4,175 research outputs found

### The Higgs Boson Mass as a Probe of the Minimal Supersymmetric Standard Model

Recently, the LEP collaborations have reported a lower bound on a Standard
Model-like Higgs boson of order 89 GeV. We discuss the implications of this
bound for the minimal supersymmetric extension of the Standard Model (MSSM). In
particular, we show that the lower bound on $\tan\beta$, which can be obtained
from the presently allowed Higgs boson mass value, becomes stronger than the
one set by the requirement of perturbative consistency of the theory up to
scales of order $M_{GUT}$ (associated with the infrared fixed-point solution of
the top quark Yukawa coupling) in a large fraction of the allowed parameter
space. The potentiality of future LEP2 searches to further probe the MSSM
parameter space is also discussed.Comment: 15 pages, 5 figures, LateX, psfi

### A 125 GeV SM-like Higgs in the MSSM and the $\gamma \gamma$ rate

We consider the possibility of a Standard Model (SM)-like Higgs in the
context of the Minimal Supersymmetric Standard Model (MSSM), with a mass of
about 125 GeV and with a production times decay rate into two photons which is
similar or somewhat larger than the SM one. The relatively large value of the
SM-like Higgs mass demands stops in the several hundred GeV mass range with
somewhat large mixing, or a large hierarchy between the two stop masses in the
case that one of the two stops is light. We find that, in general, if the
heaviest stop mass is smaller than a few TeV, the rate of gluon fusion
production of Higgs bosons decaying into two photons tends to be somewhat
suppressed with respect to the SM one in this region of parameters. However, we
show that an enhancement of the photon decay rate may be obtained for light
third generation sleptons with large mixing, which can be naturally obtained
for large values of $\tan\beta$ and sizable values of the Higgsino mass
parameter.Comment: 14 pages, 4 figures. Corrected small typos and added reference

### CPsuperH2.3: an Updated Tool for Phenomenology in the MSSM with Explicit CP Violation

We describe the Fortran code CPsuperH2.3, which incorporates the following
updates compared with its predecessor CPsuperH2.0. It implements improved
calculations of the Higgs-boson masses and mixing including stau contributions
and finite threshold effects on the tau-lepton Yukawa coupling. It incorporates
the LEP limits on the processes e^+ e^- to H_i Z, H_i H_j and the CMS limits on
H_i to tau^+ tau^- obtained from 4.6/fb of data at a centre-of-mass energy of 7
TeV. It also includes the decay mode H_i to Z gamma and the Schiff-moment
contributions to the electric dipole moments of Mercury and Radium225, with
several calculational options for the case of Mercury. These additions make
CPsuperH2.3 a suitable tool for analyzing possible CP-violating effects in the
MSSM in the era of the LHC and a new generation of EDM experimentsComment: 31 pages, 10 eps figures, 7 tables; H to Z gamma and SM BRs included;
To appear in CPC; Typos in Eq.(A.2) corrected;The program may be obtained
from http://www.hep.man.ac.uk/u/jslee/CPsuperH.html, or by contacting the
first author at [email protected]; A comment added after Eq.(15) and a typo in
Eq.(A.4) correcte

### Do electroweak precision data and Higgs-mass constraints rule out a scalar bottom quark with mass of O(5 GeV)?

We investigate the phenomenological implications of a light scalar bottom
quark, with a mass of about the bottom quark mass, within the minimal
supersymmetric standard model. The study of such a scenario is of theoretical
interest, since, depending on their production and decay modes, light sbottoms
may have escaped experimental detection up to now and, in addition, may
naturally appear for large values of \tan\beta. In this article we show that
such a light sbottom cannot be ruled out by the constraints from the
electroweak precision data and the present bound on the lightest CP-even Higgs
boson mass at LEP. It is inferred that a light sbottom scenario requires in
general a relatively light scalar top quark whose mass is typically about the
top-quark mass. It is also shown that under these conditions the lightest
CP-even Higgs boson decays predominantly into scalar bottom quarks in most of
the parameter space and that its mass is restricted to m_h ~< 123 GeV.Comment: 7 pages, 2 figures, LateX. Discussion about fine tuning and
low-energy experiments enlarged. Version to appear in Phys. Rev. Let

### The complementarity of LEP, the Tevatron and the LHC in the search for a light MSSM Higgs boson

We study the properties of the Higgs boson sector in the MSSM, putting
special emphasis on radiative effects which can affect the discovery potential
of the LHC, Tevatron and/or LEP colliders. We concentrate on the V b b-bar
channel, with V=Z or W, and on the channels with diphoton final states, which
are the dominant ones for the search for a light Standard Model Higgs boson at
LEP/Tevatron and LHC, respectively. By analyzing the regions of parameter space
for which the searches in at least one of these colliders can be particularly
difficult, we demonstrate the complementarity of these three colliders in the
search for a light Higgs boson which couples in a relevant way to the W and Z
gauge bosons (and hence plays a relevant role in the mechanism of electroweak
symmetry breaking).Comment: 35 pages, including 11 Postscript figures, using JHEP.cl

### Light Stop Searches at the LHC in Events with One Hard Photon or Jet and Missing Energy

Low energy supersymmetric models provide a solution to the hierarchy problem
and also have the necessary ingredients to solve two of the most outstanding
issues in cosmology: the origin of the baryon asymmetry and the source of dark
matter. In the MSSM, weak scale generation of the baryon asymmetry may be
achieved in the presence of light stops, with masses lower than about 130 GeV.
Moreover, the proper dark matter density may be obtained in the stop-neutralino
co-annihilation region, where the stop-neutralino mass difference is smaller
than a few tens of GeV. Searches for scalar top quarks (stops) in pair
production processes at the Tevatron and at the Large Hadron Collider (LHC)
become very challenging in this region of parameters. At the LHC, however,
light stops proceeding from the decay of gluino pairs may be identified,
provided the gluino mass is smaller than about 900 GeV. In this article we
propose an alternative method for stop searches in the co-annihilation region,
based on the search for these particles in events with missing energy plus one
hard photon or jet. We show that this method is quite efficient and, when
complemented with ongoing Tevatron searches, allows to probe stop masses up to
about 160 GeV, fully probing the region of parameters consistent with
electroweak baryogenesis in the MSSM.Comment: 17 pages, 6 figure

### Constraints on split-UED from Electroweak Precision Tests

We present strongly improved electroweak precision constraints on the
split-UED model. We find that the dominating effect arises from contributions
to the muon decay rate by the exchange of even-numbered W-boson Kaluza-Klein
modes at tree-level, which so far have not been discussed in the context of UED
models. The constraints on the split-UED parameter space are translated into
bounds on the mass difference of the first Kaluza-Klein mode of fermions and
the lightest Kaluza-Klein mode, which will be tested is the LHC.Comment: 4 pages, 2 figure

### Isolated leptons from heavy flavor decays: Theory and data

Events with isolated leptons play a prominent role in signatures of new
physics phenomena at high energy collider physics facilities. In earlier
publications, we examine the standard model contribution to isolated lepton
production from bottom and charm mesons and baryons through their semileptonic
decays (b, c -> l + X), showing that this source can overwhelm the effects of
other standard model processes in some kinematic domains. In this paper, we
show that we obtain good agreement with recent Tevatron collider data, both
validating our simulations and showing that we underestimate the magnitude of
the heavy-flavor contribution to the isolated lepton yields. We also show that
the isolation requirement acts as a narrow bandpass filter on the momentum of
the isolated lepton, and we illustrate the effect of this filter on the
background to Higgs boson observation in the dilepton mode. We introduce and
justify a new rule of thumb: isolated electrons and muons from heavy flavor
decay are produced with roughly the same distributions as b and c quarks, but
with 1/200 times the rates of b and c production, respectively.Comment: 12 pg, revtex, 5 fig, corrected typo

### Photon Signatures for Low Energy Supersymmetry Breaking and Broken R-parity

The possible phenomenological consequences of R-parity violating interactions
in the framework of low energy supersymmetry breaking are studied. It is
pointed out that even very weak R-parity violation would completely overshadow
one of the basic signatures of low energy supersymmetry breaking models, that
is, the decay of the next to lightest supersymmetric particle into a photon
(lepton) and missing energy. Thus, the observation of these decays would put
very strong limits on R-parity violating couplings. Vice-versa, if R-parity
violation is established experimentally, before a detailed knowledge of the
spectrum is obtained, it will be very difficult to distinguish gravity mediated
from low energy gauge mediated supersymmetry breaking. Those conclusions are
very model independent. We also comment on the possibility of mixing between
charged and neutral leptons with charginos and neutralinos, respectively, and
its phenomenological consequences for the photon (lepton) signatures, in
scenarios where this mixing is generated by the presence of bilinear or
trilinear R-parity violating terms in the superpotential.Comment: 12 pages, Late

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