89 research outputs found
Back-door fine-tuning in supersymmetric low scale inflation
Low scale inflation has many virtues and it has been claimed that its natural
realisation in supersymmetric standard model can be achieved rather easily. In
this letter we have demonstrated that also in this case the dynamics of the
hidden sector responsible for supersymmetry breakdown and the structure of the
soft terms affects significantly, and in fact often spoils, the would-be
inflationary dynamics. Also, we point out that the issue if the cosmological
constant cancellation in the post-inflationary vacuum strongly affects
supersymmetric inflation. It is important to note the crucial difference
between freezing of the modulus and actually stabilising it - the first
approach misses parts of the scalar potential which turn out to be relevant for
inflation. We argue, that it is more likely that the low scale supersymmetric
inflation occurs at a critical point at the origin in the field space than at
an inflection point away from the origin, as the necessary fine-tuning in the
second case is typically larger.Comment: 10
Low-scale standard supersymmetric leptogenesis
Strictly adhering to the standard supersymmetric seesaw mechanism, we present
a neutrino mass model which allows successful standard thermal leptogenesis
compatible with gravitino cosmology. At least some of the neutrino Yukawa
couplings must be much larger than the naive estimates following from the
seesaw formula. This leads to large BR(mu->e gamma), detectable in the next
round of experiments. Ratios of mu->e gamma, tau->e gamma and tau->mu gamma
branching ratios are predicted in terms of the measurable neutrino mass matrix.Comment: 15 pages, 4 eps figures; v2: typos corrected, references added,
reasoning clarified; v3: 16 pages, off-shell wash-out effects included in the
addendum (pp.15-16
Neutralino and gravitino dark matter with low reheating temperature
We examine a scenario in which the reheating temperature after
inflation is so low that it is comparable to, or lower than, the freeze out
temperature of ordinary WIMPs. In this case the dark matter relic abundance is
reduced, thus relaxing the impact of the usually strong constraint coming from
the requirement that the universe does not overclose. We first re-examine the
dynamics of freezeout during reheating. Next we apply a Bayesian approach to
study the parameter space of the MSSM with ten free parameters, the CMSSM and
the singlino-dominated regions of the NMSSM. In each case we find dramatic
departures from the usually considered regime of high , with important
implications for direct detection dark matter searches. In the MSSM we examine
WIMP mass range up to ~5 TeV, and find regions of bino dark matter over the
whole mass range, and of higgsino dark matter with mass over a similar range
but starting from the ~1 TeV value of the standard high scenario. We show
that the prospects for bino detection strongly depend on , while the
higgsino is for the most part detectable by future one-tonne detectors. The
wino, which is excluded in the standard scenario, becomes allowed again if its
mass is roughly above 3.5 TeV, and can be detectable. In the CMSSM, the bino
and higgsino mass ranges become more constrained although detection prospects
remain similar. In the Next-to-MSSM at low enough wide ranges of
singlino-dominated parameter space of the model become cosmologically allowed.
We also study the contribution to the DM relic density from direct and cascade
decays of the inflaton. Finally, we consider the case of a gravitino as dark
matter. We find strong bounds from overclosure and Big Bang Nucleosynthesis,
and derive lower limits on which depend on the gravitino mass and on the
nature of the lightest ordinary superpartner.Comment: section and references adde
On reaching the adiabatic limit in multi-field inflation
We calculate the scalar spectral index and the tensor-to-scalar ratio
in a class of recently proposed two-field no-scale inflationary models in
supergravity. We show that, in order to obtain correct predictions, it is
crucial to take into account the coupling between the curvature and the
isocurvature perturbations induced by the noncanonical form of the kinetic
terms. This coupling enhances the curvature perturbation and suppresses the
resulting tensor-to-scalar ratio to the per mille level even for values of the
slow-roll parameter . Beyond these particular models, we
emphasise that multifield models of inflation are a priori not predictive,
unless one supplies a prescription for the post-inflationary era, or an
adiabatic limit is reached before the end of inflation. We examine the
conditions that enabled us to actually derive predictions in the models under
study, by analysing the various contributions to the effective isocurvature
mass in general two-field inflationary models. In particular, we point out a
universal geometrical contribution that is important at the end of inflation,
and which can be directly extracted from the inflationary Lagrangian,
independently of a specific trajectory. Eventually, we point out that spectator
fields can lead to oscillatory features in the time-dependent power spectra at
the end of inflation. We demonstrate how these features can be model
semi-analytically as well as the theoretical uncertainties they can entail.Comment: 26 pages. 13 figures. One additional author. Substantially reworked
and extende
Axino dark matter with low reheating temperature
We examine axino dark matter in the regime of a low reheating temperature T_R
after inflation and taking into account that reheating is a non-instantaneous
process. This can have a significant effect on the dark matter abundance,
mainly due to entropy production in inflaton decays. We study both thermal and
non-thermal production of axinos in the context of the MSSM with ten free
parameters. We identify the ranges of the axino mass and the reheating
temperature allowed by the LHC and other particle physics data in different
models of axino interactions. We confront these limits with cosmological
constraints coming the observed dark matter density, large structures formation
and big bang nucleosynthesis. We find a number of differences in the
phenomenologically acceptable values of the axino mass and the reheating
temperature relative to previous studies. In particular, an upper bound on the
axino mass becomes dependent on T_R, reaching a maximum value at T_R~10^2 GeV.
If the lightest ordinary supersymmetric particle is a wino or a higgsino, we
obtain lower a limit of approximately 10 GeV for the reheating temperature. We
demonstrate also that entropy production during reheating affects the maximum
allowed axino mass and lowest values of the reheating temperature.Comment: v2: improved discussion of warm dark matter bounds, results for stau
LOSP adde
Gravitino dark matter with constraints from Higgs boson mass and sneutrino decays
We investigate gravitino dark matter produced thermally at high temperatures
and in decays of a long-lived sneutrino. We consider the Non-Universal Higgs
Model and a generalized gauge mediation model, and in each case identify
sneutrino LOSP regions of the parameter space consistent with the mass of the
Higgs-like boson observed at the LHC. We apply relevant collider and
cosmological bounds, including constraints from Big Bang Nucleosynthesis and
from warm dark matter on large scale structures. Generally, we find allowed
values of the reheating temperature TR below 10^9 GeV, i.e. somewhat smaller
than the values needed for thermal leptogenesis, even with a conservative lower
bound of 122 GeV on the Higgs mass. Requiring mass values closer to 126 GeV
implies TR below 10^7 GeV and the gravitino mass less than 10 GeV.Comment: 19 pages, 19 figures, version published in JHE
On suppressing the Higgsino-mediated proton decay in SUSY SO(10) GUT's
Using the freedom in SO(10) GUT's one can generalize the existing models
without changing the mass spectrum of fermions to obtain a significant
suppression of proton decay resulting from the baryon number violating
operators of dimension 5. In some limiting cases, their contributions can be
made negligible compared to the dimension 6 operators resulting from the heavy
gauge bosons exchange.Comment: 19 pages, 3 Postscript figures, 2 mpost figures, rearranged plots,
corrected typo
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