck temperatures. Inflation results from gluon viscous stresses at the strong force transition. Anti-gravitational (dark energy) turbulence stresses are powerful but only temporary. No permanent dark energy is needed. At the plasma-gas transition, viscous stresses cause fragmentation of plasma proto-galaxies into dark matter clumps of primordial gas planets, each of which falsifies dark-energy cold-dar...
Sapone, Domenico
2009-01-01
Dark energy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the dark energy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar field models) which is often generically called "dark energy". We then use the approximate solutions to look at the impact of the dark energy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.
Dynamical Mutation of Dark Energy
Abramo, L R; Liberato, L; Rosenfeld, R
2007-01-01
We discuss the intriguing possibility that dark energy may change its equation of state in situations where large dark energy fluctuations are present. We show indications of this dynamical mutation in some generic models of dark energy.
Cold Dark Matter from Dark Energy
Davidson, Aharon; Karasik, David; Lederer, Yoav
2001-01-01
Dark energy/matter unification is first demonstrated within the framework of a simplified model. Geodetic evolution of a cosmological constant dominated bubble Universe, free of genuine matter, is translated into a specific FRW cosmology whose effectively induced dark component highly resembles the cold dark matter ansatz. The realistic extension constitutes a dark soliton which bridges past (radiation and/or matter dominated) and future (cosmological constant dominated) Einstein regimes; its...
Domínguez, I.; Bravo, E.; Piersanti, L.; Straniero, O.; Tornambé, A.
2009-08-01
A decade ago the observations of thermonuclear supernovae at high-redhifts showed that the expansion rate of the Universe is accelerating and since then, the evidence for cosmic acceleration has gotten stronger. This acceleration requires that the Universe is dominated by dark energy, an exotic component characterized by its negative pressure. Nowadays all the available astronomical data (i.e. thermonuclear supernovae, cosmic microwave background, barionic acoustic oscillations, large scale structure, etc.) agree that our Universe is made of about 70% of dark energy, 25% of cold dark matter and only 5% of known, familiar matter. This Universe is geometrically flat, older than previously thought, its destiny is no longer linked to its geometry but to dark energy, and we ignore about 95% of its components. To understand the nature of dark energy is probably the most fundamental problem in physics today. Current astronomical observations are compatible with dark energy being the vacuum energy. Supernovae have played a fundamental role in modern Cosmology and it is expected that they will contribute to unveil the dark energy. In order to do that it is mandatory to understand the limits of supernovae as cosmological distance indicators, improving their precision by a factor 10.
Song, Y S; Song, Yong-Seon; Knox, Lloyd
2003-01-01
We study how parameter error forecasts for tomographic cosmic shear observations are affected by sky coverage, density of source galaxies, inclusion of CMB experiments, simultaneou fitting of non--dark energy parameters, and the parametrization of the history of the dark energy equation-of-state parameter w(z). We find tomographic shear-shear power spectra on large angular scales (l0.04.
Conformal Gravity: Dark Matter and Dark Energy
Nesbet, Robert K
2012-01-01
This short review examines recent progress in understanding dark matter, dark energy, and galactic halos using theory that departs minimally from standard particle physics and cosmology. Postulated strict conformal symmetry (local Weyl scaling covariance) for all elementary massless fields retains standard theory for fermions and gauge bosons but modifies Einstein-Hilbert general relativity and the Higgs scalar field model, introducing no new physical fields. Subgalactic phenomenology is retained. Without invoking dark matter, conformal gravity and a conformal Higgs model fit empirical data on galactic rotational velocities, galactic halos, and Hubble expansion including dark energy.
Conformal Gravity: Dark Matter and Dark Energy
Directory of Open Access Journals (Sweden)
Robert K. Nesbet
2013-01-01
Full Text Available This short review examines recent progress in understanding dark matter, dark energy, and galactic halos using theory that departs minimally from standard particle physics and cosmology. Strict conformal symmetry (local Weyl scaling covariance, postulated for all elementary massless fields, retains standard fermion and gauge boson theory but modifies Einstein–Hilbert general relativity and the Higgs scalar field model, with no new physical fields. Subgalactic phenomenology is retained. Without invoking dark matter, conformal gravity and a conformal Higgs model fit empirical data on galactic rotational velocities, galactic halos, and Hubble expansion including dark energy.
Comparison of dark energy models:A perspective from the latest observational data
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
We compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation,the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey,the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H0 from the Hubble Space Telescope.Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models.These statistics favor models that give a good fit with fewer parameters.Based on this analysis,we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data.For other dynamical dark energy models,we find that some of them,such as the αdark energy,constant w,generalized Chaplygin gas,Chevalliear-Polarski-Linder parametrization,and holographic dark energy models,can provide good fits to the current data,and three of them,namely,the Ricci dark energy,agegraphic dark energy,and Dvali-Gabadadze-Porrati models,are clearly disfavored by the data.
Coupling dark energy to dark matter perturbations
Marra, Valerio
2015-01-01
This Letter proposes that dark energy in the form of a scalar field could effectively couple to dark matter perturbations. The idea is that dark matter particles could annihilate/interact inside dense clumps and transfer energy to the scalar field, which would then enter an accelerated regime. This hypothesis is interesting as it provides a natural trigger for the onset of the acceleration of the universe, since dark energy starts driving the expansion of the universe when matter perturbations become sufficiently dense. Here we study a possible realization of this general idea by coupling dark energy to dark matter via the linear growth function of matter perturbations. The numerical results show that it is indeed possible to obtain a viable cosmology with the expected series of radiation, matter and dark-energy dominated eras. Moreover, the current density of dark energy is given by the value of the coupling parameters rather than by very special initial conditions for the scalar field. In other words, this ...
International Nuclear Information System (INIS)
The gravastar picture is an alternative model to the concept of a black hole, where there is an effective phase transition at or near where the event horizon is expected to form, and the interior is replaced by a de Sitter condensate. In this work a generalization of the gravastar picture is explored by considering matching of an interior solution governed by the dark energy equation of state, ω ≡ p/ρ < -1/3, to an exterior Schwarzschild vacuum solution at a junction interface. The motivation for implementing this generalization arises from the fact that recent observations have confirmed an accelerated cosmic expansion, for which dark energy is a possible candidate. Several relativistic dark energy stellar configurations are analysed by imposing specific choices for the mass function. The first case considered is that of a constant energy density, and the second choice that of a monotonic decreasing energy density in the star's interior. The dynamical stability of the transition layer of these dark energy stars to linearized spherically symmetric radial perturbations about static equilibrium solutions is also explored. It is found that large stability regions exist that are sufficiently close to where the event horizon is expected to form, so that it would be difficult to distinguish the exterior geometry of the dark energy stars, analysed in this work, from an astrophysical black hole
Dark Energy, Dark Matter and Gravity
Bertolami, Orfeu
2006-01-01
We discuss the motivation for high accuracy relativistic gravitational experiments in the Solar System and complementary cosmological tests. We focus our attention on the issue of distinguishing a generic scalar-theory of gravity as the underlying physical theory from the usual general relativistic picture, where one expects the presence of fundamental scalar fields associated, for instance, to inflation, dark matter and dark energy.
Coupling dark energy to dark matter inhomogeneities
Marra, Valerio
2016-09-01
We propose that dark energy in the form of a scalar field could effectively couple to dark matter inhomogeneities. Through this coupling energy could be transferred to/from the scalar field, which could possibly enter an accelerated regime. Though phenomenological, this scenario is interesting as it provides a natural trigger for the onset of the acceleration of the universe, since dark energy starts driving the expansion of the universe when matter inhomogeneities become sufficiently strong. Here we study a possible realization of this idea by coupling dark energy to dark matter via the linear growth function of matter perturbations. The numerical results show that it is indeed possible to obtain a viable cosmology with the expected series of radiation, matter and dark-energy dominated eras. In particular, the current density of dark energy is given by the value of the coupling parameters rather than by very special initial conditions for the scalar field. In other words, this model-unlike standard models of cosmic late acceleration-does not suffer from the so-called "coincidence problem" and its related fine tuning of initial conditions.
Interactions between dark energy and dark matter
International Nuclear Information System (INIS)
We have investigated interacting dark energy cosmologies both concerning their impact on the background evolution of the Universe and their effects on cosmological structure growth. For the former aspect, we have developed a cosmological model featuring a matter species consisting of particles with a mass that increases with time. In such model the appearance of a Growing Matter component, which is negligible in early cosmology, dramatically slows down the evolution of the dark energy scalar field at a redshift around six, and triggers the onset of the accelerated expansion of the Universe, therefore addressing the Coincidence Problem. We propose to identify this Growing Matter component with cosmic neutrinos, in which case the present dark energy density can be related to the measured average mass of neutrinos. For the latter aspect, we have implemented the new physical features of interacting dark energy models into the cosmological N-body code GADGET-2, and we present the results of a series of high-resolution simulations for a simple realization of dark energy interaction. As a consequence of the new physics, cold dark matter and baryon distributions evolve differently both in the linear and in the non-linear regime of structure formation. Already on large scales, a linear bias develops between these two components, which is further enhanced by the non-linear evolution. We also find, in contrast with previous work, that the density profiles of cold dark matter halos are less concentrated in coupled dark energy cosmologies compared with ΛCDM. Also, the baryon fraction in halos in the coupled models is significantly reduced below the universal baryon fraction. These features alleviate tensions between observations and the ΛCDM model on small scales. Our methodology is ideally suited to explore the predictions of coupled dark energy models in the fully non-linear regime, which can provide powerful constraints for the viable parameter space of such scenarios
Interactions between dark energy and dark matter
Energy Technology Data Exchange (ETDEWEB)
Baldi, Marco
2009-03-20
We have investigated interacting dark energy cosmologies both concerning their impact on the background evolution of the Universe and their effects on cosmological structure growth. For the former aspect, we have developed a cosmological model featuring a matter species consisting of particles with a mass that increases with time. In such model the appearance of a Growing Matter component, which is negligible in early cosmology, dramatically slows down the evolution of the dark energy scalar field at a redshift around six, and triggers the onset of the accelerated expansion of the Universe, therefore addressing the Coincidence Problem. We propose to identify this Growing Matter component with cosmic neutrinos, in which case the present dark energy density can be related to the measured average mass of neutrinos. For the latter aspect, we have implemented the new physical features of interacting dark energy models into the cosmological N-body code GADGET-2, and we present the results of a series of high-resolution simulations for a simple realization of dark energy interaction. As a consequence of the new physics, cold dark matter and baryon distributions evolve differently both in the linear and in the non-linear regime of structure formation. Already on large scales, a linear bias develops between these two components, which is further enhanced by the non-linear evolution. We also find, in contrast with previous work, that the density profiles of cold dark matter halos are less concentrated in coupled dark energy cosmologies compared with {lambda}{sub CDM}. Also, the baryon fraction in halos in the coupled models is significantly reduced below the universal baryon fraction. These features alleviate tensions between observations and the {lambda}{sub CDM} model on small scales. Our methodology is ideally suited to explore the predictions of coupled dark energy models in the fully non-linear regime, which can provide powerful constraints for the viable parameter
International Nuclear Information System (INIS)
In the Randall-Sundrum scenario, we analyse the dynamics of an AdS5 braneworld when conformal matter fields propagate in five dimensions. We show that conformal fields of weight -4 are associated with stable geometries which describe the dynamics of inhomogeneous dust, generalized dark radiation and homogeneous polytropic dark energy on a spherically symmetric 3-brane embedded in the compact AdS5 orbifold. We discuss aspects of the radion stability conditions and of the localization of gravity in the vicinity of the brane
Energy Technology Data Exchange (ETDEWEB)
Schrempp, L.
2008-02-15
From the observed late-time acceleration of cosmic expansion arises the quest for the nature of Dark Energy. As has been widely discussed, the cosmic neutrino background naturally qualifies for a connection with the Dark Energy sector and as a result could play a key role for the origin of cosmic acceleration. In this thesis we explore various theoretical aspects and phenomenological consequences arising from non-standard neutrino interactions, which dynamically link the cosmic neutrino background and a slowly-evolving scalar field of the dark sector. In the considered scenario, known as Neutrino Dark Energy, the complex interplay between the neutrinos and the scalar field not only allows to explain cosmic acceleration, but intriguingly, as a distinct signature, also gives rise to dynamical, time-dependent neutrino masses. In a first analysis, we thoroughly investigate an astrophysical high energy neutrino process which is sensitive to neutrino masses. We work out, both semi-analytically and numerically, the generic clear-cut signatures arising from a possible time variation of neutrino masses which we compare to the corresponding results for constant neutrino masses. Finally, we demonstrate that even for the lowest possible neutrino mass scale, it is feasible for the radio telescope LOFAR to reveal a variation of neutrino masses and therefore to probe the nature of Dark Energy within the next decade. A second independent analysis deals with the recently challenged stability of Neutrino Dark Energy against the strong growth of hydrodynamic perturbations, driven by the new scalar force felt between neutrinos. Within the framework of linear cosmological perturbation theory, we derive the equation of motion of the neutrino perturbations in a model-independent way. This equation allows to deduce an analytical stability condition which translates into a comfortable upper bound on the scalar-neutrino coupling which is determined by the ratio of the densities in cold dark
Dark Mass Creation During EWPT Via Dark Energy Interaction
Kisslinger, Leonard S.; Casper, Steven
2013-01-01
We add Dark Matter Dark Energy terms with a quintessence field interacting with a Dark Matter field to a MSSM EW Lagrangian previously used to calculate the magnetic field created during the EWPT. From the expectation value of the quintessence field we estimate the Dark Matter mass for parameters used in previous work on Dark Matter-Dark Energy interactions.
Conformal Gravity: Dark Matter and Dark Energy
Nesbet, Robert K.
2013-01-01
This short review examines recent progress in understanding dark matter, dark energy, and galactic halos using theory that departs minimally from standard particle physics and cosmology. Strict conformal symmetry (local Weyl scaling covariance), postulated for all elementary massless fields, retains standard fermion and gauge boson theory but modifies Einstein–Hilbert general relativity and the Higgs scalar field model, with no new physical fields. Subgalactic phenomenology is retai...
The dark side of cosmology: dark matter and dark energy.
Spergel, David N
2015-03-01
A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales.
Dark energy: myths and reality
Lukash, V N
2008-01-01
We discuss the questions related to dark energy in the Universe. We note that in spite of the effect of dark energy, large-scale structure is still being generated in the Universe and this will continue for about ten billion years. We also comment on some statements in the paper ``Dark energy and universal antigravitation'' by A.D. Chernin [4].
Lee, Seokcheon
2008-01-01
We consider the cosmological application of Lee-Wick theory where a field has a higher derivative kinetic operators. The higher derivative term can be eliminated by introducing a set of auxiliary fields. We investigate the cosmological evolutions of these fields as a candidate of dark energy. This model has the same structure as so called ``quintom' model except the form of potentials and the sign of the slope of the potentials. This model can give the stable late time phantom dominated scaling solution ($\\omega_{\\DE} < -1$) or tracking attractors ($\\omega_{\\DE} = 0$) depending on the choice of the slopes of the potential. In order to be a viable dark energy candidate, the present energy density contrast of dark energy ($\\Omega_{\\DE}^{(0)}$) should be close to an observed value (0.73) at the same time. However, a simple toy model of the theory can not satisfy both $\\omega_{\\DE}^{(0)} \\simeq -1$ and $\\Omega_{\\DE}^{(0)} = 0.73$. This is also true for any quintom model in literatures unless we suffer from the...
NASA's Dark Matter and Dark Energy Programs
International Nuclear Information System (INIS)
We present an overview of selected high value scientific results and prospects for future advances from NASA's “Dark” missions, i.e., those covering dark matter (DM) and dark energy (DE). This includes current missions HST, Chandra, Swift, GALEX, Suzaku, Fermi, and future missions JWST and WFIRST. These missions and earlier ones, such as WMAP, have brought about a revolution in our understanding of the fundamental properties of the universe – its age, rate of expansion, deceleration history, and composition (i.e., relative mix of luminous matter, dark matter, and dark energy). The next chapters in this story will be written by JWST and WFIRST. JWST was the highest priority of the 2000 Decadal Survey. It will observe in the near and medium infrared, and revolutionize our understanding of the high redshift universe. WFIRST is the highest ranked large space mission of the 2010 Decadal Survey. It is a NASA observatory designed to perform wide-field imaging and slitless spectroscopic surveys of the NIR sky (0.7 – 2.5μ). WFIRST will: (i) measure the expansion history of the universe, and thereby constrain dark energy, (ii) find Earth-like planets around other stars using microlensing, and (iii) perform surveys that are ∼100 times more sensitive than current NIR surveys
Baldi, Marco
2012-01-01
(Abridged) The growing role played by numerical N-body simulations in cosmological studies as a fundamental connection between theoretical modeling and direct observations has led to impressive advancements also in the development and application of specific algorithms designed to probe a wide range of Dark Energy scenarios. Over the last decade, a large number of independent and complementary investigations have been carried out in the field of Dark Energy N-body simulations, starting from the simplest case of homogeneous Dark Energy models up to the recent development of highly sophisticated iterative solvers for a variety of Modified Gravity theories. In this Review - which is meant to be complementary to the general Review by Kuhlen et al. published in this Volume - I will discuss the range of scenarios for the cosmic acceleration that have been successfully investigated by means of dedicated N-body simulations, and I will provide a broad summary of the main results that have been obtained in this rather ...
Interacting Dark Matter and Dark Energy
Farrar, G R; Farrar, Glennys R.
2004-01-01
We discuss models for the cosmological dark sector in which the energy density of a scalar field approximates Einstein's cosmological constant and the scalar field value determines the dark matter particle mass by a Yukawa coupling. A model with one dark matter family can be adjusted so the observational constraints on the cosmological parameters are close to but different from what is predicted by the Lambda CDM model. This may be a useful aid to judging how tightly the cosmological parameters are constrained by the new generation of cosmological tests that depend on the theory of structure formation. In a model with two families of dark matter particles the scalar field may be locked to near zero mass for one family. This can suppress the long-range scalar force in the dark sector and eliminate evolution of the effective cosmological constant and the mass of the nonrelativistic dark matter particles, making the model close to Lambda CDM, until the particle number density becomes low enough to allow the scal...
Holographic dark energy models: a comparison from the latest observational data
International Nuclear Information System (INIS)
The holographic principle of quantum gravity theory has been applied to the dark energy (DE) problem, and so far three holographic DE models have been proposed: the original holographic dark energy (HDE) model, the agegraphic dark energy (ADE) model, and the holographic Ricci dark energy (RDE) model. In this work, we perform the best-fit analysis on these three models, by using the latest observational data including the Union+CFA3 sample of 397 Type Ia supernovae (SNIa), the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). The analysis shows that for HDE, χmin2 = 465.912; for RDE, χmin2 = 483.130; for ADE, χmin2 = 481.694. Among these models, HDE model can give the smallest χ2min. Besides, we also use the Bayesian evidence (BE) as a model selection criterion to make a comparison. It is found that for HDE, ADE, and RDE, Δln BE = −0.86, −5.17, and −8.14, respectively. So, it seems that the HDE model is more favored by the observational data
From Dark Energy and Dark Matter to Dark Metric
Capozziello, S.; De Laurentis, M.; Francaviglia, M.; Mercadante, S
2008-01-01
It is nowadays clear that General Relativity cannot be the definitive theory of Gravitation due to several shortcomings that come out both from theoretical and experimental viewpoints. At large scales (astrophysical and cosmological) the attempts to match it with the latest observational data lead to invoke Dark Energy and Dark Matter as the bulk components of the cosmic fluid. Since no final evidence, at fundamental level, exists for such ingredients, it is clear that General Relativity pres...
Dark Energy and Structure Formation
International Nuclear Information System (INIS)
We study the gravitational dynamics of dark energy configurations. We report on the time evolution of the dark energy field configurations as well as the time evolution of the energy density to demonstrate the gravitational collapse of dark energy field configurations. We live in a Universe which is dominated by Dark Energy. According to current estimates about 75% of the Energy Density is in the form of Dark Energy. Thus when we consider gravitational dynamics and Structure Formation we expect Dark Energy to play an important role. The most promising candidate for dark energy is the energy density of fields in curved space-time. It therefore become a pressing need to understand the gravitational dynamics of dark energy field configurations. We develop and describe the formalism to study the gravitational collapse of fields given any general potential for the fields. We apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting evolution equations which determine the time evolution of field configurations as well as the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our universe.
Dark Energy and Structure Formation
Energy Technology Data Exchange (ETDEWEB)
Singh, Anupam, E-mail: morisi@ific.uv.es [Physics Department, L.N. Mittal I.I.T, Jaipur, Rajasthan (India)
2010-11-01
We study the gravitational dynamics of dark energy configurations. We report on the time evolution of the dark energy field configurations as well as the time evolution of the energy density to demonstrate the gravitational collapse of dark energy field configurations. We live in a Universe which is dominated by Dark Energy. According to current estimates about 75% of the Energy Density is in the form of Dark Energy. Thus when we consider gravitational dynamics and Structure Formation we expect Dark Energy to play an important role. The most promising candidate for dark energy is the energy density of fields in curved space-time. It therefore become a pressing need to understand the gravitational dynamics of dark energy field configurations. We develop and describe the formalism to study the gravitational collapse of fields given any general potential for the fields. We apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting evolution equations which determine the time evolution of field configurations as well as the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our universe.
Dark energy and extended dark matter halos
Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.
2012-03-01
The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even
Dark matter, dark energy and gravity
Robson, B. A.
2015-02-01
Within the framework of the Generation Model (GM) of particle physics, gravity is identified with the very weak, universal and attractive residual color interactions acting between the colorless particles of ordinary matter (electrons, neutrons and protons), which are composite structures. This gravitational interaction is mediated by massless vector bosons (hypergluons), which self-interact so that the interaction has two additional features not present in Newtonian gravitation: (i) asymptotic freedom and (ii) color confinement. These two additional properties of the gravitational interaction negate the need for the notions of both dark matter and dark energy.
Dark matter, dark energy and gravity
International Nuclear Information System (INIS)
Within the framework of the Generation Model (GM) of particle physics, gravity is identified with the very weak, universal and attractive residual color interactions acting between the colorless particles of ordinary matter (electrons, neutrons and protons), which are composite structures. This gravitational interaction is mediated by massless vector bosons (hypergluons), which self-interact so that the interaction has two additional features not present in Newtonian gravitation: (i) asymptotic freedom and (ii) color confinement. These two additional properties of the gravitational interaction negate the need for the notions of both dark matter and dark energy. (author)
Unravelling the Dark Matter - Dark Energy Paradigm
Cahill, Reginald T.
2009-01-01
The standard LambdaCDM model of cosmology is usually understood to arise from demanding that the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric satisfy the General Relativity dynamics for spacetime metrics. The FLRW data-based dominant parameter values, Omega_Lambda=0.73 and Omega_m=0.27 for the dark energy and dark matter+matter, respectively, are then determined by fitting the supernova red-shift data. However in the pressure-less flat-space case the LambdaCDM model is most easily derive...
Theoretical Models of Dark Energy
Yoo, Jaewon; Watanabe, Yuki
2012-01-01
Mounting observational data confirm that about 73% of the energy density consists of dark energy which is responsible for the current accelerated expansion of the Universe. We present observational evidences and dark energy projects. We then review various theoretical ideas that have been proposed to explain the origin of dark energy; they contain the cosmological constant, modified matter models, modified gravity models and the inhomogeneous model. The cosmological constant suffers from two ...
Dark energy: investigation and modeling
Tsujikawa, Shinji
2010-01-01
Constantly accumulating observational data continue to confirm that about 70% of the energy density today consists of dark energy responsible for the accelerated expansion of the Universe. We present recent observational bounds on dark energy constrained by the type Ia supernovae, cosmic microwave background, and baryon acoustic oscillations. We review a number of theoretical approaches that have been adopted so far to explain the origin of dark energy. This includes the cosmological constant...
Models of Interacting Dark Energy
Zimdahl, W
2012-01-01
Any non-gravitational coupling between dark matter and dark energy modifies the cosmological dynamics. Interactions in the dark sector are considered to be relevant to address the coincidence problem. Moreover, in various models the observed accelerated expansion of the Universe is a pure interaction phenomenon. Here we review recent approaches in which a coupling between both dark components is crucial for the evolution of the Universe.
Cosmic Visions Dark Energy: Science
Dodelson, Scott; Heitmann, Katrin; Hirata, Chris; Honscheid, Klaus; Roodman, Aaron; Seljak, Uroš; Slosar, Anže; Trodden, Mark
2016-01-01
Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiment...
Energy Technology Data Exchange (ETDEWEB)
Flaugher, B. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States). et al.
2015-04-11
The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250-μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. The CCDs have 15μm x 15μm pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.
Flaugher, B; Honscheid, K; Abbott, T M C; Alvarez, O; Angstadt, R; Annis, J T; Antonik, M; Ballester, O; Beaufore, L; Bernstein, G M; Bernstein, R A; Bigelow, B; Bonati, M; Boprie, D; Brooks, D; Buckley-Geer, E J; Campa, J; Cardiel-Sas, L; Castander, F J; Castilla, J; Cease, H; Cela-Ruiz, J M; Chappa, S; Chi, E; Cooper, C; da Costa, L N; Dede, E; Derylo, G; DePoy, D L; de Vicente, J; Doel, P; Drlica-Wagner, A; Eiting, J; Elliott, A E; Emes, J; Estrada, J; Neto, A Fausti; Finley, D A; Flores, R; Frieman, J; Gerdes, D; Gladders, M D; Gregory, B; Gutierrez, G R; Hao, J; Holland, S E; Holm, S; Huffman, D; Jackson, C; James, D J; Jonas, M; Karcher, A; Karliner, I; Kent, S; Kessler, R; Kozlovsky, M; Kron, R G; Kubik, D; Kuehn, K; Kuhlmann, S; Kuk, K; Lahav, O; Lathrop, A; Lee, J; Levi, M E; Lewis, P; Li, T S; Mandrichenko, I; Marshall, J L; Martinez, G; Merritt, K W; Miquel, R; Munoz, F; Neilsen, E H; Nichol, R C; Nord, B; Ogando, R; Olsen, J; Palio, N; Patton, K; Peoples, J; Plazas, A A; Rauch, J; Reil, K; Rheault, J -P; Roe, N A; Rogers, H; Roodman, A; Sanchez, E; Scarpine, V; Schindler, R H; Schmidt, R; Schmitt, R; Schubnell, M; Schultz, K; Schurter, P; Scott, L; Serrano, S; Shaw, T M; Smith, R C; Soares-Santos, M; Stefanik, A; Stuermer, W; Suchyta, E; Sypniewski, A; Tarle, G; Thaler, J; Tighe, R; Tran, C; Tucker, D; Walker, A R; Wang, G; Watson, M; Weaverdyck, C; Wester, W; Woods, R; Yanny, B
2015-01-01
The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250 micron thick fully-depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2kx4k CCDs for imaging and 12 2kx2k CCDs for guiding and focus. The CCDs have 15 microns x15 microns pixels with a plate scale of 0.263 arc sec per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construct...
Flaugher, B.; Diehl, H. T.; Honscheid, K.; Abbott, T. M. C.; Alvarez, O.; Angstadt, R.; Annis, J. T.; Antonik, M.; Ballester, O.; Beaufore, L.; Bernstein, G. M.; Bernstein, R. A.; Bigelow, B.; Bonati, M.; Boprie, D.; Brooks, D.; Buckley-Geer, E. J.; Campa, J.; Cardiel-Sas, L.; Castander, F. J.; Castilla, J.; Cease, H.; Cela-Ruiz, J. M.; Chappa, S.; Chi, E.; Cooper, C.; da Costa, L. N.; Dede, E.; Derylo, G.; DePoy, D. L.; de Vicente, J.; Doel, P.; Drlica-Wagner, A.; Eiting, J.; Elliott, A. E.; Emes, J.; Estrada, J.; Fausti Neto, A.; Finley, D. A.; Flores, R.; Frieman, J.; Gerdes, D.; Gladders, M. D.; Gregory, B.; Gutierrez, G. R.; Hao, J.; Holland, S. E.; Holm, S.; Huffman, D.; Jackson, C.; James, D. J.; Jonas, M.; Karcher, A.; Karliner, I.; Kent, S.; Kessler, R.; Kozlovsky, M.; Kron, R. G.; Kubik, D.; Kuehn, K.; Kuhlmann, S.; Kuk, K.; Lahav, O.; Lathrop, A.; Lee, J.; Levi, M. E.; Lewis, P.; Li, T. S.; Mandrichenko, I.; Marshall, J. L.; Martinez, G.; Merritt, K. W.; Miquel, R.; Muñoz, F.; Neilsen, E. H.; Nichol, R. C.; Nord, B.; Ogando, R.; Olsen, J.; Palaio, N.; Patton, K.; Peoples, J.; Plazas, A. A.; Rauch, J.; Reil, K.; Rheault, J.-P.; Roe, N. A.; Rogers, H.; Roodman, A.; Sanchez, E.; Scarpine, V.; Schindler, R. H.; Schmidt, R.; Schmitt, R.; Schubnell, M.; Schultz, K.; Schurter, P.; Scott, L.; Serrano, S.; Shaw, T. M.; Smith, R. C.; Soares-Santos, M.; Stefanik, A.; Stuermer, W.; Suchyta, E.; Sypniewski, A.; Tarle, G.; Thaler, J.; Tighe, R.; Tran, C.; Tucker, D.; Walker, A. R.; Wang, G.; Watson, M.; Weaverdyck, C.; Wester, W.; Woods, R.; Yanny, B.; DES Collaboration
2015-11-01
The Dark Energy Camera is a new imager with a 2.°2 diameter field of view mounted at the prime focus of the Victor M. Blanco 4 m telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five-element optical corrector, seven filters, a shutter with a 60 cm aperture, and a charge-coupled device (CCD) focal plane of 250 μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 megapixel focal plane comprises 62 2k × 4k CCDs for imaging and 12 2k × 2k CCDs for guiding and focus. The CCDs have 15 μm × 15 μm pixels with a plate scale of 0.″263 pixel-1. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 s with 6-9 electron readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.
Astrophysical constraints on dark energy
Ho, Chiu Man; Hsu, Stephen D. H.
2016-02-01
Dark energy (i.e., a cosmological constant) leads, in the Newtonian approximation, to a repulsive force which grows linearly with distance and which can have astrophysical consequences. For example, the dark energy force overcomes the gravitational attraction from an isolated object (e.g., dwarf galaxy) of mass 107M⊙ at a distance of 23 kpc. Observable velocities of bound satellites (rotation curves) could be significantly affected, and therefore used to measure or constrain the dark energy density. Here, isolated means that the gravitational effect of large nearby galaxies (specifically, of their dark matter halos) is negligible; examples of isolated dwarf galaxies include Antlia or DDO 190.
Quantum Field Theory of Interacting Dark Matter/Dark Energy: Dark Monodromies
D'Amico, Guido; Hamill, Teresa; Kaloper, Nemanja
2016-01-01
We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dar...
Trout, Aaron
2012-01-01
In this paper, we give a conceptual explanation of dark energy as a small negative residual scalar curvature present even in empty spacetime. This curvature ultimately results from postulating a discrete spacetime geometry, very closely related to that used in the dynamical triangulations approach to quantum gravity. In this model, there are no states which have total scalar curvature exactly zero. Moreover, numerical evidence in dimension three suggests that, at a fixed volume, the number of discrete-spacetime microstates strongly increases with decreasing curvature. Because of the resulting entropic force, any dynamics which push empty spacetime strongly toward zero scalar curvature would instead produce typically observed states with a small negative curvature. This provides a natural explanation for the empirically observed small positive value for the cosmological constant (Lambda is about 10^(-121) in Planck units.) In fact, we derive the very rough estimate Lambda=6x10^(-118) from a simple model contai...
Coupling q-deformed dark energy to dark matter
Dil, Emre
2016-01-01
We propose a novel coupled dark energy model which is assumed to occur as a q-deformed scalar field and investigate whether it will provide an expanding universe phase. We consider the q-deformed dark energy as coupled to dark matter inhomogeneities. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions. The attractor solutions imply that the coupled q-deformed dark energy model is consistent with the conventional dark energy models satisfying an acceleration phase of universe. At the end, we compare the cosmological parameters of deformed and standard dark energy models and interpret the implications.
Optimizing New Dark Energy Experiments
Energy Technology Data Exchange (ETDEWEB)
Tyson, J. Anthony [University of California, Davis
2013-08-26
Next generation “Stage IV” dark energy experiments under design during this grant, and now under construction, will enable the determination of the properties of dark energy and dark matter to unprecedented precision using multiple complementary probes. The most pressing challenge in these experiments is the characterization and understanding of the systematic errors present within any given experimental configuration and the resulting impact on the accuracy of our constraints on dark energy physics. The DETF and the P5 panel in their reports recommended “Expanded support for ancillary measurements required for the long-term program and for projects that will improve our understanding and reduction of the dominant systematic measurement errors.” Looking forward to the next generation Stage IV experiments we have developed a program to address the most important potential systematic errors within these experiments. Using data from current facilities it has been feasible and timely to undertake a detailed investigation of the systematic errors. In this DOE grant we studied of the source and impact of the dominant systematic effects in dark energy measurements, and developed new analysis tools and techniques to minimize their impact. Progress under this grant is briefly reviewed in this technical report. This work was a necessary precursor to the coming generations of wide-deep probes of the nature of dark energy and dark matter. The research has already had an impact on improving the efficiencies of all Stage III and IV dark energy experiments.
Cosmological evolution with interaction between dark energy and dark matter
Bolotin, Yuri L.; Kostenko, Alexander; Lemets, Oleg A.; Yerokhin, Danylo A.
2015-12-01
In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities. We consider a number of different models (including the holographic dark energy and dark energy in a fractal universe), with interacting dark energy and dark matter, have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of dark energy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model.
Cosmological Evolution With Interaction Between Dark Energy And Dark Matter
Bolotin, Yu L; Lemets, O A; Yerokhin, D A
2013-01-01
In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities. We consider a number of different models (including the holographic dark energy and dark energy in a fractal universe) with interacting dark energy (DE) and dark matter (DM), have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of dark energy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a Universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model (SCM).
QHD, Dark Matter and Dark Energy
Fritzsch, Harald
2014-01-01
In QHD the weak bosons, quarks and leptons are bound states of fundamental constituents, denoted as haplons. The confinement scale of the associated gauge group SU(2)_h is of the order of $\\Lambda_h\\simeq 0.3$ TeV. One scalar state has zero haplon number and is the resonance observed at the LHC. In addition, there exist new bound states of haplons with no counterpart in the SM, having a mass of the order of 0.5 TeV up to a few TeV. In particular, a neutral scalar state with haplon number 4 is stable and can provide the dark matter in the universe. The QHD, QCD and QED couplings can unify at the Planck scale. If this scale changes slowly with cosmic time, all of the fundamental couplings, the masses of the nucleons and of the DM particles, including the cosmological term (or vacuum energy density), will evolve with time. This could explain the dark energy of the universe.
Quantum Haplodynamics, Dark Matter, and Dark Energy
International Nuclear Information System (INIS)
In quantum haplodynamics (QHD) the weak bosons, quarks, and leptons are bound states of fundamental constituents, denoted as haplons. The confinement scale of the associated gauge group SU(2)h is of the order of Λh≃0.3 TeV. One scalar state has zero haplon number and is the resonance observed at the LHC. In addition, there exist new bound states of haplons with no counterpart in the SM, having a mass of the order of 0.5 TeV up to a few TeV. In particular, a neutral scalar state with haplon number 4 is stable and can provide the dark matter in the universe. The QHD, QCD, and QED couplings can unify at the Planck scale. If this scale changes slowly with cosmic time, all of the fundamental couplings, the masses of the nucleons and of the DM particles, including the cosmological term (or vacuum energy density), will evolve with time. This could explain the dark energy of the universe
Unified Description of Dark Energy and Dark Matter
Petry, Walter
2008-01-01
Dark energy in the universe is assumed to be vacuum energy. The energy-momentum of vacuum is described by a scale-dependent cosmological constant. The equations of motion imply for the density of matter (dust) the sum of the usual matter density (luminous matter) and an additional matter density (dark matter) similar to the dark energy. The scale-dependent cosmological constant is given up to an exponent which is approximated by the experimentally decided density parameters of dark matter and...
Is Dark Energy Abnormally Weighting?
Fuzfa, A.; Alimi, J. -M.
2006-01-01
We present a new interpretation of dark energy in terms of an \\textit{Abnormally Weighting Energy} (AWE). This means that dark energy does not couple to gravitation in the same way as ordinary matter, yielding a violation of the weak and strong equivalence principles on cosmological scales. The resulting cosmological mechanism accounts for the Hubble diagram of type Ia supernovae in terms of both cosmic acceleration and variation of the gravitational constant while still accounting for the pr...
Inflation with holographic dark energy
Chen, Bin; Li, Miao; Wang, Yi
2007-07-01
We investigate the corrections of the holographic dark energy to inflation paradigm. We study the evolution of the holographic dark energy in the inflationary universe in detail, and carry out a model-independent analysis on the holographic dark energy corrections to the primordial scalar power spectrum. It turns out that the corrections generically make the spectrum redder. To be consistent with the experimental data, there must be a upper bound on the reheating temperature. We also discuss the corrections due to different choices of the infrared cutoff.
Inflation with holographic dark energy
International Nuclear Information System (INIS)
We investigate the corrections of the holographic dark energy to inflation paradigm. We study the evolution of the holographic dark energy in the inflationary universe in detail, and carry out a model-independent analysis on the holographic dark energy corrections to the primordial scalar power spectrum. It turns out that the corrections generically make the spectrum redder. To be consistent with the experimental data, there must be a upper bound on the reheating temperature. We also discuss the corrections due to different choices of the infrared cutoff
Inflation with Holographic Dark Energy
Chen, B; Wang, Y; Chen, Bin; Li, Miao; Wang, Yi
2006-01-01
We investigate the corrections of the holographic dark energy to inflation paradigm. We study the evolution of the holographic dark energy in the inflationary universe in detail, and carry out a model-independent analysis on the holographic dark energy correction to the primordial scalar power spectrum. It turns out that the corrections generically make the spectrum redder. To be consistent with the experimental data, there must be a upper bound on the reheating temperature. We also discuss the corrections due to different choices of the infrared cutoff.
Dark Energy and Termonuclear Supernovae
Domíngez, I.; Bravo, E.; Piersanti, L.; Tornambé, A.; Straniero, O.; Höflich, P.
2008-12-01
Nowadays it is widely accepted that the current Universe is dominated by dark energy and exotic matter, the so called StandardModel of Cosmoloy or CDM model. All the available data (Thermonuclear Supernovae, Cosmic Microwave Background, Baryon Acoustic Oscillations, Large Scale Structure, etc.) are compatible with a flat Universe made by ~70% of dark energy. Up to now observations agree that dark energy may be the vacuum energy (or cosmological constant) although improvements are needed to constrain further its equation of state. In this context, the cosmic destiny of the Universe is no longer linked to its geometry but to the nature of dark energy; it may be flat and expand forever or collapse. To understand the nature of dark energy is probably the most fundamental problem in physics today; it may open new roads of knowledge and led to unify gravity with the other fundamental interactions in nature. It is expected that astronomical data will continue to provide directions to theorists and experimental physicists. Type Ia supernovae (SNe Ia) have played a fundamental role, showing the acceleration of the expansion rate of the Universe a decade ago, and up to now they are the only astronomical observations that provide a direct evidence of the acceleration. However, in order to determine the source of the dark energy term it is mandatory to improve the precision of supernovae as distance indicators on cosmological scale.
Cosmological Acceleration: Dark Energy or Modified Gravity?
Bludman, Sidney
2006-01-01
We review the evidence for recently accelerating cosmological expansion or "dark energy", either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any Dark Energy constituent. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-...
Holographic Gas as Dark Energy
Li, Miao; Li, Xiao-Dong; Lin, Chunshan; Wang, Yi
2008-01-01
We investigate the statistical nature of holographic gas, which may represent the quasi-particle excitations of a strongly correlated gravitational system. We find that the holographic entropy can be obtained by modifying degeneracy. We calculate thermodynamical quantities and investigate stability of the holographic gas. When applying to cosmology, we find that the holographic gas behaves as holographic dark energy, and the parameter $c$ in holographic dark energy can be calculated from our ...
Beyond two dark energy parameters
Sullivan, Scott; Joudaki, Shahab; Amblard, Alexandre; Holz, Daniel; Cooray, Asantha
2007-01-01
The relative strengths of future cosmology experiments to constrain dark energy are generally evaluated in the context of two parameter models of the equation of state with redshift. We show that next-generation surveys will be able to constrain the dark energy equation of state in three or more independent redshift bins to better than 10%. We thus propose an alternative, model-free figure of merit which is naturally extensible to arbitrary numbers of independent redshift bins.
Greyber, Howard
2009-11-01
By careful analysis of the data from the WMAP satellite, scientists were surprised to determine that about 70% of the matter in our universe is in some unknown form, and labeled it Dark Energy. Earlier, in 1998, two separate international groups of astronomers studying Ia supernovae were even more surprised to be forced to conclude that an amazing smooth transition occurred, from the expected slowing down of the expansion of our universe (due to normal positive gravitation) to an accelerating expansion of the universe that began at at a big bang age of the universe of about nine billion years. In 1918 Albert Einstein stated that his Lambda term in his theory of general relativity was ees,``the energy of empty space,'' and represented a negative pressure and thus a negative gravity force. However my 2004 ``Strong'' Magnetic Field model (SMF) for the origin of magnetic fields at Combination Time (Astro-ph0509223 and 0509222) in our big bang universe produces a unique topology for Superclusters, having almost all the mass, visible and invisible, i.e. from clusters of galaxies down to particles with mass, on the surface of an ellipsoid surrounding a growing very high vacuum. If I hypothesize, with Einstein, that there exists a constant ees force per unit volume, then, gradually, as the universe expands from Combination Time, two effects occur (a) the volume of the central high vacuum region increases, and (b) the density of positive gravity particles in the central region of each Supercluster in our universe decreases dramatically. Thus eventually Einstein's general relativity theory's repulsive gravity of the central very high vacuum region becomes larger than the positive gravitational attraction of all the clusters of galaxies, galaxies, quasars, stars and plasma on the Supercluster shell, and the observed accelerating expansion of our universe occurs. This assumes that our universe is made up mostly of such Superclusters. It is conceivable that the high vacuum
Dark Matter, Dark Energy and the Chaplygin Gas
Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D
2002-01-01
We formulate a Zel'dovich-like approximation for the Chaplygin gas equation of state P = -A/rho, and sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.
Late Forming Dark Matter in Theories of Neutrino Dark Energy
Das, Subinoy; Weiner, Neal
2006-01-01
We study the possibility of Late Forming Dark Matter (LFDM), where a scalar field, previously trapped in a metastable state by thermal or finite density effects, begins to oscillate near the era matter-radiation equality about its true minimum. Such a theory is motivated generally if the dark energy is of a similar form, but has not yet made the transition to dark matter, and, in particular, arises automatically in recently considered theories of neutrino dark energy. If such a field comprise...
Dark energy and dark matter from primordial QGP
Vaidya, Vaishali; Upadhyaya, G. K.
2015-07-01
Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.
Dark energy and dark matter from primordial QGP
Energy Technology Data Exchange (ETDEWEB)
Vaidya, Vaishali, E-mail: vaidvavaishali24@gmail.com; Upadhyaya, G. K., E-mail: gopalujiain@yahoo.co.in [School of Studies in Physics, Vikram University Ujjain (India)
2015-07-31
Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.
Dark energy and dark matter from primordial QGP
International Nuclear Information System (INIS)
Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang
Dark energy and dark matter as curvature effects
Capozziello, S.; Cardone, V F; Troisi, A.
2006-01-01
Astrophysical observations are pointing out huge amounts of dark matter and dark energy needed to explain the observed large scale structures and cosmic accelerating expansion. Up to now, no experimental evidence has been found, at fundamental level, to explain such mysterious components. The problem could be completely reversed considering dark matter and dark energy as shortcomings of General Relativity and claiming for the correct theory of gravity as that derived by matching the largest n...
Unified Dark Energy-Dark Matter model with Inverse Quintessence
Ansoldi, Stefano; Guendelman, Eduardo I.
2012-01-01
We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-conventional kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in t...
Material models of dark energy.
Pearson, Jonathan A.
2014-01-01
A new class of “dark energy” models is reviewed and developed, in which the relativistic theory of solids is used to construct material models of dark energy. These are models which include the effects of a continuous medium with well defined physical properties at the level of linearized perturbations. The formalism is constructed for a medium with arbitrary symmetry, and then specialised to isotropic media (which will be the case of interest for the majority of cosmological applications). T...
Dark Energy Coupled with Dark Matter in the Accelerating Universe
Institute of Scientific and Technical Information of China (English)
ZHANG Yang
2004-01-01
@@ To model the observed Universe containing both dark energy and dark matter, we study the effective Yang-Mills condensate model of dark energy and add a non-relativistic matter component as the dark matter, which is generated out of the decaying dark energy at a constant rate Г, a parameter of our model. For the Universe driven by these two components, the dynamic evolution still has asymptotic behaviour: the expansion of the Universe is accelerating with an asymptotically constant rate H, and the densities of both components approach to finite constant values. Moreover, ΩA≈ 0.7 for dark energy and Ωm ≈ 0.3 for dark matter are achieved if the decay rate Г is chosen such that Г/H～ 1.
Facilities for Dark Energy Investigations
Weinberg, David; Dawson, Kyle; Dore, Olivier; Frieman, Joshua; Gebhardt, Karl; Levi, Michael; Rhodes, Jason
2013-01-01
The discovery of cosmic acceleration has inspired ambitious experimental and observational efforts to understand its origin. Many of these take the form of large astronomical surveys, sometimes using new, special-purpose instrumentation, and in some cases entirely new facilities. This Report summarizes some of the major ongoing and planned dark energy experiments, focusing on those in which the U.S. community has a leading or significant supporting role. It provides background information for other Reports from the "Dark Energy and CMB" working group of the APS Division of Particles and Fields long-term planning exercise. We provide 1-2 page summaries of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) and its SDSS-IV successor eBOSS, the Dark Energy Survey (DES), the Subaru Hyper-Suprime Camera (HSC) and Prime Focus Spectrograph (PFS), the Hobby-Eberley Telescope Dark Energy Experiment (HEDTEX), the Dark Energy Spectroscopic Instrument (DESI), the Large Synpotic Survey Telescope (LSST), and the Eu...
Energy Technology Data Exchange (ETDEWEB)
Chapline, G
2005-03-08
Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena including supernovae explosions, gamma ray bursts, positron emission, and dark matter.
Laboratory tests on dark energy
International Nuclear Information System (INIS)
The physical nature of the currently observed dark energy in the universe is completely unclear, and many different theoretical models co-exist. Nevertheless, if dark energy is produced by vacuum fluctuations then there is a chance to probe some of its properties by simple laboratory tests based on Josephson junctions. These electronic devices can be used to perform 'vacuum fluctuation spectroscopy', by directly measuring a noise spectrum induced by vacuum fluctuations. One would expect to see a cutoff near 1.7 THz in the measured power spectrum, provided the new physics underlying dark energy couples to electric charge. The effect exploited by the Josephson junction is a subtile nonlinear mixing effect and has nothing to do with the Casimir effect or other effects based on van der Waals forces. A Josephson experiment of the suggested type will now be built, and we should know the result within the next 3 years
Energy Technology Data Exchange (ETDEWEB)
Binder, Gary A.; /Caltech /SLAC
2010-08-25
In order to make accurate measurements of dark energy, a system is needed to monitor the focus and alignment of the Dark Energy Camera (DECam) to be located on the Blanco 4m Telescope for the upcoming Dark Energy Survey. One new approach under development is to fit out-of-focus star images to a point spread function from which information about the focus and tilt of the camera can be obtained. As a first test of a new algorithm using this idea, simulated star images produced from a model of DECam in the optics software Zemax were fitted. Then, real images from the Mosaic II imager currently installed on the Blanco telescope were used to investigate the algorithm's capabilities. A number of problems with the algorithm were found, and more work is needed to understand its limitations and improve its capabilities so it can reliably predict camera alignment and focus.
Flaugher, Brenna
2012-03-01
The Dark Energy Survey Collaboration has built the Dark Energy Camera (DECam), a 3 square degree, 520 Megapixel CCD camera which is being mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to carry out the 5000 sq. deg. Dark Energy Survey, using 30% of the telescope time over a 5 year period. During the remainder of the time, and after the survey, DECam will be available as a community instrument. Construction of DECam is complete. The final components were shipped to Chile in Dec. 2011 and post-shipping checkout is in progress in Dec-Jan. Installation and commissioning on the telescope are taking place in 2012. A summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and commissioning will be presented.
Laboratory tests on dark energy
Beck, C
2006-01-01
The physical nature of the currently observed dark energy in the universe is completely unclear, and many different theoretical models co-exist. Nevertheless, if dark energy is produced by vacuum fluctuations then there is a chance to probe some of its properties by simple laboratory tests based on Josephson junctions. These electronic devices can be used to perform `vacuum fluctuation spectroscopy', by directly measuring a noise spectrum induced by vacuum fluctuations. One would expect to see a cutoff near 1.7 THz in the measured power spectrum, provided the new physics underlying dark energy couples to electric charge. The effect exploited by the Josephson junction is a subtile nonlinear mixing effect and has nothing to do with the Casimir effect or other effects based on van der Waals forces. A Josephson experiment of the suggested type will now be built, and we should know the result within the next 3 years.
Unified dark energy-dark matter model with inverse quintessence
Energy Technology Data Exchange (ETDEWEB)
Ansoldi, Stefano [ICRA — International Center for Relativistic Astrophysics, INFN — Istituto Nazionale di Fisica Nucleare, and Dipartimento di Matematica e Informatica, Università degli Studi di Udine, via delle Scienze 206, I-33100 Udine (UD) (Italy); Guendelman, Eduardo I., E-mail: ansoldi@fulbrightmail.org, E-mail: guendel@bgu.ac.il [Department of Physics, Ben-Gurion University of the Negeev, Beer-Sheva 84105 (Israel)
2013-05-01
We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-canonical kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an ''inverse quintessence scenario'', where the universe starts from a zero vacuum energy density state, instead of approaching it in the future.
Active galaxies can make axionic dark energy
Dimopoulos, Konstantinos; Cormack, Sam
2016-01-01
AGN jets carry helical magnetic fields, which can affect dark matter if the latter is axionic. This preliminary study shows that, in the presence of strong helical magnetic fields, the nature of the axionic condensate may change and become dark energy. Such dark energy may affect galaxy formation and galactic dynamics, so this possibility should not be ignored when considering axionic dark matter.
Dark matter and dark energy a challenge for modern cosmology
Gorini, Vittorio; Moschella, Ugo; Matarrese, Sabino
2011-01-01
This book brings together reviews from leading international authorities on the developments in the study of dark matter and dark energy, as seen from both their cosmological and particle physics side. Studying the physical and astrophysical properties of the dark components of our Universe is a crucial step towards the ultimate goal of unveiling their nature. The work developed from a doctoral school sponsored by the Italian Society of General Relativity and Gravitation. The book starts with a concise introduction to the standard cosmological model, as well as with a presentation of the theory of linear perturbations around a homogeneous and isotropic background. It covers the particle physics and cosmological aspects of dark matter and (dynamical) dark energy, including a discussion of how modified theories of gravity could provide a possible candidate for dark energy. A detailed presentation is also given of the possible ways of testing the theory in terms of cosmic microwave background, galaxy redshift su...
Holographic Dark Information Energy
Michael Paul Gough
2011-01-01
Landauer’s principle and the Holographic principle are used to derive the holographic information energy contribution to the Universe. Information energy density has increased with star formation until sufficient to start accelerating the expansion of the universe. The resulting reduction in the rate of star formation due to the accelerated expansion may provide a feedback that limits the information energy density to a constant level. The characteristics of the universe’s holographic informa...
Interacting Induced Dark Energy Model
Bahrehbakhsh, Amir F.
2016-01-01
Similar to the idea of the brane world scenarios, but based on the approach of the induced matter theory, for a non--vacuum five--dimensional version of general relativity, we propose a model in which the conventional matter sources considered as all kind of the matter (the baryonic and dark) and the induced terms emerging from the extra dimension supposed to be as dark energy. Then we investigate the FLRW type cosmological equations and illustrate that the model is capable to explain respect...
Holographic dark energy linearly interacting with dark matter
Chimento, Luis P; Richarte, Martín G
2012-01-01
We investigate a spatially flat Friedmann-Robertson-Walker (FRW) cosmological model with cold dark matter coupled to a modified holographic Ricci dark energy through a general interaction term linear in the energy densities of dark matter and dark energy, the total energy density and its derivative. Using the statistical method of $\\chi^2$-function for the Hubble data, we obtain $H_0=73.6$km/sMpc, $\\omega_s=-0.842$ for the asymptotic equation of state and $ z_{acc}= 0.89 $. The estimated values of $\\Omega_{c0}$ which fulfill the current observational bounds corresponds to a dark energy density varying in the range $0.25R < \\ro_x < 0.27R$.
Weak lensing and dark energy: the impact of dark energy on nonlinear dark matter clustering
Joudaki, Shahab; Holz, Daniel E
2009-01-01
We examine the influence of percent-level dark energy corrections to the nonlinear matter power spectrum on constraints of the dark energy equation of state from future weak lensing probes. We explicitly show that a poor approximation (off by > 10%) to the nonlinear corrections causes a > 1 sigma bias on the determination of the dark energy equation of state. Future weak lensing surveys must therefore incorporate dark energy modifications to the nonlinear matter power spectrum accurate to the percent-level, to avoid introducing significant bias in their measurements. For the WMAP5 cosmology, the more accurate power spectrum is more sensitive to dark energy properties, resulting in a factor of two improvement in dark energy equation of state constraints. We explore the complementary constraints on dark energy from future weak lensing and supernova surveys. A space-based, JDEM-like survey measures the equation of state in five independent redshift bins to ~10%, while this improves to ~5% for a wide-field ground...
The Dark Force: Astrophysical Repulsion from Dark Energy
Ho, Chiu Man
2016-01-01
Dark energy (i.e., a cosmological constant) leads, in the Newtonian approximation, to a repulsive force which grows linearly with distance. We discuss possible astrophysical effects of this "dark" force. For example, the dark force overcomes the gravitational attraction from an object (e.g., dwarf galaxy) of mass $10^7 M_\\odot$ at a distance of $~ 23$ kpc. It seems possible that observable velocities of bound satellites (rotation curves) could be significantly affected, and therefore used to measure the dark energy density.
Lorentz symmetry violation, dark matter and dark energy
Gonzalez-Mestres, Luis
2009-01-01
Taking into account the experimental results of the HiRes and AUGER collaborations, the present status of bounds on Lorentz symmetry violation (LSV) patterns is discussed. Although significant constraints will emerge, a wide range of models and values of parameters will still be left open. Cosmological implications of allowed LSV patterns are discussed focusing on the origin of our Universe, the cosmological constant, dark matter and dark energy. Superbradyons (superluminal preons) may be the actual constituents of vacuum and of standard particles, and form equally a cosmological sea leading to new forms of dark matter and dark energy.
Dark energy and dark matter as curvature effects
Capozziello, S; Troisi, A
2006-01-01
Astrophysical observations are pointing out huge amounts of dark matter and dark energy needed to explain the observed large scale structures and cosmic accelerating expansion. Up to now, no experimental evidence has been found, at fundamental level, to explain such mysterious components. The problem could be completely reversed considering dark matter and dark energy as shortcomings of General Relativity and claiming for the correct theory of gravity as that derived by matching the largest number of observational data. As a result, accelerating behavior of cosmic fluid and rotation curves of spiral galaxies are reproduced by means of curvature effects.
Gauge conditions in combined dark energy and dark matter systems
Christopherson, Adam J.
2010-01-01
When analysing a system consisting of both dark matter and dark energy, an often used practice in the literature is to neglect the perturbations in the dark energy component. However, it has recently been argued, through the use of numerical simulations, that one cannot do so. In this work we show that by neglecting such perturbations one is implicitly making a choice of gauge. As such, one no longer has the freedom to choose, for example, a gauge comoving with the dark matter -- in fact doin...
Cosmic Visions Dark Energy: Science
Dodelson, Scott; Hirata, Chris; Honscheid, Klaus; Roodman, Aaron; Seljak, Uroš; Slosar, Anže; Trodden, Mark
2016-01-01
Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV c...
Cosmic Visions Dark Energy. Science
Energy Technology Data Exchange (ETDEWEB)
Dodelson, Scott [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Heitmann, Katrin [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Hirata, Chris [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Honscheid, Klaus [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Roodman, Aaron [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Seljak, Uroš [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Slosar, Anže [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Trodden, Mark [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
2016-04-26
Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.
Holographic dark energy from minimal supergravity
Landim, Ricardo C. G.
2015-01-01
We embed models of holographic dark energy coupled to dark matter in minimal supergravity plus matter, with one chiral superfield. We analyze two cases. The first one has the Hubble radius as the infrared cutoff and the interaction between the two fluids is proportional to the energy density of the dark energy. The second case has the future event horizon as infrared cutoff while the interaction is proportional to the energy density of both components of the dark sector.
Holographic dark energy with varying gravitational constant
Jamil, Mubasher; Saridakis, Emmanuel N.; Setare, M. R.
2009-08-01
We investigate the holographic dark energy scenario with a varying gravitational constant, in flat and non-flat background geometry. We extract the exact differential equations determining the evolution of the dark energy density-parameter, which include G-variation correction terms. Performing a low-redshift expansion of the dark energy equation of state, we provide the involved parameters as functions of the current density parameters, of the holographic dark energy constant and of the G-variation.
Holographic dark energy with varying gravitational constant
International Nuclear Information System (INIS)
We investigate the holographic dark energy scenario with a varying gravitational constant, in flat and non-flat background geometry. We extract the exact differential equations determining the evolution of the dark energy density-parameter, which include G-variation correction terms. Performing a low-redshift expansion of the dark energy equation of state, we provide the involved parameters as functions of the current density parameters, of the holographic dark energy constant and of the G-variation.
Holographic dark energy with varying gravitational constant
Jamil, Mubasher; Setare, M R
2009-01-01
We investigate the holographic dark energy scenario with a varying gravitational constant, in flat and non-flat background geometry. We extract the exact differential equations determining the evolution of the dark energy density-parameter, which include $G$-variation correction terms. Performing a low-redshift expansion of the dark energy equation of state, we provide the involved parameters as functions of the current density parameters, of the holographic dark energy constant and of the $G$-variation.
Some issues concerning holographic dark energy
International Nuclear Information System (INIS)
We study the perturbation of holographic dark energy and find it to be stable. We study the fate of the universe when interacting holographic dark energy is present, and discuss a simple phenomenological classification of the interacting holographic dark energy models. We also discuss the cosmic coincidence problem in the context of holographic dark energy. We find that the coincidence problem cannot be completely solved by adding an interacting term. Inflation may provide a better solution of the coincidence problem
Some Issues Concerning Holographic Dark Energy
Li, Miao; Lin, Chunshan; Wang, Yi
2008-01-01
We study perturbation of holographic dark energy and find it be stable. We study the fate of the universe when interacting holographic dark energy is present, and discuss a simple phenomenological classification of the interacting holographic dark energy models. We also discuss the cosmic coincidence problem in the context of holographic dark energy. We find that the coincidence problem can not be completely solved by adding an interacting term. Inflation may provide a better solution of the ...
Exactly solved models of interacting dark matter and dark energy
Chimento, Luis P
2012-01-01
We introduce an effective one-fluid description of the interacting dark sector in a spatially flat Friedmann-Robertson-Walker space-time and investigate the stability of the power-law solutions. We find the "source equation" for the total energy density and determine the energy density of each dark component. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities, their first derivatives, the total energy density with its derivatives up to second order and the scale factor. We solve the evolution equations of the dark components for both interactions, examine exhaustively several examples and show cases where the problem of the coincidence is alleviated. We show that a generic nonlinear interaction gives rise to the "relaxed Chaplygin gas model" whose effective equation of state includes the variable modified Chaplygin gas model while some others nonlinear interactions yield de Sitter and power-law scenarios.
Dark energy from discrete spacetime.
Trout, Aaron D
2013-01-01
Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, [Formula: see text] in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies. PMID:24312502
Dark Energy Coupled with Relativistic Dark Matter in Accelerating Universe
Institute of Scientific and Technical Information of China (English)
张杨
2003-01-01
Recent observations favour an accelerating Universe dominated by the dark energy. We take the effective YangMills condensate as the dark energy and couple it to a relativistic matter which is created by the decaying condensate. The dynamic evolution has asymptotic behaviour with finite constant energy densities, and the fractional densities Ω∧～ 0.7 for dark energy and Ωm ～ 0.3 for relativistic matter are achieved at proper values of the decay rate. The resulting expansion of the Universe is in the de Sitter acceleration.
Quantum Field Theory of Interacting Dark Matter/Dark Energy: Dark Monodromies
D'Amico, Guido; Kaloper, Nemanja
2016-01-01
We discuss how to formulate a quantum field theory of dark energy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of dark energy are strongly constrained. Quintessence-generated long range forces and radiative stability of the quintessence potential require that such dark matter and dark energy are completely decoupled. However, if dark energy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory. Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations.
Chaplygin Gas Cosmology - Unification of Dark Matter and Dark Energy
Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D
2006-01-01
The models that unify dark matter and dark energy based upon the Chaplygin gas fail owing to the suppression of structure formation by the adiabatic speed of sound. Including string theory effects, in particular the Kalb-Ramond field, we show how nonadiabatic perturbations allow a successful structure formation.
Quantum mechanical theory behind "dark energy"?
Colin Johnson, R
2007-01-01
"The mysterious increase in the acceleration of the universe, when intuition says it should be slowing down, is postulated to be caused by dark energy - "dark" because it is undetected. Now a group of scientists in the international collaboration Essence has suggested that a quantum mechanical interpretation of Einstein's proposed "cosmological constant" is the simplest explanation for dark energy. The group measured dark energy to within 10 percent." (1,5 page)
Abdalla, Elcio; Graef, Leila; Wang, Bin
2012-01-01
We discuss a model of non perturbative decay of dark energy into hot and cold dark matter. This model provides a mechanism from the field theory to realize the energy transfer from dark energy into dark matter, which is the requirement to alleviate the coincidence problem. The advantage of the model is the fact that we accommodate a mean life compatible with the age of the universe. We also argue that supersymmetry is a natural set up, though not essential.
The Dark Energy Survey: more than dark energy - an overview
Abbott, T; Allam, S; Aleksic, J; Amara, A; Bacon, D; Balbinot, E; Banerji, M; Bechtol, K; Benoit-Levy, A; Bernstein, G M; Bertin, E; Blazek, J; Dodelson, S; Bonnett, C; Brooks, D; Bridle, S; Brunner, R J; Buckley-Geer, E; Burke, D L; Capozzi, D; Caminha, G B; Carlsen, J; Carnero-Rosell, A; Carollo, M; Carrasco-Kind, M; Carretero, J; Castander, F J; Clerkin, L; Collett, T; Conselice, C; Crocce, M; Cunha, C E; D'Andrea, C B; da Costa, L N; Davis, T M; Desai, S; Diehl, H T; Dietrich, J P; Doel, P; Drlica-Wagner, A; Etherington, J; Estrada, J; Evrard, A E; Finley, D A; Flaugher, B; Fosalba, P; Foley, R J; Frieman, J; Garcia-Bellido, J; Gaztanaga, E; Gerdes, D W; Giannantonio, T; Goldstein, D A; Gruen, D; Gruendl, R A; Guarnieri, P; Gutierrez, G; Hartley, W; Honscheid, K; Jain, B; James, D J; Jeltema, T; Jouvel, S; Kessler, R; King, A; Kirk, D; Kron, R; Kuehn, K; Kuropatkin, N; Lahav, O; Li, T S; Lima, M; Lin, H; Maia, M A G; Manera, M; Maraston, C; Marshall, J L; Martini, P; McMahon, R G; Melchior, P; Merson, A; Miller, C J; Miquel, R; Mohr, J J; Morice-Atkinson, X; Naidoo, K; Neilsen, E; Nichol, R C; Nord, B; Ogando, R; Ostrovski, F; Palmese, A; Papadopoulos, A; Peiris, H; Peoples, J; Plazas, A A; Percival, W J; Reed, S L; Romer, A K; Roodman, A; Ross, A; Rozo, E; Rykoff, E S; Sadeh, I; Sako, M; Sanchez, C; Sanchez, E; Santiago, B; Scarpine, V; Schubnell, M; Sevilla-Noarbe, I; Sheldon, E; Smith, R C; Soares-Santos, M; Sobreira, F; Soumagnac, M; Suchyta, E; Sullivan, M; Tarle, G; Thaler, J; Thomas, D; Thomas, R C; Tucker, D; Vieira, J D; Vikram, V; Walker, A R; Wechsler, R H; Wester, W; Weller, J; Whiteway, L; Wilcox, H; Yanny, B; Zhang, Y; Zuntz, J
2016-01-01
This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasi...
Material models of dark energy
Pearson, Jonathan A
2014-01-01
We review and develop a new class of "dark energy" models, in which the relativistic theory of solids is used to construct material models of dark energy. These are models which include the effects of a continuous medium with well defined physical properties at the level of linearized perturbations. The formalism is constructed for a medium with arbitrary symmetry, and then specialised to isotropic media (which will be the case of interest for the majority of cosmological applications). We develop the theory of relativistic isotropic viscoelastic media whilst keeping in mind that we ultimately want to observationally constrain the allowed properties of the material model. We do this by obtaining the viscoelastic equations of state for perturbations (the entropy and anisotropic stress), as well as identifying the consistent corner of the theory which has constant equation of state parameter $\\dot{w}=0$. We also connect to the non-relativistic theory of solids, by identifying the two quadratic invariants that a...
Gravitation and regular Universe without dark energy and dark matter
Minkevich, A. V.
2011-01-01
It is shown that isotropic cosmology in the Riemann-Cartan spacetime allows to solve the problem of cosmological singularity as well as the problems of invisible matter components - dark energy and dark matter. All cosmological models filled with usual gravitating matter satisfying energy dominance conditions are regular with respect to energy density, spacetime metrics and the Hubble parameter. At asymptotics cosmological solutions of spatially flat models describe accelerating Universe with...
Dark Energy, Gravitation and Electromagnetism
B. G. Sidharth
2004-01-01
In the context of the fact that the existence of dark energy causing the accelerated expansion of the universe has been confirmed by the WMAP and the Sloan Digital Sky Survey, we re-examine gravitation itself, starting with the formulation of Sakharov and show that it is possible to obtain gravitation in terms of the electromagnetic charge of elementary particles, once the ZPF and its effects at the Compton scale are taken into account.
Chaining Mimes in the Dark: Dark Energy Scaling from Dark Matter to Acceleration
Bielefeld, Jannis; Linder, Eric V
2014-01-01
The dark sector of the Universe need not be completely separable into distinct dark matter and dark energy components. We consider a model of early dark energy in which the dark energy mimics a dark matter component in both evolution and perturbations at early times. Barotropic aether dark energy scales as a fixed fraction, possibly greater than one, of the dark matter density and has vanishing sound speed at early times before undergoing a transition. This gives signatures not only in cosmic expansion but in sound speed and inhomogeneities, and in number of effective neutrino species. Model parameters describe the timing, sharpness of the transition, and the relative abundance at early times. Upon comparison with current data, we find viable regimes in which the dark energy behaves like dark matter at early times: for transitions well before recombination the dark energy to dark matter fraction can equal or exceed unity, while for transitions near recombination the ratio can only be a few percent. After the ...
LHC Signatures Of Scalar Dark Energy
Brax, Philippe; Englert, Christoph; Spannowsky, Michael
2016-01-01
Scalar dark energy fields that couple to the Standard Model can give rise to observable signatures at the LHC. In this work we show that $t\\bar t+$missing energy and mono-jet searches are suitable probes in the limit where the dark energy scalar is stable on collider distances. We discuss the prospects of distinguishing the dark energy character of new physics signals from dark matter signatures and the possibility of probing the self-interactions of the dark energy sector.
The Dark Energy Survey: more than dark energy - an overview
Dark Energy Survey Collaboration; Abbott, T.; Abdalla, F. B.; Aleksić, J.; Allam, S.; Amara, A.; Bacon, D.; Balbinot, E.; Banerji, M.; Bechtol, K.; Benoit-Lévy, A.; Bernstein, G. M.; Bertin, E.; Blazek, J.; Bonnett, C.; Bridle, S.; Brooks, D.; Brunner, R. J.; Buckley-Geer, E.; Burke, D. L.; Caminha, G. B.; Capozzi, D.; Carlsen, J.; Carnero-Rosell, A.; Carollo, M.; Carrasco-Kind, M.; Carretero, J.; Castander, F. J.; Clerkin, L.; Collett, T.; Conselice, C.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Davis, T. M.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Dodelson, S.; Doel, P.; Drlica-Wagner, A.; Estrada, J.; Etherington, J.; Evrard, A. E.; Fabbri, J.; Finley, D. A.; Flaugher, B.; Foley, R. J.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Giannantonio, T.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Guarnieri, P.; Gutierrez, G.; Hartley, W.; Honscheid, K.; Jain, B.; James, D. J.; Jeltema, T.; Jouvel, S.; Kessler, R.; King, A.; Kirk, D.; Kron, R.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; Lin, H.; Maia, M. A. G.; Makler, M.; Manera, M.; Maraston, C.; Marshall, J. L.; Martini, P.; McMahon, R. G.; Melchior, P.; Merson, A.; Miller, C. J.; Miquel, R.; Mohr, J. J.; Morice-Atkinson, X.; Naidoo, K.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Ostrovski, F.; Palmese, A.; Papadopoulos, A.; Peiris, H. V.; Peoples, J.; Percival, W. J.; Plazas, A. A.; Reed, S. L.; Refregier, A.; Romer, A. K.; Roodman, A.; Ross, A.; Rozo, E.; Rykoff, E. S.; Sadeh, I.; Sako, M.; Sánchez, C.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Sheldon, E.; Smith, M.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Soumagnac, M.; Suchyta, E.; Sullivan, M.; Swanson, M.; Tarle, G.; Thaler, J.; Thomas, D.; Thomas, R. C.; Tucker, D.; Vieira, J. D.; Vikram, V.; Walker, A. R.; Wechsler, R. H.; Weller, J.; Wester, W.; Whiteway, L.; Wilcox, H.; Yanny, B.; Zhang, Y.; Zuntz, J.
2016-08-01
This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be Λ+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).
Dark energy interacting with two fluids
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile)], E-mail: ncruz@lauca.usach.cl; Lepe, Samuel [Instituto de Fisica, Facultad de Ciencias Basicas y Matematicas, Universidad Catolica de Valparaiso, Avenida Brasil 2950, Valparaiso (Chile)], E-mail: slepe@ucv.cl; Pena, Francisco [Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Universidad de La Frontera, Avda. Francisco Salazar 01145, Casilla 54-D Temuco (Chile)], E-mail: fcampos@ufro.cl
2008-05-29
A cosmological model of dark energy interacting with dark matter and another general component of the universe is investigated. We found general constraints on these models imposing an accelerated expansion. The same is also studied in the case for holographic dark energy.
Lemoine, Martin; Martin, Jerome; Uzan, Jean-Philippe
2002-01-01
It has recently been proposed by Mersini et al. 01, Bastero-Gil and Mersini 02 that the dark energy could be attributed to the cosmological properties of a scalar field with a non-standard dispersion relation that decreases exponentially at wave-numbers larger than Planck scale (k_phys > M_Planck). In this scenario, the energy density stored in the modes of trans-Planckian wave-numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account natura...
Characterising Dark Energy through supernovae
Davis, Tamara M
2016-01-01
Type Ia supernovae are a powerful cosmological probe, that gave the first strong evidence that the expansion of the universe is accelerating. Here we provide an overview of how supernovae can go further to reveal information about what is causing the acceleration, be it dark energy or some modification to our laws of gravity. We first summarise the many different approaches used to explain or test the acceleration, including parametric models (like the standard model, LambdaCDM), non-parametric models, dark fluid models such as quintessence, and extensions to standard gravity. We also show how supernova data can be used beyond the Hubble diagram, to give information on gravitational lensing and peculiar velocities that can be used to distinguish between models that predict the same expansion history. Finally, we review the methods of statistical inference that are commonly used, making a point of separating parameter estimation from model selection.
Dark energy and the Boomerang data
Amendola, Luca
2000-01-01
The recent high-quality Boomerang data allow to test many competing cosmological models. Here I present a seven-parameter likelihood analysis of dark energy models with exponential potential and explicit coupling to dark matter. Such a model is conformally equivalent to a scalar field with non-minimal coupling to gravity. So far, the constraints on a dark energy - dark matter coupling were extremely weak. The Boomerang data constrain the dimensionless coupling $\\beta $ to be smaller than 0.1,...
Strangeness, cosmological cold dark matter and dark energy
International Nuclear Information System (INIS)
It is now believed that the universe is composed of a small amount of the normal luminous matter, a substantial amount of matter (cold dark matter (CDM)) which is non-luminous and a large amount of smooth energy (dark energy (DE)). Both CDM and DE seem to require ideas beyond the standard model of particle interactions. In this work, we argue that CDM and DE can arise entirely from the standard principles of strong interaction physics out of the same mechanism
Dark Matter and Dark Energy: A Physicist's Perspective
Dine, Michael
2001-01-01
For physicists, recent developments in astrophysics and cosmology present exciting challenges. We are conducting "experiments" in energy regimes some of which will be probed by accelerators in the near future, and others which are inevitably the subject of more speculative theoretical investigations. Dark matter is an area where we have hope of making discoveries both with accelerator experiments and dedicated searches. Inflation and dark energy lie in regimes where presently our only hope fo...
Cosmological acceleration. Dark energy or modified gravity?
International Nuclear Information System (INIS)
We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model ΛCDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)
Dark matter and dark energy in dwarf galaxy systems
Chernin, A. D.; Teerikorpi, P.
2014-01-01
Quantitative estimates of themaximumallowed totalmasses and sizes of the dark-matter halos in groups and associations of dwarf galaxies—special types of metagalactic populations identified in recent astronomical observations with the Hubble Space Telescope—are presented. Dwarf-galaxy systems are formed of isolated dark-matter halos with a small number of dark galaxies embedded in them. Data on the sizes of these systems and the velocity dispersions of the embedded galaxies can be used to determine lower limits on the total dark-halo masses using the virial theorem. Upper limits follow from the conditions that the systems immersed in the cosmic dark-energy background be gravitationally bound. The median maximum masses are close to 1012 M ⊙ for both groups and associations of dwarf galaxies, although the median virial masses for these two types of systems differ by approximately a factor of ten.
Why we need to see the dark matter to understand the dark energy
Kunz, Martin
2007-01-01
The cosmological concordance model contains two separate constituents which interact only gravitationally with themselves and everything else, the dark matter and the dark energy. In the standard dark energy models, the dark matter makes up some 20% of the total energy budget today, while the dark energy is responsible for about 75%. Here we show that these numbers are only robust for specific dark energy models and that in general we cannot measure the abundance of the dark constituents sepa...
Tracing dark energy with quasars
Średzińska, J; Bilicki, M; Hryniewicz, K; Krupa, M; Kurcz, A; Marziani, P; Pollo, A; Pych, W; Udalski, A
2016-01-01
The nature of dark energy, driving the accelerated expansion of the Universe, is one of the most important issues in modern astrophysics. In order to understand this phenomenon, we need precise astrophysical probes of the universal expansion spanning wide redshift ranges. Quasars have recently emerged as such a probe, thanks to their high intrinsic luminosities and, most importantly, our ability to measure their luminosity distances independently of redshifts. Here we report our ongoing work on observational reverberation mapping using the time delay of the Mg II line, performed with the South African Large Telescope (SALT).
Dark energy stars: Stable configurations
Bhar, Piyali; Rahaman, Farook; Banerjee, Ayan
2016-01-01
In present paper a spherically symmetric stellar configuration has been analyzed by assuming the matter distribution of the stellar configuration is anisotropic in nature and compared with the realistic objects, namely, the low mass X-ray binaries (LMXBs) and X-ray pulsars. The analytic solution has been obtained by utilizing the dark energy equation of state for the interior solution corresponding to the Schwarzschild exterior vacuum solution at the junction interface. Several physical properties like energy conditions, stability, mass-radius ratio, and surface redshift are described through mathematical calculations as well as graphical plots. It is found that obtained mass-radius ration of the compact stars candidates like 4U 1820-30, PSR J 1614-2230, Vela X-1 and Cen X-3 are very much consistent with the observed data by Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431, 3216 (2013)). So our proposed model would be useful in the investigation of the possible clustering of dark energy.
Dark Energy and Dark Matter in Stars Physic
Fiziev, Plamen
2014-01-01
We present the basic equations and relations for the relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which is {\\em locally} equivalent to the f(R) theories of gravity and gives an alternative description of the effects of dark matter and dark energy. The results for the simplest form of the relativistic equation of state (EOS) of neutron matter are represented. Our approach overcomes the well-known difficulties of the physics of SSSS in t...
Dark matter and dark energy from quark bag model
Brilenkov, Maxim; Jenkovszky, Laszlo; Zhuk, Alexander
2013-01-01
We calculate the present expansion of our Universe endowed with relict colored objects - quarks and gluons - that survived hadronization either as isolated islands of quark-gluon "nuggets", or spread uniformly in the Universe. In the first scenario, the quark nuggets can play the role of dark matter. In the second scenario, we demonstrate that uniform colored objects can play the role of dark energy providing the late-time accelerating expansion of the Universe.
Dark Energy: The Shadowy Reflection of Dark Matter?
Kostas Kleidis; Spyrou, Nikolaos K.
2016-01-01
In this article, we review a series of recent theoretical results regarding a conventional approach to the dark energy (DE) concept. This approach is distinguished among others for its simplicity and its physical relevance. By compromising General Relativity (GR) and Thermodynamics at cosmological scale, we end up with a model without DE. Instead, the Universe we are proposing is filled with a perfect fluid of self-interacting dark matter (DM), the volume elements of which perform hydrodynami...
Minimal metagravity vs. dark matter and/or dark energy
Pirogov, Yu. F.
2006-01-01
The minimal metagravity theory, explicitly violating the general covariance but preserving the unimodular one, is applied to study the evolution of the isotropic homogeneous Universe. The massive scalar graviton, contained in the theory in addition to the massless tensor one, is treated as a source of the dark matter and/or dark energy. The modified Friedmann equation for the scale factor of the Universe is derived. The question wether the minimal metagravity can emulate the LCDM concordance ...
The Possible Nature of Dark Energy and Dark Matter
Olivi-Tran, Nathalie
2012-01-01
open access journal International audience The nature of dark matter is linked to the fluctuations of curvature of the hyper-surface of our three dimensional universe. These fluctuations of curvature have gravitational effects and deviate radiations. While we question dark energy, as another theory by Olivi-Tran [4] accounts for the acceleration of the expansion of our universe by analyzing the nature of time.
On the dark energy clustering properties
Perrotta, Francesca; Baccigalupi, Carlo
2002-01-01
We highlight a viable mechanism leading to the formation of dark energy structures on sub-horizon cosmological scales, starting from linear perturbations in scalar-tensor cosmologies. We show that the coupling of the dark energy scalar field, or Quintessence, to the Ricci scalar induces a "dragging" of its density perturbations through the general relativistic gravitational potentials. We discuss, in particular, how this process forces dark energy to behave as a pressureless component if the ...
Interacting holographic dark energy with logarithmic correction
Jamil, Mubasher; Farooq, M. Umar
2010-01-01
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is originally motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Using this new definition, we investigate the model of interacting dark energy and derive its effective equation of s...
On the Chemical Potential of Dark Energy
Pereira, S H
2008-01-01
It is widely assumed that the observed universe is accelerating due to the existence of a new fluid component called dark energy. In this article, the thermodynamics consequences of a nonzero chemical potential on the dark energy component is discussed with special emphasis to the phantom fluid case. It is found that if the dark energy fluid is endowed with a negative chemical potential, the phantom field hypothesis becomes thermodynamically consistent with no need of negative temperatures as recently assumed in the literature.
On the Chemical Potential of Dark Energy
Pereira, S. H.
2008-01-01
It is widely assumed that the observed universe is accelerating due to the existence of a new fluid component called dark energy. In this article, the thermodynamics consequences of a nonzero chemical potential on the dark energy component is discussed with special emphasis to the phantom fluid case. It is found that if the dark energy fluid is endowed with a negative chemical potential, the phantom field hypothesis becomes thermodynamically consistent with no need of negative temperatures as...
Paths to dark energy theory and observation
Valtonen, Mauri; Chernin, Arthur D; Byrd, Gene
2012-01-01
This work provides the current theory and observations behind the cosmological phenomenon of dark energy. The approach is comprehensivewith rigorous mathematical theory and relevant astronomical observations discussed in context.The book treats the background and history starting with the new-found importance of Einstein's cosmological constant (proposed long ago for the opposite purpose) in dark energy formulation, as well as the frontiers of dark energy.
Quinstant Dark Energy Predictions for Structure Formation
Nodal, Yoelsy Leyva; Cardone, V F
2009-01-01
We explore the predictions of a class of dark energy models, quinstant dark energy, concerning the structure formation in the Universe, both in the linear and non-linear regimes. Quinstant dark energy is considered to be formed by quintessence and a negative cosmological constant. We conclude that these models give good predictions for structure formation in the linear regime, but fail to do so in the non-linear one, for redshifts larger than one.
The Dark Energy Camera (DECam)
Honscheid, K; Abbott, T; Annis, J; Antonik, M; Barcel, M; Bernstein, R; Bigelow, B; Brooks, D; Buckley-Geer, E; Campa, J; Cardiel, L; Castander, F; Castilla, J; Cease, H; Chappa, S; Dede, E; Derylo, G; Diehl, T; Doel, P; De Vicente, J; Eiting, J; Estrada, J; Finley, D; Flaugher, B; Gaztañaga, E; Gerdes, D; Gladders, M; Guarino, V; Gutíerrez, G; Hamilton, J; Haney, M; Holland, S; Huffman, D; Karliner, I; Kau, D; Kent, S; Kozlovsky, M; Kubik, D; Kühn, K; Kuhlmann, S; Kuk, K; Leger, F; Lin, H; Martínez, G; Martínez, M; Merritt, W; Mohr, J; Moore, P; Moore, T; Nord, B; Ogando, R; Olsen, J; Onal, B; Peoples, J; Qian, T; Roe, N; Sánchez, E; Scarpine, V; Schmidt, R; Schmitt, R; Schubnell, M; Schultz, K; Selen, M; Shaw, T; Simaitis, V; Slaughter, J; Smith, C; Spinka, H; Stefanik, A; Stuermer, W; Talaga, R; Tarle, G; Thaler, J; Tucker, D; Walker, A; Worswick, S; Zhao, A
2008-01-01
In this paper we describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). It consists of a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y), a modern data acquisition and control system and the associated infrastructure for operation in the prime focus cage. The focal plane includes of 62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of view and 12 smaller 2K x 2K CCDs for guiding, focus and alignment. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms, and control system for DECam are underway; delivery of the instrument to CTIO is scheduled ...
Dark Energy and Dark Matter in Stars Physic
Fiziev, Plamen
2014-01-01
We present the basic equations and relations for the relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which is {\\em locally} equivalent to the f(R) theories of gravity and gives an alternative description of the effects of dark matter and dark energy. The results for the simplest form of the relativistic equation of state (EOS) of neutron matter are represented. Our approach overcomes the well-known difficulties of the physics of SSSS in the f(R) theories of gravity introducing two novel EOS for cosmological energy-pressure densities and dilaton energy-pressure densities, as well as proper boundary conditions.
Interacting holographic dark energy with logarithmic correction
Jamil, Mubasher; Umar Farooq, M.
2010-03-01
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Employing this new definition, we investigate the model of interacting dark energy and derive its effective equation of state. Finally we establish a correspondence between generalized Chaplygin gas and entropy-corrected holographic dark energy.
Interacting holographic dark energy with entropy corrections
Jamil, Mubasher
2010-01-01
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is originally motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Using this new definition, we investigate the model of interacting dark energy and derive its effective equation of state. Finally we establish a correspondence between generalized Chaplygin gas and entropy-corrected holographic dark energy.
Interacting holographic dark energy with logarithmic correction
International Nuclear Information System (INIS)
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Employing this new definition, we investigate the model of interacting dark energy and derive its effective equation of state. Finally we establish a correspondence between generalized Chaplygin gas and entropy-corrected holographic dark energy
Dark Energy and Its Interactions with Neutrinos
Zhang, Xinmin
2005-01-01
In this talk I will firstly review on the current constraints on the equation of state of the dark energy from observational data, then present a new scenario of dark energy dubbed {\\it Quintom}. The recent fits to the type Ia supernova data and the cosmic microwave background and so on in the literature find that the behavior of dark energy is to great extent in consistency with a cosmological constant, however the dynamical dark energy scenarios are generally not ruled out, and one class of...
Genesis of Dark Energy: Dark Energy as a Consequence of Cosmological Nuclear Energy
Gupta, R. C.
2004-01-01
Recent observations on Type-Ia supernovae and low density measurement of matter (including dark matter) suggest that the present day universe consists mainly of repulsive-gravity type exotic-matter with negative-pressure often referred as dark-energy. But the mystery is about the nature of dark-energy and its puzzling questions such as why, how, where & when about the dark- energy are intriguing. In the present paper the author attempts to answer these questions while making an effort to reve...
Examining the Viability of Phantom Dark Energy
Ludwick, Kevin
2016-03-01
In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter w metric and the components of the stress-energy tensor, and we consider dynamic w and primordial isocurvature and adiabatic perturbations. We find that phantom dark energy does not necessarily have negative kinetic energy for all relevant length scales at all times and, by the same token, that quintessence dark energy does not necessarily have positive kinetic energy for all relevant length scales at all times.
The Logotropic Dark Fluid as a unification of dark matter and dark energy
Pierre-Henri Chavanis
2016-01-01
We propose a heuristic unification of dark matter and dark energy in terms of a single “dark fluid” with a logotropic equation of state P=Aln(ρ/ρP), where ρ is the rest-mass density, ρP=5.16×1099gm−3 is the Planck density, and A is the logotropic temperature. The energy density ϵ is the sum of a rest-mass energy term ρc2∝a−3 mimicking dark matter and an internal energy term u(ρ)=−P(ρ)−A=3Alna+C mimicking dark energy (a is the scale factor). The logotropic temperature is approximately given ...
Dark matter and dark energy induced by condensates
Capolupo, Antonio
2016-01-01
It is shown that the vacuum condensate induced by many phenomena behaves as a perfect fluid which, under particular conditions, has zero or negative pressure. In particular, the condensates of thermal states, of fields in curved space and of mixed particles have been analyzed. It is shown that the thermal states with the cosmic microwave radiation temperature, the Unruh and the Hawking radiations give negligible contributions to the critical energy density of the universe, while the thermal vacuum of the intercluster medium could contribute to the dark matter, together with the vacuum energy of fields in curved space-time and of mixed neutrinos. Moreover, a component of the dark energy can be represented by the vacuum of axion-like particles mixed with photons and superpartners of neutrinos. The formal analogy among the systems characterized by the condensates can open new scenarios in the possibility to detect the dark components of the universe in table top experiments.
How clustering dark energy affects matter perturbations
Mehrabi, A.; Basilakos, S.; Pace, F.
2015-09-01
The rate of structure formation in the Universe is different in homogeneous and clustered dark energy models. The degree of dark energy clustering depends on the magnitude of its effective sound speed c2_eff and for c2_eff=0 dark energy clusters in a similar fashion to dark matter while for c2_eff=1 it stays (approximately) homogeneous. In this paper we consider two distinct equations of state for the dark energy component, wd = const and w_d=w_0+w_1(z/1+z) with c2_eff as a free parameter and we try to constrain the dark energy effective sound speed using current available data including Type Ia supernovae, baryon acoustic oscillation, cosmic microwave background shift parameter (Planck and WMAP), Hubble parameter, big bang nucleosynthesis and the growth rate of structures fσ8(z). At first we derive the most general form of the equations governing dark matter and dark energy clustering under the assumption that c2_eff=const. Finally, performing an overall likelihood analysis we find that the likelihood function peaks at c2_eff=0; however, the dark energy sound speed is degenerate with respect to the cosmological parameters, namely Ωm and wd.
A Field Theory Model for Dark Matter and Dark Energy in Interaction
Micheletti, Sandro; Abdalla, Elcio; Wang, Bin
2009-01-01
We propose a field theory model for dark energy and dark matter in interaction. Comparing the classical solutions of the field equations with the observations of the CMB shift parameter, BAO, lookback time and Gold supernovae sample, we observe a possible interaction between dark sectors with energy decay from dark energy into dark matter. The observed interaction provides an alleviation to the coincidence problem.
Coupled tachyonic dark energy: a dynamical analysis
Landim, Ricardo C G
2015-01-01
In this paper we present a dynamical analysis for a coupled tachyonic dark energy with dark matter. The tachyonic field $\\phi$ is considered in the presence of barothropic fluids (matter and radiation) and the autonomous system due to the evolution equations is studied. The three cosmological eras (radiation, matter and dark energy) are described through the critical points, for a generic potential $V(\\phi)$.
Bouncing cosmologies with dark matter and dark energy
Cai, Yi-Fu; Wang, Dong-Gang; Wilson-Ewing, Edward
2016-01-01
We review matter bounce scenarios where the matter content is dark matter and dark energy. These cosmologies predict a nearly scale-invariant power spectrum with a slightly red tilt for scalar perturbations and a small tensor-to-scalar ratio. Importantly, these models predict a positive running of the scalar index, contrary to the predictions of the simplest inflationary and ekpyrotic models, and hence could potentially be falsified by future observations. We also review how bouncing cosmological space-times can arise in theories where either the Einstein equations are modified or where matter fields that violate the null energy condition are included.
Probing Dark Energy with the Kunlun Dark Universe Survey Telescope
Zhao, Gong-Bo; Wang, Lifan; Fan, Zuhui; Zhang, Xinmin
2010-01-01
Dark energy is an important science driver of many upcoming large-scale surveys. With small, stable seeing and low thermal infrared background, Dome A, Antarctica, offers a unique opportunity for shedding light on fundamental questions about the universe. We show that a deep, high-resolution imaging survey of 10,000 square degrees in \\emph{ugrizyJH} bands can provide competitive constraints on dark energy equation of state parameters using type Ia supernovae, baryon acoustic oscillations, and weak lensing techniques. Such a survey may be partially achieved with a coordinated effort of the Kunlun Dark Universe Survey Telescope (KDUST) in \\emph{yJH} bands over 5000--10,000 deg$^2$ and the Large Synoptic Survey Telescope in \\emph{ugrizy} bands over the same area. Moreover, the joint survey can take advantage of the high-resolution imaging at Dome A to further tighten the constraints on dark energy and to measure dark matter properties with strong lensing as well as galaxy--galaxy weak lensing.
Holography and holographic dark energy model
International Nuclear Information System (INIS)
The holographic principle is used to discuss the holographic dark energy model. We find that the Bekenstein-Hawking entropy bound is far from saturation under certain conditions. A more general constraint on the parameter of the holographic dark energy model is also derived
Dark energy, cosmological constant and neutrino mixing
A. Capolupo; Capozziello, S.; Vitiello, G.
2007-01-01
The today estimated value of dark energy can be achieved by the vacuum condensate induced by neutrino mixing phenomenon. Such a tiny value is recovered for a cut-off of the order of Planck scale and it is linked to the sub eV neutrino mass scale. Contributions to dark energy from auxiliary fields or mechanisms are not necessary in this approach.
Hologrphy and holographic dark energy model
Gong, Yungui; Zhang, Yuan-Zhong
2005-01-01
The holographic principle is used to discuss the holographic dark energy model. We find that the Bekenstein-Hawking entropy bound is far from saturation under certain conditions. A more general constraint on the parameter of the holographic dark energy model is also derived.
"Microscopic" approach to the Ricci dark energy
Broda, Bogusław
2011-01-01
A derivation of the Ricci dark energy from quantum field theory of fluctuating "matter" fields in a classical gravitational background is presented. The coupling to the dark energy, the parameter 'a', is estimated in the framework of our formalism, and qualitatively it appears to be within observational expectations.
Cosmological acceleration. Dark energy or modified gravity?
Energy Technology Data Exchange (ETDEWEB)
Bludman, S.
2006-05-15
We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model {lambda}CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)
A two measure model of dark energy and dark matter
Guendelman, Eduardo; Singleton, Douglas; Yongram, Nattapong
2012-01-01
In this work we construct a unified model of dark energy and dark matter. This is done with the following three elements: a gravitating scalar field, phi with a non-conventional kinetic term, as in the string theory tachyon; an arbitrary potential, V(phi); two measures -- a metric measure (sqrt{-g}) and a non-metric measure (Phi). The model has two interesting features: (i) For potentials which are unstable and would give rise to tachyonic scalar field, this model can stabilize the scalar fie...
Dark energy from a renormalization group flow
Mocioiu, I.; Roiban, R.
2012-01-01
We present evidence that a special class of gravitationally-coupled hidden sectors, in which conformal invariance is dynamically broken in a controlled way, exhibit the properties of dark energy. Such quantum field theories may appear while embedding the Standard Model in a more fundamental high energy theory. At late times, an effective dark energy field behaves similarly to an exponentially small cosmological constant while at early times its energy density partly tracks that of matter.
Cosmic Acceleration, Dark Energy and Fundamental Physics
Turner, Michael S.; Huterer, Dragan
2007-01-01
A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic acceleration is a highly elastic (p\\sim -rho), very smooth form of energy called ``dark energy'' accounting for about 75% of the Universe. The ``simplest'' explanation for dark energy is the zero-point energy density associated with the quantum vacuum; however...
Interacting Ricci Dark Energy with Logarithmic Correction
Pasqua, Antonio; Jamil, Mubasher; Myrzakulov, R
2011-01-01
Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area $A$ of the event horizon of the universe. However, such a model would have a causality problem. In this work, we consider the entropy-corrected version of the holographic dark energy model in the non-flat FRW universe and we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We obtain the equation of state (EoS) parameter $\\omega_{\\Lambda}$, the deceleration parameter $q$ and $\\Omega_D'$ in the presence of interaction between Dark Energy (DE) and Dark Matter (DM). Moreover, we reconstruct the potential and the dynamics of the tachyon, K-essence, dilaton and quintessence scalar field models according to the evolutionary behavior of the interacting entropy-corrected holographic dark energy model.
Interacting Ricci dark energy with logarithmic correction
Pasqua, Antonio; Khodam-Mohammadi, A.; Jamil, Mubasher; Myrzakulov, R.
2012-07-01
Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area A of the event horizon of the universe. However, such a model would have a causality problem. In this work, we consider the entropy-corrected version of the holographic dark energy model in the non-flat FRW universe and we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We obtain the equation of state (EoS) parameter ω Λ, the deceleration parameter q and ΩD' in the presence of interaction between Dark Energy (DE) and Dark Matter (DM). Moreover, we reconstruct the potential and the dynamics of the tachyon, K-essence, dilaton and quintessence scalar field models according to the evolutionary behavior of the interacting entropy-corrected holographic dark energy model.
Theories of Dark Energy with Screening Mechanisms
Khoury, Justin
2010-01-01
Despite the overwhelming evidence for the existence of dark energy and dark matter, their underlying fundamental physics remains unknown. This review article explores the tantalizing possibility that the dark sector includes new light degrees of freedom that mediate long-range forces on cosmological scales. To ensure consistency with laboratory and solar system tests of gravity, some screening mechanism is necessary to "hide" these degrees of freedom locally. I will focus on two broad classes...
Clustering, Angular Size and Dark Energy
R.C. Santos; Lima, J. A. S.
2008-01-01
The influence of dark matter inhomogeneities on the angular size-redshift test is investigated for a large class of flat cosmological models driven by dark energy plus a cold dark matter component (XCDM model). The results are presented in two steps. First, the mass inhomogeneities are modeled by a generalized Zeldovich-Kantowski-Dyer-Roeder (ZKDR) distance which is characterized by a smoothness parameter $\\alpha(z)$ and a power index $\\gamma$, and, second, we provide a statistical analysis t...
Investigation of dark matter-dark energy interaction cosmological model
Wang, J S
2014-01-01
In this paper, we test the dark matter-dark energy interacting cosmological model with a dynamic equation of state $w_{DE}(z)=w_{0}+w_{1}z/(1+z)$, using type Ia supernovae (SNe Ia), Hubble parameter data, baryonic acoustic oscillation (BAO) measurements, and the cosmic microwave background (CMB) observation. This interacting cosmological model has not been studied before. The best-fitted parameters with $1 \\sigma$ uncertainties are $\\delta=-0.022 \\pm 0.006$, $\\Omega_{DM}^{0}=0.213 \\pm 0.008$, $w_0 =-1.210 \\pm 0.033$ and $w_1=0.872 \\pm 0.072$ with $\\chi^2_{min}/dof = 0.990$. At the $1 \\sigma$ confidence level, we find $\\delta<0$, which means that the energy transfer prefers from dark matter to dark energy. We also find that the SNe Ia are in tension with the combination of CMB, BAO and Hubble parameter data. The evolution of $\\rho_{DM}/\\rho_{DE}$ indicates that this interacting model is a good approach to solve the coincidence problem, because the $\\rho_{DE}$ decrease with scale factor $a$. The transition r...
Fluid Mechanics Explains Cosmology, Dark Matter, Dark Energy, and Life
Gibson, Carl H
2012-01-01
Observations of the interstellar medium by the Herschel, Planck etc. infrared satellites throw doubt on standard {\\Lambda}CDMHC cosmological processes to form gravitational structures. According to the Hydro-Gravitational-Dynamics (HGD) cosmology of Gibson (1996), and the quasar microlensing observations of Schild (1996), the dark matter of galaxies consists of Proto-Globular-star-Cluster (PGC) clumps of Earth-mass primordial gas planets in metastable equilibrium since PGCs began star production at 0.3 Myr by planet mergers. Dark energy and the accelerating expansion of the universe inferred from SuperNovae Ia are systematic dimming errors produced as frozen gas dark matter planets evaporate to form stars. Collisionless cold dark matter that clumps and hierarchically clusters does not exist. Clumps of PGCs began diffusion from the Milky Way Proto-Galaxy upon freezing at 14 Myr to give the Magellanic Clouds and the faint dwarf galaxies of the 10^22 m diameter baryonic dark matter Galaxy halo. The first stars p...
Polytropic dark matter flows illuminate dark energy and accelerated expansion
Kleidis, K
2014-01-01
Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. Accordingly, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluid-like properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, the energy of this fluid's internal motions is also taken into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy needed to compromise spatial flatness, namely, to justify that, today, the total-energy density parameter is exactly unity. The poly...
Dark Energy: Observational Evidence and Theoretical Models
Novosyadlyj, B; Shtanov, Yu; Zhuk, A
2015-01-01
The book elucidates the current state of the dark energy problem and presents the results of the authors, who work in this area. It describes the observational evidence for the existence of dark energy, the methods and results of constraining of its parameters, modeling of dark energy by scalar fields, the space-times with extra spatial dimensions, especially Kaluza---Klein models, the braneworld models with a single extra dimension as well as the problems of positive definition of gravitational energy in General Relativity, energy conditions and consequences of their violation in the presence of dark energy. This monograph is intended for science professionals, educators and graduate students, specializing in general relativity, cosmology, field theory and particle physics.
Is this the end of dark energy?
Barboza, Edésio M; Abreu, Éverton M C; Neto, Jorge Ananias
2015-01-01
In this paper we investigate the limits imposed by thermodynamics to a dark energy fluid. We obtain the heat capacities and the compressibilities for a dark energy fluid. These thermodynamical variables are easily accessible experimentally for any terrestrial fluid. The thermal and mechanical stabilities require these quantities to be positive. We show that such requirements forbid the existence of a cosmic fluid with negative constant EoS parameter which excludes vacuum energy as a candidate to explain the cosmic acceleration. We also show that the current observational data from SN Ia, BAO and $H(z)$ are in conflict with the physical constraints that a general dark energy fluid with a time-dependent EoS parameter must obey which can be interpreted as an evidence against the dark energy hypothesis. Although our result excludes the vacuum energy, a geometrical cosmological term as originally introduced by Einstein in the field equations remains untouched.
Dark Energy, Particle Physics and Cosmology
Turner, Michael S.
2012-05-01
Dark energy and cosmic acceleration is one of the three pillars of the current cosmological paradigm. Moreover, both raise fundamental issues in cosmology and particle physics. In particle physics, the dark energy problem is intimately related to the perplexing issue of why the quantum energy of the vacuum is so small. In cosmology, the nature of the dark energy is crucial to understanding the destiny of the Universe. I will discuss the status of current models for dark energy -- including vacuum energy and rolling scalar fields -- their implications for cosmology and for particle physics and how they can be tested by WFIRST. I will also address the status of the possibility that cosmic acceleration is explained by modifying or replacing general relativity.
Dark Energy: The Shadowy Reflection of Dark Matter?
Kleidis, Kostas
2016-01-01
In this article, we review a series of recent theoretical results regarding a conventional approach to the dark energy (DE) concept. This approach is distinguished among others for its simplicity and its physical relevance. By compromising General Relativity (GR) and Thermodynamics at cosmological scale, we end up with a model without DE. Instead, the Universe we are proposing is filled with a perfect fluid of self-interacting dark matter (DM), the volume elements of which perform hydrodynamic flows. To the best of our knowledge, it is the first time in a cosmological framework that the energy of the cosmic fluid internal motions is also taken into account as a source of the universal gravitational field. As we demonstrate, this form of energy may compensate for the DE needed to compromise spatial flatness, while, depending on the particular type of thermodynamic processes occurring in the interior of the DM fluid (isothermal or polytropic), the Universe depicts itself as either decelerating or accelerating (...
Holographic dilatonic model of dark energy
Rozas-Fernández, Alberto
2009-01-01
We present a dilatonic description of the holographic dark energy by connecting the holographic dark energy density with the dilaton scalar-field energy density in a flat Friedmann-Robertson-Walker universe. We show that this model can describe the observed accelerated expansion of our universe with the choice c≥1 and reconstruct the kinetic term as well as the dynamics of the dilaton scalar field. © 2011 Springer-Verlag/Società Italiana di Fisica.
Probing Gravitation, Dark Energy, and Acceleration
Linder, Eric V.
2004-01-01
The acceleration of the expansion of the universe arises from unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. It is crucial for our understanding to characterize the properties of the dark energy or gravity through cosmological observations and compare and distinguish between them. In fact, close consistencies exist between a dark energy equation of state function w(z) and changes to the framework of the Friedmann cosmologi...
Supernova Constraints on Braneworld Dark Energy
Alam, Ujjaini; Sahni, Varun
2002-01-01
Braneworld models of dark energy are examined in the light of observations of high redshift type Ia supernovae. Braneworld models admit several novel and even exotic possibilities which include: (i) The effective equation of state of dark energy can be more negative than in LCDM: $w \\leq -1$; (ii) A class of braneworld models can encounter a `quiescent' future singularity at which the energy density and the Hubble parameter remain well behaved, but higher derivatives of the expansion factor (...
Paths to dark energy. Theory and observation
Energy Technology Data Exchange (ETDEWEB)
Byrd, Gene; Chernin, Arthur D.; Teerikorpi, Pekka; Valtonen, Mauri
2012-07-01
This work provides the current theory and observations behind the cosmological phenomenon of dark energy. The approach is comprehensive with rigorous mathematical theory and relevant astronomical observations discussed in context. The book treats the background and history starting with the new-found importance of Einstein's cosmological constant (proposed long ago) in dark energy formulation, as well as the frontiers of dark energy. The authors do not presuppose advanced knowledge of astronomy, and basic mathematical concepts used in modern cosmology are presented in a simple, but rigorous way. All this makes the book useful for both astronomers and physicists, and also for university students of physical sciences.
Entropy-Corrected Holographic Dark Energy
Wei, Hao
2009-01-01
The holographic dark energy (HDE) is now an interesting candidate of dark energy, which has been studied extensively in the literature. In the derivation of HDE, the black hole entropy plays an important role. In fact, the entropy-area relation can be modified due to loop quantum gravity or other reasons. With the modified entropy-area relation, we propose the so-called ``entropy-corrected holographic dark energy'' (ECHDE) in the present work. We consider many aspects of ECHDE and find some i...
Statefinder Diagnosis for Ricci Dark Energy
Feng, Chao-Jun
2008-01-01
Statefinder diagnostic is a useful method which can differ one dark energy model from each others. In this letter, we apply this method to a holographic dark energy model from Ricci scalar curvature, called the Ricci dark energy model(RDE). We plot the evolutionary trajectories of this model in the statefinder parameter-planes, and it is found that the parameter of this model plays a significant role from the statefinder viewpoint. In a very special case, the statefinder diagnostic fails to discriminate LCDM and RDE models, thus we apply a new diagnostic called the Om diagnostic proposed recently to this model in this case in Appendix A and it works well.
Statefinder parameters in two dark energy models
Panotopoulos, Grigoris
2007-01-01
The statefinder parameters ($r,s$) in two dark energy models are studied. In the first, we discuss in four-dimensional General Relativity a two fluid model, in which dark energy and dark matter are allowed to interact with each other. In the second model, we consider the DGP brane model generalized by taking a possible energy exchange between the brane and the bulk into account. We determine the values of the statefinder parameters that correspond to the unique attractor of the system at hand. Furthermore, we produce plots in which we show $s,r$ as functions of red-shift, and the ($s-r$) plane for each model.
Dark Energy as Evidence for Extra Dimensions
Milton, K A
2003-01-01
It is argued that fluctuations of quantum fields in four-dimensional space do not give rise to dark energy, but are rather a negligible contribution to dark matter. By (relativistic) dark matter we mean that the relation between pressure and energy density is $p=\\frac13 u$, while dark energy is characterized by $p=-u$. A possible source of dark energy are the fluctuations in quantum fields, including quantum gravity, inhabiting extra compactified dimensions. These fluctuations have been computed for some simple geometries, such as $S^2$, $S^4$, and $S^6$. If the extra dimensions are too small, they would give rise to a dark energy larger than that observed, whereas if they are too large they would be in conflict with experimental tests of Newton's law. This notion suggests that the size of the extra dimensions is of order 100 $\\mu$m. If the limit on the size of extra dimensions becomes lower than this bound, extra dimensions probably do not exist, and another source for cosmological dark energy will have to b...
G-corrected holographic dark energy model
Malekjani, M.; Honari-Jafarpour, M.
2013-08-01
Here we investigate the holographic dark energy model in the framework of FRW cosmology where the Newtonian gravitational constant, G, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of G, the evolutionary treatment of EoS parameter and energy density of dark energy model are calculated in the presence of time variation of G. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calculate the evolution of G-corrected deceleration parameter for holographic dark energy model and show that the dependency of G on the comic time can influence on the transition epoch from decelerated expansion to the accelerated phase. Finally we perform the statefinder analysis for G-corrected holographic model and show that this model has a shorter distance from the observational point in s- r plane compare with original holographic dark energy model.
Dark energy physics expectations at DES
Soares-Santos, Marcelle
2012-01-01
Giving rise to a new and exciting research field, observations of the last 13 years established the accelerated expansion of the Universe. This is a strong indication of new physics, either in the form of a new energy component of the Universe -- dark energy -- or of theories of gravity beyond general relativity. A powerful approach to this problem is the study of complementary cosmological probes in large optical galaxy surveys such as the Dark Energy Survey (DES). We present the expectations for dark energy physics based on the combination of four fundamental probes: galaxy clusters, weak lensing, large scale structure and supernovae. We show that DES data have constraining power to improve current measurements of the dark energy equation-of-state parameter by a factor of 3--5 and to distinguish between general relativity and modified gravity scenarios.
G-corrected holographic dark energy model
Malekjani, M
2013-01-01
Here we investigate the holographic dark energy model in the framework of FRW cosmology where the Newtonian gravitational constant,$G$, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of $G$, the evolutionary treatment of EoS parameter and energy density of dark energy model are calculated in the presence of time variation of $G$. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calculate the evolution of $G$- corrected deceleration parameter for holographic dark energy model and show that the dependency of $G$ on the comic time can influence on the transition epoch from decelerated expansion to the accelerated phase. Finally we perform the statefinder analysis for $G$- corrected holographic model and show that this model has a shorter distance from the observational point in $s-r$ plane compare with original holographic dark energy model.
Examining the viability of phantom dark energy
Ludwick, Kevin J.
2015-09-01
In the standard cosmological framework of the 0th-order Friedmann-Lemaître-Robertson-Walker (FLRW) metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter w think that phantom dark energy has negative kinetic energy categorically. Analogously, we find that field models of quintessence dark energy (wϕ>-1 ) do not necessarily have positive kinetic energy categorically. Staying within the confines of observational constraints and general relativity, for which there is good experimental validation, we consider a few reasonable departures from the standard 0th-order framework in an attempt to see if negative kinetic energy can be avoided in these settings despite an apparent w positive kinetic energy for all relevant length scales at all times.
Dark Energy, Dark Matter and Science with Constellation-X
Cardiff, Ann Hornschemeier
2005-01-01
Constellation-X, with more than 100 times the collecting area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable highthroughput, high spectral resolution studies of sources ranging from the most luminous accreting supermassive black holes in the Universe to the disks around young stars where planets form. This talk will review the updated Constellation-X science case, released in booklet form during summer 2005. The science areas where Constellation-X will have major impact include the exploration of the space-time geometry of black holes spanning nine orders of magnitude in mass and the nature of the dark energy and dark matter which govern the expansion and ultimate fate of the Universe. Constellation-X will also explore processes referred to as "cosmic feedback" whereby mechanical energy, radiation, and chemical elements from star formation and black holes are returned to interstellar and intergalactic medium, profoundly affecting the development of structure in the Universe, and will also probe all the important life cycles of matter, from stellar and planetary birth to stellar death via supernova to stellar endpoints in the form of accreting binaries and supernova remnants. This talk will touch upon all these areas, with particular emphasis on Constellation-X's role in the study of Dark Energy.
DOE and NASA joint Dark Energy mission
2003-01-01
"DOE and NASA announced their plan for a Joint Dark Energy Mission (JDEM) on October 23, 2003, at the NASA Office of Space Science Structure and Evolution of the Universe Subcommittee (SEUS) meeting" (1 paragraph).
Holographic dark energy in the DGP model
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Universidad de Santiago, Departamento de Fisica, Facultad de Ciencia, Santiago (Chile); Lepe, Samuel [Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Facultad de Ciencias, Valparaiso (Chile); Pena, Francisco [Universidad de La Frontera, Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Avda. Francisco Salazar 01145, Casilla 54-D, Temuco (Chile); Avelino, Arturo [Universidad de Guanajuato, Departamento de Fisica, DCI, Codigo Postal 37150, Leon, Guanajuato (Mexico)
2012-09-15
The braneworld model proposed by Dvali, Gabadadze, and Porrati leads to an accelerated universe without cosmological constant or any other form of dark energy. Nevertheless, we have investigated the consequences of this model when an holographic dark energy is included, taking the Hubble scale as IR cutoff. We have found that the holographic dark energy leads to an accelerated flat universe (de Sitter-like expansion) for the two branches: {epsilon}={+-}1, of the DGP model. Nevertheless, in universes with no null curvature the dark energy presents an EoS corresponding to a phantom fluid during the present era and evolving to a de Sitter-like phase for future cosmic time. In the special case in which the holographic parameter c is equal to one we have found a sudden singularity in closed universes. In this case the expansion is decelerating. (orig.)
Probing dark energy through scale dependence
Motta, Mariele; Sawicki, Ignacy; Saltas, Ippocratis D.; Amendola, Luca; Kunz, Martin
2013-12-01
We consider the consequences of having no prior knowledge of the true dark energy model for the interpretation of cosmological observations. The magnitude of redshift-space distortions and weak-lensing shear is determined by the metric on the geodesics of which galaxies and light propagate. We show that, given precise enough observations, we can use these data to completely reconstruct the metric on our past light cone and therefore to measure the scale and time dependence of the anisotropic stress and the evolution of the gravitational potentials in a model-independent manner. Since both dark matter and dark energy affect the visible sector only through the gravitational field they produce, they are inseparable without a model for dark energy: galaxy bias cannot be measured and therefore the distribution of dark matter determined; the peculiar velocity of dark matter can be identified with that of the galaxies only when the equivalence principle holds. Given these limitations, we show how one can nonetheless build tests for classes of dark energy models which depend on making measurements at multiple scales at a particular redshift. They are null tests on the model-independent observables, do not require modeling evolution in time, and do not require any parametrization of the free functions of these models—such as the sound speed. We show that one in principle could rule out or constrain the whole class of the most general scalar-tensor theories even without assuming the quasistatic limit.
Instability of holographic dark energy models
Myung, Yun Soo
2007-01-01
We investigate the difference between holographic dark energy, Chaplygin gas, and tachyon model with constant potential. For this purpose, we examine their squared speeds of sound which are evaluated to zeroth order in perturbation theory and hence depends only on time. We find that the squared speed for holographic dark energy is always negative when choosing the future event horizon as the IR cutoff, while those for Chaplygin gas and tachyon are non-negative. This means that the perfect flu...
Exact solution of phantom dark energy model
Institute of Scientific and Technical Information of China (English)
Wang Wen-Fu; Shui Zheng-Wei; Tang Bin
2010-01-01
We investigate the phantom dark energy model derived from the scalar field with a negative kinetic term. By assuming a particular relation between the time derivative of the phantom field and the Hubble function, an exact solution of the model is constructed. Absence of the 'big rip' singularity is shown explicitly. We then derive special features of phantom dark energy model and show that its predictions are consistent with all astrophysical observations.
A new gravitational model for dark energy
Institute of Scientific and Technical Information of China (English)
HUANG Chao-Guang; ZHANG Hai-Qing; GUO Han-Ying
2008-01-01
A new gravitational model for dark energy is presented based on the model of de Sitter gauge theory of gravity.In the model,in addition to the cosmological constant,the homogeneous and isotropic torsion and its coupling with curvature play an important role for dark energy.The model may supply the universe with a natural transit from decelerating expansion to accelerating expansion.
COBE-DMR-Normalized Dark Energy Cosmogony
Mukherjee, Pia; Banday, Anthony J.; Riazuelo, Alain; Górski, Krzysztof M.; Ratra, Bharat
2003-01-01
Likelihood analyses of the COBE-DMR sky maps are used to determine the normalization of the inverse-power-law-potential scalar field dark energy model. Predictions of the DMR-normalized model are compared to various observations to constrain the allowed range of model parameters. Although the derived constraints are restrictive, evolving dark energy density scalar field models remain an observationally-viable alternative to the constant cosmological constant model.
How early is early dark energy?
Pettorino, Valeria; Wetterich, Christof
2013-01-01
We investigate constraints on early dark energy (EDE) from the Cosmic Microwave Background (CMB) anisotropy, taking into account data from WMAP9 combined with latest small scale measurements from the South Pole Telescope (SPT). For a constant EDE fraction we propose a new parametrization with one less parameter but still enough to provide similar results to the ones previously studied in literature. The main emphasis of our analysis, however, compares a new set of different EDE parametrizations that reveal how CMB constraints depend on the redshift epoch at which Dark Energy was non negligible. We find that bounds on EDE get substantially weaker if dark energy starts to be non-negligible later, with early dark energy fraction Omega_e free to go up to about 5% at 2 sigma if the onset of EDE happens at z < 100. Tight bounds around 1-2% are obtained whenever dark energy is present at last scattering, even if its effects switch off afterwards. We show that the CMB mainly constrains the presence of Dark Energy ...
Dark Matter and Dark Energy from Gravitational Symmetry Breaking
Fuzfa, A
2010-01-01
We build a mechanism of gravitational symmetry breaking (GSB) of a global U(1) symmetry based on the relaxation of the equivalence principle due to the mass variation of pseudo Nambu-Goldstone dark matter (DM) particles. This GSB process is described by the modified cosmological convergence mechanism of the Abnormally Weighting Energy (AWE) Hypothesis previously introduced by the authors. Several remarkable constraints from the Hubble diagram of far-away supernovae are derived, notably on the explicit and gravitational symmetry breaking energy scales of the model. We then briefly present some consequences on neutrino masses when this mechanism is applied to the particular case of the breaking of lepton number symmetry.
Novel Probes of Gravity and Dark Energy
Jain, Bhuvnesh; Thompson, Rodger; Upadhye, Amol; Battat, James; Brax, Philippe; Davis, Anne-Christine; de Rham, Claudia; Dodelson, Scott; Erickcek, Adrienne; Gabadadze, Gregory; Hu, Wayne; Hui, Lam; Huterer, Dragan; Kamionkowski, Marc; Khoury, Justin; Koyama, Kazuya; Li, Baojui; Linder, Eric; Schmidt, Fabian; Scoccimarro, Roman; Starkman, Glenn; Stubbs, Chris; Takada, Masahiro; Tolley, Andrew; Trodden, Mark; Uzan, Jean-Philippe; Vikram, Vinu; Weltman, Amanda; Wyman, Mark; Zaritsky, Dennis; Zhao, Gongbo
2013-01-01
The discovery of cosmic acceleration has stimulated theorists to consider dark energy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth dark energy -- modified gravity and interactions of dark energy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and sp...
Falsification of dark energy by fluid mechanics
Gibson, Carl H
2012-01-01
The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating supernovae dimness, suggesting a remarkable change in the expansion rate of the Universe from a decrease since the big bang to an increase, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanical considerations falsify both the accelerating expansion and dark energy concepts. Kinematic viscosity is neglected in current standard models of self-gravitational structure formation, which rely on cold dark matter CDM condensations and clusterings that are also falsified by fluid mechanics. Weakly collisional CDM particles do not condense but diffuse away. Photon viscosity predicts superclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the plasma fragments into Earth-mass gas planets in trillion planet clumps (proto-globular-star-cluster PGCs). The hydrogen planets freeze to form the dark matter of galaxies ...
Coupling dark energy with Standard Model states
Bento, M C; Bertolami, O
2009-01-01
In this contribution one examines the coupling of dark energy to the gauge fields, to neutrinos, and to the Higgs field. In the first case, one shows how a putative evolution of the fundamental couplings of strong and weak interactions via coupling to dark energy through a generalized Bekenstein-type model may cause deviations on the statistical nuclear decay Rutherford-Soddy law. Existing bounds for the weak interaction exclude any significant deviation. For neutrinos, a perturbative approach is developed which allows for considering viable varying mass neutrino models coupled to any quintessence-type field. The generalized Chaplygin model is considered as an example. For the coupling with the Higgs field one obtains an interesting cosmological solution which includes the unification of dark energy and dark matter.
Alternative Dark Energy Models: An Overview
Lima, J A S
2004-01-01
A large number of recent observational data strongly suggest that we live in a flat, accelerating Universe composed of $\\sim$ 1/3 of matter (baryonic + dark) and $\\sim$ 2/3 of an exotic component with large negative pressure, usually named {\\bf Dark Energy} or {\\bf Quintessence}. The basic set of experiments includes: observations from SNe Ia, CMB anisotropies, large scale structure, X-ray data from galaxy clusters, age estimates of globular clusters and old high redshift galaxies (OHRG's). Such results seem to provide the remaining piece of information connecting the inflationary flatness prediction ($\\Omega_{\\rm{T}} = 1$) with astronomical observations. Theoretically, they have also stimulated the current interest for more general models containing an extra component describing this unknown dark energy, and simultaneously accounting for the present accelerating stage of the Universe. An overlook in the literature shows that at least five dark energy candidates have been proposed in the context of general re...
Report of the Dark Energy Task Force
Albrecht, Andreas; Bernstein, Gary; Cahn, Robert; Freedman, Wendy L.; Hewitt, Jacqueline; Hu, Wayne; Huth, John; Kamionkowski, Marc; Kolb, Edward W.; Knox, Lloyd; Mather, John C.
2006-01-01
Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science. These circumstances demand an ambitious observational program to determine the dark energy properties as well as possible.
Cosmic acceleration without dark energy
International Nuclear Information System (INIS)
In this work, we investigate the global dynamics of the universe within the framework of the Interacting Dark Matter (IDM) scenario. Considering that the dark matter obeys the collisional Boltzmann equation, we can obtain analytical solutions of the global density evolution, which can accommodate an accelerated expansion, equivalent to either the quintessence or the standard Λ models. This is possible if there is a disequilibrium between the DM particle creation and annihilation processes with the former process dominating, which creates an effective source term with negative pressure. We also find realistic solutions in which the present time is located after the inflection point.
Dark Matter and Dark Energy: Breaking the Continuum Hypothesis?
Directory of Open Access Journals (Sweden)
Casuso Romate E.
2006-07-01
Full Text Available In the present paper an attempt is made to develop a fractional integral and differential, deterministic and projective method based on the assumption of the essential discontinuity observed in real systems (note that more than 99 % of the volume occupied by an atom in real space has no matter. The differential treatment assumes continuous behaviour (in the form of averaging over the recent past of the system to predict the future time evolution, such that the real history of the system is “forgotten”. So it is easy to understand how problems such as unpredictability (chaos arise for many dynamical systems, as well as the great difficulty to connecting Quantum Mechanics (a probabilistic differential theory with General Relativity (a deterministic differential theory. I focus here on showing how the present theory can throw light on crucial astrophysical problems like dark matter and dark energy.
Dark Matter and Dark Energy: Breaking the Continuum Hypothesis?
Directory of Open Access Journals (Sweden)
Casuso Romate E.
2006-07-01
Full Text Available In the present paper an attempt is made to develop a fractional integral and differential, deterministic and projective method based on the assumption of the essential discontinuity observed in real systems (note that more than 99% of the volume occupied by an atom in real space has no matter. The differential treatment assumes continuous behaviour (in the form of averaging over the recent past of the system to predict the future time evolution, such that the real history of the system is "forgotten". So it is easy to understand how problems such as unpredictability (chaos arise for many dynamical systems, as well as the great difficulty to connecting Quantum Mechanics (a probabilistic differential theory with General Relativity (a deterministic differential theory. I focus here on showing how the present theory can throw light on crucial astrophysical problems like dark matter and dark energy.
Interacting Dark Energy Models -- Scalar Linear Perturbations
Perico, E L D
2016-01-01
We extend the dark sector interacting models assuming the dark energy as the sum of independent contributions $\\rho_{\\Lambda} =\\sum_i\\rho_{\\Lambda i}$, associated with (and interacting with) each of the $i$ material species. We derive the linear scalar perturbations for two interacting dark energy scenarios, modeling its cosmic evolution and identifying their different imprints in the CMB and matter power spectrum. Our treatment was carried out for two phenomenological motivated expressions of the dark energy density, $\\rho_\\Lambda(H^2)$ and $\\rho_\\Lambda(R)$. The $\\rho_\\Lambda(H^2)$ description turned out to be a full interacting model, i.e., the dark energy interacts with everyone material species in the universe, whereas the $\\rho_\\Lambda(R)$ description only leads to interactions between dark energy and the non-relativistic matter components; which produces different imprints of the two models on the matter power spectrum. A comparison with the Planck 2015 data was made in order to constrain the free para...
Dark Energy-Dark Matter Interaction from the Abell Cluster A586
Bertolami, Orfeu; Delliou, Morgan Le
2008-01-01
We find that deviation from the virial equilibrium of the Abell Cluster A586 yields evidence of the interaction between dark matter and dark energy. We argue that this interaction might imply a violation of the Equivalence Principle. Our analysis show that evidence is found in the context of two different models of dark energy-dark matter interaction.
The Logotropic Dark Fluid as a unification of dark matter and dark energy
Chavanis, Pierre-Henri
2015-01-01
We propose a heuristic unification of dark matter and dark energy in terms of a single dark fluid with a logotropic equation of state $P=A\\ln(\\rho/\\rho_P)$, where $\\rho$ is the rest-mass density, $\\rho_P$ is the Planck density, and $A$ is the logotropic temperature. The energy density $\\epsilon$ is the sum of a rest-mass energy term $\\rho c^2$ mimicking dark matter and an internal energy term $u(\\rho)=-P(\\rho)-A$ mimicking dark energy. The logotropic temperature is approximately given by $A \\simeq \\rho_{\\Lambda}c^2/\\ln(\\rho_P/\\rho_{\\Lambda})\\simeq\\rho_{\\Lambda}c^2/[123 \\ln(10)]$, where $\\rho_{\\Lambda}$ is the cosmological density. More precisely, we obtain $A=2.13\\times 10^{-9} \\, {\\rm g}\\, {\\rm m}^{-1}\\, {\\rm s}^{-2}$ that we interpret as a fundamental constant. At the cosmological scale, this model fullfills the same observational constraints as the $\\Lambda$CDM model. However, it has a nonzero velocity of sound and a nonzero Jeans length which, at the beginning of the matter era, is about $\\lambda_J=40.4\\,...
Constraints on the Coupling between Dark Energy and Dark Matter from CMB data
Murgia, Riccardo; Gariazzo, Stefano; Fornengo, Nicolao
2016-01-01
We investigate a phenomenological non-gravitational coupling between dark energy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both mode...
Dark Energy Content of Nonlinear Electromagnetism
Labun, Lance; Rafelski, Johann
2008-01-01
Quasi-constant external fields in nonlinear electromagnetism generate a contribution to the energy-momentum tensor with the form of dark energy. To provide a thorough understanding of the origin and strength of the effects, we undertake a complete theoretical and numerical study of the energy-momentum tensor $T^{\\mu\
Polytropic dark matter flows illuminate dark energy and accelerated expansion
Kleidis, K.; Spyrou, N. K.
2015-04-01
Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. In fact, polytropic processes in a DM fluid have been most successfully used in modeling dark galactic haloes, thus significantly improving the velocity dispersion profiles of galaxies. Motivated by such results, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluidlike properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, together with all the other physical characteristics, we also take the energy of this fluid's internal motions into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy, needed to compromise spatial flatness, namely, to justify that, today, the total energy density parameter is exactly unity. The polytropic cosmological model, depends on only one free parameter, the corresponding (polytropic) exponent, Γ. We find this model particularly interesting, because for Γ ≤ 0.541, without the need for either any exotic DE or the cosmological constant, the conventional pressure becomes negative enough so that the Universe accelerates its expansion at cosmological redshifts below a transition value. In fact, several physical reasons, e.g., the cosmological requirement for cold DM (CDM) and a positive velocity-of-sound square, impose further constraints on the value of Γ, which is eventually settled down to the range -0.089 standard candles, and most naturally interprets, not only when, but also why the Universe
Polytropic dark matter flows illuminate dark energy and accelerated expansion
Kleidis, K.; Spyrou, N. K.
2015-04-01
Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. In fact, polytropic processes in a DM fluid have been most successfully used in modeling dark galactic haloes, thus significantly improving the velocity dispersion profiles of galaxies. Motivated by such results, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluidlike properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, together with all the other physical characteristics, we also take the energy of this fluid's internal motions into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy, needed to compromise spatial flatness, namely, to justify that, today, the total energy density parameter is exactly unity. The polytropic cosmological model, depends on only one free parameter, the corresponding (polytropic) exponent, Γ. We find this model particularly interesting, because for Γ ≤ 0.541, without the need for either any exotic DE or the cosmological constant, the conventional pressure becomes negative enough so that the Universe accelerates its expansion at cosmological redshifts below a transition value. In fact, several physical reasons, e.g., the cosmological requirement for cold DM (CDM) and a positive velocity-of-sound square, impose further constraints on the value of Γ, which is eventually settled down to the range -0.089 < Γ ≤ 0. This cosmological model does not suffer either from the age problem or from the
"Dark energy" in the Local Void
Villata, M.
2012-05-01
The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "dark energy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter (˜5×1015 M ⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an initial "explosion" and dark energy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly permeating dark energy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies of the Universe.
Theories of Dark Energy with Screening Mechanisms
Khoury, Justin
2010-01-01
Despite the overwhelming evidence for the existence of dark energy and dark matter, their underlying fundamental physics remains unknown. This review article explores the tantalizing possibility that the dark sector includes new light degrees of freedom that mediate long-range forces on cosmological scales. To ensure consistency with laboratory and solar system tests of gravity, some screening mechanism is necessary to "hide" these degrees of freedom locally. I will focus on two broad classes of screening theories, chameleons and symmetrons, which rely respectively on the scalar field acquiring a large mass or weak coupling in the presence of large ambient matter density.
Dark Energy and Dark Matter from an additional adiabatic fluid
Dunsby, Peter K S; Reverberi, Lorenzo
2016-01-01
The Dark Sector is described by an additional barotropic fluid which evolves adiabatically during the universe's history and whose adiabatic exponent $\\gamma$ is derived from the standard definitions of specific heats. Although in general $\\gamma$ is a function of the redshift, the Hubble parameter and its derivatives, we find that our assumptions lead necessarily to solutions with $\\gamma = $ constant in a FLRW universe. The adiabatic fluid acts effectively as the sum of two distinct components, one evolving like non-relativistic matter and the other depending on the value of the adiabatic index. This makes the model particularly interesting as a way of simultaneously explaining the nature of both Dark Energy and Dark Matter, at least at the level of the background cosmology. The $\\Lambda$CDM model is included in this family of theories when $\\gamma = 0$. We fit our model to SNIa, $H(z)$ and BAO data, discussing the model selection criteria. The implications for the early-universe and the growth of small per...
Metamaterial model of tachyonic dark energy
Smolyaninov, Igor I
2014-01-01
Dark energy with negative pressure and positive energy density is believed to be responsible for the accelerated expansion of the universe. Quite a few theoretical models of dark energy are based on tachyonic fields interacting with itself and normal (bradyonic) matter. Here we propose an experimental model of tachyonic dark energy based on hyperbolic metamaterials. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2+1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. We demonstrate that this model has a self-interacting tachyonic sector having negative effective pressure and positive effective energy density. Moreover, a composite multilayer SiC-Si hyperbolic metamaterial exhibits closely separated t...
Dark radiation and dark matter coupled to holographic Ricci dark energy
Chimento, Luis P
2013-01-01
We investigate a universe filled with interacting dark matter, holographic dark energy, and dark radiation for the spatially flat Friedmann-Robertson-Walker (FRW) spacetime. We use a linear interaction to reconstruct all the component energy densities in terms of the scale factor by directly solving the balance's equations along with the source equation. We apply the $\\chi^{2}$ method to the observational Hubble data for constraining the cosmic parameters, contrast with the Union 2 sample of supernovae, and analyze the amount of dark energy in the radiation era. It turns out that our model exhibits an excess of dark energy in the recombination era whereas the stringent bound $\\Omega_{\\rm x}(z\\simeq 10^{10})<0.21$ at big-bang nucleosynthesis is fulfilled. We find that the interaction provides a physical mechanism for alleviating the triple cosmic coincidence and this leads to $\\Omega_{\\rm m0}/\\Omega_{\\rm x0} \\simeq \\Omega_{\\rm r0}/\\Omega_{\\rm x0} \\simeq {\\cal O}(1)$.
Interacting dark energy: the role of microscopic feedback in the dark sector
Avelino, P. P.
2015-01-01
We investigate the impact on the classical dynamics of dark matter particles and dark energy of a non-minimal coupling in the dark sector, assuming that the mass of the dark matter particles is coupled to a dark energy scalar field. We show that standard results can only be recovered if the space-time variation of the dark energy scalar field is sufficiently smooth on the characteristic length scale of the dark matter particles, and we determine the associated constraint dependent on both the...
Report of the Dark Energy Task Force
Albrecht, Andreas; Bernstein, Gary; Cahn, Robert; Freedman, Wendy L.; Hewitt, Jacqueline; Hu, Wayne; Huth, John; Kamionkowski, Marc; Edward W. Kolb; Knox, Lloyd; Mather, John C.; Staggs, Suzanne; Suntzeff, Nicholas B.
2006-01-01
Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a f...
Effective Theory of Interacting Dark Energy
Gleyzes, Jérôme; Langlois, David; Mancarella, Michele; Vernizzi, Filippo
2015-01-01
We present a unifying treatment of dark energy and modified gravity that allows distinct conformal-disformal couplings of matter species to the gravitational sector. In this very general approach, we derive the conditions to avoid ghost and gradient instabilities. We compute the equations of motion for background quantities and linear perturbations. We illustrate our formalism with two simple scenarios, where either cold dark matter or a relativistic fluid is nonminimally coupled. This extend...
Probing Dark Energy through Scale Dependence
Motta, Mariele; Saltas, Ippocratis D; Amendola, Luca; Kunz, Martin
2013-01-01
We consider the consequences of having no prior knowledge of the true dark energy model for the interpretation of cosmological observations. The magnitude of redshift-space distortions and weak-lensing shear is determined by the metric on the geodesics of which galaxies and light propagate. We show that, given precise enough observations, we can use these data to completely reconstruct the metric on our past lightcone and therefore to measure the scale- and time-dependence of the anisotropic stress and the evolution of the gravitational potentials in a model-independent manner. Since both dark matter and dark energy affect the visible sector only through the gravitational field they produce, they are inseparable without a model for dark energy: galaxy bias cannot be measured and therefore the distribution of dark matter determined; the peculiar velocity of dark matter can be identified with that of the galaxies only when the equivalence principle holds. Given these limitations, we show how one can nonetheless...
The Logotropic Dark Fluid as a unification of dark matter and dark energy
Chavanis, Pierre-Henri
2016-07-01
We propose a heuristic unification of dark matter and dark energy in terms of a single "dark fluid" with a logotropic equation of state P = Aln (ρ /ρP), where ρ is the rest-mass density, ρP = 5.16 ×1099gm-3 is the Planck density, and A is the logotropic temperature. The energy density ɛ is the sum of a rest-mass energy term ρc2 ∝a-3 mimicking dark matter and an internal energy term u (ρ) = - P (ρ) - A = 3 Aln a + C mimicking dark energy (a is the scale factor). The logotropic temperature is approximately given by A ≃ρΛc2 / ln (ρP /ρΛ) ≃ρΛc2 / [ 123 ln (10) ], where ρΛ = 6.72 ×10-24gm-3 is the cosmological density and 123 is the famous number appearing in the ratio ρP /ρΛ ∼10123 between the Planck density and the cosmological density. More precisely, we obtain A = 2.13 ×10-9gm-1s-2 that we interpret as a fundamental constant. At the cosmological scale, our model fulfills the same observational constraints as the ΛCDM model (they will differ in about 25 Gyrs when the logotropic universe becomes phantom). However, the logotropic dark fluid has a nonzero speed of sound and a nonzero Jeans length which, at the beginning of the matter era, is about λJ = 40.4pc, in agreement with the minimum size of the dark matter halos observed in the universe. The existence of a nonzero Jeans length may solve the missing satellite problem. At the galactic scale, the logotropic pressure balances the gravitational attraction, providing halo cores instead of cusps. This may solve the cusp problem. The logotropic equation of state generates a universal rotation curve that agrees with the empirical Burkert profile of dark matter halos up to the halo radius. In addition, it implies that all the dark matter halos have the same surface density Σ0 =ρ0rh = 141M⊙ /pc2 and that the mass of dwarf galaxies enclosed within a sphere of fixed radius ru = 300pc has the same value M300 = 1.93 ×107M⊙, in remarkable agreement with the observations
The Logotropic Dark Fluid as a unification of dark matter and dark energy
Directory of Open Access Journals (Sweden)
Pierre-Henri Chavanis
2016-07-01
Full Text Available We propose a heuristic unification of dark matter and dark energy in terms of a single “dark fluid” with a logotropic equation of state P=Aln(ρ/ρP, where ρ is the rest-mass density, ρP=5.16×1099gm−3 is the Planck density, and A is the logotropic temperature. The energy density ϵ is the sum of a rest-mass energy term ρc2∝a−3 mimicking dark matter and an internal energy term u(ρ=−P(ρ−A=3Alna+C mimicking dark energy (a is the scale factor. The logotropic temperature is approximately given by A≃ρΛc2/ln(ρP/ρΛ≃ρΛc2/[123ln(10], where ρΛ=6.72×10−24gm−3 is the cosmological density and 123 is the famous number appearing in the ratio ρP/ρΛ∼10123 between the Planck density and the cosmological density. More precisely, we obtain A=2.13×10−9gm−1s−2 that we interpret as a fundamental constant. At the cosmological scale, our model fulfills the same observational constraints as the ΛCDM model (they will differ in about 25 Gyrs when the logotropic universe becomes phantom. However, the logotropic dark fluid has a nonzero speed of sound and a nonzero Jeans length which, at the beginning of the matter era, is about λJ=40.4pc, in agreement with the minimum size of the dark matter halos observed in the universe. The existence of a nonzero Jeans length may solve the missing satellite problem. At the galactic scale, the logotropic pressure balances the gravitational attraction, providing halo cores instead of cusps. This may solve the cusp problem. The logotropic equation of state generates a universal rotation curve that agrees with the empirical Burkert profile of dark matter halos up to the halo radius. In addition, it implies that all the dark matter halos have the same surface density Σ0=ρ0rh=141M⊙/pc2 and that the mass of dwarf galaxies enclosed within a sphere of fixed radius ru=300pc has the same value M300=1.93×107M⊙, in remarkable agreement with the observations [Donato et al. [10
Anisotropic perturbations due to dark energy
Battye, R A; Battye, Richard A.; Moss, Adam
2006-01-01
A variety of observational tests seem to suggest that the universe is anisotropic. This is incompatible with the standard dogma based on adiabatic, rotationally invariant perturbations. We point out that this is a consequence of the standard decomposition of the stress-energy tensor for the cosmological fluids, and that rotational invariance need not be assumed, if there is elastic rigidity in the dark energy. The dark energy required to achieve this might be provided by point symmetric domain wall network with $P/\\rho=-2/3$, although the concept is more general. We illustrate this with reference to a model with cubic symmetry and discuss various aspects of the model.
G-corrected holographic dark energy model
Malekjani, M.; Honari-Jafarpour, M.
2013-01-01
Here we investigate the holographic dark energy model in the framework of FRW cosmology where the Newtonian gravitational constant,$G$, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of $G$, the evolutionary treatment of EoS parameter and energy density of dark energy model are calculated in the presence of time variation of $G$. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calcul...
On the geometry of dark energy
International Nuclear Information System (INIS)
Experimental evidence suggests that we live in a spatially flat, accelerating universe composed of roughly one-third of matter (baryonic + dark) and two-thirds of a negative-pressure dark component, generically called dark energy. The presence of such energy not only explains the observed accelerating expansion of the universe but also provides the remaining piece of information connecting the inflationary flatness prediction with astronomical observations. However, despite its good observational indications, the nature of dark energy still remains an open question. In this paper we explore a geometrical explanation for such a component within the context of braneworld theory without mirror symmetry, leading to a geometrical interpretation for dark energy as a warp in the universe given by the extrinsic curvature. In particular, we study the phenomenological implications of the extrinsic curvature of a Friedmann-Robertson-Walker universe in a five-dimensional constant curvature bulk, with signatures (4,1) or (3,2), as compared with the x-matter (XCDM) model. From the analysis of the geometrically modified Friedmann's equations, the deceleration parameter and the weak energy condition, we find a consistent agreement with the presently known observational data on inflation for the de Sitter bulk, but not for the anti-de Sitter case
Dark Energy and the Hubble Law
Chernin, A. D.; Dolgachev, V. P.; Domozhilova, L. M.
The Big Bang predicted by Friedmann could not be empirically discovered in the 1920th, since global cosmological distances (more than 300-1000 Mpc) were not available for observations at that time. Lemaitre and Hubble studied receding motions of galaxies at local distances of less than 20-30 Mpc and found that the motions followed the (nearly) linear velocity-distance relation, known now as Hubble's law. For decades, the real nature of this phenomenon has remained a mystery, in Sandage's words. After the discovery of dark energy, it was suggested that the dynamics of local expansion flows is dominated by omnipresent dark energy, and it is the dark energy antigravity that is able to introduce the linear velocity-distance relation to the flows. It implies that Hubble's law observed at local distances was in fact the first observational manifestation of dark energy. If this is the case, the commonly accepted criteria of scientific discovery lead to the conclusion: In 1927, Lemaitre discovered dark energy and Hubble confirmed this in 1929.
Irreversible thermodynamic description of interacting dark energy - dark matter cosmological models
Harko, Tiberiu; Lobo, Francisco S N
2012-01-01
We investigate the interaction between dark energy and dark matter in the framework of irreversible thermodynamics of open systems with matter creation/annihilation. We consider dark energy and dark matter as an interacting two component (scalar field and "ordinary" dark matter) cosmological fluid in a homogeneous spatially flat and isotropic Friedmann-Robertson-Walker (FRW) Universe. The thermodynamics of open systems as applied together with the gravitational field equations to the two comp...
Redshift drift constraints on holographic dark energy
He, Dong-Ze; Zhang, Xin
2016-01-01
The Sandage-Loeb (SL) test is a promising method for probing dark energy because it measures the redshift drift in the spectra of Lyman-$\\alpha$ forest of distant quasars, covering the "redshift desert" of $2\\lesssim z\\lesssim5$, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holographic dark energy models, i.e., the original holographic dark energy (HDE) model and the Ricci holographic dark energy (RDE) model. To avoid data inconsistency, we use the best-fit models based on current combined observational data as the fiducial models to simulate 30 mock SL test data. The results show that SL test can effectively break the existing strong degeneracy between the present-day matter density $\\Omega_{m0}$ and the Hubble constant $H_0$ in other cosmological observations. For the considered two typical dark e...
Dark energy domination in the Virgocentric flow
Chernin, A D; Nasonova, O G; Teerikorpi, P; Valtonen, M J; Dolgachev, V P; Domozhilova, L M; Byrd, G G
2010-01-01
The standard \\LambdaCDM cosmological model implies that all celestial bodies are embedded in a perfectly uniform dark energy background, represented by Einstein's cosmological constant, and experience its repulsive antigravity action. Can dark energy have strong dynamical effects on small cosmic scales as well as globally? Continuing our efforts to clarify this question, we focus now on the Virgo Cluster and the flow of expansion around it. We interpret the Hubble diagram, from a new database of velocities and distances of galaxies in the cluster and its environment, using a nonlinear analytical model which incorporates the antigravity force in terms of Newtonian mechanics. The key parameter is the zero-gravity radius, the distance at which gravity and antigravity are in balance. Our conclusions are: 1. The interplay between the gravity of the cluster and the antigravity of the dark energy background determines the kinematical structure of the system and controls its evolution. 2. The gravity dominates the qu...
Interacting Ricci Dark Energy with Logarithmic Correction
Pasqua, Antonio(Department of Physics, University of Trieste, Via Valerio, No. 2, 34127 Trieste, Italy); Khodam-Mohammadi, A.; Jamil, Mubasher; Myrzakulov, R.
2011-01-01
Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area $A$ of the event horizon of the universe. However, such a model would have a causality problem. In this work, we consider the entropy-corrected version of the holographic dark energy model in the non-flat FRW universe and we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We obtain the equation of state (EoS) para...
Dark energy and neutrino model in SUSY
International Nuclear Information System (INIS)
We consider a Mass Varying Neutrinos (MaVaNs) model in supersymmetric theory. The model includes effects of supersymmetry breaking transmitted by the gravitational interaction from the hidden sector, in which supersymmetry was broken, to the dark energy sector. Then evolutions of the neutrino mass and the equation of state parameter of the dark energy are presented in the model. It is remarked that only the mass of a sterile neutrino is variable in the case of the vanishing mixing between the left-handed and a sterile neutrino on cosmological time scale. The finite mixing makes the mass of the left-handed neutrino variable. (author)
Deformed Matter Bounce with Dark Energy Epoch
Odintsov, S. D.; Oikonomou, V.K.
2016-01-01
We extend the Loop Quantum Cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a Rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario", the Universe is contracting from an initial non-causal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, thus the model is described by a dark energy ...
Atomic Interferometry Test of Dark Energy
Brax, Philippe
2016-01-01
Atomic interferometry can be used to probe dark energy models coupled to matter. We consider the constraints coming from recent experimental results on models generalising the inverse power law chameleons such as $f(R)$ gravity in the large curvature regime, the environmentally dependent dilaton and symmetrons. Using the tomographic description of these models, we find that only symmetrons with masses smaller than the dark energy scale can be efficiently tested. In this regime, the resulting constraints complement the bounds from the E\\"otwash experiment and exclude small values of the symmetron self-coupling.
A Unified Model of Phantom Energy and Dark Matter
Douglas Singleton(Department of Physics, California State University, Fresno, CA 93740-8031 U.S.A.); Max Chaves
2008-01-01
To explain the acceleration of the cosmological expansion researchers have considered an unusual form of mass-energy generically called dark energy. Dark energy has a ratio of pressure over mass density which obeys $w=p/\\rho
Dark energy in systems of galaxies
Chernin, A. D.
2013-11-01
The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of dark energy in groups, clusters, and flows of galaxies on a spatial scale of about 1-10 Mpc. The local density of dark energy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1-3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (˜1 Mpc) can be extended to the scale of clusters (˜10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local dark energy constitute the main characteristic feature of these systems.
THE LIGHT/DARK UNIVERSE Light from Galaxies, Dark Matter and Dark Energy
Overduin, James M.; Wesson, Paul S.
1. The enigma of the dark night sky. 1.1. Why is the sky dark at night? 1.2. "By reason of distance". 1.3. Island Universe. 1.4. Non-uniform sources. 1.5. Tired light. 1.6. Absorption. 1.7. Fractal Universe. 1.8. Finite age. 1.9. Dark stars. 1.10. Curvature. 1.11. Ether voids. 1.12. Insufficient energy. 1.13. Light-matter interconversion. 1.14. Cosmic expansion. 1.15. Olbers' paradox today -- 2. The intensity of cosmic background light. 2.1. Bolometric intensity. 2.2. Time and redshift. 2.3. Matter, energy and expansion. 2.4. How important is expansion?. 2.5. Simple flat models. 2.6. Curved and multi-fluid models. 2.7. A bright sky at night? -- 3. The spectrum of cosmic background light. 3.1. Spectral intensity. 3.2. Luminosity density. 3.3. The delta function. 3.4. The normal distribution. 3.5. The thermal spectrum. 3.6. The spectra of galaxies. 3.7. The light of the night sky. 3.8. R.I.P. Olbers' paradox -- 4. Dark cosmology. 4.1. The four dark elements. 4.2. Baryons. 4.3. Dark matter. 4.4. Neutrinos. 4.5. Dark energy. 4.6. Cosmological concordance. 4.7. The coincidental Universe -- 5. The radio and microwave backgrounds. 5.1. The cosmological "constant". 5.2. The scalar field. 5.3. Decaying dark energy. 5.4. Energy density. 5.5. Source luminosity. 5.6. Bolometric intensity. 5.7. Spectral energy distribution. 5.8. Dark energy and the background light -- 6. The infrared and visible backgrounds. 6.1. Decaying axions. 6.2. Axion halos. 6.3. Bolometric intensity. 6.4. Axions and the background light -- 7. The ultraviolet background. 7.1. Decaying neutrinos. 7.2. Neutrino halos. 7.3. Halo luminosity. 7.4. Free-streaming neutrinos. 7.5. Extinction by gas and dust. 7.6. Neutrinos and the background light -- 8. The x-ray and gamma-ray backgrounds. 8.1. Weakly interacting massive particles. 8.2. Pair annihilation. 8.3. One-loop decay. 8.4. Tree-level decay. 8.5. Gravitinos. 8.6. WIMPs and the background light -- 9. The high-energy gamma-ray background. 9.1. Primordial
Interacting Ghost Dark Energy Model: Dynamical System Analysis
Golchin, Hanif; Jamali, Sara; Ebrahimi, Esmaeil
2016-01-01
We study the impacts of interaction between dark matter and dark energy in the context of ghost dark energy model. Using the dynamical system analysis, we obtain the fixed points of the system for different types of interactions while the universe is filled with radiation, matter (including dark matter and luminous matter) and dark energy components. We consider the stability of the fixed points in details for different cases. In all cases there is an unstable matter dominated epoch and a sta...
Dark Energy: The Shadowy Reflection of Dark Matter?
Directory of Open Access Journals (Sweden)
Kostas Kleidis
2016-03-01
Full Text Available In this article, we review a series of recent theoretical results regarding a conventional approach to the dark energy (DE concept. This approach is distinguished among others for its simplicity and its physical relevance. By compromising General Relativity (GR and Thermodynamics at cosmological scale, we end up with a model without DE. Instead, the Universe we are proposing is filled with a perfect fluid of self-interacting dark matter (DM, the volume elements of which perform hydrodynamic flows. To the best of our knowledge, it is the first time in a cosmological framework that the energy of the cosmic fluid internal motions is also taken into account as a source of the universal gravitational field. As we demonstrate, this form of energy may compensate for the DE needed to compromise spatial flatness, while, depending on the particular type of thermodynamic processes occurring in the interior of the DM fluid (isothermal or polytropic, the Universe depicts itself as either decelerating or accelerating (respectively. In both cases, there is no disagreement between observations and the theoretical prediction of the distant supernovae (SNe Type Ia distribution. In fact, the cosmological model with matter content in the form of a thermodynamically-involved DM fluid not only interprets the observational data associated with the recent history of Universe expansion, but also confronts successfully with every major cosmological issue (such as the age and the coincidence problems. In this way, depending on the type of thermodynamic processes in it, such a model may serve either for a conventional DE cosmology or for a viable alternative one.
Cosmological Constant or Variable Dark Energy?
Institute of Scientific and Technical Information of China (English)
XU Li-Xin; ZHANG Cheng-Wu; LIU Hong-Ya
2007-01-01
@@ Selection statics of the Akaike information criterion (AIC) model and the Bayesian information criterion (BIC)model are applied to the Λ-cold dark matter (ΛCDM) cosmological model, the constant equation of state of dark energy, w =constant, and the parametrized equation of state of dark energy, w(z) = w0 + w1z/(1 + z),to determine which one is the better cosmological model to describe the evolution of the universe by combining the recent cosmic observational data including Sne Ia, the size of baryonic acoustic oscillation (BAO) peak from SDSS, the three-year WMAP CMB shift parameter. The results show that AIC, BIC and current datasets are not powerful enough to discriminate one model from the others, though odds suggest differences between them.
Dissipative or Conservative cosmology with dark energy ?
Szydlowski, M; Hrycyna, Orest; Szydlowski, Marek
2006-01-01
All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analysed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property -- acceleration -- is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in 1D potential which is parametrised by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We characterise the class of dark energy models that admit late time de Sitter attractor solution in terms of the potential function of corresponding conservative system. We argue that inclusion of dissipation effects makes the model more realistic because of its structural stabil...
Effective field theory of modified gravity with two scalar fields: dark energy and dark matter
Gergely, László Á.; Tsujikawa, Shinji
2014-01-01
We present a framework for discussing the cosmology of dark energy and dark matter based on two scalar degrees of freedom. An effective field theory of cosmological perturbations is employed. A unitary gauge choice renders the dark energy field into the gravitational sector, for which we adopt a generic Lagrangian depending on three-dimensional geometrical scalar quantities arising in the ADM decomposition. We add to this dark-energy associated gravitational sector a scalar field $\\phi$ and i...
Deformed Matter Bounce with Dark Energy Epoch
Odintsov, S D
2016-01-01
We extend the Loop Quantum Cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a Rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario", the Universe is contracting from an initial non-causal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, thus the model is described by a dark energy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the dark energy era is quintessential like which follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the dark energy era, a Rip singularity exists, where the scale factor and Hubble rate diverge, however the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, firstly th...
New physics at low energies and dark matter-dark energy transmutation
Guendelman, E. I.; Kaganovich, A. B.
2004-01-01
A field theory is proposed where the regular fermionic matter and the dark fermionic matter can be different states of the same "primordial" fermion fields. In regime of the fermion densities typical for normal particle physics, the primordial fermions split into three families identified with regular fermions. When fermion energy density becomes comparable with dark energy density, the theory allows transition to new type of states. The possibility of such Cosmo-Low Energy Physics (CLEP) sta...
Holographic principle and dark energy
Myung, Yun Soo
2004-01-01
We discuss the relationship between holographic entropy bounds and gravitating systems. In order to obtain a holographic energy density, we introduce the Bekenstein-Hawking entropy $S_{\\rm BH}$ and its corresponding energy $E_{\\rm BH}$ using the Friedman equation. We show that the holographic energy bound proposed by Cohen {\\it et al} comes from the Bekenstein-Hawking bound for a weakly gravitating system. Also we find that the holographic energy density with the future event horizon deriving...
Institute of Scientific and Technical Information of China (English)
张鑫
2011-01-01
最近的宇宙学观测表明,人类熟悉的原子物质(重子物质)只占宇宙总能量的4％左右,而剩下的能量成分都是看不见的暗物质和暗能量,其中暗物质占23％,暗能量占73％.当前,暗物质和暗能量的起源和物理本质都不清楚,揭开它们的神秘本质是现代基础科学所面临的最大挑战之一.暗物质虽然神秘,但是它所产生的引力是和原子物质一样的正常引力.而暗能量就不同了,它更加神秘莫测,它产生的引力实际上是一种排斥力.正是由于暗能量的排斥力的驱动,我们的宇宙现在正在加速膨胀.暗能量在当前的物理学理论框架下面临着严重的问题.实际上,它的物理本性和量子引力理论有着深刻的联系.因此,暗能量的理论研究将为自下而上地建立一个完整的量子引力理论提供重要的线索.在简要论述了与暗能量相关的各种问题来龙去脉的基础上,描述了这个领域的概况.%Recent cosmological observations show that, atoms (or, baryons) only occupy 4% of the cosmic contents, and other 96% components are nonluminous dark matter and dark energy, explaining 23% and 73% of the total energy of the universe, respectively. Currently, the natures of dark matter and dark energy are both enigmatic, and so the revelation of their exotic natures raises one of the biggest challenges for the modern fundamental science. Dark energy is more mysterious than dark matter in that its gravity is repulsive, driving the current expansion of the universe to accelerate. Dark energy suffers from severe theoretical problems within the current framework of physics. In fact, the physical nature of dark energy is in deep connection with the underlying quantum gravity theory. Thus, the theoretical studies on dark energy may provide significant clues for the bottom-up exploration of a full quantum theory of gravitation. This paper will explain various dark energy-relevant problems, and briefly
Dark Energy and Dark Matter in a Superfluid Universe
Huang, Kerson
2013-01-01
The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over macroscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free, i.e., the interaction must grow from zero during the big bang, and this singles out the Halpern-Huang potential, which has exponential behavior for large fields. It leads to an equivalent cosmological constant that decays like a power law, and this gives dark energy without "fine-tuning". Quantum turbulence (chaotic vorticity) in the early universe was able to create all the matter in the universe, fulfilling the inflation scenario. In the present universe, the superfluid can be phenomenologically described by a nonline...
Examining the Viability of Phantom Dark Energy
Ludwick, Kevin J
2015-01-01
In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter $w < -1$ (known as phantom dark energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the value of best fit from Planck and WMAP9 for present-day $w$ is indeed less than $-1$. We find that it is not as obvious as one might think that phantom dark energy has negative kinetic energy categorically. Staying within the confines of observational constraints and general relativity, for which there is good experimental validation, we consider a few reasonable departures from the standard 0th-order framework in an attempt to see if negative kinetic energy can be avoided in these settings despite an apparent $w<-1$. We consider a more accurate description of the universe through the perturbing of the isotropic and homogeneous FLRW metric and the components of the stress-energy tensor, and we ...
The Joint Dark Energy Mission (JDEM) Omega
Gehrels, Neil
2010-01-01
[JDEM-Omega is one of the three concepts that contributed to the Wide-Field Infrared Survey Telescope (WFIRST) mission advocated by the Astro2010 Decadal Survey. It is the concept on which the recommended observatory configuration is based.] The Joint Dark Energy Mission (JDEM) is a space-based observatory designed to perform precision measurements of the nature of dark energy in the Universe. It will make an order of magnitude progress in measuring the equation of state parameters of the Universe of most importance for understanding dark energy. JDEM-Omega is a wide-field space telescope operating in the near infrared. Dark energy measurements will be made via large surveys of galaxies and supernova monitoring. These will be an order of magnitude larger surveys than currently available and will provide enormous catalogs of astrophysical objects for many communities ranging from solar system to galaxy to galaxies/clusters to cosmology. JDEM-Omega is a mission concept collaboratively developed by NASA and the ...
The year in ideas; dark energy
Burdick, A
2002-01-01
Gravity should halt the expansion of the universe but a few years ago a study of supernovae showed that in fact cosmic expansion is speeding up. To explain this, cosmologists have postulated that a strange, repulsive force, which they call dark energy, is at work, counteracting gravity and pushing galaxies apart at an accelerating rate (1/2 page).
Dark Energy and the Preposterous Universe
Carroll, Sean M.
2001-01-01
A brief review is offered of the theoretical background concerning dark energy: what is required by observations, what sort of models are being considered, and how they fit into particle physics and gravitation. Contribution to the SNAP (SuperNova Acceleration Probe) Yellow Book.
The Dark Energy Spectroscopic Instrument (DESI)
Flaugher, Brenna; Bebek, Chris
2014-07-01
The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar spectroscopic redshift survey. The DESI instrument consists of a new wide-field (3.2 deg. linear field of view) corrector plus a multi-object spectrometer with up to 5000 robotically positioned optical fibers and will be installed at prime focus on the Mayall 4m telescope at Kitt Peak, Arizona. The fibers feed 10 three-arm spectrographs producing spectra that cover a wavelength range from 360-980 nm and have resolution of 2000-5500 depending on the wavelength. The DESI instrument is designed for a 14,000 sq. deg. multi-year survey of targets that trace the evolution of dark energy out to redshift 3.5 using the redshifts of luminous red galaxies (LRGs), emission line galaxies (ELGs) and quasars. DESI is the successor to the successful Stage-III BOSS spectroscopic redshift survey and complements imaging surveys such as the Stage-III Dark Energy Survey (DES, currently operating) and the Stage-IV Large Synoptic Survey Telescope (LSST, planned start early in the next decade).
A nonuniform dark energy fluid : perturbation equations.
Halle, A.; Zhao, H.; Li, B.
2008-01-01
We propose that galactic dark matter can be described by a nonuniform dark energy fluid. The underlying field is a decaying vector field, which might corresponds to a photon-like but massive particle of 4 degrees of dynamical freedom. We propose a very general Lagrangian for this vector field. The model includes a continuous spectrum of plausible gravity theories, for example, quintessence, f(R), Einstein-Aether, MOND, TeVeS, BSTV, V-Λ theories, and the inflaton scalar field as special cases....
Unification of Dark Matter and Dark Energy: the Inhomogeneous Chaplygin Gas
Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D
2001-01-01
We extend the world model of Kamenshchik et al. to large perturbations by formulating a Zeldovich-like approximation. We sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.
Dark Energy Found Stifling Growth in Universe
2008-12-01
WASHINGTON -- For the first time, astronomers have clearly seen the effects of "dark energy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how dark energy has stifled the growth of galaxy clusters and combining this with previous studies, scientists have obtained the best clues yet about what dark energy is and what the destiny of the universe could be. This work, which took years to complete, is separate from other methods of dark energy research such as supernovas. These new X-ray results provide a crucial independent test of dark energy, long sought by scientists, which depends on how gravity competes with accelerated expansion in the growth of cosmic structures. Techniques based on distance measurements, such as supernova work, do not have this special sensitivity. Scientists think dark energy is a form of repulsive gravity that now dominates the universe, although they have no clear picture of what it actually is. Understanding the nature of dark energy is one of the biggest problems in science. Possibilities include the cosmological constant, which is equivalent to the energy of empty space. Other possibilities include a modification in general relativity on the largest scales, or a more general physical field. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Ghostly Glow Reveals a Hidden Class of Long-Wavelength Radio Emitters Powerful Nearby Supernova Caught By Web Cassiopeia A Comes Alive Across Time and Space To help decide between these options, a new way of looking at dark energy is required. It is accomplished by observing how cosmic acceleration affects the growth of galaxy clusters over time. "This result could be described as 'arrested development of the universe'," said Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research. "Whatever is forcing the expansion of the universe to speed up is also forcing its
Dark energy interacting with neutrinos and dark matter: a phenomenological theory
Kremer, G. M.
2007-01-01
A model for a flat homogeneous and isotropic Universe composed of dark energy, dark matter, neutrinos, radiation and baryons is analyzed. The fields of dark matter and neutrinos are supposed to interact with the dark energy. The dark energy is considered to obey either the van der Waals or the Chaplygin equations of state. The ratio between the pressure and the energy density of the neutrinos varies with the red-shift simulating massive and non-relativistic neutrinos at small red-shifts and n...
Constraints on the coupling between dark energy and dark matter from CMB data
Murgia, R.; Gariazzo, S.; Fornengo, N.
2016-04-01
We investigate a phenomenological non-gravitational coupling between dark energy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both models are found to be compatible with all cosmological observables, but in the case where dark matter decays into dark energy, the tension with the independent determinations of H0 and σ8, already present for standard cosmology, increases: this model in fact predicts lower H0 and higher σ8, mostly as a consequence of the higher amount of dark matter at early times, leading to a stronger clustering during the evolution. Instead, when dark matter is fed by dark energy, the reconstructed values of H0 and σ8 nicely agree with their local determinations, with a full reconciliation between high- and low-redshift observations. A non-zero coupling between dark energy and dark matter, with an energy flow from the former to the latter, appears therefore to be in better agreement with cosmological data.
Energy Technology Data Exchange (ETDEWEB)
Piattella, O.F.; Martins, D.L.A.; Casarini, L., E-mail: oliver.piattella@pq.cnpq.br, E-mail: denilsonluizm@gmail.com, E-mail: casarini.astro@gmail.com [Department of Physics, Universidade Federal do Espírito Santo, avenida Ferrari 514, 29075-910 Vitória, Espírito Santo (Brazil)
2014-10-01
We consider a cosmological model of the late universe constituted by standard cold dark matter plus a dark energy component with constant equation of state w and constant effective speed of sound. By neglecting fluctuations in the dark energy component, we obtain an equation describing the evolution of sub-horizon cold dark matter perturbations through the epoch of dark matter-dark energy equality. We explore its analytic solutions and calculate an exact w-dependent correction for the dark matter growth function, logarithmic growth function and growth index parameter through the epoch considered. We test our analytic approximation with the numerical solution and find that the discrepancy is less than 1% for 0k = during the cosmic evolution up to a = 100.
International Nuclear Information System (INIS)
We consider a cosmological model of the late universe constituted by standard cold dark matter plus a dark energy component with constant equation of state w and constant effective speed of sound. By neglecting fluctuations in the dark energy component, we obtain an equation describing the evolution of sub-horizon cold dark matter perturbations through the epoch of dark matter-dark energy equality. We explore its analytic solutions and calculate an exact w-dependent correction for the dark matter growth function, logarithmic growth function and growth index parameter through the epoch considered. We test our analytic approximation with the numerical solution and find that the discrepancy is less than 1% for 0k = during the cosmic evolution up to a = 100
Dark energy in perturbative string cosmology
International Nuclear Information System (INIS)
The apparent observation of dark energy poses problems for string theory. In de Sitter space, or in quintessence models, one cannot define a gauge-invariant S-matrix. We argue that eternal quintessence does not arise in weakly coupled string theory, but point out that it is difficult to define an S-matrix even in the presence of perturbative potentials for the moduli. The solutions of the Fischler-Susskind equations all have Big Bang or Big Crunch Singularities. We believe that an S-matrix (or S-vector) exists in this context but cannot be calculated by purely perturbative methods. We study the possibility of metastable de Sitter vacua in such weakly coupled scenarios, and conclude that the S-matrix of the extreme weak coupling region cannot probe de Sitter physics. We also consider proposed explanations of the dark energy from the perspective of string theory, and find that most are implausible. We note that it is possible that the axion constitutes both the dark matter and the dark energy. (author)
Thermodynamical description of the interaction between holographic dark energy and dark matter
International Nuclear Information System (INIS)
We present a thermodynamical description of the interaction between holographic dark energy and dark matter. If holographic dark energy and dark matter evolve separately, each of them remains in thermodynamic equilibrium. A small interaction between them may be viewed as a stable thermal fluctuation that brings a logarithmic correction to the equilibrium entropy. From this correction we obtain a physical expression for the interaction which is consistent with phenomenological descriptions and passes reasonably well the observational tests
Thermodynamical description of the interaction between holographic dark energy and dark matter
Wang, Bin; Pavon, Diego; Abdalla, Elcio
2008-01-01
We present a thermodynamical description of the interaction between dark energy and dark matter. If dark energy and dark matter evolve separately, each of them remains in thermodynamic equilibrium. A small interaction between them may be viewed as a stable thermal fluctuation that brings a logarithmic correction to the equilibrium entropy. From this correction we obtain a physical expression for the interaction which is consistent with phenomenological descriptions and passes reasonably well the observational tests.
Thermodynamical description of the interaction between holographic dark energy and dark matter
Wang, Bin; Lin, Chi-Yong; Pavón, Diego; Abdalla, Elcio
2008-04-01
We present a thermodynamical description of the interaction between holographic dark energy and dark matter. If holographic dark energy and dark matter evolve separately, each of them remains in thermodynamic equilibrium. A small interaction between them may be viewed as a stable thermal fluctuation that brings a logarithmic correction to the equilibrium entropy. From this correction we obtain a physical expression for the interaction which is consistent with phenomenological descriptions and passes reasonably well the observational tests.
A Conjecture on the Origin of Dark Energy
Institute of Scientific and Technical Information of China (English)
GAO Shan
2005-01-01
@@ A conjecture on the origin of the dark energy in our universe is proposed. The analysis indicates that the dark energy may originate from the quantum fluctuations of space-time limited in our universe.
Can Holographic dark energy increase the mass of the wormhole?
Chattopadhyay, Surajit; Altaibayeva, Aziza; Myrzakulov, Ratbay
2014-01-01
In this work, we have studied accretion of dark energy (DE) onto Morris- Thorne wormhole with three different forms, namely, holographic dark energy, holographic Ricci dark energy and modified holographic Ricci dark energy . Considering the scale factor in power-law form we have observed that as the holographic dark energy accretes onto wormhole, the mass of the wormhole is decreasing. In the next phase we considered three parameterization schemes that are able to get hold of quintessence as well as phantom phases. Without any choice of scale factor we reconstructed Hubble parameter from conservation equation and dark energy densities and subsequently got the mass of the wormhole separately for accretion of the three dark energy candidates. It was observed that if these dark energies accrete onto the wormhole, then for quintessence stage, wormhole mass decreases up to a certain finite value and then again increases to aggressively during phantom phase of the universe.
Cosmic Visions Dark Energy: Technology
Energy Technology Data Exchange (ETDEWEB)
Dodelson, Scott [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Heitmann, Katrin [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Hirata, Chris [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Honscheid, Klaus [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Roodman, Aaron [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Seljak, Uroš [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Slosar, Anže [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Trodden, Mark [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
2016-04-26
A strong instrumentation and detector R&D program has enabled the current generation of cosmic frontier surveys. A small investment in R&D will continue to pay dividends and enable new probes to investigate the accelerated expansion of the universe. Instrumentation and detector R&D provide critical training opportunities for future generations of experimentalists, skills that are important across the entire Department of Energy High Energy Physics program.
Comic Visions Dark Energy: Technology
Dodelson, Scott; Hirata, Chris; Honscheid, Klaus; Roodman, Aaron; Seljak, Uroš; Slosar, Anže; Trodden, Mark
2016-01-01
A strong instrumentation and detector R&D program has enabled the current generation of cosmic frontier surveys. A small investment in R&D will continue to pay dividends and enable new probes to investigate the accelerated expansion of the universe. Instrumentation and detector R&D provide critical training opportunities for future generations of experimentalists, skills that are important across the entire Department of Energy High Energy Physics program.
Can we distinguish early dark energy from a cosmological constant?
Shi, D.; Baugh, C. M.
2016-01-01
Early dark energy (EDE) models are a class of quintessence dark energy with a dynamically evolving scalar field which display a small but non-negligible amount of dark energy at the epoch of matter-radiation equality. Compared with a cosmological constant, the presence of dark energy at early times changes the cosmic expansion history and consequently the shape of the linear theory power spectrum and potentially other observables. We constrain the cosmological parameters in the EDE cosmology ...
Cosmological constraints on coupled dark energy
Yang, Weiqiang; Wu, Yabo; Lu, Jianbo
2016-01-01
The coupled dark energy model provides a possible approach to mitigate the coincidence problem of cosmological standard model. Here, the coupling term is assumed as $\\bar{Q}=3H\\xi_x\\bar{\\rho}_x$, which is related to the interaction rate and energy density of dark energy. We derive the background and perturbation evolution equations for several coupled models. Then, we test these models by currently available cosmic observations which include cosmic microwave background radiation from Planck 2015, baryon acoustic oscillation, type Ia supernovae, $f\\sigma_8(z)$ data points from redshift-space distortions, and weak gravitational lensing. The constraint results tell us the interaction rate is close to zero in 1$\\sigma$ region, it is very hard to distinguish different coupled models from other ones.
Dark energy from the motions of neutrinos
Simpson, Fergus; Pena-Garay, Carlos; Verde, Licia
2016-01-01
We demonstrate that a scalar field is unable to reverse its direction of motion while continuously exchanging energy with another fluid. If the rate of transfer is modulated by the scalar's acceleration, the field can undergo a rapid process of freezing, despite being displaced from the local minimum of its potential. This enables dark energy to form from any potential, regardless of its shape. The field's equation of state mimicks that of a cosmological constant. We present a physically motivated realisation in the form of a derivative neutrino-majoron coupling. Coherent motions, which form only once the neutrinos become non-relativistic, could be responsible for instigating the freezing process. This would provide a natural resolution to the dark energy coincidence problem, while avoiding the dynamical instabilities associated with mass-varying neutrino models. Finally we discuss possible means by which this model could be experimentally verified.
Cosmological dynamics of tachyonic teleparallel dark energy
Otalora, G
2013-01-01
A detailed dynamical analysis of the tachyonic teleparallel dark energy model, in which a non-canonical scalar field (tachyon field) is non-minimally coupled to gravitation, is performed. It is found that, when the non-minimal coupling is ruled by a dynamically changing coefficient $\\alpha\\equiv f_{,\\phi}/f$, with $f(\\phi)$ an arbitrary function of the scalar field $\\phi$, the universe may experience a field-matter-dominated era "$\\phi$MDE", in which it has some portions of the energy density of $\\phi$ in the matter dominated era. This is the most significant difference in relation to the so-called teleparallel dark energy scenario, in which a canonical scalar field (quintessence) is non-minimally coupled to gravitation.
Metamaterial Model of Tachyonic Dark Energy
Directory of Open Access Journals (Sweden)
Igor I. Smolyaninov
2014-02-01
Full Text Available Dark energy with negative pressure and positive energy density is believed to be responsible for the accelerated expansion of the universe. Quite a few theoretical models of dark energy are based on tachyonic fields interacting with itself and normal (bradyonic matter. Here, we propose an experimental model of tachyonic dark energy based on hyperbolic metamaterials. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2 + 1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. We demonstrate that this model has a self-interacting tachyonic sector having negative effective pressure and positive effective energy density. Moreover, a composite multilayer SiC-Si hyperbolic metamaterial exhibits closely separated tachyonic and bradyonic sectors in the long wavelength infrared range. This system may be used as a laboratory model of inflation and late time acceleration of the universe.
Holographic Dark Energy Model with Modified Variable Chaplygin Gas
Paul, B. C.
2010-01-01
In this letter we consider a correspondence between holographic dark energy and variable modified Chaplygin gas to obtain a holographic dark energy model of the universe. The corresponding potential of the scalar field has been reconstructed which describes the modified variable Chaplygin gas. The stability of the holographic dark energy in this case is also discussed.
Dynamics of minimally coupled dark energy in spherical halos of dark matter
Novosyadlyj, Bohdan; Tsizh, Maksym; Kulinich, Yurij
2016-01-01
We analyse the evolution of scalar field dark energy in the spherical halos of dark matter at the late stages of formation of gravitationally bound systems in the expanding Universe. The dynamics of quintessential dark energy at the center of dark matter halo strongly depends on the value of effective sound speed $c_s$ (in units of speed of light). If $c_s\\sim1$ (classical scalar field) then the dark energy in the gravitationally bound systems is only slightly perturbed and its density is pra...
Deformed matter bounce with dark energy epoch
Odintsov, S. D.; Oikonomou, V. K.
2016-09-01
We extend the loop quantum cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario," the Universe is contracting from an initial noncausal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, and thus the model is described by a dark energy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the dark energy era is quintessential as what follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the dark energy era, a rip singularity exists, where the scale factor and Hubble rate diverge; however, the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, first that the ordinary loop quantum cosmology matter bounce evolution stops, thus ending the infinite repetition of the ordinary matter bounce scenario. Second, the fact that both the pressure and the density become complex probably indicates that the description of the cosmic evolution within the theoretical context of loop quantum cosmology ceases to describe the physics of the system and possibly a more fundamental theory of quantum gravity is needed near the would be rip singularity. We describe the qualitative features of the model, and we also investigate how this cosmology could be realized by a viscous fluid in the context of loop quantum cosmology. In addition to this, we show how this deformed model can be realized by a canonical scalar field filled Universe, in the context of loop quantum cosmology. Finally, we demonstrate how the model can be generated by a vacuum F (R ) gravity.
Entropy in the Present and Early Universe and Vacuum Energy
Shalyt-Margolin, A. E.
2010-03-01
It is demonstrated that entropy and its density play a significant role in solving the problem of the vacuum energy density (cosmological constant) in the Universe and hence the dark energy problem. Taking this in mind, two most popular models for dark energy-Holographic Dark Energy Model and Agegraphic Dark Energy Model-are analyzed. It is shown that the fundamental quantities in the first of these models may be expressed in terms of a new small parameter. Besides, the results obtained on the uncertainty relation of the pair ``cosmological constant-volume of space-time,'' where the cosmological constant is a dynamic quantity, are reconsidered and generalized up to the Generalized Uncertainty Relation (GUP).
A more general interacting model of holographic dark energy
Yu, Fei; Zhang, Jingfei; Lu, Jianbo; Wang, Wei; Gui, Yuanxing
2010-01-01
So far, there have been no theories or observational data that deny the presence of interaction between dark energy and dark matter. We extend naturally the holographic dark energy (HDE) model, proposed by Granda and Oliveros, in which the dark energy density includes not only the square of the Hubble scale, but also the time derivative of the Hubble scale to the case with interaction and the analytic forms for the cosmic parameters are obtained under the specific boundary conditions. The var...
Coupled dark energy: a dynamical analysis with complex scalar field
Landim, Ricardo C G
2016-01-01
The dynamical analysis for coupled dark energy with dark matter is presented, where a complex scalar field is taken into account and it is considered in the presence of a barothropic fluid. We consider three dark energy candidates: quintessence, phantom and tachyon. The critical points are found and their stabilities analyzed, leading to the three cosmological eras (radiation, matter and dark energy), for a generic potential. The results presented here enlarge the previous analyses found in the literature.
Statefinder Diagnostic for Dark Energy Models in Bianchi I Universe
Sharif, M
2013-01-01
In this paper, we investigate the statefinder, the deceleration and equation of state parameters when universe is composed of generalized holographic dark energy or generalized Ricci dark energy for Bianchi I universe model. These parameters are found for both interacting as well as non-interacting scenarios of generalized holographic or generalized Ricci dark energy with dark matter and generalized Chaplygin gas. We explore these parameters graphically for different situations. It is concluded that these models represent accelerated expansion of the universe.
An Interacting Dark Energy Model with Nonminimal Derivative Coupling
Nozari, Kourosh; Behrouz, Noushin
2016-01-01
We study cosmological dynamics of an extended gravitational theory that gravity is coupled non-minimally with derivatives of a dark energy component and there is also a phenomenological interaction between the dark energy and dark matter. Depending on the direction of energy flow between the dark sectors, the phenomenological interaction gets two different signs. We show that this feature affects the existence of attractor solution, the rate of growth of perturbations and stability of the sol...
Coupled dark energy: a dynamical analysis with complex scalar field
Landim, Ricardo C. G.
2016-01-01
The dynamical analysis for coupled dark energy with dark matter is presented, where a complex scalar field is taken into account and it is considered in the presence of a barothropic fluid. We consider three dark-energy candidates: quintessence, phantom, and tachyon. The critical points are found and their stabilities analyzed, leading to the three cosmological eras (radiation, matter, and dark energy), for a generic potential. The results presented here extend the previous analyses found in ...
Coupled dark energy: a dynamical analysis with complex scalar field
Energy Technology Data Exchange (ETDEWEB)
Landim, Ricardo C.G. [Universidade de Sao Paulo, Instituto de Fisica, Caixa Postal 66318, Sao Paulo, SP (Brazil)
2016-01-15
The dynamical analysis for coupled dark energy with dark matter is presented, where a complex scalar field is taken into account and it is considered in the presence of a barothropic fluid. We consider three dark-energy candidates: quintessence, phantom, and tachyon. The critical points are found and their stabilities analyzed, leading to the three cosmological eras (radiation, matter, and dark energy), for a generic potential. The results presented here extend the previous analyses found in the literature. (orig.)
Dark energy from the string axiverse.
Kamionkowski, Marc; Pradler, Josef; Walker, Devin G E
2014-12-19
String theories suggest the existence of a plethora of axionlike fields with masses spread over a huge number of decades. Here, we show that these ideas lend themselves to a model of quintessence with no super-Planckian field excursions and in which all dimensionless numbers are order unity. The scenario addresses the "Why now?" problem-i.e., Why has accelerated expansion begun only recently?-by suggesting that the onset of dark-energy domination occurs randomly with a slowly decreasing probability per unit logarithmic interval in cosmic time. The standard axion potential requires us to postulate a rapid decay of most of the axion fields that do not become dark energy. The need for these decays is averted, though, with the introduction of a slightly modified axion potential. In either case, a universe like ours arises in roughly 1 in 100 universes. The scenario may have a host of observable consequences. PMID:25554872
Singularity Problem in Teleparallel Dark Energy Models
Geng, Chao-Qiang; Lee, Chung-Chi
2013-01-01
We study the singularity problem in teleparallel dark energy models. A future singularity may occur due to the non-minimal coupling of the dark energy scalar field to teleparallel gravity that effectively changes the gravitational coupling strength and can even make it diverge. This singularity may be avoided by a binding-type self-potential that keeps the scalar field away from the singularity point. For demonstration we analyze the model with a quadratic potential and show how the (non)occurrence of the singularity depends on the initial conditions and the steepness of the potential, both of which affect the competition between the self-interaction and the non-minimal coupling. To examine the capability of the binding-type potential to fit observational data and meanwhile to avoid the singularity, we perform the data fitting for this model and show that the observationally viable region up to the $3\\sigma$ confidence level is free of the future singularity.
Virialization-induced curvature versus dark energy
Ostrowski, Jan J; Buchert, Thomas
2013-01-01
The concordance model is successful in explaining numerous observable phenomena at the price of introducing an exotic source of unknown origin: dark energy. Dark energy dominance occurs at recent epochs, when we expect most cosmological structures to have already formed, and thus, when the error induced by forcing the homogeneous FLRW metric onto the data is expected to be the most significant. We propose a way to quantify the impact of deviations from homogeneity on the evolution of cosmological parameters. Using a multi-scale partitioning approach and the virialization fraction estimated from numerical simulations in an Einstein-de Sitter model, we obtain an observationally realistic distance modulus over redshifts 0 < z < 3 by a relativistic correction of the FLRW metric.
Atom-interferometry constraints on dark energy
Hamilton, Paul; Haslinger, Philipp; Simmons, Quinn; Müller, Holger; Khoury, Justin
2015-01-01
If dark energy---which drives the accelerated expansion of the universe---consists of a new light scalar field, it might be detectable as a "fifth force" between normal-matter objects, in potential conflict with precision tests of gravity. There has, however, been much theoretical progress in developing theories with screening mechanisms, which can evade detection by suppressing forces in regions of high density, such as the laboratory. One prominent example is the chameleon field. We reduce the effect of this screening mechanism by probing the chameleon with individual atoms rather than bulk matter. Using a cesium matter-wave interferometer near a spherical mass in an ultra-high vacuum chamber, we constrain a wide class of dynamical dark energy theories. Our experiment excludes a range of chameleon theories that reproduce the observed cosmic acceleration.
Cosmological electromagnetic fields and dark energy
Jimenez, Jose Beltran
2008-01-01
Understanding why the expansion of the universe is presently accelerating is one of the most important open questions in modern cosmology. In this work we show that the presence of a temporal electromagnetic field on cosmological scales generates an effective cosmological constant which could be responsible for the acceleration. Primordial electromagnetic quantum fluctuations produced during electroweak scale inflation could naturally explain the presence of this field and the measured value of the dark energy density. This mechanism could be discriminated from a true cosmological constant by observations of CMB and structure formation. In the same way as the presence of matter or radiation in the Universe breaks global Lorentz symmetry, the existence of dark energy could be signalling the breakdown of electromagnetic gauge invariance on cosmological scales.
Strong gravitational lensing and dark energy complementarity
Energy Technology Data Exchange (ETDEWEB)
Linder, Eric V.
2004-01-21
In the search for the nature of dark energy most cosmological probes measure simple functions of the expansion rate. While powerful, these all involve roughly the same dependence on the dark energy equation of state parameters, with anticorrelation between its present value w{sub 0} and time variation w{sub a}. Quantities that have instead positive correlation and so a sensitivity direction largely orthogonal to, e.g., distance probes offer the hope of achieving tight constraints through complementarity. Such quantities are found in strong gravitational lensing observations of image separations and time delays. While degeneracy between cosmological parameters prevents full complementarity, strong lensing measurements to 1 percent accuracy can improve equation of state characterization by 15-50 percent. Next generation surveys should provide data on roughly 105 lens systems, though systematic errors will remain challenging.
A CMB/Dark Energy Cosmic Duality
DEFF Research Database (Denmark)
Enqvist, Kari; Sloth, Martin Snoager
2004-01-01
We investigate a possible connection between the suppression of the power at low multipoles in the CMB spectrum and the late time acceleration. We show that, assuming a cosmic IR/UV duality between the UV cutoff and a global infrared cutoff given by the size of the future event horizon, the equat......We investigate a possible connection between the suppression of the power at low multipoles in the CMB spectrum and the late time acceleration. We show that, assuming a cosmic IR/UV duality between the UV cutoff and a global infrared cutoff given by the size of the future event horizon......, the equation of state of the dark energy can be related to the apparent cutoff in the CMB spectrum. The present limits on the equation of state of dark energy are shown to imply an IR cutoff in the CMB multipole interval of 9>l>8.5....
Scale Dependence of Dark Energy Antigravity
Perivolaropoulos, L
2001-01-01
We investigate the effects of negative pressure induced by dark energy (cosmological constant or quintessence) on the dynamics at various astrophysical scales. Negative pressure induces a repulsive term (antigravity) in Newton's law which dominates on large scales. Assuming a value of the cosmological constant consistent with the recent SnIa data we determine the critical scale $r_c$ beyond which antigravity dominates the dynamics ($r_c \\sim 1Mpc $) and discuss some of the dynamical effects implied. We show that dynamically induced mass estimates on the scale of the Local Group and beyond are significantly modified due to negative pressure. We also briefly discuss possible dynamical tests (eg effects on local Hubble flow) that can be applied on relatively small scales (a few $Mpc$) to determine the density and equation of state of dark energy.
Scale Dependence of Dark Energy Antigravity
Perivolaropoulos, L.
2002-09-01
We investigate the effects of negative pressure induced by dark energy (cosmological constant or quintessence) on the dynamics at various astrophysical scales. Negative pressure induces a repulsive term (antigravity) in Newton's law which dominates on large scales. Assuming a value of the cosmological constant consistent with the recent SnIa data we determine the critical scale $r_c$ beyond which antigravity dominates the dynamics ($r_c \\sim 1Mpc $) and discuss some of the dynamical effects implied. We show that dynamically induced mass estimates on the scale of the Local Group and beyond are significantly modified due to negative pressure. We also briefly discuss possible dynamical tests (eg effects on local Hubble flow) that can be applied on relatively small scales (a few $Mpc$) to determine the density and equation of state of dark energy.
Atom-interferometry constraints on dark energy
Hamilton, Paul; Jaffe, Matt; Haslinger, Philipp; Simmons, Quinn; Müller, Holger; Khoury, Justin
2015-01-01
If dark energy --- which drives the accelerated expansion of the universe --- consists of a light scalar field, it might be detectable as a "fifth force" between normal-matter objects, in potential conflict with precision tests of gravity. Chameleon fields and other theories with screening mechanisms, however, can evade these tests by suppressing the forces in regions of high density, such as the laboratory. Using a cesium matter-wave interferometer near a spherical mass in an ultra-high vacu...
Dark Energy from $\\alpha$-Attractors
Linder, Eric V
2015-01-01
A class of inflation theories called $\\alpha$-attractors has been investigated recently with interesting properties interpolating between quadratic potentials, the Starobinsky model, and an attractor limit. Here we examine their use for late time cosmic acceleration. We generalize the class and demonstrate how it can interpolate between thawing and freezing dark energy, and reduce the fine tuning of initial conditions, allowing $w\\approx-1$ for a prolonged period or as a de Sitter attractor.
A Possible Origin of Dark Energy
Institute of Scientific and Technical Information of China (English)
T. D. Lee
2004-01-01
@@ We discuss the possibility that the existence of dark energy may be due to the presence ofa spin zero field φ(x), either elementary or composite. In the presence of other matter field, the transformation φ(x) → φ(x) + constant can generate a negative pressure, like the cosmological constant. In this picture, our universe can be thought as a very large bag, similar to the much smaller MIT bag model for a single nucleon.
Cosmological dark energy effects from entanglement
International Nuclear Information System (INIS)
The thorny issue of relating information theory to cosmology is here addressed by assuming a possible connection between quantum entanglement measures and observable universe. In particular, we propose a cosmological toy model, where the equation of state of the cosmological fluid, which drives the today observed cosmic acceleration, can be inferred from quantum entanglement between different cosmological epochs. In such a way the dynamical dark energy results as byproduct of quantum entanglement.
Redshift drift constraints on holographic dark energy
He, Dong-Ze; Zhang, Jing-Fei; Xin ZHANG
2016-01-01
The Sandage-Loeb (SL) test is a promising method for probing dark energy because it measures the redshift drift in the spectra of Lyman-$\\alpha$ forest of distant quasars, covering the "redshift desert" of $2\\lesssim z\\lesssim5$, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holograp...
Dark energy: A scientometric mapping of publications
Directory of Open Access Journals (Sweden)
Anil Sagar
2013-01-01
Full Text Available This paper attempts to highlight the growth and development of dark energy literature and make the quantitative and qualitative assessment by way of analyzing various features of research output based on Web of Science database. A total of 5858 publications were published on dark energy, which received 157,581 citations during 1999-2011. The average number of publications per year was 450.62, and the average number of citations per publication was 26.90. The publications peaked in 2011 with 934 publications, and the highest number of citations (26,404 were received in 2003. There were 3857 (65.84% single country publications from 74 countries and 2001 (34.16% multi-country collaborative publications. The highest number of publications were from Europe with 3723 (41.15% publications and 126,747 (39.88% citations followed by Asia with 2614 (28.89% publications and 63,267 (19.90% citations, and North America with 1980 (21.89% publications and 105,132 (33.08% citations. European scientists have been playing an important role on dark energy-related research followed by Asian Scientists. The exponential growth of publications was observed during the period. USA had the highest share (26.84% of publications followed Peoples Republic of China with 13.74% publications, England with 11.71% publications, Italy with 10.84% publications, Spain with 7.90% publications, Germany with 7.27% publications, and India with 7.07% publications. Astronomy and Astrophysics accounts for the largest share 3920 (66.92% of publications in the total worldwide output on dark energy which received 117,919 (74.83% citations followed by Multidisciplinary Physics with 1242 (21.20% publications, 29,775 (18.90% citations and 23.97 average citations per publication. More than 80% of the publications appeared only in 15 key-journals.
Cosmological dark energy effects from entanglement
Energy Technology Data Exchange (ETDEWEB)
Capozziello, Salvatore, E-mail: capozziello@na.infn.it [Dipartimento di Fisica, Università di Napoli “Federico II”, Via Cinthia, 80126 Napoli (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Sez. di Napoli, Via Cinthia, 80126 Napoli (Italy); Luongo, Orlando [Dipartimento di Fisica, Università di Napoli “Federico II”, Via Cinthia, 80126 Napoli (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Sez. di Napoli, Via Cinthia, 80126 Napoli (Italy); Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de México (UNAM) (Mexico); Mancini, Stefano [Scuola di Scienze and Tecnologie, Università di Camerino, 62032 Camerino (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Sez. di Perugia, Via Pascoli, 06123 Perugia (Italy)
2013-06-03
The thorny issue of relating information theory to cosmology is here addressed by assuming a possible connection between quantum entanglement measures and observable universe. In particular, we propose a cosmological toy model, where the equation of state of the cosmological fluid, which drives the today observed cosmic acceleration, can be inferred from quantum entanglement between different cosmological epochs. In such a way the dynamical dark energy results as byproduct of quantum entanglement.
"Dark energy" in the Local Void
Villata, M.
2012-01-01
The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "dark energy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can ac...
Detecting dark energy with wavelets on the sphere
McEwen, Jason D.
2007-09-01
Dark energy dominates the energy density of our Universe, yet we know very little about its nature and origin. Although strong evidence in support of dark energy is provided by the cosmic microwave background, the relic radiation of the Big Bang, in conjunction with either observations of supernovae or of the large scale structure of the Universe, the verification of dark energy by independent physical phenomena is of considerable interest. We review works that, through a wavelet analysis on the sphere, independently verify the existence of dark energy by detecting the integrated Sachs-Wolfe effect. The effectiveness of a wavelet analysis on the sphere is demonstrated by the highly statistically significant detections of dark energy that are made. Moreover, the detection is used to constrain properties of dark energy. A coherent picture of dark energy is obtained, adding further support to the now well established cosmological concordance model that describes our Universe.
Detecting dark energy with wavelets on the sphere
McEwen, J D
2007-01-01
Dark energy dominates the energy density of our Universe, yet we know very little about its nature and origin. Although strong evidence in support of dark energy is provided by the cosmic microwave background, the relic radiation of the Big Bang, in conjunction with either observations of supernovae or of the large scale structure of the Universe, the verification of dark energy by independent physical phenomena is of considerable interest. We review works that, through a wavelet analysis on the sphere, independently verify the existence of dark energy by detecting the integrated Sachs-Wolfe effect. The effectiveness of a wavelet analysis on the sphere is demonstrated by the highly statistically significant detections of dark energy that are made. Moreover, the detection is used to constrain properties of dark energy. A coherent picture of dark energy is obtained, adding further support to the now well established cosmological concordance model that describes our Universe.
Interaction between Dark Matter and Dark Energy and the Cosmological Coincidence Problem
Kourosh Nozari; Noushin Behrouz; Narges Rashidi
2014-01-01
We consider a quintessence model of dark energy inspired by scalar-tensor theories of gravity where the scalar field is nonminimally coupled to gravity and dark matter. By considering exponential potential as self-interaction potential, the stability and existence of the critical points are discussed in details. With nonminimally coupled dark sector with gravity, we obtain scaling solutions to address the coincidence problem by considering complex velocity for dark matter. The statefinder dia...
Machian gravity and a cosmology without dark matter and dark energy
Das, Santanu
2012-01-01
The standard model of cosmology is based on the general theory of relativity and demands more than 95\\% of the universe to consist of dark matter and dark energy that has no direct observational evidence till date. The foundation of the concept these dark components are based on a fixed relation between the strength of the gravitational field and the matter density. Alternate models are put forward in past to explain the observations without dark components in the universe. Though they have t...
Halo Mass Functions in Early Dark Energy Cosmologies
Francis, Matthew J.; Lewis, Geraint F.; Linder, Eric V.
2008-01-01
We examine the linear density contrast at collapse time, $\\delta_c$ for large-scale structure in dynamical dark energy cosmologies, including models with early dark energy. Contrary to previous results, we find that as long as dark energy is homogeneous on small scales, $\\delta_c$ is insensitive to dark energy properties for parameter values fitting current data, including the case of early dark energy. This is significant since using the correct $\\delta_c$ is crucial for accurate Press-Schec...
The continuous tower of scalar fields as a system of interacting dark matter–dark energy
Directory of Open Access Journals (Sweden)
Paulo Santos
2015-10-01
Full Text Available This paper aims to introduce a new parameterisation for the coupling Q in interacting dark matter and dark energy models by connecting said models with the Continuous Tower of Scalar Fields model. Based upon the existence of a dark matter and a dark energy sectors in the Continuous Tower of Scalar Fields, a simplification is considered for the evolution of a single scalar field from the tower, validated in this paper. This allows for the results obtained with the Continuous Tower of Scalar Fields model to match those of an interacting dark matter–dark energy system, considering that the energy transferred from one fluid to the other is given by the energy of the scalar fields that start oscillating at a given time, rather than considering that the energy transference depends on properties of the whole fluids that are interacting.
Redshift drift exploration for interacting dark energy
Geng, Jia-Jia; Zhang, Jing-Fei; Zhang, Xin
2015-01-01
By detecting redshift drift in the spectra of Lyman-$\\alpha$ forest of distant quasars, Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the "redshift desert" of $2 \\lesssim z \\lesssim5$. Thus this method is definitely an important supplement to the other geometric measurements and will play a crucial role in cosmological constraints. In this paper, we quantify the ability of SL test signal by a CODEX-like spectrograph for constraining interacting dark energy. Four typical interacting dark energy models are considered: (\\romannumeral1) $Q=\\gamma H\\rho_c$, (\\romannumeral2) $Q=\\gamma H\\rho_{de}$, (\\romannumeral3) $Q=\\gamma H_0\\rho_c$, and (\\romannumeral4) $Q=\\gamma H_0\\rho_{de}$. The results show that for all the considered interacting dark energy models, relative to the current joint SN+BAO+CMB+$H_0$ observations, the constraints on $\\Omega_m$ and $H_0$ would be improved by about 60\\% and 30--40\\%, while the constraints on $w$ and $\\gamma$ would be slightly improved, with a 30-y...
Dark energy with gravitational lens time delays
Treu, T; Cyr-Racine, F -Y; Fassnacht, C D; Keeton, C R; Linder, E V; Moustakas, L A; Bradac, M; Buckley-Geer, E; Collett, T; Courbin, F; Dobler, G; Finley, D A; Hjorth, J; Kochanek, C S; Komatsu, E; Koopmans, L V E; Meylan, G; Natarajan, P; Oguri, M; Suyu, S H; Tewes, M; Wong, K C; Zabludoff, A I; Zaritsky, D; Anguita, T; Brunner, R J; Cabanac, R; Falco, E E; Fritz, A; Seidel, G; Howell, D A; Giocoli, C; Jackson, N; Lopez, S; Metcalf, R B; Motta, V; Verdugo, T
2013-01-01
Strong lensing gravitational time delays are a powerful and cost effective probe of dark energy. Recent studies have shown that a single lens can provide a distance measurement with 6-7 % accuracy (including random and systematic uncertainties), provided sufficient data are available to determine the time delay and reconstruct the gravitational potential of the deflector. Gravitational-time delays are a low redshift (z~0-2) probe and thus allow one to break degeneracies in the interpretation of data from higher-redshift probes like the cosmic microwave background in terms of the dark energy equation of state. Current studies are limited by the size of the sample of known lensed quasars, but this situation is about to change. Even in this decade, wide field imaging surveys are likely to discover thousands of lensed quasars, enabling the targeted study of ~100 of these systems and resulting in substantial gains in the dark energy figure of merit. In the next decade, a further order of magnitude improvement will...
Probing the dark energy methods and strategies
Huterer, D; Huterer, Dragan; Turner, Michael S.
2001-01-01
The presence of dark energy in the Universe is inferred directly from the accelerated expansion of the Universe, and indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3 of the critical density, is very smoothly distributed, and has large negative pressure. Its nature is very much unknown. Most of its discernible consequences follow from its effect on evolution of the expansion rate of the Universe, which in turn affects the growth of density perturbations and the age of the Universe, and can be probed by the classical kinematic cosmological tests. Absent a compelling theoretical model (or even a class of models), we describe the dark energy by an effective equation-of-state w=p_X/\\rho_X which is allowed to vary with time. We describe and compare different approaches for determining w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies and clusters, and CMB anisotropy, focusing particular attention on the use of a sample of s...
Constraining the Properties of Dark Energy
Huterer, D; Huterer, Dragan; Turner, Michael S.
2001-01-01
The presence of dark energy in the Universe is inferred directly from the accelerated expansion of the Universe, and indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3 of the critical density, is very smoothly distributed, and has large negative pressure. Its nature is very much unknown. Most of its discernible consequences follow from its effect on evolution of the expansion rate of the Universe, which in turn affects the growth of density perturbations and the age of the Universe, and can be probed by the classical kinematic cosmological tests. Absent a compelling theoretical model (or even a class of models), we describe dark energy by an effective equation of state w=p_X/rho_X which is allowed to vary with time. We describe and compare different approaches for determining w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies and clusters, and CMB anisotropy, focusing particular attention on the use of a sample of severa...
Using atom interferometry to detect dark energy
Burrage, Clare; Copeland, Edmund J.
2016-04-01
We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the universe on giga-parsec scales may be found through metre scale laboratory-based atom interferometry experiments. To do that, we first introduce the idea that scalar fields could be responsible for dark energy and show that in order to be compatible with fifth force constraints, these fields must have a screening mechanism which hides their effects from us within the solar system. Particular emphasis is placed on one such screening mechanism known as the chameleon effect where the field's mass becomes dependent on the environment. The way the field behaves in the presence of a spherical source is determined and we then go on to show how in the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the chameleon field - this has already been used to rule out large regions of the chameleon parameter space and maybe one day will be able to detect the force due to the dark energy field in the laboratory.
Gupta, R. C.; Pradhan, Anirudh
2009-01-01
Recent observations on Type-Ia supernovae and low density ($\\Omega_{m} = 0.3$) measurement of matter including dark matter suggest that the present-day universe consists mainly of repulsive-gravity type `exotic matter' with negative-pressure often said `dark energy' ($\\Omega_{x} = 0.7$). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the dark energy, are intriguing. In the present paper the authors attempt to answer these questio...
The Localized Energy Distribution of Dark Energy Star Solutions
Paul Halpern; Michael Pecorino
2013-01-01
We examine the question of energy localization for an exact solution of Einstein's equations with a scalar field corresponding to the phantom energy interpretation of dark energy. We apply three different energy-momentum complexes, the Einstein, the Papapetrou, and the Møller prescriptions, to the exterior metric and determine the energy distribution for each. Comparing the results, we find that the three prescriptions yield identical energy distributions.
Adiabatic instability in coupled dark energy-dark matter models
Bean, Rachel; Flanagan, Eanna E.; Trodden, Mark
2007-01-01
We consider theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the universe. Such theories can possess an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, which is set by the local dark matter density. We show that if the coupling strength is much larger than gravitational, then the adiabatic regime is always subject to an instability. The instability, whi...
Large Synoptic Survey Telescope: Dark Energy Science Collaboration
,
2012-01-01
This white paper describes the LSST Dark Energy Science Collaboration (DESC), whose goal is the study of dark energy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of dark energy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for dark energy science that has been defined by its members and the comprehensive three-year work plan they have developed for implementing that framework. The analysis working groups cover five key probes of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia supernovae, and strong lensing. The computing working groups span cosmological simulations, galaxy catalogs, photon simulations and a systematic software and computational framework for LSST dark energy data analysis. The technical working groups make the connection between dark energy science and the LSST system. The working groups ha...
Influences of dark energy and dark matter on gravitational time advancement
Energy Technology Data Exchange (ETDEWEB)
Ghosh, Samrat; Bhadra, Arunava [University of North Bengal, High Energy and Cosmic Ray Research Center, Siliguri (India)
2015-10-15
The effect of dark matter/energy on the gravitational time advancement (negative effective time delay) has been investigated considering a few dark energy/matter models including cosmological constant. It is found that dark energy gives only a (positive) gravitational time delay, irrespective of the position of the observer, whereas a pure Schwarzschild geometry leads to a gravitational time advancement when the observer is situated at a relatively stronger gravitational field point in the light trajectory. Consequently, there will be no time advancement effect at all at radial distances where the gravitational field due to dark energy is stronger than the gravitational field of the Schwarzschild geometry. (orig.)
Influences of dark energy and dark matter on gravitational time advancement
International Nuclear Information System (INIS)
The effect of dark matter/energy on the gravitational time advancement (negative effective time delay) has been investigated considering a few dark energy/matter models including cosmological constant. It is found that dark energy gives only a (positive) gravitational time delay, irrespective of the position of the observer, whereas a pure Schwarzschild geometry leads to a gravitational time advancement when the observer is situated at a relatively stronger gravitational field point in the light trajectory. Consequently, there will be no time advancement effect at all at radial distances where the gravitational field due to dark energy is stronger than the gravitational field of the Schwarzschild geometry. (orig.)
2008-01-01
observations show that the temperature changes with radius are much steeper than predicted by the currently favoured models, indicating that most of the near-infrared emission emerges from hot material located very close to the star, that is, within one or two times the Earth-Sun distance (1-2 AU). This also implies that dust cannot exist so close to the star, since the strong energy radiated by the star heats and ultimately destroys the dust grains. ESO PR Photo 03/08 ESO PR Photo 03b/08 The Region Around MWC 147 "We have performed detailed numerical simulations to understand these observations and reached the conclusion that we observe not only the outer dust disc, but also measure strong emission from a hot inner gaseous disc. This suggests that the disc is not a passive one, simply reprocessing the light from the star," explained Kraus. "Instead, the disc is active, and we see the material, which is just transported from the outer disc parts towards the forming star." ESO PR Photo 03/08 ESO PR Photo 03c/08 Close-up on MWC 147 The best-fit model is that of a disc extending out to 100 AU, with the star increasing in mass at a rate of seven millionths of a solar mass per year. "Our study demonstrates the power of ESO's VLTI to probe the inner structure of discs around young stars and to reveal how stars reach their final mass," said Stefan Kraus. More Information The authors report their results in a paper in the Astrophysical Journal ("Detection of an inner gaseous component in a Herbig Be star accretion disk: Near- and mid-infrared spectro-interferometry and radiative transfer modeling of MWC 147", by Stefan Kraus, Thomas Preibisch, Keichii Ohnaka").
Advanced Dark Energy Physics Telescope (ADEPT)
Energy Technology Data Exchange (ETDEWEB)
Charles L. Bennett
2009-03-26
In 2006, we proposed to NASA a detailed concept study of ADEPT (the Advanced Dark Energy Physics Telescope), a potential space mission to reliably measure the time-evolution of dark energy by conducting the largest effective volume survey of the universe ever done. A peer-review panel of scientific, management, and technical experts reported back the highest possible 'excellent' rating for ADEPT. We have since made substantial advances in the scientific and technical maturity of the mission design. With this Department of Energy (DOE) award we were granted supplemental funding to support specific extended research items that were not included in the NASA proposal, many of which were intended to broadly advance future dark energy research, as laid out by the Dark Energy Task Force (DETF). The proposed work had three targets: (1) the adaptation of large-format infrared arrays to a 2 micron cut-off; (2) analytical research to improve the understanding of the dark energy figure-of- merit; and (3) extended studies of baryon acoustic oscillation systematic uncertainties. Since the actual award was only for {approx}10% of the proposed amount item (1) was dropped and item (2) work was severely restricted, consistent with the referee reviews of the proposal, although there was considerable contradictions between reviewer comments and several comments that displayed a lack of familiarity with the research. None the less, item (3) was the focus of the work. To characterize the nature of the dark energy, ADEPT is designed to observe baryon acoustic oscillations (BAO) in a large galaxy redshift survey and to obtain substantial numbers of high-redshift Type Ia supernovae (SNe Ia). The 2003 Wilkinson Microwave Anisotropy Probe (WMAP) made a precise determination of the BAO 'standard ruler' scale, as it was imprinted on the cosmic microwave background (CMB) at z {approx} 1090. The standard ruler was also imprinted on the pattern of galaxies, and was first
A look to nonlinear interacting Ghost dark energy cosmology
Khurshudyan, Martiros
2016-07-01
In this paper, we organize a look to nonlinear interacting Ghost dark energy cosmology involving a discussion on the thermodynamics of the Ghost dark energy, when the universe is bounded via the Hubble horizon. One of the ways to study a dark energy model, is to reconstruct thermodynamics of it. Ghost dark energy is one of the models of the dark energy which has an explicitly given energy density as a function of the Hubble parameter. There is an active discussion towards various cosmological scenarios, where the Ghost dark energy interacts with the pressureless cold dark matter (CDM). Recently, various models of the varying Ghost dark energy has been suggested, too. To have a comprehensive understanding of suggested models, we will discuss behavior of the cosmological parameters on parameter-redshift z plane. Some discussion on Om and statefinder hierarchy analysis of these models is presented. Moreover, up to our knowledge, suggested forms of interaction between the Ghost dark energy and cold dark matter (CDM) are new, therefore, within obtained results, we provide new contribution to previously discussed models available in the literature. Our study demonstrates that the forms of the interactions considered in the Ghost dark energy cosmology are not exotic and the justification of this is due to the recent observational data.
Dark energy in scalar-tensor theories
Energy Technology Data Exchange (ETDEWEB)
Moeller, J.
2007-12-15
We investigate several aspects of dynamical dark energy in the framework of scalar-tensor theories of gravity. We provide a classification of scalar-tensor coupling functions admitting cosmological scaling solutions. In particular, we recover that Brans-Dicke theory with inverse power-law potential allows for a sequence of background dominated scaling regime and scalar field dominated, accelerated expansion. Furthermore, we compare minimally and non-minimally coupled models, with respect to the small redshift evolution of the dark energy equation of state. We discuss the possibility to discriminate between different models by a reconstruction of the equation-of-state parameter from available observational data. The non-minimal coupling characterizing scalar-tensor models can - in specific cases - alleviate fine tuning problems, which appear if (minimally coupled) quintessence is required to mimic a cosmological constant. Finally, we perform a phase-space analysis of a family of biscalar-tensor models characterized by a specific type of {sigma}-model metric, including two examples from recent literature. In particular, we generalize an axion-dilaton model of Sonner and Townsend, incorporating a perfect fluid background consisting of (dark) matter and radiation. (orig.)
Dark energy in scalar-tensor theories
International Nuclear Information System (INIS)
We investigate several aspects of dynamical dark energy in the framework of scalar-tensor theories of gravity. We provide a classification of scalar-tensor coupling functions admitting cosmological scaling solutions. In particular, we recover that Brans-Dicke theory with inverse power-law potential allows for a sequence of background dominated scaling regime and scalar field dominated, accelerated expansion. Furthermore, we compare minimally and non-minimally coupled models, with respect to the small redshift evolution of the dark energy equation of state. We discuss the possibility to discriminate between different models by a reconstruction of the equation-of-state parameter from available observational data. The non-minimal coupling characterizing scalar-tensor models can - in specific cases - alleviate fine tuning problems, which appear if (minimally coupled) quintessence is required to mimic a cosmological constant. Finally, we perform a phase-space analysis of a family of biscalar-tensor models characterized by a specific type of σ-model metric, including two examples from recent literature. In particular, we generalize an axion-dilaton model of Sonner and Townsend, incorporating a perfect fluid background consisting of (dark) matter and radiation. (orig.)
Necessity of Dark Energy from Thermodynamic Arguments
International Nuclear Information System (INIS)
Considering the cosmic fluid as a quasi-static thermodynamic system, the status of the generalized second law of thermodynamics is investigated and the valid range of the equation of state parameter is derived for a few important cosmological models. Our study shows that the satisfaction of the laws of thermodynamics in these cosmological models requires the existence of some kind of energy in our universe with ω<−1/3. In other words, the existence of a dark energy component, or equivalently modified gravity theory, is unavoidable if the cosmological model is to approach thermal equilibrium in late times
Necessity of Dark Energy from Thermodynamic Arguments
Directory of Open Access Journals (Sweden)
H. Moradpour
2014-01-01
Full Text Available Considering the cosmic fluid as a quasi-static thermodynamic system, the status of the generalized second law of thermodynamics is investigated and the valid range of the equation of state parameter is derived for a few important cosmological models. Our study shows that the satisfaction of the laws of thermodynamics in these cosmological models requires the existence of some kind of energy in our universe with ω<−1/3. In other words, the existence of a dark energy component, or equivalently modified gravity theory, is unavoidable if the cosmological model is to approach thermal equilibrium in late times.
Viscous dark energy and phantom evolution
Energy Technology Data Exchange (ETDEWEB)
Cataldo, Mauricio [Departamento de Fisica, Facultad de Ciencias, Universidad del Bio-Bio, Avenida Collao 1202, Casilla 5-C, Concepcion (Chile)]. E-mail: mcataldo@ubiobio.cl; Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile)]. E-mail: ncruz@lauca.usach.cl; Lepe, Samuel [Instituto de Fisica, Facultad de Ciencias Basicas y Matematicas, Pontificia Universidad Catolica de Valparaiso, Avenida Brasil 2950, Valparaiso (Chile)]. E-mail: slepe@ucv.cl
2005-07-14
In order to study if the bulk viscosity may induce a big rip singularity on the flat FRW cosmologies, we investigate dissipative processes in the universe within the framework of the standard Eckart theory of relativistic irreversible thermodynamics, and in the full causal Israel-Stewart-Hiscock theory. We have found cosmological solutions which exhibit, under certain constraints, a big rip singularity. We show that the negative pressure generated by the bulk viscosity cannot avoid that the dark energy of the universe to be phantom energy.
A transitioning universe with anisotropic dark energy
Yadav, Anil Kumar
2016-08-01
In this paper, we present a model of transitioning universe with minimal interaction between perfect fluid and anisotropic dark energy in Bianchi I space-time. The two sources are assumed to minimally interacted and therefore their energy momentum tensors are conserved separately. The explicit expression for average scale factor are considered in hybrid form that gives time varying deceleration parameter which describes both the early and late time physical features of universe. We also discuss the physical and geometrical properties of the model derived in this paper. The solution is interesting physically as it explain accelerating universe as well as singularity free universe.
A transitioning universe with anisotropic dark energy
Yadav, Anil Kumar
2016-01-01
In this paper, we present a model of transitioning universe with minimal interaction between perfect fluid and anisotropic dark energy in Bianchi I space-time. The two sources are assumed to minimally interacted and therefore their energy momentum tensors are conserved separately. The explicit expression for average scale factor are considered in hybrid form that gives time varying deceleration parameter which describes both the early and late time physical features of universe. We also discuss the physical and geometrical properties of the model derived in this paper. The solution is interesting physically as it explain accelerating universe as well as singularity free universe.
Quintessence interacting dark energy from induced matter theory of gravity
Reyes, L. M.; Aguilar, Jose Edgar Madriz
2009-01-01
In the context of the induced matter theory of gravity, we investigate the possibility of deriving a 4D quintessential scenario where an interaction between dark energy and dark matter is allowed, and the dark energy component is modeled by a minimally coupled scalar field. Regarding the Ponce de Leon metric, we found that it is possible to obtain such scenario on which the energy densities of dark matter and dark energy, are both depending of the fifth extra coordinate. We obtain that the 4D...
Repulsive gravity model for dark energy
Hohmann, Manuel
2010-01-01
We construct a multimetric gravity theory containing N >= 3 copies of standard model matter and a corresponding number of metrics. In the Newtonian limit, this theory generates attractive gravitational forces within each matter sector, and repulsive forces of the same strength between matter from different sectors. This result demonstrates that the recently proven no-go theorem that forbids gravity theories of this type in N = 2 cannot be extended beyond the bimetric case. We apply our theory to cosmology and show that the repulsion between different types of matter may induce the observed accelerating expansion of the universe. In this way dark energy can be explained simply by dark copies of the well-understood standard model.
Repulsive gravity model for dark energy
Hohmann, Manuel; Wohlfarth, Mattias N. R.
2010-05-01
We construct a multimetric gravity theory containing N≥3 copies of standard model matter and a corresponding number of metrics. In the Newtonian limit, this theory generates attractive gravitational forces within each matter sector and repulsive forces of the same strength between matter from different sectors. This result demonstrates that the recently proven no-go theorem that forbids gravity theories of this type in N=2 cannot be extended beyond the bimetric case. We apply our theory to cosmology and show that the repulsion between different types of matter may induce the observed accelerating expansion of the universe. In this way dark energy can be explained simply by dark copies of the well-understood standard model.
"Dark energy" in the Local Void
Villata, M
2012-01-01
The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "dark energy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter ($\\sim5\\times10^{15}\\,M_\\odot$) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require vo...
Interacting vacuum energy in the dark sector
Energy Technology Data Exchange (ETDEWEB)
Chimento, L. P. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, Cuidad Universitaria, Buenos Aires 1428 (Argentina); Carneiro, S. [Instituto de Física, Uníversídade Federal da Bahia, 40210-340, Salvador, BA (Brazil)
2015-03-26
We analyse three cosmological scenarios with interaction in the dark sector, which are particular cases of a general expression for the energy flux from vacuum to matter. In the first case the interaction leads to a transition from an unstable de Sitter phase to a radiation dominated universe, avoiding in this way the initial singularity. In the second case the interaction gives rise to a slow-roll power-law inflation. Finally, the third scenario is a concordance model for the late-time universe, with the vacuum term decaying into cold dark matter. We identify the physics behind these forms of interaction and show that they can be described as particular types of the modified Chaplygin gas.
How Dark Energy Affects the MOND Theory in Clusters
Man Ho Chan
2012-01-01
Modified Newtonian Dynamics (MOND) is one of the successful theories to explain the dark matter problem in galaxies. However, the data from clusters and the cosmic microwave background (CMB) indicate some dark matter should exist in larger scales. In addition, recent dynamical studies of clusters show that the effect of dark energy should not be ignored in cluster scale. In this article, I will demonstrate how dark energy affects the cluster mass calculation by using MOND. Also, I will show t...
Gravity and Anti-gravity of Fermions: the Unification of Dark Matter and Dark Energy
Chen, X S
2005-01-01
Massive gravity with second and fourth derivatives is shown to give both attractive and repulsive gravity between fermions. In contrast to the attractive gravity correlated with energy-momentum tensor, the repulsive gravity is proportional to the graviton mass. Therefore, weakly interacting fermions with energy smaller than the graviton mass are both dark matter and dark energy: Their overall gravity is attractive with normal matter but repulsive among themselves. Detailed analyses reveal that this unified dark scenario can properly account for the observed dark matter/energy phenomena: galaxy rotation curves, transition from early cosmic deceleration to recent acceleration; and naturally overcome other dark scenarios' difficulties: the substructure and cuspy core problems, the difference of dark halo distributions in galaxies and clusters, and the cosmic coincidence.
Dark energy and key physical parameters of clusters of galaxies
Bisnovatyi-Kogan, G S; 10.1007/s10509-011-0936-y
2012-01-01
We study physics of clusters of galaxies embedded in the cosmic dark energy background. Under the assumption that dark energy is described by the cosmological constant, we show that the dynamical effects of dark energy are strong in clusters like the Virgo cluster. Specifically, the key physical parameters of the dark mater halos in clusters are determined by dark energy: 1) the halo cut-off radius is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the dark energy antigravity; 2) the halo averaged density is equal to two densities of dark energy; 3) the halo edge (cut-off) density is the dark energy density with a numerical factor of the unity order slightly depending on the halo profile. The cluster gravitational potential well in which the particles of the dark halo (as well as galaxies and intracluster plasma) move is strongly affected by dark energy: the maximum of the potential is located at the zero-gravity radius of the cluster.
Dark energy and key physical parameters of clusters of galaxies
Bisnovatyi-Kogan, G. S.; Chernin, A. D.
2012-04-01
We study physics of clusters of galaxies embedded in the cosmic dark energy background. Under the assumption that dark energy is described by the cosmological constant, we show that the dynamical effects of dark energy are strong in clusters like the Virgo cluster. Specifically, the key physical parameters of the dark mater halos in clusters are determined by dark energy: (1) the halo cut-off radius is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the dark energy antigravity; (2) the halo averaged density is equal to two densities of dark energy; (3) the halo edge (cut-off) density is the dark energy density with a numerical factor of the unity order slightly depending on the halo profile. The cluster gravitational potential well in which the particles of the dark halo (as well as galaxies and intracluster plasma) move is strongly affected by dark energy: the maximum of the potential is located at the zero-gravity radius of the cluster.
Holographic dark energy interacting with dark matter in a closed Universe
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile); Lepe, Samuel [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4950, Valparaiso (Chile); Pena, Francisco [Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Universidad de La Frontera, Avda. Francisco Salazar 01145, Casilla 54-D Temuco (Chile); Saavedra, Joel [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4950, Valparaiso (Chile)], E-mail: joel.saavedra@ucv.cl
2008-11-27
A cosmological model of an holographic dark energy interacting with dark matter throughout a decaying term of the form Q=3({lambda}{sub 1}{rho}{sub DE}+{lambda}{sub 2}{rho}{sub m})H is investigated. General constraint on the parameters of the model are found when accelerated expansion is imposed and we found a phantom scenario, without any reference to a specific equation of state for the dark energy. The behavior of equation of state for dark energy is also discussed.
Unified dark matter and dark energy description in a chiral cosmological model
Abbyazov, Renat R
2014-01-01
We show the way of dark matter and dark energy presentation via ansatzs on the kinetic energies of the fields in the two-component chiral cosmological model. To connect a kinetic interaction of dark matter and dark energy with observational data the reconstruction procedure for the chiral metric component $h_{22}$ and the potential of (self)interaction $V$ has been developed. The reconstruction of $h_{22}$ and $V$ for the early and later inflation have been performed. The proposed model is confronted to $\\Lambda CDM$ model as well.
Unified Dark Matter and Dark Energy Description in a Chiral Cosmological Model
Abbyazov, Renat R.; Chervon, Sergey V.
2013-03-01
We show the way of dark matter and dark energy presentation via ansatzs on the kinetic energies of the fields in the two-component chiral cosmological model (CCM). To connect a kinetic interaction of dark matter and dark energy with observational data the reconstruction procedure for the chiral metric component h22 and the potential of (self-)interaction V has been developed. The reconstruction of h22 and V for the early and later inflation have been performed. The proposed model is confronted to ΛCDM model as well.
Induced gravity and the attractor dynamics of dark energy/dark matter
Cervantes-Cota, Jorge L; de Putter, Roland; Linder, Eric V.
2010-01-01
Attractor solutions that give dynamical reasons for dark energy to act like the cosmological constant, or behavior close to it, are interesting possibilities to explain cosmic acceleration. Coupling the scalar field to matter or to gravity enlarges the dynamical behavior; we consider both couplings together, which can ameliorate some problems for each individually. Such theories have also been proposed in a Higgs-like fashion to induce gravity and unify dark energy and dark matter origins. We...
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei; Wang, Sai
2016-11-01
The local measurement of H0 is in tension with the prediction of Λ cold dark matter model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on cosmic microwave background, the baryon acoustic oscillation, large-scale structure, supernovae, H(z) and H0 to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The H0 tension can be moderately alleviated, but not totally released.
Redshift drift exploration for interacting dark energy
Energy Technology Data Exchange (ETDEWEB)
Geng, Jia-Jia; Li, Yun-He; Zhang, Jing-Fei [Northeastern University, Department of Physics, College of Sciences, Shenyang (China); Zhang, Xin [Northeastern University, Department of Physics, College of Sciences, Shenyang (China); Peking University, Center for High Energy Physics, Beijing (China)
2015-08-15
By detecting redshift drift in the spectra of the Lyman-α forest of distant quasars, the Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the ''redshift desert'' of 2
Redshift drift exploration for interacting dark energy
International Nuclear Information System (INIS)
By detecting redshift drift in the spectra of the Lyman-α forest of distant quasars, the Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the ''redshift desert'' of 2
Observational constraints on teleparallel dark energy
Energy Technology Data Exchange (ETDEWEB)
Geng, Chao-Qiang; Lee, Chung-Chi [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300, R.O.C. (China); Saridakis, Emmanuel N., E-mail: geng@phys.nthu.edu.tw, E-mail: g9522545@oz.nthu.edu.tw, E-mail: Emmanuel_Saridakis@baylor.edu [National Center for Theoretical Sciences, Hsinchu, Taiwan 300, R.O.C. (China)
2012-01-01
We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) observations to constrain the recently proposed teleparallel dark energy scenario based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. Using the power-law, the exponential and the inverse hyperbolic cosine potential ansatzes, we show that the scenario is compatible with observations. In particular, the data favor a nonminimal coupling, and although the scalar field is canonical the model can describe both the quintessence and phantom regimes.
Observational Constraints on Teleparallel Dark Energy
Geng, Chao-Qiang; Saridakis, Emmanuel N
2011-01-01
We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) observations to constrain the recently proposed teleparallel dark energy scenario based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. Using the power-law, the exponential and the inverse hyperbolic cosine potential ansatzes, we show that the scenario is compatible with observations. In particular, the data favor a nonminimal coupling, and although the scalar field is canonical the model can describe both the quintessence and phantom regimes.
Neutron interferometry constrains dark energy chameleon fields
Directory of Open Access Journals (Sweden)
H. Lemmel
2015-04-01
Full Text Available We present phase shift measurements for neutron matter waves in vacuum and in low pressure Helium using a method originally developed for neutron scattering length measurements in neutron interferometry. We search for phase shifts associated with a coupling to scalar fields. We set stringent limits for a scalar chameleon field, a prominent quintessence dark energy candidate. We find that the coupling constant β is less than 1.9×107 for n=1 at 95% confidence level, where n is an input parameter of the self-interaction of the chameleon field φ inversely proportional to φn.
Probing Dark Energy with Atom Interferometry
Burrage, Clare; Hinds, E A
2015-01-01
Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.
Gravity and Cosmology with Interacting Dark Energy
Silbergleit, A. S.
2016-01-01
Dark energy (DE) is not necessarily uniform when other sources of gravity are present: interaction with matter leads to its variation in space and time. We study cosmological implications of this fact by analyzing cosmological models in which DE density interacts with matter and thus changes with time. We model the DE--matter interaction by specifying the rate of change of the DE density as an arbitrary function of it and the density of matter, in a single--phase case. In the case of several ...
Cosmic structure, averaging and dark energy
Wiltshire, David L
2013-01-01
These lecture notes review the theoretical problems associated with coarse-graining the observed inhomogeneous structure of the universe at late epochs, of describing average cosmic evolution in the presence of growing inhomogeneity, and of relating average quantities to physical observables. In particular, a detailed discussion of the timescape scenario is presented. In this scenario, dark energy is realized as a misidentification of gravitational energy gradients which result from gradients in the kinetic energy of expansion of space, in the presence of density and spatial curvature gradients that grow large with the growth of structure. The phenomenology and observational tests of the timescape model are discussed in detail, with updated constraints from Planck satellite data. In addition, recent results on the variation of the Hubble expansion on < 100/h Mpc scales are discussed. The spherically averaged Hubble law is significantly more uniform in the rest frame of the Local Group of galaxies than in t...
Dark energy from primordial inflationary quantum fluctuations.
Ringeval, Christophe; Suyama, Teruaki; Takahashi, Tomo; Yamaguchi, Masahide; Yokoyama, Shuichiro
2010-09-17
We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the Universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.
Unified description of dark energy and dark matter in mimetic matter model
Matsumoto, Jiro
2016-01-01
The existence of dark matter and dark energy in cosmology is implied by various observations, however, they are still unclear because they have not been directly detected. In this Letter, an unified model of dark energy and dark matter that can explain the evolution history of the Universe later than inflationary era, the time evolution of the growth rate function of the matter density contrast, the flat rotation curves of the spiral galaxies, and the gravitational experiments in the solar system is proposed in mimetic matter model.
Interacting dark matter and q-deformed dark energy with particle creation and annihilation
Kolay, Erdinc; Dil, Emre
2016-01-01
We propose a new model for studying the dark constituents of the universe by regarding the dark energy as a q-deformed scalar field interacting with the dark matter, in the framework of standard general relativity. Here we assume the number of particles in each mode of the q-deformed scalar field varies in time by the particle creation and annihilation. We first describe the q-deformed scalar field dark energy quantum field theoretically, then construct the action and the dynamical structure ...
The continuous tower of scalar fields as a system of interacting dark matter–dark energy
Paulo Santos
2016-01-01
This paper aims to introduce a new parameterisation for the coupling Q in interacting dark matter and dark energy models by connecting said models with the Continuous Tower of Scalar Fields model. Based upon the existence of a dark matter and a dark energy sectors in the Continuous Tower of Scalar Fields, a simplification is considered for the evolution of a single scalar field from the tower, validated in this paper. This allows for the results obtained with the Continuous Tower of Scalar Fi...
Dissipative or conservative cosmology with dark energy?
International Nuclear Information System (INIS)
All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analyzed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property-acceleration-is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in a one-dimensional potential which is parameterized by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We characterize the class of dark energy models that admit late time de Sitter attractor solution in terms of the potential function of corresponding conservative system. We argue that inclusion of dissipation effects makes the model more realistic because of its structural stability. We also confront viscous models with SNIa observations. The best fitted models are obtained by minimizing the χ2 function which is illustrated by residuals and χ2 levels in the space of model independent parameters. The general conclusion is that SNIa data supports the viscous model without the cosmological constant. The obtained values of χ2 statistic are comparable for both the viscous model and ΛCDM model. The Bayesian information criteria are used to compare the models with different power-law parameterization of viscous effects. Our result of this analysis shows that SNIa data supports viscous cosmology more than the ΛCDM model if the coefficient in viscosity parameterization is fixed. The Bayes factor is also used to obtain the posterior probability of the model
Can the Existence of Dark Energy be Directly Detected?
Energy Technology Data Exchange (ETDEWEB)
Perl, Martin L.; /SLAC /KIPAC, Menlo Park
2011-11-23
The majority of astronomers and physicists accept the reality of dark energy and also believe that it can only be studied indirectly through observation of the motions of stars and galaxies. In this paper I open the experimental question of whether it is possible to directly detect dark energy through the presence of dark energy density. Two thirds of this paper outlines the major aspects of dark energy density as now comprehended by the astronomical and physics community. The final third summarizes various proposals for direct detection of dark energy density or its possible effects. At this time I do not have a fruitful answer to the question: Can the Existence of Dark Energy Be Directly Detected?
Can the Existence of Dark Energy Be Directly Detected?
Perl, Martin L
2008-01-01
The majority of astronomers and physicists accept the reality of dark energy and also believe that it can only be studied indirectly through observation of the motions of stars and galaxies. In this paper I open the experimental question of whether it is possible to directly detect dark energy through the presence of dark energy density. Two thirds of this paper outlines the major aspects of dark energy density as now comprehended by the astronomical and physics community. The final third summarizes various proposals for direct detection of dark energy density or its possible effects. At this time I do not have a fruitful answer to the question: Can the Existence of Dark Energy Be Directly Detected?
Introducing the Dark Energy Universe Simulation Series (DEUSS)
Rasera, Y; Courtin, J; Roy, F; Corasaniti, P-S; Fuzfa, A; Boucher, V
2010-01-01
In this "Invisible Universe" proceedings, we introduce the Dark Energy Universe Simulation Series (DEUSS) which aim at investigating the imprints of realistic dark energy models on cosmic structure formation. It represents the largest dynamical dark energy simulation suite to date in term of spatial dynamics. We first present the 3 realistic dark energy models (calibrated on latest SNIa and CMB data): LambdaCDM, quintessence with Ratra-Peebles potential, and quintessence with Sugra potential. We then isolate various contributions for non-linear matter power spectra from a series of pre-DEUSS high-resolution simulations (130 million particles). Finally, we introduce DEUSS which consist in 9 Grand Challenge runs with 1 billion particles each thus probing scales from 4 Gpc down to 3 kpc at z=0. Our goal is to make these simulations available to the community through the "Dark Energy Universe Virtual Observatory" (DEUVO), and the "Dark Energy Universe Simulations" (DEUS) consortium.
An Interacting Dark Energy Model with Nonminimal Derivative Coupling
Nozari, Kourosh
2016-01-01
We study cosmological dynamics of an extended gravitational theory that gravity is coupled non-minimally with derivatives of a dark energy component and there is also a phenomenological interaction between the dark energy and dark matter. Depending on the direction of energy flow between the dark sectors, the phenomenological interaction gets two different signs. We show that this feature affects the existence of attractor solution, the rate of growth of perturbations and stability of the solutions. By considering an exponential potential as a self-interaction potential of the scalar field, we obtain accelerated scaling solutions that are attractors and have the potential to alleviate the coincidence problem. While in the absence of the nonminimal derivative coupling there is no attractor solution for phantom field when energy transfers from dark matter to dark energy, we show an attractor solution exists if one considers an explicit nonminimal derivative coupling for phantom field in this case of energy tran...
Dark Matter Relic Abundance and Scalar-Tensor Dark Energy
Catena, R.; N. Fornengo(University of Torino); A. Masiero; Pietroni, M.; Rosati, F
2004-01-01
Scalar-tensor theories of gravity provide a consistent framework to accommodate an ultra-light quintessence scalar field. While the equivalence principle is respected by construction, deviations from General Relativity and standard cosmology may show up at nucleosynthesis, CMB, and solar system tests of gravity. After imposing all the bounds coming from these observations, we consider the expansion rate of the universe at WIMP decoupling, showing that it can lead to an enhancement of the dark...
Dark Energy and Dark Matter from an additional adiabatic fluid
Dunsby, Peter K. S.; Luongo, Orlando; Reverberi, Lorenzo
2016-01-01
The Dark Sector is described by an additional barotropic fluid which evolves adiabatically during the universe's history and whose adiabatic exponent $\\gamma$ is derived from the standard definitions of specific heats. Although in general $\\gamma$ is a function of the redshift, the Hubble parameter and its derivatives, we find that our assumptions lead necessarily to solutions with $\\gamma = $ constant in a FLRW universe. The adiabatic fluid acts effectively as the sum of two distinct compone...
International Nuclear Information System (INIS)
In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann–Robertson–Walker space–time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier–Polarski–Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch
Energy Technology Data Exchange (ETDEWEB)
Kumar, Suresh, E-mail: sukuyd@gmail.com [Department of Mathematics, BITS Pilani, Pilani Campus, Rajasthan, 333031 (India); Xu, Lixin, E-mail: lxxu@dlut.edu.cn [Institute of Theoretical Physics, School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian, 116024 (China)
2014-10-07
In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann–Robertson–Walker space–time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier–Polarski–Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.
$f(T)$ theories from holographic dark energy models
Huang, Peng; Huang, Yong-Chang(Institute of Theoretical Physics, Beijing University of Technology, 100124, Beijing, China)
2013-01-01
We reconstruct $f(T)$ theories from three different holographic dark energy models in different time durations. For the HDE model, the dark energy dominated era with new setting up is chosen for reconstruction, and the radiation dominated era is chosen when the involved model changes into NADE. For the RDE model, radiation, matter and dark energy dominated time durations are all investigated. We also investigate the limitation which prevents an arbitrary choice of the time duration for recons...
Decaying Holographic Dark Energy and Emergence of Friedmann Universe
Mathew, Titus K.
2011-01-01
A universe started in almost de Sitter phase with time varying holographic dark energy corresponding to a time varying cosmological term is considered. The time varying cosmological dark energy and the created matter are consistent with the Einstein's equation. The general conservation law for decaying dark energy and created matter is stated. By asuming that the initial matter were crated in relativistic form, we have analysed the possibility of evolving the universe from de Sitter phase to ...
Zero Cosmological Constant and Nonzero Dark Energy from Holographic Principle
Lee, Jae-Weon
2010-01-01
It is shown that the first law of thermodynamics and the holographic principle applied to an arbitrary large cosmic causal horizon naturally demand the zero cosmological constant and non-zero dynamical dark energy in the form of the holographic dark energy. Semiclassical analysis shows that the holographic dark energy has a parameter $d=1$ and an equation of state comparable to current observational data, if the entropy of the horizon saturates the Bekenstein-Hawking bound. This result indica...
Cosmic dynamics with entropy corrected holographic dark energy
Sadjadi, H Mohseni
2010-01-01
We investigate the model of holographic dark energy with logarithmic correction to its energy density. This modification is motivated from the loop quantum gravity corrections to the entropy-area law. We also consider an interaction between dark energy and dark matter. The behavior of the Hubble parameter (specially in the late time) is studied. Besides, conditions under which an accelerated universe can decelerate and also successive acceleration-deceleration phases can be occurred in the evolution of the universe is investigated.
Constraints on Dark Energy Models from Weak Gravity Conjecture
Institute of Scientific and Technical Information of China (English)
CHEN Xi-Ming; LIU Jie; GONG Yun-Gui
2008-01-01
@@ We study the constraints on the dark energy model with constant equation of state parameter w = p/p and the holographic dark energy model by using the weak gravity conjecture. The combination of weak gravity conjecture and the observational data gives w < -0.7 at the 3σ confidence level. The holographic dark energy model realized by a scalar field is in swampland.
Dark Energy: Reason for the Existence of a Classical Universe?
Huang, Peng; Li, Miao; Li, Nan
2015-01-01
Dark energy is investigated from the perspective of quantum cosmology. By treating the existence of a classical universe as a constraint, it is found that the normal ordering ambiguity factor q in Wheeler-DeWitt equation tends to take its value on domain (-1, 3). Furthermore, to ensure the existence of a classical universe, there must be dark energy in the universe. It is in this sense we propose that dark energy is the reason for the existence of a classical universe.
Gravity and Cosmology with Interacting Dark Energy
Silbergleit, A S
2016-01-01
Dark energy (DE) is not necessarily uniform when other sources of gravity are present: interaction with matter leads to its variation in space and time. We study cosmological implications of this fact by analyzing cosmological models in which DE density interacts with matter and thus changes with time. We model the DE--matter interaction by specifying the rate of change of the DE density as an arbitrary function of it and the density of matter, in a single--phase case. In the case of several matter components interacting with dark energy we assume the rate of every interacting phase density to be an arbitrary function of this density and the DE density. We describe some properties of cosmological solutions valid for a general law of DE--matter interaction, and discuss physical admissibility of the interaction laws. We study numerous families of exact solutions, both singular, non-singular, and mixed. Some of them exhibit interesting properties, such as, for instance, absence of the horizon problem due to the ...
Probing dark energy via galaxy cluster outskirts
Morandi, Andrea
2016-01-01
We present a Bayesian approach to combine $Planck$ data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters ($0.056 3$ keV) observed with $Chandra$. We exploited the high-level of similarity of the emission measure in the cluster outskirts as cosmology proxy. The cosmological parameters are thus constrained assuming that the emission measure profiles at different redshift are weakly self-similar, that is their shape is universal, explicitly allowing for temperature and redshift dependency of the gas fraction. This cosmological test, in combination with $Planck$+SNIa data, allows us to put a tight constraint on the dark energy models. For a constant-$w$ model, we have $w=-1.010\\pm0.030$ and $\\Omega_m=0.311\\pm0.014$, while for a time-evolving equation of state of dark energy $w(z)$ we have $\\Omega_m=0.308\\pm 0.017$, $w_0=-0.993\\pm0.046$ and $w_a=-0.123\\pm0.400$. Constraints on the cosmology are further improved by adding priors on the gas f...
Using Atom Interferometry to Detect Dark Energy
Burrage, Clare
2015-01-01
We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the Universe on giga-parsec scales may be found through metre scale laboratory based atom interferometry experiments. To do that, we first introduce the idea that scalar fields could be responsible for dark energy and show that in order to be compatible with fifth force constraints these fields must have a screening mechanism which hides their effects from us within the solar system. Particular emphasis is placed on one such screening mechanism known as the chameleon effect where the field's mass becomes dependent on the environment. The way the field behaves in the presence of a spherical source is determined and we then go on to show how in the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the ...
Dynamical dark energy: Current constraints and forecasts
Upadhye, A; Steinhardt, P J; Upadhye, Amol; Ishak, Mustapha; Steinhardt, Paul J.
2004-01-01
We consider how well the dark energy equation of state $w$ as a function of red shift $z$ will be measured using current and anticipated experiments. We use a procedure which takes fair account of the uncertainties in the functional dependence of $w$ on $z$, as well as the parameter degeneracies, and avoids the use of strong prior constraints. We apply the procedure to current data from WMAP, SDSS, and the supernova searches, and obtain results that are consistent with other analyses using different combinations of data sets. The effects of systematic experimental errors and variations in the analysis technique are discussed. Next, we use the same procedure to forecast the dark energy constraints achieveable by the end of the decade, assuming 8 years of WMAP data and realistic projections for ground-based measurements of supernovae and weak lensing. We find the $2 \\sigma$ constraints on the current value of $w$ to be $\\Delta w_0 (2 \\sigma) = 0.12$, and on $dw/dz$ (between $z=0$ and $z=1$) to be $\\Delta w_1 (2...
Probing Dark Energy with Constellation-X
Energy Technology Data Exchange (ETDEWEB)
Rapetti, David; Allen, Steven W.; /KIPAC, Menlo Park
2006-09-08
Constellation-X (Con-X) will carry out two powerful and independent sets of tests of dark energy based on X-ray observations of galaxy clusters, providing comparable accuracy to other leading dark energy probes. The first group of tests will measure the absolute distances to clusters, primarily using measurements of the X-ray gas mass fraction in the largest, dynamically relaxed clusters, but with additional constraining power provided by follow-up observations of the Sunyaev-Zel'dovich (SZ) effect. As with supernovae studies, such data determine the transformation between redshift and true distance, d(z), allowing cosmic acceleration to be measured directly. The second, independent group of tests will use the exquisite spectroscopic capabilities of Con-X to determine scaling relations between X-ray observables and mass. Together with forthcoming X-ray and SZ cluster surveys, these data will help to constrain the growth of structure, which is also a strong function of cosmological parameters.
DESTINY: The Dark Energy Space Telescope
Lauer, T. R.; Destiny Science Team
2005-08-01
The Dark Energy Space Telescope (DESTINY) is an all-grism NIR 1.8-m survey camera optimized to return richly sampled Hubble diagrams of Type Ia and Type II supernovae (SN) over the redshift range 0.5 the Universe as a function of time, and characterizing the nature of the so-called ``dark energy" component of the Universe. SN will be discovered by repeated imaging of a 7.5-sq.-deg. area located at the north ecliptic poles. Grism spectra with resolving power λ/Δλ = R˜75 will provide broad-band spectrophotometry, redshifts, SN classification, and valuable time-resolved diagnostic data for understanding the SN explosion physics. This methodology features only a single mode of operation with no time-critical interactions, a single detector technology, and a single instrument. Although grism spectroscopy is slow compared with SN detection in any single broad-band filter for photometry, or to conventional slit spectra for spectral diagnostics, the multiplex advantage of being able to observe a large field of view simultaneously over a full octave in wavelength makes this approach highly competitive.
DESTINY, the Dark Energy Space Telescope
Lauer, T. R.; Morse, J. A.; Destiny Science Team
2003-12-01
We describe a mission concept for a 1.8-meter near-infrared (NIR) grism-mode space telescope optimized to return richly sampled Hubble diagrams of Type Ia and Type II supernovae (SNe) over the redshift range 0.5 the Universe as a function of time, and characterizing the nature of dark energy. The central concept for our proposed Dark Energy Space Telescope (DESTINY) is an all-grism NIR survey camera. SNe will be discovered by repeated imaging of an area located at the north ecliptic pole. Grism spectra with resolving power l/Dl = R * 100 will provide broad-band spectrophotometry, redshifts, SNe classification, as well as valuable time-resolved diagnostic data for understanding the SN explosion physics. Our approach features only a single mode of operation, a single detector technology, and a single instrument. Although grism spectroscopy is slow compared to SN detection in any single broad-band filter for photometry, or to conventional slit spectra for spectral diagnostics, the multiplex advantage of observing a large field-of-view over a full octave in wavelength simultaneously makes this approach highly competitive.
Dark Energy and Doubly Coupled Bigravity
Brax, Philippe; Noller, Johannes
2016-01-01
We analyse the late time cosmology and the gravitational properties of doubly coupled bigravity in the vielbein formalism when the mass of the massive graviton is of the order of the present Hubble rate. We focus on one of the two branches of background cosmology where the ratio between the scale factors of the two metrics is algebraically determined. The Universe evolves from a matter dominated epoch to a dark energy dominated era where the equation of state of dark energy can always be made close to -1 now by appropriately tuning the graviton mass. We also analyse the perturbative spectrum of the theory in the quasi static approximation well below the strong coupling scale where no instability is present and we show that there are five scalar degrees of freedom, two vectors and two gravitons. In a cosmological FRW background for both metrics, four of the five scalars are Newtonian potentials which lead to a modification of gravity on large scales. In this scalar sector, gravity is modified with effects on b...
Holographic Dark Energy with Cosmological Constant
Hu, Yazhou; Li, Nan; Zhang, Zhenhui
2015-01-01
Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the $\\Lambda$HDE model. By studying the $\\Lambda$HDE model theoretically, we find that the parameters $c$ and $\\Omega_{hde}$ are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the $\\Lambda$HDE model by using the recent observational data. We find the model yields $\\chi^2_{\\rm min}=426.27$ when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant $\\Lambda$CDM model (431.35). At 68.3\\% CL, we obtain $-0.07<\\Omega_{\\Lambda0}<0.68$ and correspondingly $0.04<\\Omega_{hde0}<0.79$, implying at present there is considerable degeneracy bet...
Probing dark energy via galaxy cluster outskirts
Morandi, Andrea; Sun, Ming
2016-04-01
We present a Bayesian approach to combine Planck data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters (0.056 z z) we have Ωm = 0.308 ± 0.017, w0 = -0.993 ± 0.046 and wa = -0.123 ± 0.400. Constraints on the cosmology are further improved by adding priors on the gas fraction evolution from hydrodynamic simulations. Current data favour the cosmological constant with w ≡ -1, with no evidence for dynamic dark energy. We checked that our method is robust towards different sources of systematics, including background modelling, outlier measurements, selection effects, inhomogeneities of the gas distribution and cosmic filaments. We also provided for the first time constraints on which definition of cluster boundary radius is more tenable, namely based on a fixed overdensity with respect to the critical density of the Universe. This novel cosmological test has the capacity to provide a generational leap forward in our understanding of the equation of state of dark energy.
Initial conditions for the Galileon dark energy
Germani, Cristiano
2016-01-01
Galileon models are among the most appealing candidates for Dark Energy. The reason is twofold: classically, they provide a tracking solution leading to an almost DeSitter space starting from very generic initial conditions in the deep radiation era. The second reason is the standard lore that Galileons are quantum mechanically stable. The latter property is certainly true in flat space-time, thanks to the non-renormalization theorems of galilean coupling constants. However, in a cosmological background, we show that quantum effects might dominate the classical trajectory. Assuming the radiation era to last at least up to the electroweak phase transition, the trajectory with initial conditions sitting on the tracker is ruled out. On the other hand, it is always possible to find a sub-space of initial conditions such that the dark energy solution approaches stably the tracker at late times. Fixing the value of initial conditions that best fit current data, and assuming that the galileon effective theory is val...
Triple Unification of Inflation, Dark matter and Dark energy in Chaotic Braneworld Inflation
Lin, Chia-Min
2009-01-01
In this paper, we show that in the framework of chaotic braneworld inflation, after preheating, the remaining oscillating inflaton field can play the role of dark matter with the observed level. Augmented by a non-zero effective cosmological constant $\\Lambda_4$ on the brane, triple unification of inflation, dark matter and dark energy by a single field is realized. Our model perhaps is the simplest one in the market of theories to achieve triple unification.
Instability in interacting dark sector: An appropriate Holographic Ricci dark energy model
Herrera, Ramon; Hipolito-Ricaldi, W. S.; Videla, Nelson
2016-01-01
In this paper we investigate the consequences of phantom crossing considering the perturbative dynamics in models with interaction in their dark sector. By mean of a general study of gauge-invariant variables in comoving gauge, we relate the sources of instabilities in the structure formation process with the phantom crossing. In order to illustrate these relations and its consequences in more detail, we consider a specific case of an holographic dark energy interacting with dark matter. We f...
Exacerbating the cosmological constant problem with interacting dark energy
Marsh, M. C. David
2016-01-01
Future cosmological surveys will probe the expansion history of the universe and constrain phenomenological models of dark energy. Such models do not address the fine-tuning problem of the vacuum energy, i.e. the cosmological constant problem (c.c.p.), but can make it spectacularly worse. We show that this is the case for 'interacting dark energy' models in which the masses of the dark matter states depend on the dark energy sector. If realised in nature, these models have far-reaching implic...
Large Synoptic Survey Telescope: Dark Energy Science Collaboration
LSST Dark Energy Science Collaboration
2012-01-01
This white paper describes the LSST Dark Energy Science Collaboration (DESC), whose goal is the study of dark energy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of dark energy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for dark energy science that has been defined by its members and the comprehensive three-year w...
Nonparametric Dark Energy Reconstruction from Supernova Data
Holsclaw, Tracy; Sanso, Bruno; Lee, Herbert; Heitmann, Katrin; Habib, Salman; Higdon, David
2010-01-01
Understanding the origin of the accelerated expansion of the Universe poses one of the greatest challenges in physics today. Lacking a compelling fundamental theory to test, observational efforts are targeted at a better characterization of the underlying cause. If a new form of mass-energy, dark energy, is driving the acceleration, the redshift evolution of the equation of state parameter w(z) will hold essential clues as to its origin. To best exploit data from observations it is necessary to develop a robust and accurate reconstruction approach, with controlled errors, for w(z). We introduce a new, nonparametric method for solving the associated statistical inverse problem based on Gaussian Process modeling and Markov chain Monte Carlo sampling. Applying this method to recent supernova measurements, we reconstruct the continuous history of w out to redshift z=1.5.
Dark energy towards observational tests and data
Capozziello, S
2008-01-01
A huge amount of good quality data converges towards the picture of a spatially flat universe undergoing the today observed phase of accelerated expansion. This new observational trend is commonly addressed as Precision Cosmology. Despite of the excellent surveys, the nature of dark energy, dominating the matter-energy content of the universe, is still unknown and a lot of different scenarios are viable candidates to explain cosmic acceleration. Methods to test these cosmological models are based on distance measurements and lookback time toward astronomical objects used as standard candles. The related degeneracy problem is the signal that more data at low 0
Cosmic accelerated expansion and the entropy corrected holographic dark energy
Sadjadi, H. Mohseni; Jamil, Mubasher
2010-01-01
By considering the logarithmic correction to the energy density, we study the behavior of Hubble parameter in the holographic dark energy model. We assume that the universe is dominated by interacting dark energy and matter and the accelerated expansion of the universe, which may be occurred in the early universe or late time, is studied.
Constraining neutrinos and dark energy with galaxy clustering in the dark energy survey
Zablocki, Alan
2016-08-01
We determine the forecast errors on the absolute neutrino mass scale and the equation of state of dark energy by combining synthetic data from the Dark Energy Survey (DES) and the cosmic microwave background Planck surveyor. We use angular clustering of galaxies for DES in seven redshift shells up to z ˜1.7 including cross-correlations between different redshift shells. We study models with massless and massive neutrinos and three different dark energy models: Λ cold dark matter (CDM) (w =-1 ), w CDM (constant w ), and waCDM [evolving equation of state parameter w (a )=w0+wa(1 -a )]. We include the impact of uncertainties in modeling galaxy bias using a constant and a redshift-evolving bias model. For the Λ CDM model we obtain an upper limit for the sum of neutrino masses from DES +Planck of Σ mνneutrino masses increases to 0.29 eV. DES will be able to place competitive upper limits on the sum of neutrino masses of 0.1-0.3 eV and could therefore strongly constrain the inverted mass hierarchy of neutrinos. In a w CDM model the 1 σ error on constant w is Δ w =0.03 from DES galaxy clustering and Planck. Allowing Σ mν as a free parameter increases the error on w by a factor of 2, with Δ w =0.06 . In a waCDM model, in which the dark energy equation of state varies with time, the errors are Δ w0=0.2 and Δ wa=0.42 . Including neutrinos and redshift-dependent galaxy bias increases the errors to Δ w0=0.39 and Δ wa=0.99 .
Gravitational Field Equations and Theory of Dark Matter and Dark Energy
Ma, Tian
2012-01-01
The main objective of this article is to derive a new set of gravitational field equations and to establish a new unified theory for dark energy and dark matter. The new gravitational field equations with scalar potential are derived using the Einstein-Hilbert functional, and the scalar potential is a natural outcome of the divergence-free constraint of the variational elements. Associated with this scalar potential is the scalar potential energy density $\\Phi$, which represents a new type of energy caused by the non-uniform distribution of matter in the universe. The negative part of this potential energy density $\\Phi$ represents the dark matter, which produces attraction, and the positive part represents the dark energy, which drives the acceleration of expanding galaxies. In addition, this potential energy density $\\Phi$ is conserved with mean zero: $\\int_M \\Phi dM=0$. Furthermore, the new field equations resolve a few difficulties encountered by the classical Einstein field equations.
Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion
Huterer, Dragan; Bean, Rachel; Connolly, Andrew; Dawson, Kyle; Dodelson, Scott; Evrard, August; Jain, Bhuvnesh; Jarvis, Michael; Linder, Eric; Mandelbaum, Rachel; May, Morgan; Raccanelli, Alvise; Reid, Beth; Rozo, Eduardo; Schmidt, Fabian; Sehgal, Neelima; Slosar, Anže; van Engelen, Alex; Wu, Hao-Yi; Zhao, Gongbo
2013-01-01
The quantity and quality of cosmic structure observations have greatly accelerated in recent years. Further leaps forward will be facilitated by imminent projects, which will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to the nature of dark matter and dark energy. Dark energy and gravity both affect how rapidly structure grows; the greater the acceleration, the more suppressed the growth of structure, while the greater the gravity, the more enhanced the growth. While distance measurements also constrain dark energy, the comparison of growth and distance data tests whether General Relativity describes the laws of physics accurately on large scales. Modified gravity models are able to reproduce the distance measurements but at the cost of altering the growth of structure (these signatures are described in more detail in the accompanying paper on Novel Probes of Gravity and Dark Energy)....
Interaction between Dark Matter and Dark Energy and the Cosmological Coincidence Problem
Directory of Open Access Journals (Sweden)
Kourosh Nozari
2014-01-01
Full Text Available We consider a quintessence model of dark energy inspired by scalar-tensor theories of gravity where the scalar field is nonminimally coupled to gravity and dark matter. By considering exponential potential as self-interaction potential, the stability and existence of the critical points are discussed in details. With nonminimally coupled dark sector with gravity, we obtain scaling solutions to address the coincidence problem by considering complex velocity for dark matter. The statefinder diagnostic shows that the equation of state reaches ΛCDM model in the future.
Testing the Interaction between Dark Energy and Dark Matter with Planck Data
Costa, André A; Wang, Bin; Ferreira, Elisa G M; Abdalla, E
2013-01-01
Interacting Dark Energy and Dark Matter is used to go beyond the standard cosmology. We base our arguments on Planck data and conclude that an interaction is compatible with the observations and can provide a strong argument towards consistency of different values of cosmological parameters.
Modified Gravitational Theory as an Alternative to Dark Energy and Dark Matter
Moffat, J. W.
2004-01-01
The problem of explaining the acceleration of the expansion of the universe and the observational and theoretical difficulties associated with dark matter and dark energy are discussed. The possibility that Einstein gravity does not correctly describe the large-scale structure of the universe is considered and an alternative gravity theory is proposed as a possible resolution to the problems.
A Kinematical Approach to Dark Energy Studies
Energy Technology Data Exchange (ETDEWEB)
Rapetti, David; Allen, Steven W.; Amin, Mustafa A.; Blandford, Roger D.; /KIPAC, Menlo Park
2006-06-06
We present and employ a new kinematical approach to cosmological ''dark energy'' studies. We construct models in terms of the dimensionless second and third derivatives of the scale factor a(t) with respect to cosmic time t, namely the present-day value of the deceleration parameter q{sub 0} and the cosmic jerk parameter, j(t). An elegant feature of this parameterization is that all {Lambda}CDM models have j(t) = 1 (constant), which facilitates simple tests for departures from the {Lambda}CDM paradigm. Applying our model to the three best available sets of redshift-independent distance measurements, from type Ia supernovae and X-ray cluster gas mass fraction measurements, we obtain clear statistical evidence for a late time transition from a decelerating to an accelerating phase. For a flat model with constant jerk, j(t) = j, we measure q{sub 0} = -0.81 {+-} 0.14 and j = 2.16{sub -0.75}{sup +0.81}, results that are consistent with {Lambda}CDM at about the 1{sigma} confidence level. A standard ''dynamical'' analysis of the same data, employing the Friedmann equations and modeling the dark energy as a fluid with an equation of state parameter, w (constant), gives {Omega}{sub m} = 0.306{sub -0.040}{sup +0.042} and w = -1.15{sub -0.18}{sup +0.14}, also consistent with {Lambda}CDM at about the 1{sigma} level. In comparison to dynamical analyses, the kinematical approach uses a different model set and employs a minimum of prior information, being independent of any particular gravity theory. The results obtained with this new approach therefore provide important additional information and we argue that both kinematical and dynamical techniques should be employed in future dark energy studies, where possible. Our results provide further interesting support for the concordance {Lambda}CDM paradigm.
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei; Wang, Sai
2016-08-01
The local measurement of H0 is in tension with the prediction of ΛCDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, H(z) and H0 to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The H0 tension can be moderately alleviated, but not totally released.
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei
2016-01-01
The local measurement of $H_0$ is in tension with the prediction of $\\Lambda$CDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, $H(z)$ and $H_0$ to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The $H_0$ tension can be moderately alleviated, but not totally released.
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei; Wang, Sai
2016-01-01
The local measurement of $H_0$ is in tension with the prediction of $\\Lambda$CDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, $H(z)$ and $H_0$ to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The $H_0$ tension can be moderately alleviated, but not tota...
Quintessence models of Dark Energy with non-minimal coupling
Gonzalez, Tame; Leon, Genly; Quiros, Israel
2005-01-01
We explore quintessence models of dark energy which exhibit non-minimal coupling between the dark matter and the dark energy components of the cosmic fluid. The kind of coupling chosen is inspired in scalar-tensor theories of gravity. We impose a suitable dynamics of the expansion allowing to derive exact Friedmann-Robertson-Walker solutions once the coupling function is given as input. Coupling functions that lead to self-interaction potentials of the single and double exponential types are ...
Holographic Dark Energy Model and Scalar-Tensor Theories
Bisabr, Yousef
2008-01-01
We study the holographic dark energy model in a generalized scalar tensor theory. In a universe filled with cold dark matter and dark energy, the effect of potential of the scalar field is investigated in the equation of state parameter. We show that for a various types of potentials, the equation of state parameter is negative and transition from deceleration to acceleration expansion of the universe is possible.
Parametrized post-Friedmannian framework for interacting dark energy theories
Skordis, Constantinos; Pourtsidou, Alkistis; Copeland, E.J.
2015-01-01
We present the most general parametrisation of models of dark energy in the form of a scalar field which is explicitly coupled to dark matter. We follow and extend the Parameterized Post-Friedmannian approach, previously applied to modified gravity theories, in order to include interacting dark energy. We demonstrate its use through a number of worked examples and show how the initially large parameter space of free functions can be significantly reduced and constrained to include only a few ...
Evolution of Interacting Viscous Dark Energy Model in Einstein Cosmology
Institute of Scientific and Technical Information of China (English)
CHEN Ju-Hua; ZHOU Sheng; WANG Yong-Jiu
2011-01-01
We investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model. By using the linearizing theory of the dynamical system, we find that, in our model,there exists a stable late time scaling solution which corresponds to the accelerating universe. We also find the unstable solution under some appropriate parameters. In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy with the dark matter. However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model. That is to say, both the non-perfect fluid model and the interacting the dark energy cosmic model can alleviate or soften the singularity of the universe.%@@ We investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model.By using the linearizing theory of the dynamical system, we find that, in our model, there exists a stable late time scaling solution which corresponds to the accelerating universe.We also find the unstable solution under some appropriate parameters.In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy with the dark matter.However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model.That is to say, both the non-perfect fluid model and the interacting the dark energy cosmic model can alleviate or soften the singularity of the universe.
Reconstruction of interaction rate in Holographic dark energy
Mukherjee, Ankan
2016-01-01
The present work is based on the holographic dark energy model with Hubble horizon as the infrared cut-off. The interaction rate between dark energy and dark matter has been reconstructed for two different parameterizations of the deceleration parameter. Observational constraints on the model parameters have been obtained by maximum likelihood analysis using the observational Hubble parameter data (OHD), type Ia supernova data (SNe), baryon acoustic oscillation data (BAO) and the distance pri...
Weak lensing in the Dark Energy Survey
Troxel, Michael
2016-03-01
I will present the current status of weak lensing results from the Dark Energy Survey (DES). DES will survey 5000 square degrees in five photometric bands (grizY), and has already provided a competitive weak lensing catalog from Science Verification data covering just 3% of the final survey footprint. I will summarize the status of shear catalog production using observations from the first year of the survey and discuss recent weak lensing science results from DES. Finally, I will report on the outlook for future cosmological analyses in DES including the two-point cosmic shear correlation function and discuss challenges that DES and future surveys will face in achieving a control of systematics that allows us to take full advantage of the available statistical power of our shear catalogs.
Dark Energy Detected with Supervoids and Superclusters
Granett, Benjamin R; Szapudi, István
2008-01-01
The observed apparent acceleration of the universe is usually attributed to negative pressure from a mysterious dark energy. This acceleration causes the gravitational potential to decay, heating or cooling photons travelling through crests or troughs of large-scale matter density fluctuations. This phenomenon, the late-time integrated Sachs-Wolfe (ISW) effect, has been detected, albeit at low significance, by cross-correlating various galaxy surveys with the Cosmic Microwave Background (CMB). Recently, the best evidence has come from the statistical combination of results from multiple correlated galaxy data sets. Here we show that vast structures identified in a galaxy survey project an image onto the CMB; stacking regions aligned with superclusters produces a hot spot, and supervoids, a cold spot. At over 4 sigma, this is the clearest evidence of the ISW effect to date. For the first time, our findings pin the effect to discrete structures. The ISW signal from supervoids and superclusters can be combined w...
Entropic-force dark energy reconsidered
Basilakos, Spyros
2014-01-01
We reconsider the entropic-force model in which both kind of Hubble terms ${\\dot H}$ and $H^{2}$ appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions, namely the scale factor, deceleration parameter, matter density and growth of linear matter perturbations. However, we find that the entropic-force model is not viable at the background and perturbation levels due to the fact that the entropic formulation does not add a constant term in the Friedmann equations. On the other hand, if on mere phenomenological grounds we replace the ${\\dot H}$ dependence of the effective DE density with a linear term $H$ without including a constant additive term, we find that the transition from deceleration to acceleration becomes possible but the recent structure formation data \
Essential Building Blocks of Dark Energy
Gleyzes, Jerome; Piazza, Federico; Vernizzi, Filippo
2013-01-01
We propose a minimal description of single field dark energy/modified gravity within the effective field theory formalism for cosmological perturbations, which encompasses most existing models. We start from a generic Lagrangian given as an arbitrary function of the lapse and of the extrinsic and intrinsic curvature tensors of the time hypersurfaces in unitary gauge, i.e. choosing as time slicing the uniform scalar field hypersurfaces. Focusing on linear perturbations, we identify seven Lagrangian operators that lead to equations of motion containing at most two (space or time) derivatives, the time-dependent coefficients of three of these operators being determined only by the background evolution. We then establish a dictionary that translates any existing or future model whose Lagrangian can be written in the above form into our parametrized framework. As an illustration, we show that Horndeski's-or generalized Galileon-theories can be described, up to linear order, by only six of the seven operators menti...
Baryogenesis, neutrino masses, and dynamical dark energy
Energy Technology Data Exchange (ETDEWEB)
Eisele, M.T.
2007-10-09
This thesis considers several models that connect different areas of particle physics and cosmology. Our first discussion in this context concerns a baryogenesis scenario, in which the baryon asymmetry of our universe is created through the dynamics of a dark energy field, thereby illustrating that these two topics might be related. Subsequently, several neutrino mass models are analyzed, which make use of an extra-dimensional setting to overcome certain problems of their fourdimensional counterparts. The central discussion of this thesis concerns a leptogenesis model with many standard model singlets. Amongst other things, we show that the presence of these states can lower the standard bound for the necessary reheating temperature of the universe by at least one and a half orders of magnitude. To further motivate this approach, we also discuss an explicit, extradimensional leptogenesis scenario that naturally yields many of the ingredients required in this context. (orig.)
Supernovae, dark energy and the accelerating universe
Perlmutter, Saul
1999-01-01
Based on an analysis of 42 high-redshift supernovae discovered by the supernovae cosmology project, we have found evidence for a positive cosmological constant, Lambda, and hence an accelerating universe. In particular, the data are strongly inconsistent with a Lambda=0 flat cosmology, the simplest inflationary universe model. The size of our supernova sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We will discuss results of these and other studies and the ongoing hunt for further loopholes to evade the apparent consequences of the measurements. We will present further work that begins to constrain the alternative physics theories of "dark energy" that have been proposed to explain these results. Finally, we propose a new concept for a definitive supernova measurement of the cosmological parameters.
Generalized dark energy interactions with multiple fluids
van de Bruck, Carsten; Mimoso, José P; Nunes, Nelson J
2016-01-01
In the search for an explanation for the current acceleration of the Universe, scalar fields are the most simple and useful tools to build models of dark energy. This field, however, must in principle couple with the rest of the world and not necessarily in the same way to different particles or fluids. We provide the most complete dynamical system analysis to date, consisting of a canonical scalar field conformally and disformally coupled to both dust and radiation. We perform a detailed study of the existence and stability conditions of the systems and comment on constraints imposed on the disformal coupling from Big-Bang Nucleosynthesis and given current limits on the variation of the fine-structure constant.
Dark energy camera installation at CTIO: overview
Abbott, Timothy M.; Muñoz, Freddy; Walker, Alistair R.; Smith, Chris; Montane, Andrés.; Gregory, Brooke; Tighe, Roberto; Schurter, Patricio; van der Bliek, Nicole S.; Schumacher, German
2012-09-01
The Dark Energy Camera (DECam) has been installed on the V. M. Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. This major upgrade to the facility has required numerous modifications to the telescope and improvements in observatory infrastructure. The telescope prime focus assembly has been entirely replaced, and the f/8 secondary change procedure radically changed. The heavier instrument means that telescope balance has been significantly modified. The telescope control system has been upgraded. NOAO has established a data transport system to efficiently move DECam's output to the NCSA for processing. The observatory has integrated the DECam highpressure, two-phase cryogenic cooling system into its operations and converted the Coudé room into an environmentally-controlled instrument handling facility incorporating a high quality cleanroom. New procedures to ensure the safety of personnel and equipment have been introduced.
About Dark Energy and Dark Matter in a Three-Dimensional Quantum Vacuum Model
Fiscaletti, Davide
2016-10-01
A model of a three-dimensional quantum vacuum based on Planck energy density as a universal property of a granular space is suggested. The possibility to provide an unifying explanation of dark matter and dark energy as phenomena linked with the fluctuations of the three-dimensional quantum vacuum is explored. The changes and fluctuations of the quantum vacuum energy density generate a curvature of space-time similar to the curvature produced by a "dark energy" density. The formation of large scale structures in the universe associated to the flattening of the orbital speeds of the spiral galaxies can be explained in terms of primary fluctuations of the quantum vacuum energy density without attracting the idea of dark matter.
Interacting Ghost Dark Energy Model: Dynamical System Analysis
Golchin, Hanif; Ebrahimi, Esmaeil
2016-01-01
We study the impacts of interaction between dark matter and dark energy in the context of ghost dark energy model. Using the dynamical system analysis, we obtain the fixed points of the system for different types of interactions while the universe is filled with radiation, matter (including dark matter and luminous matter) and dark energy components. We consider the stability of the fixed points in details for different cases. In all cases there is an unstable matter dominated epoch and a stable late time dark energy dominated phase. However, we find that adding the linear interaction, the evolution of ghost dark energy model does not contain the radiation dominated epoch in the early times which is a necessary point in any cosmic model. This failure resolved when we add the non-linear interaction to the model. We also find an upper bound for the value of the coupling constant of the interaction between dark matter and dark energy as b < 0.57 . This bound is necessary to have a decelerating and unstable ma...
Effective field theory of modified gravity with two scalar fields: dark energy and dark matter
Gergely, László Á
2014-01-01
We present a framework for discussing the cosmology of dark energy and dark matter based on two scalar degrees of freedom. An effective field theory of cosmological perturbations is employed. A unitary gauge choice renders the dark energy field into the gravitational sector, for which we adopt a generic Lagrangian depending on three-dimensional geometrical scalar quantities arising in the ADM decomposition. We add to this dark-energy associated gravitational sector a scalar field $\\phi$ and its kinetic energy $X$ as dark matter variables. Compared to the single-field case, we find that there are additional conditions to obey in order to keep the equations of motion for linear cosmological perturbations at second order. For such a second-order multi-field theory we derive conditions under which ghosts and Laplacian instabilities of the scalar and tensor perturbations are absent. We apply our general results to models with dark energy emerging in the framework of the Horndeski theory and dark matter described b...
Dynamics of minimally coupled dark energy in spherical halos of dark matter
Novosyadlyj, Bohdan; Kulinich, Yurij
2016-01-01
We analyse the evolution of scalar field dark energy in the spherical halos of dark matter at the late stages of formation of gravitationally bound systems in the expanding Universe. The dynamics of quintessential dark energy at the center of dark matter halo strongly depends on the value of effective sound speed $c_s$ (in units of speed of light). If $c_s\\sim1$ (classical scalar field) then the dark energy in the gravitationally bound systems is only slightly perturbed and its density is practically the same as in cosmological background. The dark energy with small value of sound speed ($c_s<0.1$), on the contrary, is important dynamical component of halo at all stages of their evolution: linear, non-linear, turnaround, collapse, virialization and later up to current epoch. These properties of dark energy can be used for constraining the value of effective sound speed $c_s$ by comparison the theoretical predictions with observational data related to the large scale gravitationally bound systems.
On the Effective Equation of State of Dark Energy
DEFF Research Database (Denmark)
Sloth, Martin Snoager
2010-01-01
In an effective field theory model with an ultraviolet momentum cutoff, there is a relation between the effective equation of state of dark energy and the ultraviolet cutoff scale. It implies that a measure of the equation of state of dark energy different from minus one, does not rule out vacuum...
Logarithmic entropy corrected holographic dark energy with nonminimal kinetic coupling
Amani, Ali R.; Sadeghi, J.; Farajollahi, H.; Pourali, M.
2012-01-01
In this paper, we have considered a cosmological model with the non--minimal kinetic coupling terms and investigated its cosmological implications with respect to the logarithmic entropy-- corrected holographic dark energy (LECHDE). The correspondence between LECHDE in flat FRW cosmology and the phantom dark energy model with the aim to interpret the current universe acceleration is also examined.
Baryon acoustic oscillation intensity mapping of dark energy.
Chang, Tzu-Ching; Pen, Ue-Li; Peterson, Jeffrey B; McDonald, Patrick
2008-03-01
The expansion of the Universe appears to be accelerating, and the mysterious antigravity agent of this acceleration has been called "dark energy." To measure the dynamics of dark energy, baryon acoustic oscillations (BAO) can be used. Previous discussions of the BAO dark energy test have focused on direct measurements of redshifts of as many as 10(9) individual galaxies, by observing the 21 cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three-dimensional intensity mapping. If our estimates gain acceptance they may be the starting point for a new class of dark energy experiments dedicated to large angular scale mapping of the radio sky, shedding light on dark energy. PMID:18352692
Baryon Acoustic Oscillation Intensity Mapping of Dark Energy
Chang, Tzu-Ching; Peterson, Jeffrey B; McDonald, Patrick
2007-01-01
The expansion of the universe appears to be accelerating, and the mysterious anti-gravity agent of this acceleration has been called ``dark energy''. To measure the dynamics of dark energy, Baryon Acoustic Oscillations (BAO) can be used. Previous discussions of the BAO dark energy test have focused on direct measurements of redshifts of as many as 10^9 individual galaxies, by observing the 21cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three dimensional brightness mapping. If our estimates gain acceptance they may be the starting point for a new class of dark energy experiments dedicated to large angular scale mapping of the radio sky, shedding light on dark energy.
Baryon Acoustic Oscillation Intensity Mapping of Dark Energy
Chang, Tzu-Ching; Pen, Ue-Li; Peterson, Jeffrey B.; McDonald, Patrick
2008-03-01
The expansion of the Universe appears to be accelerating, and the mysterious antigravity agent of this acceleration has been called “dark energy.” To measure the dynamics of dark energy, baryon acoustic oscillations (BAO) can be used. Previous discussions of the BAO dark energy test have focused on direct measurements of redshifts of as many as 109 individual galaxies, by observing the 21 cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three-dimensional intensity mapping. If our estimates gain acceptance they may be the starting point for a new class of dark energy experiments dedicated to large angular scale mapping of the radio sky, shedding light on dark energy.
Marginalized Fisher Forecast for Horndeski Dark Energy Models
Leung, Jason S -Y
2016-01-01
We use effective field theory (EFT) formalism to forecast the constraint on Horndeski class of dark energy models with future supernova and galaxy surveys. Previously (Gleyzes {\\it et al.}) computed unmarginalized constraints (68\\% CL error $\\sim 10^{-3}$--$10^{-2}$) on EFT dark energy parameters by fixing all other parameters. We extend the previous work by allowing all cosmological parameters and nuisance parameters to vary and marginalizing over them. We find that (i) the constraints on EFT dark energy parameters are typically worsen by a factor of few after marginalization, and (ii) the constraint on the dark energy equation of state $w$ is not significantly affected by the inclusion of EFT dark energy parameters.
Generalized perturbations in modified gravity and dark energy
Pearson, Jonathan Andrew
2012-01-01
When recent observational data and the GR+FRW+CDM model are combined we obtain the result that the Universe is accelerating, where the acceleration is due to some not-yet-understood "dark sector". There has been a considerable number of theoretical models constructed in an attempt to provide a description of the dark sector: dark energy and modified gravity theories. The proliferation of modified gravity and dark energy models has brought to light the need to construct a "generic" way to para...
Dynamics of Quintessence Models of Dark Energy with Exponential Coupling to the Dark Matter
Gonzalez, Tame; Leon, Genly; Quiros, Israel
2007-01-01
We explore quintessence models of dark energy which exhibit non-minimal coupling between the dark matter and the dark energy components of the cosmic fluid. The kind of coupling chosen is inspired in scalar-tensor theories of gravity. We impose a suitable dynamics of the expansion allowing to derive exact Friedmann-Robertson-Walker solutions once the coupling function is given as input. Self-interaction potentials of single and double exponential types emerge as result of our choice of the co...
Rudra, Prabir; Biswas, Ritabrata(Indian Institute of Engineering Sceince and Technology Shibpur (Formerly, Bengal Engineering and Science University Shibpur), 711 013, Howrah, West Bengal, India); Debnath, Ujjal
2012-01-01
In this work the collapsing process of a spherically symmetric star, made of dust cloud, in the background of dark energy is studied for two different gravity theories separately, i.e., DGP Brane gravity and Loop Quantum gravity. Two types of dark energy fluids, namely, Modified Chaplygin gas and Generalised Cosmic Chaplygin gas are considered for each model. Graphs are drawn to characterize the nature and the probable outcome of gravitational collapse. A comparative study is done between the...
Li, En-Kun; Geng, Jin-Ling
2014-01-01
The modified holographic Ricci dark energy coupled to interacting relativistic and non-relativistic dark matter is considered in the nonflat Friedmann-Robertson-Walker universe. Through examining the deceleration parameter, one can find that the transition time of the Universe from decelerating to accelerating phase in the interacting holographic Ricci dark energy model is close to that in the $\\Lambda$ cold dark matter model. The evolution of modified holographic Ricci dark energy's state parameter and the evolution of dark matter and dark energy's densities shows that the dark energy holds the dominant position from the near past to the future. By studying the statefinder diagnostic and the evolution of the total pressure, one can find that this model could explain the Universe's transition from the radiation to accelerating expansion stage through the dust stage. According to the $Om$ diagnostic, it is easy to find that when the interaction is weak and the proportion of relativistic dark matter in total da...
Gravitational energy as dark energy: Cosmic structure and apparent acceleration
Wiltshire, David L
2011-01-01
Below scales of about 100/h Mpc our universe displays a complex inhomogeneous structure dominated by voids, with clusters of galaxies in sheets and filaments. The coincidence that cosmic expansion appears to start accelerating at the epoch when such structures form has prompted a number of researchers to question whether dark energy is a signature of a failure of the standard cosmology to properly account, on average, for the distribution of matter we observe. Here I discuss the timescape scenario, in which cosmic acceleration is understood as an apparent effect, due to gravitational energy gradients that grow when spatial curvature gradients become significant with the nonlinear growth of cosmic structure. I discuss conceptual issues related to the averaging problem, and their impact on the calibration of local geometry to the solutions of the volume-average evolution equations corrected by backreaction, and the question of nonbaryonic dark matter in the timescape framework. I further discuss recent work on ...
Holographic Dark Energy Like in $f(R)$ Gravity
Saaidi, Kh
2010-01-01
We investigate the corresponding relation between $f(R)$ gravity and holographic dark energy. We introduce a kind of energy density from $f(R)$ which has role of the same as holographic dark energy. We obtain the differential equation that specify the evolution of the introduced energy density parameter based on varying gravitational constant. We find out a relation for the equation of state parameter to low redshifts which containing varying $G$ correction.
Holographic dark energy and f(R) gravity
Aghamohammadi, A.; Saaidi, Kh
2011-02-01
We investigate the corresponding relation between f(R) gravity and holographic dark energy. We introduce a type of energy density from f(R) that has the same role as holographic dark energy. We obtain the differential equation that specifies the evolution of the introduced energy density parameter based on a varying gravitational constant. We discover the relation for the equation of state parameter for low redshifts that contains varying G correction.
Holographic dark energy and f(R) gravity
International Nuclear Information System (INIS)
We investigate the corresponding relation between f(R) gravity and holographic dark energy. We introduce a type of energy density from f(R) that has the same role as holographic dark energy. We obtain the differential equation that specifies the evolution of the introduced energy density parameter based on a varying gravitational constant. We discover the relation for the equation of state parameter for low redshifts that contains varying G correction.
Holographic dark energy and f(R) gravity
Energy Technology Data Exchange (ETDEWEB)
Aghamohammadi, A [Faculty of Science, Islamic Azad University of Sanandaj, Sanandaj (Iran, Islamic Republic of); Saaidi, Kh, E-mail: ksaaidi@uok.ac.ir, E-mail: agha35484@yahoo.com [Department of Physics, Faculty of Science, University of Kurdistan, Sanandaj (Iran, Islamic Republic of)
2011-02-15
We investigate the corresponding relation between f(R) gravity and holographic dark energy. We introduce a type of energy density from f(R) that has the same role as holographic dark energy. We obtain the differential equation that specifies the evolution of the introduced energy density parameter based on a varying gravitational constant. We discover the relation for the equation of state parameter for low redshifts that contains varying G correction.
Reconstruction of interaction rate in Holographic dark energy
Mukherjee, Ankan
2016-01-01
The present work is based on the holographic dark energy model with Hubble horizon as the infrared cut-off. The interaction rate between dark energy and dark matter has been reconstructed for two different parameterizations of the deceleration parameter. Observational constraints on the model parameters have been obtained by maximum likelihood analysis using the observational Hubble parameter data (OHD), type Ia supernova data (SNe), baryon acoustic oscillation data (BAO) and the distance prior of cosmic microwave background (CMB) namely the CMB shift parameter data (CMBShift). The nature of the dark energy equation of state parameter has also been studied for the present models. The dark energy equation of state shows a phantom nature at present. Different information criteria and the Bayesian evidence, which have been invoked in the context of model selection, show that the these two models are at close proximity of each other.
New holographic dark energy model with non-linear interaction
Oliveros, A
2014-01-01
In this paper the cosmological evolution of a holographic dark energy model with a non-linear interaction between the dark energy and dark matter components in a FRW type flat universe is analysed. In this context, the deceleration parameter $q$ and the equation state $w_{\\Lambda}$ are obtained. We found that, as the square of the speed of sound remains positive, the model is stable under perturbations since early times; it also shows that the evolution of the matter and dark energy densities are of the same order for a long period of time, avoiding the so--called coincidence problem. We have also made the correspondence of the model with the dark energy densities and pressures for the quintessence and tachyon fields. From this correspondence we have reconstructed the potential of scalar fields and their dynamics.
Quintessence interacting dark energy from induced matter theory of gravity
Reyes, L M
2009-01-01
In the context of the induced matter theory of gravity, we investigate the possibility of deriving a 4D quintessential scenario where an interaction between dark energy and dark matter is allowed, and the dark energy component is modeled by a minimally coupled scalar field. Regarding the Ponce de Leon metric, we found that it is possible to obtain such scenario on which the energy densities of dark matter and dark energy, are both depending of the fifth extra coordinate. We obtain that the 4D induced scalar potential for the quintessence scalar field, has the same algebraic form to the one found by Zimdahl and Pavon in the context of usual 4D cosmology.
Modified gravity models of dark energy
Tsujikawa, Shinji
2011-01-01
We review recent progress of modified gravity models of dark energy--based on f(R) gravity, scalar-tensor theories, braneworld gravity, Galileon gravity, and other theories. In f(R) gravity and Brans-Dicke theory it is possible to design viable models consistent with local gravity constraints under a chameleon mechanism, while satisfying conditions for the cosmological viability. The Dvali-Gabadazde-Porrati braneworld model can be compatible with local gravity constraints through a nonlinear field self-interaction arising from a brane-bending mode, but the self-accelerating solution contains a ghost mode in addition to the tension with observational data about the cosmic expansion history. The extension of the field self-interaction to more general forms satisfying a Galilean symmetry in the flat space-time allows a possibility to avoid the appearance of ghosts and Laplacian instabilities, while the late-time cosmic acceleration can be realized by the field kinetic energy. We study the evolution of cosmologic...
Interacting dark matter and q-deformed dark energy with particle creation and annihilation
Kolay, Erdinc
2016-01-01
We propose a new model for studying the dark constituents of the universe by regarding the dark energy as a q-deformed scalar field interacting with the dark matter, in the framework of standard general relativity. Here we assume the number of particles in each mode of the q-deformed scalar field varies in time by the particle creation and annihilation. We first describe the q-deformed scalar field dark energy quantum field theoretically, then construct the action and the dynamical structure of these interacting dark sector, in order to study the dynamics of the model. In the following section, we perform the phase space analysis of the model to confirm and interpret our proposal by searching the stable attractor solutions implying the late-time accelerating phase of the universe. We then obtain the result that when interaction and equation of state parameter of the dark matter evolves from the present day values into a particular value, the dark energy turns out to be a q-deformed scalar field.
Measuring dark energy spatial inhomogeneity with supernova data
Cooray, Asantha; Caldwell, Robert
2008-01-01
The gravitational lensing distortion of distant sources by the large-scale distribution of matter in the Universe has been extensively studied. In contrast, very little is known about the effects due to the large-scale distribution of dark energy. We discuss the use of Type Ia supernovae as probes of the spatial inhomogeneity and anisotropy of dark energy. We show that a shallow, almost all-sky survey can limit rms dark energy fluctuations at the horizon scale down to a fractional energy density of ~10^-4
Cosmological anisotropy from non-comoving dark matter and dark energy
Harko, Tiberiu
2013-01-01
We consider a cosmological model in which the two major fluid components of the Universe, dark energy and dark matter, flow with distinct four-velocities. This cosmological configuration is equivalent to a single anisotropic fluid, expanding with a four-velocity that is an appropriate combination of the two fluid four-velocities. The energy density of the single cosmological fluid is larger than the sum of the energy densities of the two perfect fluids, i.e., dark energy and dark matter, respectively, and contains a correction term due to the anisotropy generated by the differences in the four-velocities. Furthermore, the gravitational field equations of the two-fluid anisotropic cosmological model are obtained for a Bianchi type I geometry. By assuming that the non-comoving motion of the dark energy and dark matter induces small perturbations in the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker type cosmological background, and that the anisotropy parameter is small, the equations of the cosm...
Dark energy and the accelerating universe: progress, problems and prospects
Energy Technology Data Exchange (ETDEWEB)
Lima, J.A.S. [Universidade de Sao Paulo (IAG/USP), SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas
2012-07-01
Full text: A large number of recent observational data strongly suggest that we live in a flat, accelerating Universe composed by nearly 1/3 of matter (baryonic + dark) and 2/3 of an exotic component with large negative pressure, usually named Dark Energy. The basic set of experiments includes: observations from SNe Ia, CMB anisotropies, baryon acoustic oscillations (BAO) and X-ray data from galaxy clusters. Within the general relativity, the simplest explanation for dark energy is the cosmological constant associated with the zero-point energy density of all quantum fields present in the Universe. However, all estimates for its value are many orders-of-magnitude too large. Many alternative ideas include more exotic candidates for dark energy among them an extremely light scalar field. However, some possible explanations for the present accelerating stage also invokes gravitational physics beyond general relativity. In this way, several observations using satellites and ground-based telescopes are in operation or being planned to test whether dark energy is the cosmological constant or something more exotic, as well as to decide whether or not the standard general relativity can explain cosmic acceleration. In the current view, dark energy is an interesting example of new physics, and, certainly, its possible existence is one of the most profound mysteries of modern physics. In this talk we present a simplified picture of the main results and discuss briefly the difficulties underlying the dark energy paradigm and some of its possible alternatives. (author)
Cosmological consequences of interacting modified holographic Ricci dark energy
Chattopadhyay, Surajit
2016-07-01
In this present work, we have studied various aspects of modified holographic Ricci dark energy interacting with pressureless dark matter in a flat Friedman-Robertson-Walker universe. We have observed that reconstructed Hubble parameter H={dot{a}}/{a}, expressed as a function of redshift z=a^{-1}-1, exhibits an increasing pattern with evolution of the universe. The equation of state parameter has behaved like ``quintessence" for various combinations of α and β. Deceleration parameter has stayed in negative level and this has indicated accelerated expansion of the universe. Fractional densities expressed as function of z has indicated transition of the universe from a matter dominated to dark energy dominated phase. Finally we have created statefinder trajectories in {r-s} plane and we have observed that for modified holographic Ricci dark energy interacting with pressureless dark matter it is possible to attain ΛCDM phase of the universe.
New constraints on interacting dark energy from cosmic chronometers
Nunes, Rafael C.; Pan, Supriya; Saridakis, Emmanuel N.
2016-07-01
We use the latest compilation of observational Hubble parameter measurements estimated with the differential evolution of cosmic chronometers, in combination with the local value of the Hubble constant recently measured with 2.4% precision, to constrain the cosmological scenario where dark energy interacts directly with the dark matter sector. To diminish the degeneracy between the parameters we additionally consider standard probes, such as supernovae type Ia from joint light-curve analysis samples, baryon acoustic oscillation distance measurements (BAO), and cosmic microwave background data from Planck 2015 estimations. Our analysis shows that the direct interaction between dark energy and dark matter is mildly favored, while the dark energy equation-of-state parameter is w <-1 at a 3 σ confidence level.
New constraints on interacting dark energy from cosmic chronometers
Nunes, Rafael C; Saridakis, Emmanuel N
2016-01-01
We use the latest compilation of observational Hubble parameter measurements estimated with the differential evolution of cosmic chronometers, in combination with the local value of the Hubble constant recently measured with 2.4% precision, to constrain the cosmological scenario where dark energy interacts directly with the dark matter sector. To diminish the degeneracy between the parameters we additionally consider standard probes, such as Supernovae Type Ia from joint light curves (JLA) sample and Baryon Acoustic Oscillation distance measurements (BAO). Our analysis shows that the direct interaction between dark energy and dark matter is mildly favored. This result is in qualitative agreement with the results of other observational works, and the fact that it has been extracted using novel observational data acts as an additional argument in favor of interacting dark energy.
Zhao, HongSheng
2008-01-01
Empirical theories of Dark Matter like MOND gravity and of Dark Energy like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general hence natural framework? Here we propose the natural Lagrangian of such a framework based on simple dimensional analysis and co-variant symmetry requirements, and explore various outcomes in a top-down fashion. Our framework preserves the co-variant formulation of GR, but allows the expanding physical metric be bent by a single new species of Dark Fluid flowing in space-time. Its non-uniform stress tensor and current vector are simply functions of a vector field of variable norm, resembling the 4-vector electromagnetic potential description for the photon fluid, but is dark (e.g., by very early decoupling from the baryon-radiation fluid). The Dark Fluid framework naturally branches into a continuous spectrum of theories with Dark Energy and Dark Matter effects, including the $f(R)$ gravity, TeVeS-like theories, Einstein-Ae...
Buchert, Thomas
2010-01-01
We outline the key-steps towards the construction of a physical, fully relativistic cosmology, in which we aim to trace Dark Energy and Dark Matter back to physical properties of space. The influence of inhomogeneities on the effective evolution history of the Universe is encoded in backreaction terms and expressed through spatially averaged geometrical invariants. These are absent and interpreted as missing dark fundamental sources in the standard model. In the inhomogeneous case they can be interpreted as energies of an emerging scalar field (the morphon). These averaged invariants vanish for a homogeneous geometry, where the morphon is in an unstable equilibrium state. If this state is perturbed, the morphon can act as a classical inflaton in the Early Universe and its de-balanced energies can mimic the dark sources in the Late Universe, depending on spatial scale as Dark Energy or as Dark Matter, respectively. We lay down a line of arguments that is qualitatively conclusive, and we outline open problems o...
Wang, B.; Abdalla, E.; Atrio-Barandela, F.; Pavón, D.
2016-09-01
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.
Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D
2016-09-01
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.