195 research outputs found
Spontaneous CP Violation in Non-Minimal Supersymmetric Models
We study the possibilities of spontaneous CP violation in the Next-to-Minimal
Supersymmetric Standard Model with an extra singlet tadpole term in the scalar
potential. We calculate the Higgs boson masses and couplings with radiative
corrections including dominant two loop terms. We show that it is possible to
satisfy the LEP constraints on the Higgs boson spectrum with non-trivial
spontaneous CP violating phases. We also show that these phases could account
for the observed value of epsilonK.Comment: 21 pages, 7 Figures in Encapsulated Postscrip
Boson-boson scattering and Higgs production at the LHC from a six fermion point of view: four jets + l processes at \O(\alpha_{em}^6)
Boson-boson scattering and Higgs production in boson-boson fusion hold the
key to electroweak symmetry breaking. In order to analyze these essential
features of the Standard Model we have performed a partonic level study of all
processes at the LHC using the exact matrix
elements at \O(\alpha_{em}^6) provided by \Phase, a new MC generator. These
processes include also three boson production and the purely electroweak
contribution to \toptop production as well as all irreducible backgrounds.
Kinematical cuts have been studied in order to enhance the VV scattering signal
over background. \Phase has been compared with different Monte Carlo's showing
that a complete calculation is necessary for a correct description of the
process.Comment: 26 pages, 19 figure
Collider phenomenology of Higgs bosons in Left-Right symmetric Randall-Sundrum models
We investigate the collider phenomenology of a left-right symmetric
Randall-Sundrum model with fermions and gauge bosons in the bulk. We find that
the model is allowed by precision electroweak data as long as the ratio of the
(unwarped) Higgs vev to the curvature scale is . In that region
there can be substantial modifications to the Higgs properties. In particular,
the couplings to and are reduced, the coupling to gluons is enhanced,
and the coupling to can receive shifts in either direction. The
Higgs mass bound from LEP II data can potentially be relaxed to GeV.Comment: 21 pages, 11 figures. Minor changes to numerics; replaced with
published versio
Z-Decays to b Quarks and the Higgs Boson Mass
A model independent analysis of the most recent averages of precision
electroweak data from LEP and SLD finds a 3 deviation of the parameter
from the Standard Model prediction.
The fitted value of shows a strong dependence on the inclusion or
exclusion of b quark data, and the Standard Model fits have poor confidence
levels of a few percent when the latter are included.
The good fits obtained to lepton data, c quark data and the directly measured
top quark mass, give GeV and indicate that the
Higgs boson mass is most likely less than 200 GeV.Comment: 15 pages, 3 figures, 6 table
Constraints on Supersymmetric Flavour Models from b->s gamma
We consider the effects of departures from minimal flavour violations (MFV)
in the context of CMSSM-like theories. Second and third generation off-diagonal
elements in the Yukawa, sfermion, and trilinear mass matrices are taken to be
non-zero at the GUT scale. These are run down together with MSSM parameters to
the electroweak scale. We apply constraints from fermion masses and CKM matrix
elements to limit the range of the new free parameters of the model. We
determine the effect of the departure from MFV on the branching ratio of b->s
gamma. We find that only when the expansion parameter in the down-squark sector
is relatively large there is a noticeable effect, which tends to relax the
lower limit from b->s gamma on the universal gaugino mass. We also find that
the expansion parameter associated with the slepton sector needs to be smaller
than the corresponding parameter in the down-squark sector in order to be
compliant with the bound imposed by the branching ratio of tau-> mu gamma.Comment: Comments: 43 pages, 14 figures. Version accepted for publication:
typos corrected, rewritten for better understanding and references adde
Phenomenology of GUT-less Supersymmetry Breaking
We study models in which supersymmetry breaking appears at an intermediate
scale, M_{in}, below the GUT scale. We assume that the soft
supersymmetry-breaking parameters of the MSSM are universal at M_{in}, and
analyze the morphology of the constraints from cosmology and collider
experiments on the allowed regions of parameter space as M_{in} is reduced from
the GUT scale. We present separate analyses of the (m_{1/2},m_0) planes for
tan(beta)=10 and tan(beta)=50, as well as a discussion of non-zero trilinear
couplings, A_0. Specific scenarios where the gaugino and scalar masses appear
to be universal below the GUT scale have been found in mirage-mediation models,
which we also address here. We demand that the lightest neutralino be the LSP,
and that the relic neutralino density not conflict with measurements by WMAP
and other observations. At moderate values of M_{in}, we find that the allowed
regions of the (m_{1/2},m_0) plane are squeezed by the requirements of
electroweak symmetry breaking and that the lightest neutralino be the LSP,
whereas the constraint on the relic density is less severe. At very low M_{in},
the electroweak vacuum conditions become the dominant constraint, and a
secondary source of astrophysical cold dark matter would be necessary to
explain the measured relic density for nearly all values of the soft
SUSY-breaking parameters and tan(beta). We calculate the neutralino-nucleon
cross sections for viable scenarios and compare them with the present and
projected limits from direct dark matter searches.Comment: 35 pages, 9 figures; typos corrected, references adde
Markov Chain Monte Carlo Exploration of Minimal Supergravity with Implications for Dark Matter
We explore the full parameter space of Minimal Supergravity (mSUGRA),
allowing all four continuous parameters (the scalar mass m_0, the gaugino mass
m_1/2, the trilinear coupling A_0, and the ratio of Higgs vacuum expectation
values tan beta) to vary freely. We apply current accelerator constraints on
sparticle and Higgs masses, and on the b -> s gamma branching ratio, and
discuss the impact of the constraints on g_mu-2. To study dark matter, we apply
the WMAP constraint on the cold dark matter density. We develop Markov Chain
Monte Carlo (MCMC) techniques to explore the parameter regions consistent with
WMAP, finding them to be considerably superior to previously used methods for
exploring supersymmetric parameter spaces. Finally, we study the reach of
current and future direct detection experiments in light of the WMAP
constraint.Comment: 16 pages, 4 figure
Graviton production with 2 jets at the LHC in large extra dimensions
We study Kaluza-Klein (KK) graviton production in the large extra dimensions
model via 2 jets plus missing transverse momentum signatures at the LHC. We
make predictions for both the signal and the dominant Zjj and Wjj backgrounds,
where we introduce missing P_T-dependent jet selection cuts that ensure the
smallness of the 2-jet rate over the 1-jet rate. With the same jet selection
cuts, the distributions of the two jets and their correlation with the missing
transverse momentum provide additional evidence for the production of an
invisible massive object.Comment: 8 pages, 10 figures, 1 table; Version to be printed in JHE
Hadronic Contributions to the Photon Vacuum Polarization and their Role in Precision Physics
I review recent evaluations of the hadronic contribution to the shift in the
fine structure constant and to the anomalous magnetic moment of the muon.
Substantial progress in a precise determination of these important observables
is a consequence of substantially improved total cross section measurement by
the CMD-2 and BES II collaborations and an improved theoretical understanding.
Prospects for further possible progress is discussed.Comment: 17 pages 7 figures 2 tables, update: incl. CMD-2 data, reference
Neutralino, axion and axino cold dark matter in minimal, hypercharged and gaugino AMSB
Supersymmetric models based on anomaly-mediated SUSY breaking (AMSB)
generally give rise to a neutral wino as a WIMP cold dark matter (CDM)
candidate, whose thermal abundance is well below measured values. Here, we
investigate four scenarios to reconcile AMSB dark matter with the measured
abundance: 1. non-thermal wino production due to decays of scalar fields ({\it
e.g} moduli), 2. non-thermal wino production due to decays of gravitinos, 3.
non-thermal wino production due to heavy axino decays, and 4. the case of an
axino LSP, where the bulk of CDM is made up of axions and thermally produced
axinos. In cases 1 and 2, we expect wino CDM to constitute the entire measured
DM abundance, and we investigate wino-like WIMP direct and indirect detection
rates. Wino direct detection rates can be large, and more importantly, are
bounded from below, so that ton-scale noble liquid detectors should access all
of parameter space for m_{\tz_1}\alt 500 GeV. Indirect wino detection rates via
neutrino telescopes and space-based cosmic ray detectors can also be large. In
case 3, the DM would consist of an axion plus wino admixture, whose exact
proportions are very model dependent. In this case, it is possible that both an
axion and a wino-like WIMP could be detected experimentally. In case 4., we
calculate the re-heat temperature of the universe after inflation. In this
case, no direct or indirect WIMP signals should be seen, although direct
detection of relic axions may be possible. For each DM scenario, we show
results for the minimal AMSB model, as well as for the hypercharged and gaugino
AMSB models.Comment: 29 pages including 13 figure
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