arXiv subjects

Ahmad Kiasatpour

Publications and source records attributed to Ahmad Kiasatpour.

3 recordsLinked to original sources

arXiv2016

CMB and reheating constraints to α-attractor inflationary models

After Planck 2013, a broad class of inflationary models called α-attractors was developed which has universal observational predictions. For small values of the parameter α, the models have good consistency with the recent CMB data. In this work, we first calculate analytically (and verify numerically) the predictions of these models for spectral index, n_s and tensor-to-scalar ratio, r and then using BICEP2/Keck 2015 data we impose constraints on α-attractors. Then, we study the reheating in α-attractors. The reheating temperature, T_{re} and the number of e-folds during reheating, N_{re} are calculated as functions of n_s. Using these results, we determine the range of free parameter αfor two clasees of α-attractors which satisfy the constraints of recent CMB data.

astro-ph.CO↗

arXiv2015

A Non-minimally Coupled Potential for Inflation and Dark Energy after Planck 2015: A Comprehensive Study

In this work we introduce a new plateau-like inflationary model including a quadratic scalar potential coupled non-minimally to gravity. This potential has a dominant constant energy density at early times which can realize successful inflation. It also includes an infinitesimal non-zero term $V_0$ responsible for explaining dark energy which causing the universe to expand accelerating at the late time. We show that this model predicts small tensor-to-scalar ratio of the order of $r\approx 0.01$ which is fully consistent with Planck constraints. Using the lower and upper bounds on reheating temperature, we provide additional constraints on the non-minimal coupling parameter $ξ$ of the model. We also study the preheating stage predicted by this kind of potentials using numerical calculations.

hep-th↗

arXiv2015

Bulk Viscosity and Particle Creation in the Inflationary Cosmology

We study particle creation in the presence of bulk viscosity of cosmic fluid in the early universe within the framework of open thermodynamical systems. Since the first-order theory of non-equilibrium thermodynamics is non-causal and unstable, we try to solve the bulk viscosity equation of the cosmic fluid with particle creation through the full causal theory. By adopting an appropriate function for particle creation rate of "Creation of Cold Dark Matter" model, we obtain analytical solutions which do not suffer from the initial singularity and are in agreement with equivalent solutions of Lambda-CDM model. We constrain the free parameter of particle creation in our model based on recent Planck data. It is also found that the inflationary solution is driven by bulk viscosity with or without particle creation.

gr-qc↗