399 research outputs found
Supersymmetric Benchmarks with Non-Universal Scalar Masses or Gravitino Dark Matter
We propose and examine a new set of benchmark supersymmetric scenarios, some
of which have non-universal Higgs scalar masses (NUHM) and others have
gravitino dark matter (GDM). The scalar masses in these models are either
considerably larger or smaller than the narrow range allowed for the same
gaugino mass m_{1/2} in the constrained MSSM (CMSSM) with universal scalar
masses m_0 and neutralino dark matter. The NUHM and GDM models with larger m_0
may have large branching ratios for Higgs and/or production in the cascade
decays of heavier sparticles, whose detection we discuss. The phenomenology of
the GDM models depends on the nature of the next-to-lightest supersymmetric
particle (NLSP), which has a lifetime exceeding 10^4 seconds in the proposed
benchmark scenarios. In one GDM scenario the NLSP is the lightest neutralino
\chi, and the supersymmetric collider signatures are similar to those in
previous CMSSM benchmarks, but with a distinctive spectrum. In the other GDM
scenarios based on minimal supergravity (mSUGRA), the NLSP is the lighter stau
slepton {\tilde \tau}_1, with a lifetime between ~ 10^4 and 3 X 10^6 seconds.
Every supersymmetric cascade would end in a {\tilde \tau}_1, which would have a
distinctive time-of-flight signature. Slow-moving {\tilde \tau}_1's might be
trapped in a collider detector or outside it, and the preferred detection
strategy would depend on the {\tilde \tau}_1 lifetime. We discuss the extent to
which these mSUGRA GDM scenarios could be distinguished from gauge-mediated
models.Comment: 52 pages LaTeX, 13 figure
Analytic Results for Virtual QCD Corrections to Higgs Production and Decay
We consider the production of a Higgs boson via gluon-fusion and its decay
into two photons. We compute the NLO virtual QCD corrections to these processes
in a general framework in which the coupling of the Higgs boson to the external
particles is mediated by a colored fermion and a colored scalar. We present
compact analytic results for these two-loop corrections that are expressed in
terms of Harmonic Polylogarithms. The expansion of these corrections in the low
and high Higgs mass regimes, as well as the expression of the new Master
Integrals which appear in the reduction of the two-loop amplitudes, are also
provided. For the fermionic contribution, we provide an independent check of
the results already present in the literature concerning the Higgs boson and
the production and decay of a pseudoscalar particle.Comment: 19 pages, 3 figures, version accepted by JHE
Slepton Oscillation at Large Hadron Collider
Measurement of Lepton-Flavor Violation (LFV) in the minimal SUSY Standard
Model (MSSM) at Large Hadron Collider (LHC) is studied based on a realistic
simulation. We consider the LFV decay of the second-lightest neutralino,
, in the case
where the flavor mixing exists in the right-handed sleptons. We scan the
parameter space of the minimal supergravity model (MSUGRA) and a more generic
model in which we take the Higgsino mass as a free parameter. We find
that the possibility of observing LFV at LHC is higher if is smaller than
the MSUGRA prediction; the LFV search at LHC can cover the parameter range
where the decay can be suppressed by the cancellation among
the diagrams for this case.Comment: 29 pages, 10 figure
A Detailed Study of the Gluino Decay into the Third Generation Squarks at the CERN LHC
In supersymmetric models a gluino can decay into tb\tilde{\chi}^{\pm}_1
through a stop or a sbottom. The decay chain produces an edge structure in the
m_{tb} distribution. Monte Carlo simulation studies show that the end point and
the edge height would be measured at the CERN LHC by using a sideband
subtraction technique. The stop and sbottom masses as well as their decay
branching ratios are constrained by the measurement. We study interpretations
of the measurement in the minimal supergravity model. We also study the gluino
decay into tb and \tilde{\chi}^{\pm}_2 as well as the influence of the stop
left-right mixing on the m_{bb} distribution of the tagged events.Comment: revtex, 20 pages in PRD format, 35 eps file
Measurement of SUSY masses via cascade decays for SPS 1a
If R-parity conserving supersymmetry exists below the TeV-scale, new particles will be produced and decay in cascades at the LHC. The lightest supersymmetric particle will escape the detectors, thereby complicating the full reconstruction of the decay chains. In this paper we expand on existing methods for determining the masses of the particles in the cascade from endpoints of kinematical distributions. We perform scans in the mSUGRA parameter space to delimit the region where this method is applicable. From the examination of theoretical distributions for a wide selection of mass scenarios it is found that caution must be exerted when equating the theoretical endpoints with the experimentally obtainable ones. We provide analytic formulae for the masses in terms of the endpoints most readily available. Complications due to the composite nature of the endpoint expressions are discussed in relation to the detailed analysis of two points on the SPS 1a line. Finally we demonstrate how a Linear Collider measurement can improve dramatically on the precision of the masses obtained
A New Parametrization of the Seesaw Mechanism and Applications in Supersymmetric Models
We present a new parametrization of the minimal seesaw model, expressing the
heavy-singlet neutrino Dirac Yukawa couplings and Majorana
masses in terms of effective light-neutrino observables and an
auxiliary Hermitian matrix In the minimal supersymmetric version of the
seesaw model, the latter can be related directly to other low-energy
observables, including processes that violate charged lepton flavour and CP.
This parametrization enables one to respect the stringent constraints on
muon-number violation while studying the possible ranges for other observables
by scanning over the allowed parameter space of the model. Conversely, if any
of the lepton-flavour-violating process is observed, this measurement can be
used directly to constrain and As applications, we
study flavour-violating decays and the electric dipole moments of
leptons in the minimal supersymmetric seesaw model.Comment: Important references adde
Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation
The transverse momentum distribution is computed for inclusive Higgs
boson production at the energy of the CERN Large Hadron Collider. We focus on
the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and
incorporate contributions from the quark-gluon and quark-antiquark channels.
Using an impact-parameter -space formalism, we include all-orders
resummation of large logarithms associated with emission of soft gluons. Our
resummed results merge smoothly at large with the fixed-order
expectations in perturbative quantum chromodynamics, as they should, with no
need for a matching procedure. They show a high degree of stability with
respect to variation of parameters associated with the non-perturbative input
at low . We provide distributions for Higgs boson masses
from to 200 GeV. The average transverse momentum at zero rapidity
grows approximately linearly with mass of the Higgs boson over the range ~GeV. We provide analogous results
for boson production, for which we compute GeV. The
harder transverse momentum distribution for the Higgs boson arises because
there is more soft gluon radiation in Higgs boson production than in
production.Comment: 42 pages, latex, 26 figures. All figures replaced. Some changes in
wording. Published in Phys. Rev. D67, 034026 (2003
Electroweak Symmetry Breaking via UV Insensitive Anomaly Mediation
Anomaly mediation solves the supersymmetric flavor and CP problems. This is
because the superconformal anomaly dictates that supersymmetry breaking is
transmitted through nearly flavor-blind infrared physics that is highly
predictive and UV insensitive. Slepton mass squareds, however, are predicted to
be negative. This can be solved by adding D-terms for U(1)_Y and U(1)_{B-L}
while retaining the UV insensitivity. In this paper we consider electroweak
symmetry breaking via UV insensitive anomaly mediation in several models. For
the MSSM we find a stable vacuum when tanbeta < 1, but in this region the top
Yukawa coupling blows up only slightly above the supersymmetry breaking scale.
For the NMSSM, we find a stable electroweak breaking vacuum but with a chargino
that is too light. Replacing the cubic singlet term in the NMSSM superpotential
with a term linear in the singlet we find a stable vacuum and viable spectrum.
Most of the parameter region with correct vacua requires a large superpotential
coupling, precisely what is expected in the ``Fat Higgs'' model in which the
superpotential is generated dynamically. We have therefore found the first
viable UV complete, UV insensitive supersymmetry breaking model that solves the
flavor and CP problems automatically: the Fat Higgs model with UV insensitive
anomaly mediation. Moreover, the cosmological gravitino problem is naturally
solved, opening up the possibility of realistic thermal leptogenesis.Comment: 27 pages, 3 figures, 1 tabl
Higgs Boson Decay into Hadronic Jets
The remarkable agreement of electroweak data with standard model (SM)
predictions motivates the study of extensions of the SM in which the Higgs
boson is light and couples in a standard way to the weak gauge bosons.
Postulated new light particles should have small couplings to the gauge bosons.
Within this context it is natural to assume that the branching fractions of the
light SM-like Higgs boson mimic those in the standard model. This assumption
may be unwarranted, however, if there are non-standard light particles coupled
weakly to the gauge bosons but strongly to the Higgs field. In particular, the
Higgs boson may effectively decay into hadronic jets, possibly without
important bottom or charm flavor content. As an example, we present a simple
extension of the SM, in which the predominant decay of the Higgs boson occurs
into a pair of light bottom squarks that, in turn, manifest themselves as
hadronic jets. Discovery of the Higgs boson remains possible at an
electron-positron linear collider, but prospects at hadron colliders are
diminished substantially.Comment: 30 pages, 7 figure
Tau Decays to Mu + Eta in Supersymmetric Models
The existence of large \nu_\mu-\nu_\tau mixing suggests the likelihood of
large smuon-stau mixing in supersymmetric models, leading to \mu and \tau
number violation. In addition to interesting signatures in slepton and
neutralino production and decay, this will lead to rare \tau decays, such as
\tau --> mu \gamma. Recently, it has been pointed out that the \tau --> 3\mu
branching ratio could be substantial in the large \tan\beta region of parameter
space, due to an induced \mu-\tau-Higgs vertex. In this paper, another
signature, \tau --> \mu \eta is considered. In the large \tan\beta region, it
is shown that the branching ratio of \tau --> \mu \eta is 8.4 times the
branching ratio of \tau --> 3\mu, independent of any unknown parameters, and it
will thus give the most stringent bound on Higgs-mediated lepton flavor
violation, and may provide its first signature. In the other regions of
parameter space, where \tau --> \mu \gamma is the most prominent decay, the
branching ratio for \tau --> \mu \eta is always substantially lower.Comment: 5 pages, 2 figures. Paragraph about CLEO measurements added. Version
to appear in PR
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