5,827 research outputs found
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
Testing the gaugino AMSB model at the Tevatron via slepton pair production
Gaugino AMSB models-- wherein scalar and trilinear soft SUSY breaking terms
are suppressed at the GUT scale while gaugino masses adopt the AMSB form--
yield a characteristic SUSY particle mass spectrum with light sleptons along
with a nearly degenerate wino-like lightest neutralino and quasi-stable
chargino. The left- sleptons and sneutrinos can be pair produced at
sufficiently high rates to yield observable signals at the Fermilab Tevatron.
We calculate the rate for isolated single and dilepton plus missing energy
signals, along with the presence of one or two highly ionizing chargino tracks.
We find that Tevatron experiments should be able to probe gravitino masses into
the ~55 TeV range for inoAMSB models, which corresponds to a reach in gluino
mass of over 1100 GeV.Comment: 14 pages including 6 .eps figure
Testing Yukawa-unified SUSY during year 1 of LHC: the role of multiple b-jets, dileptons and missing E_T
We examine the prospects for testing SO(10) Yukawa-unified supersymmetric
models during the first year of LHC running at \sqrt{s}= 7 TeV, assuming
integrated luminosity values of 0.1 to 1 fb^-1. We consider two cases: the
Higgs splitting (HS) and the D-term splitting (DR3) models. Each generically
predicts light gluinos and heavy squarks, with an inverted scalar mass
hierarchy. We hence expect large rates for gluino pair production followed by
decays to final states with large b-jet multiplicity. For 0.2 fb^-1 of
integrated luminosity, we find a 5 sigma discovery reach of m(gluino) ~ 400 GeV
even if missing transverse energy, E_T^miss, is not a viable cut variable, by
examining the multi-b-jet final state. A corroborating signal should stand out
in the opposite-sign (OS) dimuon channel in the case of the HS model; the DR3
model will require higher integrated luminosity to yield a signal in the OS
dimuon channel. This region may also be probed by the Tevatron with 5-10 fb^-1
of data, if a corresponding search in the multi-b+ E_T^miss channel is
performed. With higher integrated luminosities of ~1 fb^-1, using E_T^miss plus
a large multiplicity of b-jets, LHC should be able to discover Yukawa-unified
SUSY with m(gluino) up to about 630 GeV. Thus, the year 1 LHC reach for
Yukawa-unified SUSY should be enough to either claim a discovery of the gluino,
or to very nearly rule out this class of models, since higher values of
m(gluino) lead to rather poor Yukawa unification.Comment: 32 pages including 31 EPS figure
Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions
Determining the solvation free energies of single ions in water is one of the
most fundamental problems in physical chemistry and yet many unresolved
questions remain. In particular, the ability to decompose the solvation free
energy into simple and intuitive contributions will have important implications
for models of electrolyte solution. Here, we provide definitions of the various
types of single ion solvation free energies based on different simulation
protocols. We calculate solvation free energies of charged hard spheres using
density functional theory interaction potentials with molecular dynamics
simulation (DFT-MD) and isolate the effects of charge and cavitation, comparing
to the Born (linear response) model. We show that using uncorrected Ewald
summation leads to unphysical values for the single ion solvation free energy
and that charging free energies for cations are approximately linear as a
function of charge but that there is a small non-linearity for small anions.
The charge hydration asymmetry (CHA) for hard spheres, determined with quantum
mechanics, is much larger than for the analogous real ions. This suggests that
real ions, particularly anions, are significantly more complex than simple
charged hard spheres, a commonly employed representation.Comment: 28 pages, 5 figure
Real single ion solvation free energies with quantum mechanical simulation
Single ion solvation free energies are one of the most important properties
of electrolyte solutions and yet there is ongoing debate about what these
values are. Only the values for neutral ion pairs are known. Here, we use DFT
interaction potentials with molecular dynamics simulation (DFT-MD) combined
with a modified version of the quasi-chemical theory (QCT) to calculate these
energies for the lithium and fluoride ions. A method to correct for the error
in the DFT functional is developed and very good agreement with the
experimental value for the lithium fluoride pair is obtained. Moreover, this
method partitions the energies into physically intuitive terms such as surface
potential, cavity and charging energies which are amenable to descriptions with
reduced models. Our research suggests that lithium's solvation free energy is
dominated by the free energetics of a charged hard sphere, whereas fluoride
exhibits significant quantum mechanical behavior that cannot be simply
described with a reduced model.Comment: 13 pages, 4 figure
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
Is "just-so" Higgs splitting needed for t-b-\tau Yukawa unified SUSY GUTs?
Recent renormalization group calculations of the sparticle mass spectrum in
the Minimal Supersymmetric Standard Model (MSSM) show that t-b-\tau Yukawa
coupling unification at M_{\rm GUT} is possible when the mass spectra follow
the pattern of a radiatively induced inverted scalar mass hierarchy. The
calculation is entirely consistent with expectations from SO(10) SUSY GUT
theories, with one exception: it seems to require MSSM Higgs soft term mass
splitting at M_{\rm GUT}, dubbed "just-so Higgs splitting" (HS) in the
literature, which apparently violates the SO(10) gauge symmetry. Here, we
investigate three alternative effects: {\it i}). SO(10) D-term splitting, {\it
ii}). inclusion of right hand neutrino in the RG calculation, and {\it iii}).
first/third generation scalar mass splitting. By combining all three effects
(the DR3 model), we find t-b-\tau Yukawa unification at M_{\rm GUT} can be
achieved at the 2.5% level. In the DR3 case, we expect lighter (and possibly
detectable) third generation and heavy Higgs scalars than in the model with HS.
In addition, the light bottom squark in DR3 should be dominantly a right state,
while in the HS model, it is dominantly a left state.Comment: 21 pages with 11 .eps figures; revised version added two reference
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
SUPERSYMMETRY REACH OF AN UPGRADED TEVATRON COLLIDER
We examine the capability of a TeV Tevatron collider
to discover supersymmetry, given a luminosity upgrade to amass of
data. We compare with the corresponding reach of the Tevatron Main Injector
( of data). Working within the framework of minimal supergravity
with gauge coupling unification and radiative electroweak symmetry breaking, we
first calculate the regions of parameter space accessible via the clean
trilepton signal from \tw_1\tz_2\to 3\ell +\eslt production, with detailed
event generation of both signal and major physics backgrounds. The trilepton
signal can allow equivalent gluino masses of up to GeV to
be probed if is small. If is large, then GeV can
be probed for and large values of , the
rate for \tz_2\to\tz_1\ell\bar{\ell} is suppressed by interference effects,
and there is {\it no} reach in this channel. We also examine regions where the
signal from \tw_1\overline{\tw_1}\to \ell\bar{\ell}+\eslt is detectable.
Although this signal is background limited, it is observable in some regions
where the clean trilepton signal is too small. Finally, the signal
\tw_1\tz_2\to jets+\ell\bar{\ell} +\eslt can confirm the clean trilepton
signal in a substantial subset of the parameter space where the trilepton
signal can be seen. We note that although the clean trilepton signal may allow
Tevatron experiments to identify signals in regions of parameter space beyond
the reach of LEP II, the dilepton channels generally probe much the same region
as LEP II.Comment: 19 page REVTEX file; a uuencoded PS file with PS figures is available
via anonymous ftp at ftp://hep.fsu.edu/preprints/baer/FSUHEP950301.u
Yukawa-unified natural supersymmetry
Previous work on t-b-\tau Yukawa-unified supersymmetry, as expected from SUSY
GUT theories based on the gauge group SO(10), tended to have exceedingly large
electroweak fine-tuning (EWFT). Here, we examine supersymmetric models where we
simultaneously require low EWFT ("natural SUSY") and a high degree of Yukawa
coupling unification, along with a light Higgs scalar with m_h\sim125 GeV. As
Yukawa unification requires large tan\beta\sim50, while EWFT requires rather
light third generation squarks and low \mu\sim100-250 GeV, B-physics
constraints from BR(B\to X_s\gamma) and BR(B_s\to \mu+\mu-) can be severe. We
are able to find models with EWFT \Delta\lesssim 50-100 (better than 1-2% EWFT)
and with Yukawa unification as low as R_yuk\sim1.3 (30% unification) if
B-physics constraints are imposed. This may be improved to R_yuk\sim1.2 if
additional small flavor violating terms conspire to improve accord with
B-constraints. We present several Yukawa-unified natural SUSY (YUNS) benchmark
points. LHC searches will be able to access gluinos in the lower 1-2 TeV
portion of their predicted mass range although much of YUNS parameter space may
lie beyond LHC14 reach. If heavy Higgs bosons can be accessed at a high rate,
then the rare H, A\to \mu+\mu- decay might allow a determination of
tan\beta\sim50 as predicted by YUNS models. Finally, the predicted light
higgsinos should be accessible to a linear e+e- collider with \sqrt{s}\sim0.5
TeV.Comment: 18 pages, 7 figures, pdflatex; 3 references adde
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