We investigate cosmology of massive electrodynamics and explore the possibility whether massive photon could provide an explanation of the dark energy. The action is given by the scalar-vector-tensor theory of gravity which is obtained by nonminimal coupling of the massive Stueckelberg QED with gravity and its cosmological consequences are studied by paying a particular attention to the role of photon mass. We find that the theory allows cosmological evolution where the radiationand matter-dominated epochs are followed by a long period of virtually constant dark energy that closely mimics ΛCDM model and the main source of the current acceleration is provided by the nonvanishing photon mass governed by the relation Λ ∼ m 2 . A detailed numerical analysis shows that the nonvanishing photon mass of the order of ∼ 10 −34 eV is consistent with the current observations. This magnitude is far less than the most stringent limit on the photon mass available so far, which is of the order of m ≤ 10 −27 eV.

We introduce a minimal and yet comprehensive framework with CP -and classical scalesymmetries, in order to simultaneously address the hierarchy problem, neutrino masses, dark matter, and inflation. One complex gauge singlet scalar and three flavors of the right-handed Majorana neutrinos are added to the standard model content, facilitating the see-saw mechanism, among others. An adimensional theory of gravity (Agravity) is employed, allowing for the trans-Planckian field excursions. The weak and Planck scales are induced by the Higgs portal and the scalar non-minimal couplings, respectively, once a Coleman-Weinberg dynamically-generated vacuum expectation value for the singlet scalar is obtained. All scales are free from any mutual quadratic destabilization. The CP -symmetry prevents a decay of the pseudoscalar singlet, rendering it a suitable WIMPzilla dark matter candidate with the correct observational relic abundance. Identifying the pseudoNambu-Goldstone boson of the (approximate) scale symmetry with the inflaton field, the model accommodates successful slow-roll inflation, compatible with the observational data. We reach the conclusion that a pseudo-Nambu-Goldstone inflaton, within a classically scale-symmetric framework, yields lighter WIMPzillas.

We investigate the cosmological implications of the generalized and extended uncertainty principle (GEUP), and whether it could provide an explanation for the dark energy. The consequence of the GEUP is the existence of a minimum and a maximum length, which can in turn modify the entropy area law and also modify the Friedmann equation. The cosmological consequences are studied by paying particular attention to the role of these lengths. We find that the theory allows a cosmological evolution where the radiation-and matter-dominated epochs are followed by a long period of virtually constant dark energy, that closely mimics the ΛCDM model. The main cause of the current acceleration arises from the maximum length scale β, governed by the relation Λ ∼ −β −1 W (−β −1 ). Using recent observational data (the Hubble parameters, type Ia supernovae, and baryon acoustic oscillations, together with the Planck or WMAP 9-year data of the cosmic microwave background radiation), we estimate constraints to the minimum length scale α 10 81 and the maximum length scale β ∼ −10 −2 .

We study cosmological consequences of the dark spinor model when torsion is included. Only some components of the torsion are allowed to be non-vanishing in homogeneous and isotropic cosmology, but there exist freedoms in the choice of these components which is consistent with the evolution equations. We exploit this and discuss several cases which can result in interesting cosmological consequences. Especially, we show that there exist exact cosmological solutions in which the Universe began its acceleration only recently and this solution is an attractor. This corresponds to a specific form of the torsion with a mild fine-tuning which can address the coincidence problem.PACS numbers: 95.35.+d, 04.20.Jb, 95.36.+x

We consider a deformed single field inflation model in terms of three SO(3) symmetric moduli fields. We find that spatially linear solutions for the moduli fields induce a phase transition during the early stage of the inflation and the suppression of scalar power spectrum at large scales. This suppression can be an origin of anomalies for large scale perturbation modes in the cosmological observation.

We consider the linear perturbations for the single scalar field inflation model interacting with an additional triad of scalar fields. The background solutions of the three additional scalar fields depend on spatial coordinates with a constant gradient α and the ensuing evolution preserves the homogeneity of the cosmological principle. After we discuss the properties of background evolution including an exact solution for the exponential-type potential, we investigate the linear perturbations of the scalar and tensor modes in the background of the slow-roll inflation. In our model with small α, the comoving wavenumber has a lower bound ∼ αM P to have well-defined initial quantum states. We find that cosmological quantities, for instance, the power spectrums and spectral indices of the comoving curvature and isocurvature perturbations, and the running of the spectral indices have small corrections depending on the lower bound. Similar behaviors happen for the tensor perturbation with the same lower bound.

We consider five dimensional conformal gravity theory which describes an anisotropic extra dimension. Reducing the theory to four dimensions yields Brans-Dicke theory with a potential and a hidden parameter α which implements the anisotropy between the four dimensional spacetime and the extra dimension. We find that a range of value of the parameter α can address the current dark energy density compared to the Planck energy density. Constraining the parameter α and the other cosmological model parameters using the recent observational data consisting of the Hubble parameters, type Ia supernovae, and baryon acoustic oscillations, together with the Planck or WMAP 9-year data of the cosmic microwave background radiation, we find α > −2.05 for Planck data and α > −2.09 for WMAP 9-year data at 95% confidence level. We also obtained constraints on the rate of change of the effective Newtonian constant (G eff ) at present and the variation of G eff since the epoch of recombination to be consistent with observation. arXiv:1709.08499v2 [astro-ph.CO]

Abstract:We investigate cosmological consequences of nonlinear sigma model coupled with a cosmological fluid which satisfies the continuity equation. The target space action is of the de Sitter type and is composed of four scalar fields. The potential which is a function of only one of the scalar fields is also introduced. We perform a general analysis of the ensuing cosmological equations and give various critical points and their properties. Then, we show that the model exhibits an exact cosmological solution which yields a transition from matter domination into dark energy epoch and compare it with the Λ-CDM behavior. Especially, we calculate the age of the Universe and show that it is consistent with the observational value if the equation of the state ω f of the cosmological fluid is within the range of 0.13 < ω f < 0.22. Some implication of this result is also discussed.