1,402 research outputs found
Inflection point inflation within supersymmetry
We propose to address the fine tuning problem of inflection point inflation
by the addition of extra vacuum energy that is present during inflation but
disappears afterwards. We show that in such a case, the required amount of fine
tuning is greatly reduced. We suggest that the extra vacuum energy can be
associated with an earlier phase transition and provide a simple model, based
on extending the SM gauge group to SU(3)_C \times SU(2)_L\times U(1)_Y\times
U(1)_{B-L}, where the Higgs field of U(1)_{B-L} is in a false vacuum during
inflation. In this case, there is virtually no fine tuning of the soft SUSY
breaking parameters of the flat direction which serves as the inflaton.
However, the absence of radiative corrections which would spoil the flatness of
the inflaton potential requires that the U(1)_{B-L} gauge coupling should be
small with g_{B-L}\leq 10^{-4}.Comment: 6 pages, 1 figur
Longevity of supersymmetric flat directions
We examine the fate of supersymmetric flat directions. We argue that the
non-perturbative decay of the flat direction via preheating is an unlikely
event. In order to address this issue, first we identify the physical degrees
of freedom and their masses in presence of a large flat direction VEV (Vacuum
Expectation Value). We explicitly show that the (complex) flat direction and
its fermionic partner are the only light {\it physical} fields in the spectrum.
If the flat direction VEV is much larger than the weak scale, and it has a
rotational motion, there will be no resonant particle production at all. The
case of multiple flat directions is more involved. We illustrate that in many
cases of physical interest, the situation becomes effectively the same as that
of a single flat direction, or collection of independent single directions. In
such cases preheating is not relevant. In an absence of a fast non-perturbative
decay, the flat direction survives long enough to affect thermalization in
supersymmetric models as described in hep-ph/0505050 and hep-ph/0512227. It can
also ``terminate'' an early stage of non-perturbative inflaton decay as
discussed in hep-ph/0603244.Comment: 9 revtex pages, v3: expanded discussion on two flat directions, minor
modifications, conclusions unchange
Leptogenesis as the source of gravitino dark matter and density perturbations
We investigate the possibility that the entropy producing decay of a
right-handed sneutrino condensate can simultaneously be the source of the
baryon asymmetry, of gravitino dark matter, and of cosmological density
perturbations. For generic values of soft supersymmetry breaking terms in the
visible sector of 1-10 TeV, condensate decay can yield the dark matter
abundance for gravitinos in the mass range 1 MeV to 1 TeV, provided that the
resulting reheat temperature is below GeV. The abundance of thermally
produced gravitinos before and after sneutrino decay is then negligible. We
consider different leptogenesis mechanisms to generate a sufficient asymmetry,
and find that low-scale soft leptogenesis works most naturally at such
temperatures. The condensate can easily generate sufficient density
perturbations if its initial amplitude is , for a
Hubble expansion rate during inflation GeV. Right-handed sneutrinos
may therefore at the same time provide a source for baryogenesis, dark matter
and the seed of structure formation.Comment: 12 pages. Cosmetic changes made and references added. Final version
to appear in Phys. Rev.
Reheating in supersymmetric high scale inflation
Motivated by Refs \cite{am1,am2}, we analyze how the inflaton decay reheats
the Universe within supersymmetry. In a non-supersymmetric case the inflaton
usually decays via preheating unless its couplings to other fields are very
small. Naively one would expect that supersymmetry enhances bosonic preheating
as it introduces new scalars such as squarks and sleptons. On the contrary, we
point out that preheating is unlikely within supersymmetry. The reason is that
flat directions in the scalar potential, classified by gauge invariant
combinations of slepton and squark fields, are generically displaced towards a
large vacuum expectation value (VEV) in the early Universe. They induce
supersymmetry preserving masses to the inflaton decay products through the
Standard Model Yukawa couplings, which kinematically blocks preheating for VEVs
GeV. The decay will become allowed only after the flat directions
start oscillating, and once the flat direction VEV is sufficiently redshifted.
For models with weak scale supersymmetry, this generically happens at a Hubble
expansion rate: , at which time the
inflaton decays in the perturbative regime. This is to our knowledge first
analysis where the inflaton decay to the Standard Model particles is treated
properly within supersymmetry. There are number of important consequences: no
overproduction of dangerous supersymmetric relics (particularly gravitinos), no
resonant excitation of superheavy dark matter, and no non-thermal leptogenesis
through non-perturbative creation of the right-handed (s)neutrinos. Finally
supersymmetric flat directions can even spoil hybrid inflation all together by
not allowing the auxiliary field become tachyonic.Comment: 13 revtex pages, 2 tables. Title changed, few clarifications added,
final version accepted for publication in Phys. Rev.
Unifying inflation and dark matter
We present a simple model where a scalar field is responsible for cosmic
inflation and generates the seed for structure formation, while its thermal
relic abundance explains dark matter in the universe. The inflaton
self-coupling also explains the observed neutrino masses. All the virtues can
be attained in a minimal extension of the Standard Model gauge group around the
TeV scale. We can also unveil these properties in the forthcoming ground based
experiments.Comment: 4 pages, 3 figures. Submitted conference proceedings, based on a talk
presented at UCLA DM08 conferenc
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