7,500 research outputs found
Impact of Muon Anomalous Magnetic Moment on Supersymmetric Models
The recent measurement of a_\mu =\frac{g_\mu -2}{2} by the E821 Collaboration
at Brookhaven deviates from the quoted Standard Model (SM) central value
prediction by 2.6\sigma. The difference between SM theory and experiment may be
easily accounted for in a variety of particle physics models employing weak
scale supersymmetry (SUSY). Other supersymmetric models are distinctly
disfavored. We evaluate a_\mu for various supersymmetric models, including
minimal supergravity (mSUGRA), Yukawa unified SO(10) SUSY GUTs, models with
inverted mass hierarchies (IMH), models with non-universal gaugino masses,
gauge mediated SUSY breaking models (GMSB), anomaly-mediated SUSY breaking
models (AMSB) and models with gaugino mediated SUSY breaking (inoMSB). Models
with Yukawa coupling unification or multi-TeV first and second generation
scalars are disfavored by the a_\mu measurement.Comment: 25 page REVTEX file with 10 PS figures. Minor rewording, typos
corrected, references adde
The Reach of the Fermilab Tevatron and CERN LHC for Gaugino Mediated SUSY Breaking Models
In supersymmetric models with gaugino mediated SUSY breaking (inoMSB), it is
assumed that SUSY breaking on a hidden brane is communicated to the visible
brane via gauge superfields which propagate in the bulk. This leads to GUT
models where the common gaugino mass is the only soft SUSY breaking
term to receive contributions at tree level. To obtain a viable phenomenology,
it is assumed that the gaugino mass is induced at some scale beyond the
GUT scale, and that additional renormalization group running takes place
between and as in a SUSY GUT. We assume an SU(5) SUSY GUT above
the GUT scale, and compute the SUSY particle spectrum expected in models with
inoMSB. We use the Monte Carlo program ISAJET to simulate signals within the
inoMSB model, and compute the SUSY reach including cuts and triggers approriate
to Fermilab Tevatron and CERN LHC experiments. We find no reach for SUSY by the
Tevatron collider in the trilepton channel. %either with or without %identified
tau leptons. At the CERN LHC, values of (1160) GeV can be probed
with 10 (100) fb of integrated luminosity, corresponding to a reach in
terms of of 2150 (2500) GeV. The inoMSB model and mSUGRA can likely
only be differentiated at a linear collider with sufficient energy to
produce sleptons and charginos.Comment: 17 page revtex file with 9 PS figure
Probing Neutralino Resonance Annihilation via Indirect Detection of Dark Matter
The lightest neutralino of R-parity conserving supersymmetric models serves
as a compelling candidate to account for the presence of cold dark matter in
the universe. In the minimal supergravity (mSUGRA) model, a relic density can
be found in accord with recent WMAP data for large values of the parameter
, where neutralino annihilation in the early universe occurs via the
broad s-channel resonance of the pseudoscalar Higgs boson . We map out rates
for indirect detection of neutralinos via 1. detection of neutrinos arising
from neutralino annihilation in the core of the earth or sun and 2. detection
of gamma rays, antiprotons and positrons arising from neutralino annihilation
in the galactic halo. If indeed -resonance annihilation is the main sink for
neutralinos in the early universe, then signals may occur in the gamma ray,
antiproton and positron channels, while a signal in the neutrino channel would
likely be absent. This is in contrast to the hyperbolic branch/focus point
(HB/FP) region where {\it all} indirect detection signals are likely to occur,
and also in contrast to the stau co-annihilation region, where {\it none} of
the indirect signals are likely to occur.Comment: 12 pages including 4 eps figure
Hidden SUSY at the LHC: the light higgsino-world scenario and the role of a lepton collider
While the SUSY flavor, CP and gravitino problems seem to favor a very heavy
spectrum of matter scalars, fine-tuning in the electroweak sector prefers low
values of superpotential mass \mu. In the limit of low \mu, the two lightest
neutralinos and light chargino are higgsino-like. The light charginos and
neutralinos may have large production cross sections at LHC, but since they are
nearly mass degenerate, there is only small energy release in three-body
sparticle decays. Possible dilepton and trilepton signatures are difficult to
observe after mild cuts due to the very soft p_T spectrum of the final state
isolated leptons. Thus, the higgsino-world scenario can easily elude standard
SUSY searches at the LHC. It should motivate experimental searches to focus on
dimuon and trimuon production at the very lowest p_T(\mu) values possible. If
the neutralino relic abundance is enhanced via non-standard cosmological dark
matter production, then there exist excellent prospects for direct or indirect
detection of higgsino-like WIMPs. While the higgsino-world scenario may easily
hide from LHC SUSY searches, a linear e^+e^- collider or a muon collider
operating in the \sqrt{s}\sim 0.5-1 TeV range would be able to easily access
the chargino and neutralino pair production reactions.Comment: 20 pages including 12 .eps figure
Partial wave treatment of Supersymmetric Dark Matter in the presence of CP - violation
We present an improved partial wave analysis of the dominant LSP annihilation
channel to a fermion-antifermion pair which avoids the non-relativistic
expansion being therefore applicable near thresholds and poles. The method we
develop allows of contributions of any partial wave in the total angular
momentum J in contrast to partial wave analyses in terms of the orbital angular
momentum L of the initial state, which is usually truncated to p-waves, and
yields very accurate results. The method is formulated in such a way as to
allow easy handling of CP-violating phases residing in supersymmetric
parameters. We apply this refined partial wave technique in order to calculate
the neutralino relic density in the constrained MSSM (CMSSM) in the presence of
CP-violating terms occurring in the Higgs - mixing parameter \mu and trilinear
A coupling for large tanb. The inclusion of CP-violating phases in mu and A
does not upset significantly the picture and the annihilation of the LSP's to a
b b_bar, through Higgs exchange, is still the dominant mechanism in obtaining
cosmologically acceptable neutralino relic densities in regions far from the
stau-coannihilation and the `focus point'. Significant changes can occur if we
allow for phases in the gaugino masses and in particular the gluino mass.Comment: 23 pages LaTeX, 10 eps figures, version to appear in PR
Neutralino dark matter in mSUGRA/CMSSM with a 125 GeV light Higgs scalar
The minimal supergravity (mSUGRA or CMSSM) model is an oft-used framework for
exhibiting the properties of neutralino (WIMP) cold dark matter (CDM). However,
the recent evidence from Atlas and CMS on a light Higgs scalar with mass
m_h\simeq 125 GeV highly constrains the superparticle mass spectrum, which in
turn constrains the neutralino annihilation mechanisms in the early universe.
We find that stau and stop co-annihilation mechanisms -- already highly
stressed by the latest Atlas/CMS results on SUSY searches -- are nearly
eliminated if indeed the light Higgs scalar has mass m_h\simeq 125 GeV.
Furthermore, neutralino annihilation via the A-resonance is essentially ruled
out in mSUGRA so that it is exceedingly difficult to generate
thermally-produced neutralino-only dark matter at the measured abundance. The
remaining possibility lies in the focus-point region which now moves out to
m_0\sim 10-20 TeV range due to the required large trilinear soft SUSY breaking
term A_0. The remaining HB/FP region is more fine-tuned than before owing to
the typically large top squark masses. We present updated direct and indirect
detection rates for neutralino dark matter, and show that ton scale noble
liquid detectors will either discover mixed higgsino CDM or essentially rule
out thermally-produced neutralino-only CDM in the mSUGRA model.Comment: 17 pages including 9 .eps figure
WMAPing the Universe: Supersymmetry, Dark Matter, Dark Energy, Proton Decay and Collider Physics
In this review we discuss constraints on minimal supersymmetric models of
particle physics implied by the recent astrophysical observations of WMAP.
Although the prospects of detecting supersymmetry increase and 90 percent of
the available MSSM parameter space can safely be reached by the sensitivity of
future colliders, nevertheless we pay particular emphasis on discussing regions
of the appropriate phase diagrams, which -if realized - would imply that
detection of supersymmetry, at least in the context of minimal models, could be
out of colliders reach. We also discuss the importance of a precise
determination of the radiative corrections to the muon anomalous magnetic
moment, both theoretically and experimentally. Finally, we briefly commend upon
recent evidence, supported by observations, on a dark energy component of the
Universe, of as yet unknown origin, covering 73 percent of its energy content.Comment: Review paper, 69 pages Latex, 35 eps figures incorporate
Trileptons from Chargino-Neutralino Production at the CERN Large Hadron Collider
We study direct production of charginos and neutralinos at the CERN Large
Hadron Collider. We simulate all channels of chargino and neutralino production
using ISAJET 7.07. The best mode for observing such processes appears to be
pp\to\tw_1\tz_2\to 3\ell +\eslt. We evaluate signal expectations and
background levels, and suggest cuts to optimize the signal. The trilepton mode
should be viable provided m_{\tg}\alt 500-600~GeV; above this mass, the decay
modes \tz_2\to\tz_1 Z and \tz_2\to H_{\ell}\tz_1 become dominant, spoiling
the signal. In the first case, the leptonic branching fraction for decay is
small and additional background from is present, while in the second case,
the trilepton signal is essentially absent. For smaller values of ,
the trilepton signal should be visible above background, especially if
and m_{\tell}\ll m_{\tq}, in which case the leptonic
decays of \tz_2 are enhanced. Distributions in dilepton mass
can yield direct information on neutralino masses due to
the distribution cutoff at m_{\tz_2}-m_{\tz_1}. Other distributions that may
lead to an additional constraint amongst the chargino and neutralino masses are
also examined.Comment: preprint nos. FSU-HEP-940310 and UH-511-786-94, 13 pages (REVTEX)
plus 7 uuencoded figures attache
Target dark matter detection rates in models with a well-tempered neutralino
In the post-LEP2 era, and in light of recent measurements of the cosmic
abundance of cold dark matter (CDM) in the universe from WMAP, many
supersymmetric models tend to predict 1. an overabundance of CDM and 2.
pessimistically low rates for direct detection of neutralino dark matter.
However, in models with a ``well-tempered neutralino'', where the neutralino
composition is adjusted to give the measured abundance of CDM, the neutralino
is typically of the mixed bino-wino or mixed bino-higgsino state. Along with
the necessary enhancement to neutralino annihilation rates, these models tend
to give elevated direct detection scattering rates compared to predictions from
SUSY models with universal soft breaking terms. We present neutralino direct
detection cross sections from a variety of models containing a well-tempered
neutralino, and find cross section asymptotes with detectable scattering rates.
These asymptotic rates provide targets that various direct CDM detection
experiments should aim for. In contrast, in models where the neutralino mass
rather than its composition is varied to give the WMAP relic density via either
resonance annihilation or co-annihilation, the neutralino remains essentially
bino-like, and direct detection rates may be below the projected reaches of all
proposed experiments.Comment: 13 pages including 1 EPS figur
Sparticle mass spectra from SU(5) SUSY GUT models with Yukawa coupling unification
Supersymmetric grand unified models based on the gauge group SU(5) often
require in addition to gauge coupling unification, the unification of b-quark
and -lepton Yukawa couplings. We examine SU(5) SUSY GUT parameter space
under the condition of Yukawa coupling unification using 2-loop MSSM
RGEs including full 1-loop threshold effects. The Yukawa-unified solutions
break down into two classes. Solutions with low tan\beta ~3-11 are
characterized by gluino mass ~1-4 TeV and squark mass ~1-5 TeV. Many of these
solutions would be beyond LHC reach, although they contain a light Higgs scalar
with mass <123 GeV and so may be excluded should the LHC Higgs hint persist.
The second class of solutions occurs at large tan\beta ~35-60, and are a subset
of unified solutions. Constraining only unification to ~5%
favors a rather light gluino with mass ~0.5-2 TeV, which should ultimately be
accessible to LHC searches. While our unified solutions can be
consistent with a picture of neutralino-only cold dark matter, invoking
additional moduli or Peccei-Quinn superfields can allow for all of our
Yukawa-unified solutions to be consistent with the measured dark matter
abundance.Comment: 19 pages, 5 figures, 1 table, PDFLate
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