arXiv subjects

Ioannis Dalianis

Publications and source records attributed to Ioannis Dalianis.

25 records · Page 2Linked to original sources

arXiv2015

Suppressing gravitino thermal production with a temperature-dependent messenger coupling

We show that the constraints on GMSB theories from the gravitino cosmology can be significantly relaxed if the messenger-spurion coupling is temperature dependent. We demonstrate this novel mechanism in a scenario in which this coupling depends on the VEV of an extra singlet field $S$ that interacts with the thermalized plasma which can result in a significantly suppressed gravitino production rate. In such a scenario the relic gravitino abundance is determined by the thermal dynamics of the $S$ field and it is easy to fit the observed dark matter abundance evading the stringent constraints on the reheating temperature, thus making gravitino dark matter consistent with thermal leptogenesis.

hep-ph↗

arXiv2015

On the initial conditions for inflation with plateau potentials: the $R+R^2$ (super)gravity case

We discuss the initial conditions problem for inflation driven by the vacuum energy of a plateau potential, and in particular the Starobinsky inflation. We show that the supergravity embedding of the $R+R^2$ theory naturally decreases the size of the acausal homogeneity, required for the low-scale inflation to occur, thanks to the presence of the dynamical pure supergravitational "auxiliary" fields. We examine the evolution of the $R+R^2$ fields within a FLRW Universe. We also find a dependence of the initial conditions problem on the background spatial curvature.

gr-qc↗

arXiv2015

Non-minimal derivative couplings and inflation in supergravity

In this article we motivate and review the embedding of the gravitationally enhanced friction mechanism in supergravity. The very interesting feature is that inflationary models which utilize this mechanism drive inflation for a wider range of parameter values and predict lower values for the tensor-to-scalar ratio.

hep-th↗

arXiv2011

Cosmological aspects of gauge mediated supersymmetry breakdown

In this thesis, we study the details of some fundamental cosmological problems of the gauge mediated supersymmetry breakdown and we probe the supersymmetry breaking sector by cosmological arguments. We manifest that problems like the metastable vacuum selection and the gravitino overproduction in the reheated early universe are naturally absent in the most general class of gauge mediation models without including additional ingredients or assumptions. We also find that the gravitino can generically account for the bulk dark matter of the universe. Cosmological implications of a stringy UV-completion of the supersymmetry breaking sector have been also considered.

hep-ph↗

arXiv2011

R-Symmetry and Gravitino Abundance

Supersymmetry breaking sectors generically have an approximate global U(1) $R$-symmetry. Thermal effects tend to restore the $R$-symmetry in the reheated early universe. We revisit the gravitino generation from the thermal plasma and we argue that an $R$-symmetric phase suppresses the gaugino masses and thereby the production of the helicity $\pm 1/2$ gravitino component. For reasonable values of the hidden sector parameters the gravitino can account for the dark matter of the universe with a relic abundance characterized by a remarkable insensitivity to the reheating temperature.

hep-ph↗

arXiv2011

Thermally Favourable Gauge Mediation

We discuss the thermal evolution of the spurion and messenger fields of ordinary gauge mediation models taking into account the Standard Model degrees of freedom. It is shown that for thermalized messengers the metastable susy breaking vacuum becomes thermally selected provided that the susy breaking sector is sufficiently weakly coupled to messengers or to any other observable field.

hep-ph↗

arXiv2010

Cosmological vacuum selection and metastable susy breaking

We study gauge mediation in a wide class of O'Raifeartaigh type models where supersymmetry breaking metastable vacuum is created by gravity and/or quantum corrections. We examine their thermal evolution in the early universe and the conditions under which the susy breaking vacuum can be selected. It is demonstrated that thermalization typically makes the metastable supersymmetry breaking cosmologically disfavoured but this is not always the case. Initial conditions with the spurion displaced from the symmetric thermal minimum and a small coupling to the messenger sector can result in the realization of the susy breaking vacuum even if the reheating temperature is high. We show that this can be achieved without jeopardizing the low energy phenomenology. In addition, we have found that deforming the models by a supersymmetric mass term for messengers in such a way that the susy breaking minimum and the susy preserving minima are all far away from the origin does not change the conclusions. The basic observations are expected to hold also in the case of models with an anomalous U(1) group.

hep-ph↗