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Showing papers on "Cosmology published in 2004"


Journal ArticleDOI
TL;DR: For a flat universe with a cosmological constant, the transition between the two epochs is constrained to be at z = 0.46 ± 0.13 as mentioned in this paper, and w = -1.02 ± (and w < -0.76 at the 95% confidence level) for an assumed static equation of state of dark energy.
Abstract: We have discovered 16 Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to provide the first conclusive evidence for cosmic deceleration that preceded the current epoch of cosmic acceleration. These objects, discovered during the course of the GOODS ACS Treasury program, include 6 of the 7 highest redshift SNe Ia known, all at z > 1.25, and populate the Hubble diagram in unexplored territory. The luminosity distances to these objects and to 170 previously reported SNe Ia have been determined using empirical relations between light-curve shape and luminosity. A purely kinematic interpretation of the SN Ia sample provides evidence at the greater than 99% confidence level for a transition from deceleration to acceleration or, similarly, strong evidence for a cosmic jerk. Using a simple model of the expansion history, the transition between the two epochs is constrained to be at z = 0.46 ± 0.13. The data are consistent with the cosmic concordance model of ΩM ≈ 0.3, ΩΛ ≈ 0.7 (χ = 1.06) and are inconsistent with a simple model of evolution or dust as an alternative to dark energy. For a flat universe with a cosmological constant, we measure ΩM = 0.29 ± (equivalently, ΩΛ = 0.71). When combined with external flat-universe constraints, including the cosmic microwave background and large-scale structure, we find w = -1.02 ± (and w < -0.76 at the 95% confidence level) for an assumed static equation of state of dark energy, P = wρc2. Joint constraints on both the recent equation of state of dark energy, w0, and its time evolution, dw/dz, are a factor of ~8 more precise than the first estimates and twice as precise as those without the SNe Ia discovered with HST. Our constraints are consistent with the static nature of and value of w expected for a cosmological constant (i.e., w0 = -1.0, dw/dz = 0) and are inconsistent with very rapid evolution of dark energy. We address consequences of evolving dark energy for the fate of the universe.

4,236 citations


Book
01 Mar 2004
TL;DR: In this paper, the authors present in a manifestly gauge-invariant form the theory of classical linear gravitational perturbations in part I, and a quantum theory of cosmological perturbation in part II.
Abstract: We present in a manifestly gauge-invariant form the theory of classical linear gravitational perturbations in part I, and a quantum theory of cosmological perturbations in part II. Part I includes applications to several important examples arising in cosmology: a univese dominated by hydrodynamical matter, a universe filled with scalar-field matter, and higher-derivative theories of gravity. The growth rates of perturbations are calculated analytically in most interesting cases. The analysis is applied to study the evolution of fluctuations in inflationary universe models. Part II includes a unified description of the quantum generation and evolution of inhomogeneities about a classial Friedmann background. The method is based on standard canonical quantization of the action for cosmological perturbations which has been reduced to an expression in terms of a single gauge-invariant variable. The spectrum of density perturbations originating in quantum fluctuations is calculated in universe with hydrodynamical matter, in inflationary universe models with scalar-field matter, and in higher-derivative theories of gravity. The gauge-invariant theory of classical and quantized cosmological perturbations developed in parts I and II is applied in part III to several interesting physical problems. It allows a simple derivation of the relation between temperature anistropes in the cosmic microwave background. radiation and the gauge-invariant potential for metric perturbations. The generation and evolution of gravitational waves is studied. As another example, a simple analysis of entropy perturbations and non-scale-invariant spectra in inflationary universe models is presented. The gauge-invariant theory of cosmological perturbations also allows a consistent and gauge-invariant definition of statistical fluctuations.

2,785 citations


Journal ArticleDOI
Miao Li1
TL;DR: In this article, a model for holographic dark energy is proposed, following the idea that the short distance cutoff is related to the infrared cut-off, and the model predicts the equation of state of the dark energy at the present time to be characterized by w = -0.90.

1,834 citations


Journal ArticleDOI
TL;DR: A review of models of inflation and their predictions for the primordial non-Gaussianity in the density perturbations which are thought to be at the origin of structures in the Universe is given in this article.

1,222 citations


Journal ArticleDOI
TL;DR: In this article, an inventory of the cosmic mean densities of energy associated with all known states of matter and radiation at the present epoch is presented, and a global portrait of the effects of the physical processes of cosmic evolution is presented.
Abstract: We present an inventory of the cosmic mean densities of energy associated with all the known states of matter and radiation at the present epoch. The observational and theoretical bases for the inventory have become rich enough to allow estimates with observational support for the densities of energy in some 40 forms. The result is a global portrait of the effects of the physical processes of cosmic evolution.

543 citations


Journal ArticleDOI
TL;DR: In this paper, the authors consider particle decays during the cosmic dark ages with two aims: (1) to explain the high optical depth reported by the Wilkinson Microwave Anisotropy Probe (WMAP), and (2) to provide new constraints to the parameter space for decaying particles.
Abstract: We consider particle decays during the cosmic dark ages with two aims: (1) to explain the high optical depth reported by the Wilkinson Microwave Anisotropy Probe (WMAP), and (2) to provide new constraints to the parameter space for decaying particles. We delineate the decay channels in which most of the decay energy ionizes and heats the intergalactic medium gas [and thus affects the cosmic microwave background (CMB)], and those in which most of the energy is carried away—e.g. photons with energies 100 keV<~E<~1 TeV—and thus appears as a contribution to diffuse x-ray and gamma-ray backgrounds. The new constraints to the decay-particle parameters from the CMB power spectrum thus complement those from the cosmic x-ray and gamma-ray backgrounds. Although decaying particles can indeed produce an optical depth consistent with that reported by WMAP, in so doing they produce new fluctuations in the CMB temperature and polarization power spectra. For decay lifetimes less than the age of the Universe, the induced power spectra generally violate current constraints, while the power spectra are usually consistent if the lifetime is longer than the age of the Universe.

411 citations


Journal ArticleDOI
Massimo Giovannini1
TL;DR: In this article, the authors describe the physical motivations and the open theoretical problems related to the existence of large-scale magnetic fields in galaxies, clusters and super-clusters, and present a review of the physical and theoretical aspects of magnetization.
Abstract: Cosmology, high-energy physics and astrophysics are today converging to the study of large scale magnetic fields. While the experimental evidence for the existence of large scale magnetization in galaxies, clusters and super-clusters is rather compelling, the origin of the phenomenon remains puzzling especially in light of the most recent observations. The purpose of the present review is to describe the physical motivations and the open theoretical problems related to the existence of large scale magnetic fields.

381 citations


Journal ArticleDOI
TL;DR: In this paper, a cosmological parameter analysis on the l < 2000 primary anisotropy data is presented, and the role of the small-scale cosmic microwave background data in breaking parameter degeneracies.
Abstract: Two years of microwave background observations with the Cosmic Background Imager (CBI) have been combined to give a sensitive, high-resolution angular power spectrum over the range 400 2000 power previously seen with the CBI is reduced. Under the assumption that any signal in excess of the primary anisotropy is due to a secondary Sunyaev-Zeldovich anisotropy in distant galaxy clusters, we use CBI, Arcminute Cosmology Bolometer Array Receiver, and Berkeley-Illinois-Maryland Association array data to place a constraint on the present-day rms mass fluctuation on 8 h-1 Mpc scales, σ8. We present the results of a cosmological parameter analysis on the l < 2000 primary anisotropy data that show significant improvements in the parameters as compared to WMAP alone, and we explore the role of the small-scale cosmic microwave background data in breaking parameter degeneracies.

361 citations


Journal ArticleDOI
TL;DR: In this paper, the role of tachyon fields in cosmology as compared to the well-established use of minimally coupled scalar fields is investigated, and a specific one-parameter family of tachyonic models based on a perfect fluid mixed with a positive cosmological constant is studied.
Abstract: We study the role that tachyon fields may play in cosmology as compared to the well-established use of minimally coupled scalar fields. We first elaborate on a kind of correspondence existing between tachyons and minimally coupled scalar fields; corresponding theories give rise to the same cosmological evolution for a particular choice of the initial conditions but not for any other. This leads us to study a specific one-parameter family of tachyonic models based on a perfect fluid mixed with a positive cosmological constant. For positive values of the parameter, one needs to modify Sen's action and use the $\ensuremath{\sigma}$ process of resolution of singularities. The physics described by this model is dramatically different and much richer than that of the corresponding scalar field. For particular choices of the initial conditions, the universe, which does mimic for a long time a de Sitter--like expansion, ends up in a finite time in a special type of singularity that we call a big brake. This singularity is characterized by an infinite deceleration.

324 citations


Journal ArticleDOI
TL;DR: In this article, it is proposed that dark energy may become dominant over standard matter due to universe expansion (curvature decrease), and two models: non-linear gravity-matter system and modified gravity may provide an effective phantom or effective quintessence dark energy which complies with the conjecture.

319 citations


Journal ArticleDOI
TL;DR: In this article, the authors review cosmological aspects of brane world scenarios such as the Randall-Sundrum brane model and two-brane systems with a bulk scalar field.
Abstract: Recent developments in the physics of extra dimensions have opened up new avenues to test such theories. We review cosmological aspects of brane world scenarios such as the Randall–Sundrum brane model and two-brane systems with a bulk scalar field. We start with the simplest brane world scenario leading to a consistent cosmology: a brane embedded in an anti-de Sitter space–time. We generalize this setting to the case with a bulk scalar field and then to two-brane systems.We discuss different ways of obtaining a low-energy effective theory for two-brane systems, such as the moduli space approximation and the low-energy expansion. A comparison between the different methods is given. Cosmological perturbations are briefly discussed as well as early universe scenarios such as the cyclic model and the born-again brane world model. Finally we also present some physical consequences of brane world scenarios on the cosmic microwave background and the variation of constants.

Book
19 Jul 2004
TL;DR: Gamma ray astronomy, the branch of high energy astrophysics that studies the sky in energetic γ-ray photons, is destined to play a crucial role in the exploration of nonthermal phenomena in the Universe in their most extreme and violent forms.
Abstract: Gamma ray astronomy, the branch of high energy astrophysics that studies the sky in energetic γ-ray photons, is destined to play a crucial role in the exploration of nonthermal phenomena in the Universe in their most extreme and violent forms. The great potential of this discipline offers impressive coverage of many “hot topics” of modern astrophysics and cosmology, such as the origin of galactic and extragalactic cosmic rays, particle acceleration and radiation processes under extreme astrophysical conditions, and the search for dark matter. The recent observational results and exciting theoretical predictions provide a strong rationale for a deep study of cosmic radiation with forthcoming satellite-borne and ground-based detectors in the so-called very high energy domain of the electromagnetic spectrum above 1010 eV.This invaluable book presents the motivations and highlights the principal objectives of the field, as well as demonstrates its intrinsic links to other branches of high energy astrophysics. Preference is given to three topical areas: (i) origin of cosmic rays; (ii) physics and astrophysics of relativistic jets; (iii) observational gamma ray cosmology. Also, an essential part of the book is devoted to the discussion of the principal mechanisms of production and absorption of energetic γ-rays in different astrophysical environments, as well as to the description of the detection methods of high energy cosmic γ-radiation.

Journal ArticleDOI
TL;DR: In this paper, the expected low-frequency gravitational wave signal from coalescing massive black hole (MBH) binaries at the center of galaxies in a hierarchical structure formation scenario was computed in the quadrupole approximation and results in a gravitational wave background (GWB) with a well-defined shape that reflects the different mechanisms driving the late orbital evolution.
Abstract: We compute the expected low-frequency gravitational wave signal from coalescing massive black hole (MBH) binaries at the center of galaxies in a hierarchical structure formation scenario in which seed holes of intermediate mass form far up in the dark halo "merger tree." The merger history of dark matter halos and associated MBHs is followed via cosmological Monte Carlo realizations of the merger hierarchy from redshift z = 20 to the present in a ΛCDM cosmology. MBHs get incorporated through halo mergers into larger and larger structures, sink to the center because of dynamical friction against the dark matter background, accrete cold material in the merger remnant, and form MBH binary systems. Stellar dynamical (three-body) interactions cause the hardening of the binary at large separations, while gravitational wave emission takes over at small radii and leads to the final coalescence of the pair. A simple scheme is applied in which the "loss cone" is constantly refilled and a constant stellar density core forms because of the ejection of stars by the shrinking binary. The integrated emission from inspiraling MBH binaries at all redshifts is computed in the quadrupole approximation and results in a gravitational wave background (GWB) with a well-defined shape that reflects the different mechanisms driving the late orbital evolution. The characteristic strain spectrum has the standard hc(f) ∝ f-2/3 behavior only in the range f = 10-9 to 10-6 Hz. At lower frequencies the orbital decay of MBH binaries is driven by the ejection of background stars ("gravitational slingshot"), and the strain amplitude increases with frequency, hc(f) ∝ f. In this range the GWB is dominated by 109-1010 M☉ MBH pairs coalescing at 0 z 2. At higher frequencies, f > 10-6 Hz, the strain amplitude, as steep as hc(f) ∝ f-1.3, is shaped by the convolution of last stable circular orbit emission by lighter binaries (102-107 M☉) populating galaxy halos at all redshifts. We discuss the observability of inspiraling MBH binaries by a low-frequency gravitational wave experiment such as the planned Laser Interferometer Space Antenna (LISA). Over a 3 yr observing period LISA should resolve this GWB into discrete sources, detecting ≈60 (≈250) individual events above an S/N = 5 (S/N = 1) confidence level.

Journal ArticleDOI
TL;DR: In this paper, the idea of relating the infrared and ultraviolet cutoffs is applied to the Brans-Dicke theory of gravitation and it is shown that the Hubble scale or the particle horizon as the infrared cutoff will not give accelerating expansion.
Abstract: The idea of relating the infrared and ultraviolet cutoffs is applied to the Brans-Dicke theory of gravitation. We find that 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.

Journal ArticleDOI
TL;DR: In this article, the authors used the best known 15 gamma-ray bursts (GRBs) to estimate the burst energy accurately enough to probe the intermediate-redshift (z < 10) universe.
Abstract: The best measure of the universe should be done using a standard "ruler" at any redshift. Type Ia supernovae (SN Ia) probe the universe up to z ~ 1.5, while the cosmic microwave background (CMB) primary anisotropies concern basically z ~ 1000. Apparently, gamma-ray bursts (GRBs) are all but standard candles. However, their emission is collimated, and the collimation-corrected energy correlates tightly with the frequency at which most of the radiation of the prompt is emitted, as found by Ghirlanda et al. Through this correlation we can infer the burst energy accurately enough to probe the intermediate-redshift (z < 10) universe. Using the best known 15 GRBs we find very encouraging results that emphasize the cosmological GRB role. A combined fit with SN Ia yields ΩM = 0.37 ± 0.10 and ΩΛ = 0.87 ± 0.23. Assuming in addition a flat universe, the parameters are constrained to be ΩM = 0.29 ± 0.04 and ΩΛ = 0.71 ± 0.05. GRBs accomplish the role of "missing link" between SN Ia and CMB primary anisotropies. They can provide a new insight on the cosmic effects of dark energy, complementary to the one supplied by CMB secondary anisotropies through the integrated Sachs-Wolfe effect. The unexpected standard candle cosmological role of GRBs motivates us with the most optimistic hopes for what can be obtained when the GRB-dedicated satellite, Swift, is launched.

Journal ArticleDOI
TL;DR: In this paper, the authors analyse the implications of the latest cosmological data sets for distance-duality and find a 2-sigma violation caused by excess brightening of SN-Ia at z > 0.5, perhaps due to lensing magnification bias.
Abstract: In cosmology, distances based on standard candles (e.g. supernovae) and standard rulers (e.g. baryon oscillations) agree as long as three conditions are met: (1) photon number is conserved, (2) gravity is described by a metric theory with (3) photons travelling on unique null geodesics. This is the content of distance-duality (the reciprocity relation) which can be violated by exotic physics. Here we analyse the implications of the latest cosmological data sets for distance-duality. While broadly in agreement and confirming acceleration we find a 2-sigma violation caused by excess brightening of SN-Ia at z > 0.5, perhaps due to lensing magnification bias. This brightening has been interpreted as evidence for a late-time transition in the dark energy but because it is not seen in the d_A data we argue against such an interpretation. Our results do, however, rule out significant SN-Ia evolution and extinction: the "replenishing" grey-dust model with no cosmic acceleration is excluded at more than 4-sigma despite this being the best-fit to SN-Ia data alone, thereby illustrating the power of distance-duality even with current data sets.

Journal ArticleDOI
TL;DR: In this paper, the authors study the space-time evolution of the fine structure constant, α, inside evolving spherical overdensities in a lambda-CDM Friedmann universe using the spherical infall model.

Journal ArticleDOI
29 Oct 2004-Science
TL;DR: This key agreement between the phase of the observed polarization spectrum and that predicted on the basis of the total intensity spectrum provides support for the standard model of cosmology, in which dark matter and dark energy are the dominant constituents.
Abstract: Polarization observations of the cosmic microwave background with the Cosmic Background Imager from September 2002 to May 2004 provide a significant detection of the E-mode polarization and reveal an angular power spectrum of polarized emission showing peaks and valleys that are shifted in phase by half a cycle relative to those of the total intensity spectrum. This key agreement between the phase of the observed polarization spectrum and that predicted on the basis of the total intensity spectrum provides support for the standard model of cosmology, in which dark matter and dark energy are the dominant constituents, the geometry is close to flat, and primordial density fluctuations are predominantly adiabatic with a matter power spectrum commensurate with inflationary cosmological models.

Journal ArticleDOI
TL;DR: In this article, the authors cross-correlate the cosmic microwave background temperature anisotropies observed by the Wilkinson Microwave Anisotropy Probe (WMAP) with the projected distribution of extended sources in the Two Micron All Sky Survey (2MASS).
Abstract: We cross-correlate the cosmic microwave background temperature anisotropies observed by the Wilkinson Microwave Anisotropy Probe (WMAP) with the projected distribution of extended sources in the Two Micron All Sky Survey (2MASS). By modeling the theoretical expectation for this signal, we extract the signatures of dark energy [integrated Sachs-Wolfe effect (ISW)], hot gas [thermal Sunyaev-Zeldovich (SZ) effect], and microwave point sources in the cross-correlation. Our strongest signal is the thermal SZ, at the $3.1--3.7\ensuremath{\sigma}$ level, which is consistent with the theoretical prediction based on observations of x-ray clusters. We also see the ISW signal at the $2.5\ensuremath{\sigma}$ level, which is consistent with the expected value for the concordance $\ensuremath{\Lambda}\mathrm{CDM}$ cosmology, and is an independent signature of the presence of dark energy in the Universe. Finally, we see the signature of microwave point sources at the $2.7\ensuremath{\sigma}$ level.

Journal ArticleDOI
TL;DR: In this article, the authors constrain the mass density of the universe and the nature of dark energy for a sample of 12 gamma-ray burst (GRB) with known redshift, peak energy, and break time of afterglow light curves.
Abstract: An E-gamma,E-jet proportional to E-p'(1.5) relationship with a small scatter for current gamma-ray burst (GRB) data was recently reported, where E-gamma,E-jet is the beaming-corrected gamma-ray energy and E'(p) is the nuF(nu) peak energy in the local observer frame. By considering this relationship for a sample of 12 GRBs with known redshift, peak energy, and break time of afterglow light curves, we constrain the mass density of the universe and the nature of dark energy. We find that the mass density Omega(M) = 0.35(-0.15)(+0.15) (at the 1 sigma confidence level) for a flat universe with a cosmological constant, and the w parameter of an assumed static dark energy equation of state w = -0.84(-0.83)(+0.57) ( 1 sigma). Our results are consistent with those from Type Ia supernovae. A larger sample established by the upcoming Swift satellite is expected to provide further constraints.

Journal ArticleDOI
TL;DR: In this article, the authors investigate the formation of large scale structure is independent of the nature of the cold dark matter (CDM), however the fate of very small scale inhomogeneities depends on themicro-physics of the CDM particles.
Abstract: The formation of large scale structure is independent of the nature of the cold darkmatter (CDM), however the fate of very small scale inhomogeneities depends on themicro-physics of the CDM particles. We investigate the matter power spectrum forscales that enter the Hubble radius well before matter-radiation equality, and followits evolution until the time when the first inhomogeneities become non-linear. Ourfocus lies on weakly interacting massive particles (WIMPs), and as a concrete exam-ple we analyze the case when the lightest supersymmetric particle is a bino. We showthat collisional damping and free-streaming of WIMPs lead to a matter power spec-trum with a sharp cut-off at about 10 −6 M ⊙ and a maximum close to that cut-off. Wealso calculate the transfer function for the growth of the inhomogeneities in the lin-ear regime. These three effects (collisional damping, free-streaming and gravitationalgrowth) are combined to provide a WMAP normalized primordial CDM power spec-trum, which could serve as an input for high resolution CDM simulations. The smallestinhomogeneities typically enter the non-linear regime at a redshift of about 60.Key words: cosmology: theory – dark matter – early Universe

Journal ArticleDOI
TL;DR: In this article, the authors review the concept of a parallel mirror world which has the same particle physics as the observable world and couples to the latter by gravity and perhaps other very weak forces.
Abstract: We briefly review the concept of a parallel 'mirror' world which has the same particle physics as the observable world and couples to the latter by gravity and perhaps other very weak forces. The nucleosynthesis bounds demand that the mirror world should have a smaller temperature than the ordinary one. By this reason its evolution should substantially deviate from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. In particular, we show that in the context of certain baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one. Moreover, we show that mirror baryons could naturally constitute the dominant dark matter component of the Universe, and discuss its cosmological implications.

Journal ArticleDOI
TL;DR: In this paper, the authors used the precise measurement of cosmological parameters to predict the guaranteed rates of production of WIMPs in association with photons at electron-positron colliders.
Abstract: Assuming that cosmological dark matter consists of weakly interacting massive particles, we use the recent precise measurement of cosmological parameters to predict the guaranteed rates of production of such particles in association with photons at electron-positron colliders. Our approach is based on general physical principles such as detailed balancing and soft/collinear factorization. It leads to predictions that are valid across a broad range of models containing WIMPs, including supersymmetry, universal extra dimensions, and many others. We also discuss the discovery prospects for the predicted experimental signatures.

Journal ArticleDOI
TL;DR: In this paper, the first-year Wilkinson Microwave Anisotropy Probe (WMAP) data, in combination with any one of a number of other cosmic probes, show that we live in a flat Λ-dominated cold dark matter (CDM) universe with Ωm ≈ 0.28, h = 0.33, and no dark energy component (ΩΛ = 0) would produce an anticorrelation between the matter distribution and the CMB.
Abstract: The first-year Wilkinson Microwave Anisotropy Probe (WMAP) data, in combination with any one of a number of other cosmic probes, show that we live in a flat Λ-dominated cold dark matter (CDM) universe with Ωm ≈ 0.27 and ΩΛ ≈ 0.73. In this model the late-time action of the dark energy, through the integrated Sachs-Wolfe effect, should produce cosmic microwave background (CMB) anisotropies correlated with matter density fluctuations at z 2 (Crittenden & Turok 1996). The measurement of such a signal is an important independent check of the model. We cross-correlate the NRAO VLA Sky Survey (NVSS) radio source catalog (Condon et al. 1998) with the WMAP data in search of this signal, and see indications of the expected correlation. Assuming a flat ΛCDM cosmology, we find ΩΛ > 0 (95% CL, statistical errors only) with the peak of the likelihood at ΩΛ = 0.68, consistent with the preferred WMAP value. A closed model with Ωm = 1.28, h = 0.33, and no dark energy component (ΩΛ = 0), marginally consistent with the WMAP CMB TT angular power spectrum, would produce an anticorrelation between the matter distribution and the CMB. Our analysis of the cross-correlation of the WMAP data with the NVSS catalog rejects this cosmology at the 3 σ level.

Journal ArticleDOI
TL;DR: In this paper, the authors derive the modified gravitational force law necessary to generate any given cosmology, without reference to the fundamental theory, revealing modifications of gravity at scales typically much smaller than today's horizon, and discuss how, through these modifications, the growth of density perturbations, the late-time integrated Sachs-Wolfe effect, and even solar-system measurements may be sensitive to whether today's cosmic acceleration is generated by dark energy or modified gravitational dynamics.
Abstract: The nature of the fuel that drives today's cosmic acceleration is an open and tantalizing mystery. We entertain the suggestion that the acceleration is not the manifestation of yet another new ingredient in the cosmic gas tank, but rather a signal of our first real lack of understanding of gravitational physics. By requiring that the underlying gravity theory respect Birkhoff's law, we derive the modified gravitational force law necessary to generate any given cosmology, without reference to the fundamental theory, revealing modifications of gravity at scales typically much smaller than today's horizon. We discuss how, through these modifications, the growth of density perturbations, the late-time integrated Sachs-Wolfe effect, and even solar-system measurements may be sensitive to whether today's cosmic acceleration is generated by dark energy or modified gravitational dynamics, and are subject to imminent observational discrimination. We argue how these conclusions can be more generic, and probably not dependent on the validity of Birkhoff's law.

Journal ArticleDOI
TL;DR: The generalized Chaplygin gas (gCg), parametrized by an equation of state, p = −A/ρ α,w as recently proposed to be a candidate of the unified dark matter/energy (UDME) scenarios, is investigated in this article.
Abstract: Although various cosmological observations congruously suggest that our universe is dominated by two dark com- ponents, the cold dark matter without pressure and the dark energy with negative pressure, the nature and origin of these components is yet unknow. The generalized Chaplygin gas (gCg), parametrized by an equation of state, p = −A/ρ α ,w as recently proposed to be a candidate of the unified dark matter/energy (UDME) scenarios. In this work, we investigate some observational constraints on it. We mainly focus our attention on the constraints from recent measurements of the X-ray gas mass fractions in clusters of galaxies published by Allen et al. (2002, MNRAS, 334, L11; 2003, 342, 257) and the dimensionless coordinate distances to type Ia supernovae and Fanaroff-Riley type IIb radio galaxies compiled by Daly & Djorgovski (2003, ApJ, 597, 9). We obtain the confidence region on the two parameters fully characterizing gCg, As ≡ A/ρ (1+α) gCg0 and α, from a combined analysis of these databases, where ρgCg0 is the energy density of gCg at present. It is found that As = 0.70 +0.16 −0.17 and α = −0.09 +0.54 −0.33 , at a 95% confidence level, which is consistent within the errors with the standard dark matter + dark energy model, i.e., the case of α = 0. Particularly, the standard Chaplygin gas (α = 1) is ruled out as a feasible UDME by the data at a 99% confidence level.

Journal ArticleDOI
TL;DR: In this article, it was shown that the addition of a nonlinear term to the Lagrangian of the electromagnetic field yields a fluid with an asymptotically super-negative equation of state, causing an accelerated expansion of the universe.
Abstract: It is shown that the addition of a nonlinear term to the Lagrangian of the electromagnetic field yields a fluid with an asymptotically super-negative equation of state, causing an accelerated expansion of the Universe. Some general properties of nonlinear electromagnetism in cosmology are also discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the universe and explain why these misconceptions do not violate special relativity and link these concepts to observational tests.
Abstract: We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard ΛCDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ‘observable universe’ and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23σ.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the evolution of the cosmological parameters from the point of view of quantum field theory in curved space-time using the renormalization group (RG) approach.
Abstract: The renormalization group (RG) approach to cosmology is an efficient method to study the possible evolution of the cosmological parameters from the point of view of quantum field theory in curved space-time. In this work we continue our previous investigations of the RG method based on potential low-energy effects induced from physics at very high energy scales M_X near M_P. In the present instance we assume that both the Newton constant, G, and the cosmological term, \Lambda, can be functions of a scale parameter \mu. It turns out that G(\mu) evolves according to a logarithmic law which may lead to asymptotic freedom of gravity, similar to the gauge coupling in QCD. At the same time \Lambda(\mu) evolves quadratically with \mu. We study the consistency and cosmological consequences of these laws when \mu=H. Furthermore, we propose to extend this method to the astrophysical domain after identifying the local RG scale at the galactic level. It turns out that Kepler's third law of celestial mechanics receives quantum corrections that may help to explain the flat rotation curves of the galaxies without introducing the dark matter hypothesis. The origin of these effects (cosmological and astrophysical) could be linked, in our framework, to physics at M_X= 10^{16-17} GeV.

Journal ArticleDOI
TL;DR: In this article, the authors quantitatively present the physical information extractable from the observable correlation function in deep redshift space in a framework of linear theory, and show that the baryon ridge in the correlation function serves as a statistically circular object in the AP effect.
Abstract: Recent developments in galaxy surveys enable us to investigate the deep, high-redshift, universe. We quantitatively present the physical information extractable from the observable correlation function in deep redshift space in a framework of linear theory. The correlation function depends on the underlying power spectrum, velocity distortions, and the Alcock-Paczy?ski (AP) effect. The underlying power spectrum is sensitive to the constituents of matter in the universe, the velocity distortions are sensitive to the galaxy bias as well as the amount of total matter, and the Alcock-Paczy?ski effect is sensitive to the dark energy components. Measuring the dark energy by means of the baryonic feature in the correlation function is one of the most interesting applications. We show that the baryon ridge in the correlation function serves as a statistically circular object in the AP effect. In order to sufficiently constrain the dark energy components, the redshift range of the galaxy survey should be as broad as possible. The survey area on the sky should be smaller at deep redshifts than at shallow redshifts to keep the number density as dense as possible. We illustrate an optimal survey design that is useful in cosmology. Assuming future redshift surveys of z 3, which are within the reach of present-day technology, achievable error bounds on cosmological parameters are estimated by calculating the Fisher matrix. According to an illustrated design, the equation of state of dark energy can be constrained within ?5% error assuming that the bias is unknown and marginalized over. Even when all the other cosmological parameters should be simultaneously determined, the error bound for the equation of state is up to ?10%.