180 research outputs found
Volume modulus inflection point inflation and the gravitino mass problem
Several models of inflection point inflation with the volume modulus as the
inflaton are investigated. Non-perturbative superpotentials containing two
gaugino condensation terms or one such term with threshold corrections are
considered. It is shown that the gravitino mass may be much smaller than the
Hubble scale during inflation if at least one of the non-perturbative terms has
a positive exponent. Higher order corrections to the Kahler potential have to
be taken into account in such models. Those corrections are used to stabilize
the potential in the axion direction in the vicinity of the inflection point.
Models with only negative exponents require uplifting and in consequence have
the supersymmetry breaking scale higher than the inflation scale. Fine-tuning
of parameters and initial conditions is analyzed in some detail for both types
of models. It is found that fine-tuning of parameters in models with heavy
gravitino is much stronger than in models with light gravitino. It is shown
that recently proposed time dependent potentials can provide a solution to the
problem of the initial conditions only in models with heavy gravitino. Such
potentials can not be used to relax fine tuning of parameters in any model
because this would lead to values of the spectral index well outside the
experimental bounds.Comment: 27 pages, 9 figures, comments and references added, version to be
publishe
Inflation, moduli (de)stabilization and supersymmetry breaking
We study the cosmological inflation from the viewpoint of the moduli
stabilization. We study the scenario that the superpotential has a large value
during the inflation era enough to stabilize moduli, but it is small in the
true vacuum. This scenario is discussed by using a simple model, one type of
hybrid models.Comment: 17 pages, 7 figure
Supergravity Higgs Inflation and Shift Symmetry in Electroweak Theory
We present a model of inflation in a supergravity framework in the Einstein
frame where the Higgs field of the next to minimal supersymmetric standard
model (NMSSM) plays the role of the inflaton. Previous attempts which assumed
non-minimal coupling to gravity failed due to a tachyonic instability of the
singlet field during inflation. A canonical K\"{a}hler potential with
\textit{minimal coupling} to gravity can resolve the tachyonic instability but
runs into the -problem. We suggest a model which is free of the
-problem due to an additional coupling in the K\"{a}hler potential which
is allowed by the Standard Model gauge group. This induces directions in the
potential which we call K-flat. For a certain value of the new coupling in the
(N)MSSM, the K\"{a}hler potential is special, because it can be associated with
a certain shift symmetry for the Higgs doublets, a generalization of the shift
symmetry for singlets in earlier models. We find that K-flat direction has
This shift symmetry is broken by interactions coming from
the superpotential and gauge fields. This direction fails to produce successful
inflation in the MSSM but produces a viable model in the NMSSM. The model is
specifically interesting in the Peccei-Quinn (PQ) limit of the NMSSM. In this
limit the model can be confirmed or ruled-out not just by cosmic microwave
background observations but also by axion searches.Comment: matches the published version at JCA
Inflation with racetrack superpotential and matter field
Several models of inflation with the racetrack superpotential for the volume
modulus coupled to a matter field are investigated. In particular, it is shown
that two classes of racetrack inflation models, saddle point and inflection
point ones, can be constructed in a fully supersymmetric framework with the
matter field F-term as a source of supersymmetry breaking and uplifting. Two
models of F-term supersymmetry breaking are considered: the Polonyi model and
the quantum corrected O'Raifeartaigh model. In the former case, both classes of
racetrack inflation models differ significantly from the corresponding models
with non-supersymmetric uplifting. The main difference is a quite strong
dominance of the inflaton by the matter field. In addition, fine-tuning of the
parameters is relaxed as compared to the original racetrack models. In the case
of the racetrack inflation models coupled to the O'Raifeartaigh model, the
matter field is approximately decoupled from the inflationary dynamics. In all
of the above models the gravitino mass is larger than the Hubble scale during
inflation. The possibility of having the gravitino much lighter than the Hubble
scale is also investigated. It is very hard to construct models with light
gravitino in which the volume modulus dominates inflation. On the other hand,
models in which the inflationary dynamics is dominated by the matter field are
relatively simple and seem to be more natural.Comment: 40 pages, 13 figures, references added, typos corrected, version to
be publishe
Volume modulus inflation and a low scale of SUSY breaking
The relation between the Hubble constant and the scale of supersymmetry
breaking is investigated in models of inflation dominated by a string modulus.
Usually in this kind of models the gravitino mass is of the same order of
magnitude as the Hubble constant which is not desirable from the
phenomenological point of view. It is shown that slow-roll saddle point
inflation may be compatible with a low scale of supersymmetry breaking only if
some corrections to the lowest order Kahler potential are taken into account.
However, choosing an appropriate Kahler potential is not enough. There are also
conditions for the superpotential, and e.g. the popular racetrack
superpotential turns out to be not suitable. A model is proposed in which
slow-roll inflation and a light gravitino are compatible. It is based on a
superpotential with a triple gaugino condensation and the Kahler potential with
the leading string corrections. The problem of fine tuning and experimental
constraints are discussed for that model.Comment: 28 pages, 8 figures, comments and references added, minor change in
notation, version to be publishe
Inflation on an Open Racetrack
We present a variant of warped D-brane inflation by incorporating multiple
sets of holomorphically-embedded D7-branes involved in moduli stabilization
with extent into a warped throat. The resultant D3-brane motion depends on the
D7-brane configuration and the relative position of the D3-brane in these
backgrounds. The non-perturbative moduli stabilization superpotential takes the
racetrack form, but the additional D3-brane open string moduli dependence
provides more flexibilities in model building. For concreteness, we consider
D3-brane motion in the warped deformed conifold with the presence of multiple
D7-branes, and derive the scalar potential valid for the entire throat. By
explicit tuning of the microphysical parameters, we obtain inflationary
trajectories near an inflection point for various D7-brane configurations.
Moreover, the open racetrack potential admits approximate Minkowski vacua
before uplifting. We demonstrate with a concrete D-brane inflation model where
the Hubble scale during inflation can exceed the gravitino mass. Finally, the
multiple sets of D7-branes present in this open racetrack setup also provides a
mechanism to stabilize the D3-brane to metastable vacua in the intermediate
region of the warped throat.Comment: 29 pages, 15 figures, pre-print number and references adde
Yukawa unification in SO(10) with light sparticle spectrum
We investigate supersymmetric SO(10) GUT model with \mu<0. The requirements
of top-bottom-tau Yukawa unification, correct radiative electroweak symmetry
breaking and agreement with the present experimental data may be met when the
soft masses of scalars and gauginos are non-universal. We show how appropriate
non-universalities can easily be obtained in the SO(10) GUT broken to the
Standard Model. We discuss how values of BR(b-->s \gamma) and (g-2)_\mu
simultaneously in a good agreement with the experimental data can be achieved
in SO(10) model with \mu<0. In the region of the parameter space preferred by
our analysis there are two main mechanisms leading to the LSP relic abundance
consistent with the WMAP results. One is the co-annihilation with the stau and
the second is the resonant annihilation via exchange of the Z boson or the
light Higgs scalar. A very interesting feature of SO(10) models with negative
\mu is that they predict relatively light sparticle spectra. Even the heaviest
superpartners may easily have masses below 1.5 TeV in contrast to multi-TeV
particles typical for models with positive \mu.Comment: 23 pages, 5 figure
Constraining compressed supersymmetry using leptonic signatures
We study the impact of the multi-lepton searches at the LHC on supersymmetric
models with compressed mass spectra. For such models the acceptances of the
usual search strategies are significantly reduced due to requirement of large
effective mass and missing E_T. On the other hand, lepton searches do have much
lower thresholds for missing E_T and p_T of the final state objects. Therefore,
if a model with a compressed mass spectrum allows for multi-lepton final
states, one could derive constraints using multi-lepton searches. For a class
of simplified models we study the exclusion limits using ATLAS multi-lepton
search analyses for the final states containing 2-4 electrons or muons with a
total integrated luminosity of 1-2/fb at \sqrt{s}=7 TeV. We also modify those
analyses by imposing additional cuts, so that their sensitivity to compressed
supersymmetric models increase. Using the original and modified analyses, we
show that the exclusion limits can be competitive with jet plus missing E_T
searches, providing exclusion limits up to gluino masses of 1 TeV. We also
analyse the efficiencies for several classes of events coming from different
intermediate state particles. This allows us to assess exclusion limits in
similar class of models with different cross sections and branching ratios
without requiring a Monte Carlo simulation.Comment: 18 pages, 5 figure
Accidental Inflation in the Landscape
We study some aspects of fine tuning in inflationary scenarios within string
theory flux compactifications and, in particular, in models of accidental
inflation. We investigate the possibility that the apparent fine-tuning of the
low energy parameters of the theory needed to have inflation can be generically
obtained by scanning the values of the fluxes over the landscape. Furthermore,
we find that the existence of a landscape of eternal inflation in this model
provides us with a natural theory of initial conditions for the inflationary
period in our vacuum. We demonstrate how these two effects work in a small
corner of the landscape associated with the complex structure of the Calabi-Yau
manifold P^4_[1,1,1,6,9] by numerically investigating the flux vacua of a
reduced moduli space. This allows us to obtain the distribution of observable
parameters for inflation in this mini-landscape directly from the fluxes.Comment: 40 pages, 11 figure
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