Rouzbeh Allahverdi

Reheating in Inflationary Cosmology: Theory and Applications

Reheating is an important part of inflationary cosmology. It describes the production of Standard Model particles after the phase of accelerated expansion. We review the reheating process with a focus on an in-depth discussion of the preheating stage, which is characterized by exponential particle production due to a parametric resonance or tachyonic instability. We give a brief overview of the thermalization process after preheating and end with a survey of some applications to supersymmetric theories and to other issues in cosmology, such as baryogenesis, dark matter, and metric preheating.

Cladogenesis: Baryon-Dark Matter Coincidence from Branchings in Moduli Decay

We propose late-time moduli decay as the common origin of baryons and dark matter. The baryon asymmetry is produced from the decay of new TeV-scale particles, while dark matter is created from the (chain) decay of R-parity odd particles without undergoing any annihilation. The baryon and dark matter abundances are mainly controlled by the dilution factor from moduli decay, which is typically in the range 10{sup -9}-10{sup -7}. The exact number densities are determined by simple branching fractions from modulus decay, which are expected to be of similar order in the absence of symmetries. This scenario can naturally lead to the observed baryon asymmetry and, for moderate suppression of the two-body decays of the modulus to R-parity odd particles, can also yield the correct dark matter abundance for a dark matter mass in the (5-500) GeV range.

Nonthermal dark matter in string compactifications

Non-thermal cosmological histories are capable of greatly increasing the available parameter space of different particle physics dark matter (DM) models and are well-motivated by the ubiquity of late-decaying gravitationally coupled scalars in UV theories like string theory. A non-thermal DM model is presented in the context of LARGE Volume Scenarios in type IIB string theory. The model is capable of addressing both the moduli-induced gravitino problem as well as the problem of overproduction of axionic dark radiation and/or DM. We show that the right abundance of neutralino DM can be obtained in both thermal under and overproduction cases for DM masses between O(GeV) to O(TeV). In the latter case the contribution of the QCD axion to the relic density is totally negligible, while in the former case it can be comparable to that of the neutralino thus resulting in a multi-component DM scenario.

Reheating and supersymmetric flat-direction baryogenesis

Abstract We re-examine Affleck–Dine baryo/leptogenesis from the oscillation of condensates along flat directions of the supersymmetric standard model, which attained large vevs at the end of the inflationary epoch. The key observation is that superpotential interactions couple the flat directions to other fields, which acquire masses induced by the flat-direction vev that may be sufficiently small for them to be kinematically accessible to inflaton decay. The resulting plasma of inflaton decay products then may act on the flat directions via these superpotential Yukawa couplings, inducing thermal masses and supersymmetry-breaking A terms. In such cases the flat directions start their oscillations at an earlier time than usually estimated. The oscillations are also terminated earlier, due to evaporation of the flat direction condensate produced by its interaction with the plasma of inflaton decay products. In these cases we find that estimates for the resulting baryon/lepton asymmetry of the universe are substantially altered. We identify scenarios for the Yukawa couplings to the flat directions, and the order and mass scale of higher-dimensional superpotential interactions that set the initial flat direction vev, that might lead to acceptable baryo/leptogenesis.

keV Photon Emission from Light Nonthermal Dark Matter

We propose a possible explanation for the recent claim of an excess at 3.5 keV in the X-ray spectrum within a minimal extension of the standard model that explains dark matter and baryon abundance of the universe. The dark matter mass in this model is

A Supersymmetric

{\cal O}({\rm GeV})

B^-

and its relic density has a non-thermal origin. The model includes two colored scalars of

L Dark Matter Model and the Observed Anomalies in the Cosmic Rays

{\cal O}({\rm TeV})

Non-perturbative production of matter and rapid thermalization after MSSM inflation

mass (

Attraction towards an inflection point inflation

X_{1,2}