A test of the Copernican principle

The blackbody nature of the cosmic microwave background (CMB) radiation spectrum is used in a modern test of the Copernican principle. The reionized universe serves as a mirror to reflect CMB photons, thereby permitting a view of ourselves and the local gravitational potential. By comparing with measurements of the CMB spectrum, a limit is placed on the possibility that we occupy a privileged location, residing at the center of a large void. The Hubble diagram inferred from lines of sight originating at the center of the void may be misinterpreted to indicate cosmic acceleration. Current limits on spectral distortions are shown to exclude the largest voids which mimic cosmic acceleration. More sensitive measurements of the CMB spectrum could prove the existence of such a void or confirm the validity of the Copernican principle.     

Time and distance constraints on accelerating cosmological models

The absence of guidance from fundamental physics about the mechanism behind cosmic acceleration has given rise to a number of alternative cosmological scenarios. These are based either on modifications of general relativistic gravitation theory on large scales or on the existence of new fields in Nature. In this Letter we investigate the observational viability of some accelerating cosmological models in light of 32 age measurements of passively evolving galaxies as a function of redshift and recent estimates of the product of the cosmic microwave background acoustic scale and the baryonic acoustic oscillation peak scale. By using information-criteria model selection, we select the best-fit models and rank the alternative scenarios. We show that some of these models may provide a better fit to the data than does the current standard cosmological constant dominated (ΛCDM) model.     

The imprint of inflation on the cosmic microwave background

The cosmic microwave background is the most precise and the most simple cosmological dataset. This makes it our most prominent window to the physics of the very early Universe. In this article I give an introduction to the physics of the cosmic microwave background and show in some detail how primordial fluctuations from inflation are imprinted in the temperature anisotropy and polarisation spectrum of the CMB. I discuss the main signatures that are suggesting an inflationary phase for the generation of initial fluctuations.     

Late time neutrino masses, the LSND experiment, and the cosmic microwave background

Models with low-scale breaking of global symmetries in the neutrino sector provide an alternative to the seesaw mechanism for understanding why neutrinos are light. Such models can easily incorporate light sterile neutrinos required by the Liquid Scintillator Neutrino Detector experiment. Furthermore, the constraints on the sterile neutrino properties from nucleosynthesis and large-scale structure can be removed due to the nonconventional cosmological evolution of neutrino masses and densities. We present explicit, fully realistic supersymmetric models, and discuss the characteristic signatures predicted in the angular distributions of the cosmic microwave background.     

Topology and Fragility in Cosmology

We introduce the notion of topological fragility and briefly discuss some examples from the literature. An important example of this type of fragility is the way globally anisotropic Bianchi V generalisations of the FLRW k = –1 model result in a radical restriction on the allowed topology of spatial sections, thereby excluding compact cosmological models with negatively curved three-sections with anisotropy. An outcome of this is to exclude chaotic mixing in such models, which may be relevant, given the many recent attempts at employing compact FLRW k = –1 models to produce chaotic mixing in the cosmic microwave background radiation, if the Universe turns out to be globally anisotropic.     

Massive neutrinos and cosmology

The present experimental results on neutrino flavour oscillations provide evidence for non-zero neutrino masses, but give no hint on their absolute mass scale, which is the target of beta decay and neutrinoless double-beta decay experiments. Crucial complementary information on neutrino masses can be obtained from the analysis of data on cosmological observables, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure. In this review we describe in detail how free-streaming massive neutrinos affect the evolution of cosmological perturbations. We summarize the current bounds on the sum of neutrino masses that can be derived from various combinations of cosmological data, including the most recent analysis by the WMAP team. We also discuss how future cosmological experiments are expected to be sensitive to neutrino masses well into the sub-eV range.     

A Quantum Mechanical Relation Connecting Time,Temperature, and Cosmological Constant of the Universe: Gamow’S Relation Revisited as a Special Case

Considering our expanding universe as made up of gravitationally interacting particles which describe particles of luminous matter, dark matter and dark energy which is represented by a repulsive harmonic potential among the points in the flat 3-space and incorporating Mach’s principle into our theory, we derive a quantum mechanical relation connecting, temperature of the cosmic microwave background radiation, age, and cosmological constant of the universe. When the cosmological constant is zero, we get back Gamow’s relation with a much better coefficient. Otherwise, our theory predicts a value of the cosmological constant 2.0×10⁻⁵⁶ cm⁻² when the present values of cosmic microwave background temperature of 2.728 K and age of the universe 14 billion years are taken as input.     

Indication for primordial anisotropies in the neutrino background from the Wilkinson microwave anisotropy probe and the Sloan digital sky survey

We demonstrate that combining cosmic microwave background anisotropy measurements from the 1st year Wilkinson Microwave Anisotropy Probe observations with clustering data from the Sloan galaxy redshift survey yields an indication for primordial anisotropies in the cosmological neutrino background.     

Cosmic microwave background anisotropy constraints on relict neutrinos

I discuss basic theory of effect of the properties of the cosmological relict neutrinos on the observations of the cosmic microwave background anisotropy.     

Time drift of cosmological redshifts as a test of the Copernican principle

We present the time drift of the cosmological redshift in a general spherically symmetric spacetime. We demonstrate that its observation would allow us to test the Copernican principle and so determine if our Universe is radially inhomogeneous, an important issue in our understanding of dark energy. In particular, when combined with distance data, this extra observable allows one to fully reconstruct the geometry of a spacetime describing a spherically symmetric underdense region around us, purely from background observations.     

Kasner Cosmological Models with Two-Fluid Source in General Relativity

In this paper we present Bianchi type-I metric of the Kasner form describing two-fluid source of the universe in general relativity. In Kasner cosmological models one fluid is a radiation field modeling the cosmic microwave background, while the other is a matter field, modeling material content of the universe. The radiation and matter content of the universe are in interactive phase. We have also presented anisotropic, homogeneous nature of Kasner cosmological models with two-fluid. The behavior of fluid parameters and kinematical parameters of the models are also discussed.     

Cosmology

Precise astronomical observations of the cosmic expansion and the anisotropies of the cosmic microwave background have confirmed the simple cosmological “big bang” models. They have also produced evidence for a strange composition of the cosmic matter and energy density. The known baryons contribute only 5 percent to the cosmic substrate, while 25 percent are due to unknown dark matter particles, and 70 percent seem to come from a mysterious dark energy component which presently acts like a cosmological constant accelerating the cosmic expansion.     

Higher Dimensional Plane Symmetric Cosmological Models with Two-Fluid Source in General Relativity

We consider anisotropic, homogeneous two-fluid plane symmetric cosmological models in higher dimensions. Here one fluid represents the matter content of the universe and another fluid is chosen to model the CMB (cosmic microwave background) radiation. The radiation and matter content of the universe are in interactive phase. Also we have discussed the behaviour of fluid parameters and kinematical parameters.     

The cosmology of the nonsymmetric theory of gravitation

We show that during cosmological inflation the nonsymmetric metric tensor theory of gravitation develops a spectrum which is potentially observable by cosmic microwave background observations, and may be the most sensitive probe of the scale of cosmic inflation.     

A cosmological concordance model with dynamical vacuum term

We demonstrate that creation of dark-matter particles at a constant rate implies the existence of a cosmological term that decays linearly with the Hubble rate. We discuss the cosmological model that arises in this context and test it against observations of the first acoustic peak in the cosmic microwave background (CMB) anisotropy spectrum, the Hubble diagram for supernovas of type Ia (SNIa), the distance scale of baryonic acoustic oscillations (BAO) and the distribution of large scale structures (LSS). We show that a good concordance is obtained, albeit with a higher value of the present matter abundance than in the ΛCDM model. We also comment on general features of the CMB anisotropy spectrum and on the cosmic coincidence problem.     

Inflationary potential from 21 cm tomography and Planck

Three-dimensional neutral hydrogen mapping using the redshifted 21 cm line has recently emerged as a promising cosmological probe. Within the framework of slow-roll reconstruction, we analyze how well the inflationary potential can be reconstructed by combining data from 21 cm experiments and cosmic microwave background data from the Planck satellite. We consider inflationary models classified according to the amplitude of their tensor component, and show that 21 cm measurements can significantly improve constraints on the slow-roll parameters and determine the shape of the inflationary potential.     

Asymmetric Dark Matter: Theories,signatures, and constraints

We review theories of Asymmetric Dark Matter (ADM), their cosmological implications and detection. While there are many models of ADM in the literature, our review of existing models will center on highlighting the few common features and important mechanisms for generation and transfer of the matter–anti-matter asymmetry between dark and visible sectors. We also survey ADM hidden sectors, the calculation of the relic abundance for ADM, and how the DM asymmetry may be erased at late times through oscillations. We consider cosmological constraints on ADM from the cosmic microwave background, neutron stars, the Sun, and brown and white dwarves. Lastly, we review indirect and direct detection methods for ADM, collider signatures, and constraints.     

Evidence for dark energy from the cosmic microwave background alone using the Atacama Cosmology Telescope lensing measurements

For the first time, measurements of the cosmic microwave background radiation (CMB) alone favor cosmologies with w = -1 dark energy over models without dark energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing deflection power spectrum from the Atacama Cosmology Telescope with temperature and polarization power spectra from the Wilkinson Microwave Anisotropy Probe. The lensing data break the geometric degeneracy of different cosmological models with similar CMB temperature power spectra. Our CMB-only measurement of the dark energy density Ω(Λ) confirms other measurements from supernovae, galaxy clusters, and baryon acoustic oscillations, and demonstrates the power of CMB lensing as a new cosmological tool.     

Cosmology with massive neutrinos coupled to dark energy

Cosmological consequences of a coupling between massive neutrinos and dark energy are investigated. In such models, the neutrino mass is a function of a scalar field, which plays the role of dark energy. The evolution of the background and cosmological perturbations are discussed. We find that mass-varying neutrinos can leave a significant imprint on the anisotropies in the cosmic microwave background and even lead to a reduction of power on large angular scales.     

Characterizing the peak in the cosmic microwave background angular power spectrum

A peak has been unambiguously detected in the cosmic microwave background angular spectrum. Here we characterize its properties with fits to phenomenological models. We find that the TOCO and BOOM/NA data determine the peak location to be in the range 175-243 and 151-259, respectively (at 95% confidence) and determine the peak amplitude to be between approximately 70 and 90 &mgr;K. The peak shape is consistent with inflation-inspired flat, cold dark matter plus cosmological constant models of structure formation with adiabatic, nearly scale invariant initial conditions. It is inconsistent with open models and presents a great challenge to defect models.