Fermionic decay of a massive scalar in the early Universe

We derive a curved space generalization of a scalar to fermion decay rate with a Yukawa coupling in expanding Friedmann-Robertson-Walker universes. This is done using the full theory of quantum fields in curved spacetime and the added-up transition probability method. It is found that in an expanding universe the usual Minkowskian decay rates are considerably modified for early times. For conformally coupled scalars the decay rate is modified by a positive additive term proportional to the inverse of mass and related to the expansion rate of the Universe. We compare and contrast our results with previous studies on scalar to scalar decay and find that in general the decay channel into fermions is the dominant channel of decay in the very early Universe.Comment: 9 pages, 2 figures. Corrected some minor misprint

Fermionic decay of a massive scalar in the early universe

We derive a curved space generalization of a scalar to fermion decay rate with a Yukawa coupling in expanding Friedmann-Robertson-Walker universes. This is done using the full theory of quantum fields in curved spacetime and the added-up transition probability method. It is found that in an expanding universe the usual Minkowskian decay rates are considerably modified for early times. For conformally coupled scalars the decay rate is modified by a positive additive term proportional to the inverse of mass and related to the expansion rate of the Universe. We compare and contrast our results with previous studies on scalar to scalar decay and find that in general the decay channel into fermions is the dominant channel of decay in the very early Universe

Is nonperturbative inflatino production during preheating a real threat to cosmology?

We discuss toy models where supersymmetry is broken due to non-vanishing time-varying vacuum expectation value of the inflaton field during preheating. We discuss the production of inflatino the superpartner of inflaton due to vacuum fluctuations and then we argue that they do not survive until nucleosynthesis and decay along with the inflaton to produce a thermal bath after preheating. Thus the only relevant remnant is the helicity \pm 3/2 gravitinos which can genuinely cause problem to nucleosynthesis.Comment: 10 pages, Updates to match the accepted version in Phys. Rev.

Sequestered Dark Matter

We show that hidden-sector dark matter is a generic feature of the type IIB string theory landscape and that its lifetime may allow for a discovery through the observation of very energetic gamma-rays produced in the decay. Throats or, equivalently, conformally sequestered hidden sectors are common in flux compactifications and the energy deposited in these sectors can be calculated if the reheating temperature of the standard model sector is known. Assuming that throats with various warp factors are available in the compact manifold, we determine which throats maximize the late-time abundance of sequestered dark matter. For such throats, this abundance agrees with cosmological data if the standard model reheating temperature was 10^10 - 10^11 GeV. In two distinct scenarios, the mass of dark matter particles, i.e. the IR scale of the throat, is either around 10^5 GeV or around 10^10 GeV. The lifetime and the decay channels of our dark matter candidates depend crucially on the fact that the Klebanov-Strassler throat is supersymmetric. Furthermore, the details of supersymmetry breaking both in the throat and in the visible sector play an essential role. We identify a number of scenarios where this type of dark matter can be discovered via gamma-ray observations.Comment: 36 pages, 3 figures; v2: references added, v3: introduction extended and typos correcte

Two component WIMP-FImP dark matter model with singlet fermion, scalar and pseudo scalar

We explore a two component dark matter model with a fermion and a scalar. In this scenario the Standard Model (SM) is extended by a fermion, a scalar and an additional pseudo scalar. The fermionic component is assumed to have a global ${\rm U(1)}_{\rm DM}$ and interacts with the pseudo scalar via Yukawa interaction while a $\mathbb{Z}_2$ symmetry is imposed on the other component -- the scalar. These ensure the stability of both the dark matter components. Although the Lagrangian of the present model is CP conserving, however the CP symmetry breaks spontaneously when the pseudo scalar acquires a vacuum expectation value (VEV). The scalar component of the dark matter in the present model also develops a VEV on spontaneous breaking of the $\mathbb{Z}_2$ symmetry. Thus the various interactions of the dark sector and the SM sector are progressed through the mixing of the SM like Higgs boson, the pseudo scalar Higgs like boson and the singlet scalar boson. We show that the observed gamma ray excess from the Galactic Centre, self-interaction of dark matter from colliding clusters as well as the 3.55 keV X-ray line from Perseus, Andromeda etc. can be simultaneously explained in the present two component dark matter model.Comment: 35 pages, 5 figure

Thermal and non-thermal production of dark matter via Z'-portal(s)

We study the genesis of dark matter in the primordial Universe for representative classes of Z'-portals models. For weak-scale Z' mediators we compute the range of values of the kinetic mixing allowed by WMAP/PLANCK experiments corresponding to a FIMP regime. We show that very small values of the kinetic coupling (1.e-12 < delta < 1.e-11) are sufficient to produce the right amount of dark matter. We also analyse the case of very massive gauge mediators, whose mass is larger than the reheating temperature, "T_RH", with a weak-scale coupling to ordinary matter. Relic abundance constraints then impose a direct correlation between T_RH and the effective scale "Lambda" of the interactions: Lambda ~ 1.e3--1.e5 * T_RH. Finally we describe in some detail the process of dark thermalisation and study its consequences on the computation of the relic abundance.Comment: version accepted for publication in JCA