5 research outputs found
Kahler potentials for the MSSM inflation and the spectral index
Recently it has been argued that some of the fine-tuning problems of the MSSM
inflation associated with the existence of a saddle point along a flat
direction may be solved naturally in a class of supergravity models. Here we
extend the analysis and show that the constraints on the Kahler potentials in
these models are considerably relaxed when the location of the saddle point is
treated as a free variable. We also examine the effect of supergravity
corrections on inflationary predictions and find that they can slightly alter
the value of the spectral index. As an example, for flat direction field values
we find while the
prediction of the MSSM inflation without any corrections is .Comment: 13 pages, one figure. Typos corrected and a reference adde
Supergravity origin of the MSSM inflation
We consider the supergravity origin of the recently proposed MSSM
inflationary model, which relies on the existence of a saddle point along a
dimension six flat direction. We derive the conditions that the Kahler
potential has to satisfy for the saddle point to exist irrespective of the
hidden sector vevs. We show that these conditions are satisfied by a simple
class of Kahler potentials, which we find to have a similar form as in various
string theory compactifications. For these potentials, slow roll MSSM inflation
requires no fine tuning of the soft supersymmetry breaking parameters.Comment: v3: 10 pages, no figures; version accepted for publication. Typos
correcte
A-term inflation and the smallness of the neutrino masses
The smallness of the neutrino masses may be related to inflation. The minimal
supersymmetric Standard Model (MSSM) with small Dirac neutrino masses already
has all the necessary ingredients for a successful inflation. In this model the
inflaton is a gauge-invariant combination of the right-handed sneutrino, the
slepton, and the Higgs field, which generate a flat direction suitable for
inflation if the Yukawa coupling is small enough. In a class of models, the
observed microwave background anisotropy and the tilted power spectrum are
related to the neutrino masses.Comment: 13 pages, 1 figure, uses JHEP3.cls, minor modifications, final
version accepted for publication in JCA
Supersymmetric Thermalization and Quasi-Thermal Universe: Consequences for Gravitinos and Leptogenesis
Motivated by our earlier paper \cite{am}, we discuss how the infamous
gravitino problem has a natural built in solution within supersymmetry.
Supersymmetry allows a large number of flat directions made up of {\it gauge
invariant} combinations of squarks and sleptons. Out of many at least {\it one}
generically obtains a large vacuum expectation value during inflation. Gauge
bosons and Gauginos then obtain large masses by virtue of the Higgs mechanism.
This makes the rate of thermalization after the end of inflation very small and
as a result the Universe enters a {\it quasi-thermal phase} after the inflaton
has completely decayed. A full thermal equilibrium is generically established
much later on when the flat direction expectation value has substantially
decareased. This results in low reheat temperatures, i.e., , which are compatible with the stringent bounds arising from the
big bang nucleosynthesis. There are two very important implications: the
production of gravitinos and generation of a baryonic asymmetry via
leptogenesis during the quasi-thermal phase. In both the cases the abundances
depend not only on an effective temperature of the quasi-thermal phase (which
could be higher, i.e., ), but also on the state of equilibrium
in the reheat plasma. We show that there is no ``thermal gravitino problem'' at
all within supersymmetry and we stress on a need of a new paradigm based on a
``quasi-thermal leptogenesis'', because in the bulk of the parameter space the
{\it old} thermal leptogenesis cannot account for the observed baryon
asymmetry.Comment: 53 pages. Final version published in JCA
Towards constraints on the SUSY seesaw from flavour-dependent leptogenesis
We systematically investigate constraints on the parameters of the
supersymmetric type-I seesaw mechanism from the requirement of successful
thermal leptogenesis in the presence of upper bounds on the reheat temperature
of the early Universe. To this end, we solve the
flavour-dependent Boltzmann equations in the MSSM, extended to include
reheating. With conservative bounds on , leading to mildly
constrained scenarios for thermal leptogenesis, compatibility with observation
can be obtained for extensive new regions of the parameter space, due to
flavour-dependent effects. On the other hand, focusing on (normal) hierarchical
light and heavy neutrinos, the hypothesis that there is no CP violation
associated with the right-handed neutrino sector, and that leptogenesis
exclusively arises from the CP-violating phases of the matrix,
is only marginally consistent. Taking into account stricter bounds on
further suggests that (additional) sources of CP violation must
arise from the right-handed neutrino sector, further implying stronger
constraints for the right-handed neutrino parameters.Comment: 42 pages, 12 figures; final version published in JCAP; numerical
results for the efficiency factor can be downloaded from
http://www.newphysics.eu/leptogenesis