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We consider a Lorentz-violating theory of gravity where the aether vector is taken to be nondynamical. This "ponderable aether theory" is almost the same as Einstein-aether theory (where the aether vector is dynamical), but involves…
The joint realm of quantum mechanics and the general-relativistic description of gravitation is becoming increasingly accessible to terrestrial experiments and observations. In this essay we study the emerging indications of the violation…
We analyse the Einstein equivalence principle (EEP) for a Hubble observer in Friedmann-Lemaitre-Robertson-Walker spacetime. We show that the affine structure of light cone in the FLRW spacetime should be treated locally in terms of the…
Dark energy may be the first sign of new fundamental physics in the Universe, taking either a physical form or revealing a correction to Einsteinian gravity. Weak gravitational lensing and galaxy peculiar velocities provide complementary…
We review several theoretical aspects of the Equivalence Principle (EP). We emphasize the unsatisfactory fact that the EP maintains the absolute character of the coupling constants of physics while General Relativity, and its…
In this paper, bulk viscosity is introduced in new holographic dark energy (HDE) to describe the effects of cosmic non-perfect fluid on the evolution of the universe in modified $f(R,T)$ gravity. Assuming $f(R,T)=R+\lambda T$, where $R$ is…
Motivated by recent astrophysical observations of quasar absorption systems, we formulate a simple theory where the electron to proton mass ratio $\mu =m_{e}/m_{p}$ is allowed to vary in space-time. In such a minimal theory only the…
We investigate the constraints on cosmological parameters especially for EoS of dark energy, inflationary parameters, neutrino mass and curvature of universe using simulated Planck data. Firstly we determine cosmological parameters with…
Clusters of galaxies have been used to measure a subtle effect predicted by Einstein: gravitational redshift. This signal encodes pristine information about our Universe, since it is sensitive to the depth of the clusters' gravitational…
We study physical consequences of the Einstein equivalence principle (EEP) for a Hubble observer in FLRW universe. We introduce the local inertial coordinates with the help of a special conformal transformation. The local inertial metric is…
Cosmological scalar perturbation theory studied in the Newtonian gauge depends on two potentials $\Phi$ and $\Psi$. In General Relativity (GR) they must coincide ($\Phi=\Psi$) in the absence of anisotropic stresses sourced by the energy…
An analysis of cosmological mixed dark matter models in spatially flat Friedmann Universe with zero $\Lambda$-term is presented. We argue that the introduction of cosmic gravity waves helps to satisfy observational constraints. The analysis…
If the reported measurements of the time variation of the fine structure constant from observations of distant QSOs are correct, combined with the Oklo limit they would strongly constrain the class of the quintessence potential. If these…
Taking into consideration of a fractal structure for the black hole horizon, Barrow argued that the area law of entropy get modified due to quantum-gravitational effects. Accordingly, the corrected entropy takes the form $S\sim…
In this paper we consider very weakly interacting and ultra light scalar and pseudoscalar dark matter candidates. We show that quantum gravity has important implications for such models and that the masses of the singlet scalar and…
We investigate the possibility of testing of the Einstein Equivalence Principle (EEP) using measurements of anomalous magnetic moments of elementary particles. We compute the one loop correction for the $g-2$ anomaly within the class of non…
Based on quantum mechanical framework for the minimal length uncertainty, we demonstrate that the generalized uncertainty principle (GUP) parameter could be best constrained by recent gravitational waves observations on one hand. On other…
An important and long-standing puzzle in the history of modern physics is the gross inconsistency between theoretical expectations and cosmological observations of the vacuum energy density, by at least 60 orders of magnitude, otherwise…
Anisotropy data analysis leaves a significant degeneracy between primeval spectral index (n_s) and cosmic opacity to CMB photons (\tau). Low--l polarization measures, in principle, can remove it. We perform a likelihood analysis to see how…
The cosmological constant problem is usually considered an inevitable feature of any effective theory capturing well-tested gravitational and matter physics, without regard to the details of short-distance gravitational couplings. In this…