297 research outputs found
SUSY dark matter(s)
We review here the status of different dark matter candidates in the context
of supersymmetric models, in particular the neutralino as a realization of the
WIMP-mechanism and the gravitino. We give a summary of the recent bounds in
direct and indirect detection and also of the LHC searches relevant for the
dark matter question. We discuss also the implications of the Higgs discovery
for the supersymmetric dark matter models and give the prospects for the future
years.Comment: 16 pages, 3 figure
Spinor-Vector Duality in Heterotic String Orbifolds
The three generation heterotic-string models in the free fermionic
formulation are among the most realistic string vacua constructed to date,
which motivated their detailed investigation. The classification of free
fermion heterotic string vacua has revealed a duality under the exchange of
spinor and vector representations of the SO(10) GUT symmetry over the space of
models. We demonstrate the existence of the spinor-vector duality using
orbifold techniques, and elaborate on the relation of these vacua to free
fermionic models.Comment: 20 pages. v2 minor corrections. Version to appear on JHEP. v3
misprints correcte
Singlet-doublet Higgs mixing and its implications on the Higgs mass in the PQ-NMSSM
We examine the implications of singlet-doublet Higgs mixing on the properties
of a Standard Model (SM)-like Higgs boson within the Peccei-Quinn invariant
extension of the NMSSM (PQ-NMSSM). The SM singlet added to the Higgs sector
connects the PQ and visible sectors through a PQ-invariant non-renormalizable
K\"ahler potential term, making the model free from the tadpole and domain-wall
problems. For the case that the lightest Higgs boson is dominated by the
singlet scalar, the Higgs mixing increases the mass of a SM-like Higgs boson
while reducing its signal rate at collider experiments compared to the SM case.
The Higgs mixing is important also in the region of parameter space where the
NMSSM contribution to the Higgs mass is small, but its size is limited by the
experimental constraints on the singlet-like Higgs boson and on the lightest
neutralino constituted mainly by the singlino whose Majorana mass term is
forbidden by the PQ symmetry. Nonetheless the Higgs mixing can increase the
SM-like Higgs boson mass by a few GeV or more even when the Higgs signal rate
is close to the SM prediction, and thus may be crucial for achieving a 125 GeV
Higgs mass, as hinted by the recent ATLAS and CMS data. Such an effect can
reduce the role of stop mixing.Comment: 26 pages, 3 figures; published in JHE
Thermal production of axino Dark Matter
We reconsider thermal production of axinos in the early universe, adding: a)
missed terms in the axino interaction; b) production via gluon decays
kinematically allowed by thermal masses; c) a precise modeling of reheating. We
find an axino abunance a few times larger than previous computations.Comment: 6 pages, 2 figures. Final version, to appear on JHE
Sparticle Spectrum of Large Volume Compactification
We examine the large volume compactification of Type IIB string theory or its
F theory limit and the associated supersymmetry breakdown and soft terms. It is
crucial to incorporate the loop-induced moduli mixing, originating from
radiative corrections to the Kahler potential. We show that in the presence of
moduli mixing, soft scalar masses generically receive a D-term contribution of
the order of the gravitino mass m_{3/2} when the visible sector cycle is
stabilized by the D-term potential of an anomalous U(1) gauge symmetry, while
the moduli-mediated gaugino masses and A-parameters tend to be of the order of
m_{3/2}/8pi^2. It is noticed also that a too large moduli mixing can
destabilize the large volume solution by making it a saddle point.Comment: 29 page
Gravitino dark matter in the constrained next-to-minimal supersymmetric standard model with neutralino next-to-lightest superpartner
The viability of a possible cosmological scenario is investigated. The
theoretical framework is the constrained next-to-minimal supersymmetric
standard model (cNMSSM), with a gravitino playing the role of the lightest
supersymmetric particle (LSP) and a neutralino acting as the next-to-lightest
supersymmetric particle (NLSP). All the necessary constraints from colliders
and cosmology have been taken into account. For gravitino we have considered
the two usual production mechanisms, namely out-of equillibrium decay from the
NLSP, and scattering processes from the thermal bath. The maximum allowed
reheating temperature after inflation, as well as the maximum allowed gravitino
mass are determined.Comment: 20 pages, 5 figure
Discrete R-symmetries and Anomaly Universality in Heterotic Orbifolds
We study discrete R-symmetries, which appear in 4D low energy effective field
theory derived from hetetoric orbifold models. We derive the R-symmetries
directly from geometrical symmetries of orbifolds. In particular, we obtain the
corresponding R-charges by requiring that the couplings be invariant under
these symmetries. This allows for a more general treatment than the explicit
computations of correlation functions made previously by the authors, including
models with discrete Wilson lines, and orbifold symmetries beyond
plane-by-plane rotational invariance. Surprisingly, for the cases covered by
earlier explicit computations, the R-charges differ from the previous result.
We study the anomalies associated with these R-symmetries, and comment on the
results.Comment: 21 pages, 2 figures. Minor changes, typos corrected. Matches JHEP
published versio
R-parity violating resonant stop production at the Large Hadron Collider
We have investigated the resonant production of a stop at the Large Hadron
Collider, driven by baryon number violating interactions in supersymmetry. We
work in the framework of minimal supergravity models with the lightest
neutralino being the lightest supersymmetric particle which decays within the
detector. We look at various dilepton and trilepton final states, with or
without b-tags. A detailed background simulation is performed, and all possible
decay modes of the lighter stop are taken into account. We find that higher
stop masses are sometimes easier to probe, through the decay of the stop into
the third or fourth neutralino and their subsequent cascades. We also comment
on the detectability of such signals during the 7 TeV run, where, as expected,
only relatively light stops can be probed. Our conclusion is that the resonant
process may be probed, at both 10 and 14 TeV, with the R-parity violating
coupling {\lambda}"_{312} as low as 0.05, for a stop mass of about 1 TeV. The
possibility of distinguishing between resonant stop production and
pair-production is also discussed.Comment: 20 pages, 4 figures, 6 tables; Version accepted by JHE
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
Supersymmetric Vacua in Random Supergravity
We determine the spectrum of scalar masses in a supersymmetric vacuum of a
general N=1 supergravity theory, with the Kahler potential and superpotential
taken to be random functions of N complex scalar fields. We derive a random
matrix model for the Hessian matrix and compute the eigenvalue spectrum.
Tachyons consistent with the Breitenlohner-Freedman bound are generically
present, and although these tachyons cannot destabilize the supersymmetric
vacuum, they do influence the likelihood of the existence of an `uplift' to a
metastable vacuum with positive cosmological constant. We show that the
probability that a supersymmetric AdS vacuum has no tachyons is formally
equivalent to the probability of a large fluctuation of the smallest eigenvalue
of a certain real Wishart matrix. For normally-distributed matrix entries and
any N, this probability is given exactly by P = exp(-2N^2|W|^2/m_{susy}^2),
with W denoting the superpotential and m_{susy} the supersymmetric mass scale;
for more general distributions of the entries, our result is accurate when N >>
1. We conclude that for |W| \gtrsim m_{susy}/N, tachyonic instabilities are
ubiquitous in configurations obtained by uplifting supersymmetric vacua.Comment: 26 pages, 6 figure
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