arXiv subjects

Alireza Talebian

Publications and source records attributed to Alireza Talebian.

21 records · Page 2Linked to original sources

arXiv2020

Mimetic Inflation

We study inflationary solution in an extension of mimetic gravity with the higher derivative interactions coupled to gravity. Because of the higher derivative interactions, the setup is free from the ghost and gradient instabilities while it hosts a number of novel properties. The dispersion relation of scalar perturbations develops quartic momentum correction similar to the setup of ghost inflation. Furthermore, the tilt of tensor perturbations can take either signs with a modified consistency relation between the tilt and the amplitude of tensor perturbations. Despite the presence of higher derivative interactions coupled to gravity, the tensor perturbations propagate with a speed equal to the speed of light as required by the LIGO observations. Furthermore, the higher derivative interactions induce non-trivial interactions in cubic Hamiltonian, generating non-Gaussianities in various shapes such as the equilateral, orthogonal, and squeezed configurations with observable amplitudes.

gr-qc↗

arXiv2020

Revisiting Magnetogenesis during Inflation

We revisit the mechanism of primordial magnetogenesis during inflation by taking into account the dynamics of the stochastic noises of the electromagnetic perturbations. We obtain the associated Langevin and Fokker-Planck equations for the electromagnetic fields and solve them analytically. It is shown that while the backreactions of the electric field energy density may spoil inflation too early, but there are regions of parameter space where the usual decaying behavior of the magnetic fields are replaced by a mean-reverting process of stochastic dynamics. As a result, the magnetic fields settle down into an equilibrium state with the amplitude significantly larger than what is obtained in the absence of the stochastic noises. We show that magnetic fields with present time amplitude $\sim 10^{-13}$ Gauss and coherent length ${\rm Mpc}$ can be generated while the backreactions of the electric field perturbations are under control.

gr-qc↗

arXiv2019

Stochastic Effects in Anisotropic Inflation

We revisit the stochastic effects in the model of anisotropic inflation containing a $U(1)$ gauge field. We obtain the Langevin equations for the inflaton and gauge fields perturbations and solve them analytically. We show that if the initial value of the electric field is larger than its classical attractor value, then the random stochastic forces associated with the gauge field is balanced by the frictional damping (classical) force and the electric field falls into an equilibrium (stationary) regime. As a result, the classical attractor value of the electric field is replaced by its stationary value. We show that the probability of generating quadrupolar statistical anisotropy consistent with CMB constraints can be significant.

gr-qc↗