arXiv subjects

Lotfi Boubekeur

Publications and source records attributed to Lotfi Boubekeur.

22 records · Page 2Linked to original sources

arXiv2005

Hilltop Inflation

We study `hilltop' inflation, in which inflation takes place near a maximum of the potential. Viewed as a model of inflation after the observable Universe leaves the horizon (observable inflation) hilltop inflation is rather generic. If the potential steepens monotonically, observable hilltop inflation gives a tiny tensor fraction (r< 0.002). The usual F- and D-term models may easily be transmuted to hilltop models by Planck-suppressed terms, making them more natural. The only commonly-considered model of observable inflation which is definitely not hilltop is tree-level hybrid inflation. Viewed instead as an initial condition, we explain that hilltop inflation is more generic than seems to have been previously recognized, adding thereby to the credibility of the idea that eternal inflation provides the pre-inflationary initial condition.

hep-ph↗

arXiv2002

Leptogenesis and rescattering in supersymmetric models

The observed baryon asymmetry of the Universe can be due to the $B-L$ violating decay of heavy right handed (s)neutrinos. The amount of the asymmetry depends crucially on their number density. If the (s)neutrinos are generated thermally, in supersymmetric models there is limited parameter space leading to enough baryons. For this reason, several alternative mechanisms have been proposed. We discuss the nonperturbative production of sneutrino quanta by a direct coupling to the inflaton. This production dominates over the corresponding creation of neutrinos, and it can easily (i.e. even for a rather small inflaton-sneutrino coupling) lead to a sufficient baryon asymmetry. We then study the amplification of MSSM degrees of freedom, via their coupling to the sneutrinos, during the rescattering phase which follows the nonperturbative production. This process, which mainly influences the (MSSM) $D-$flat directions, is very efficient as long as the sneutrinos quanta are in the relativistic regime. The rapid amplification of the light degrees of freedom may potentially lead to a gravitino problem. We estimate the gravitino production by means of a perturbative calculation, discussing the regime in which we expect it to be reliable.

hep-ph↗

arXiv2002

Leptogenesis at Low Scale

A typical problem of the leptogenesis scenario is the mismatch between the maximum reheat temperature implied by gravitino overproduction bound and the minimum temperature required to create thermally the lightest right-handed neutrino. We explore the possibility of baryogenesis via leptogenesis in the presence of low scale mass right-handed neutrino. In such a scenario, right-handed neutrinos are created thermally at low reheat temperatures without relying on non-perturbative production mechanisms. We focus on two specific realizations of the scenario, namely the out-of-equilibrium decay of right-handed neutrinos (Fukugita-Yanagida) and the leptogenesis via the $LH_u$ flat direction (Affleck-Dine). We find that in general, the two scenarios are able to produce the required baryon excess for a reasonable amount of CP violation.

hep-ph↗

arXiv2001

Universal Singlets, Supergravity and Inflation

In supersymmetric theories, the occurrence of universal singlets is a delicate issue, because they usually induce tadpoles that destabilize the hierarchy. We study the effects of these tadpoles in supersymmetric hybrid inflation models. The resulting scenario is generically modified, but it is still possible to achieve inflation in a natural way. It is argued that singlets, despite the problems associated with their presence, can lead to interesting cosmological consequences.

hep-ph↗