498 research outputs found
Suppression of the neutralino relic density with supersymmetric CP violation
We study pair annihilations of the neutralino dark matter in the minimal
supersymmetric standard model with CP violation. We consider the case that the
higgsino mass and the trilinear scalar couplings have CP-violating phases of
order unity, taking a scenario that the scalar fermions in the first two
generations are much heavier than those in the third generation to avoid a
severe constraint from experimental limits on electric dipole moments. It is
found that, when the lightest neutralino () is bino-like, the cross
sections of the -boson pair production and the
lightest Higgs boson pair production for
nonrelativistic neutralinos can be significantly enhanced by the phase of the
higgsino mass. The relic density of the neutralino can be considerably
suppressed by this effect. However, even this suppression is not enough to make
bino-like dark matter consistent with a cosmological constraint. We also
discuss the effect of CP violation on the positron flux from neutralino pair
annihilations in the galactic halo.Comment: 37 pages, 16 figures. Numerical erros are corrected in the new
versio
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 brane world cosmology
The thermal relic density of the neutralino dark matter in the brane world
cosmology is studied. Since the expansion law at a high energy regime in the
brane world cosmology is modified from the one in the standard cosmology, the
resultant relic density can be altered. It has been found that, if the five
dimensional Planck mass is lower than TeV, the brane world
cosmological effect is significant at the decoupling time and the resultant
relic density is enhanced. We calculate the neutralino relic density in the
Constrained Minimal Supersymmetric Standard Model (CMSSM) and show that the
allowed region is dramatically modified from the one in the standard cosmology
and eventually disappears as is decreasing. We also find a new lower
bound on TeV based on the neutralino dark matter hypothesis,
namely the lower bound in order for the allowed region of the neutralino dark
matter to exist.Comment: 12 pages, 8 figure
Light wino dark matter in brane world cosmology
The thermal relic density of the wino-like neutralino dark matter in the
brane world cosmology is studied. The expansion law at a high energy regime in
the brane world cosmology is modified from the one in the standard cosmology,
and the resultant relic density can be enhanced if the five dimensional Planck
mass is low enough. We calculate the wino-like neutralino relic density
in the anomaly mediated supersymmetry breaking scenario and show that the
allowed region is dramatically modified from the one in the standard cosmology
and the wino-like neutralino with mass of order 100 GeV can be a good candidate
for the dark matter. Since the allowed region disappears eventually as is
decreasing, we can find a lower bound on TeV according to the
neutralino dark matter hypothesis, namely the lower bound in order for the
allowed region of the neutralino dark matter to exist.Comment: 16 pages, 9 figures, final versio
Higgs bosons near 125 GeV in the NMSSM with constraints at the GUT scale
We study the NMSSM with universal Susy breaking terms (besides the Higgs
sector) at the GUT scale. Within this constrained parameter space, it is not
difficult to find a Higgs boson with a mass of about 125 GeV and an enhanced
cross section in the diphoton channel. An additional lighter Higgs boson with
reduced couplings and a mass <123 GeV is potentially observable at the LHC. The
NMSSM-specific Yukawa couplings lambda and kappa are relatively large and
tan(beta) is small, such that lambda, kappa and the top Yukawa coupling are of
order 1 at the GUT scale. The lightest stop can be as light as 105 GeV, and the
fine-tuning is modest. WMAP constraints can be satisfied by a dominantly
higgsino-like LSP with substantial bino, wino and singlino admixtures and a
mass of ~60-90 GeV, which would potentially be detectable by XENON100.Comment: 20 pages, 14 figure
Upper and Lower Limits on Neutralino WIMP Mass and Spin--Independent Scattering Cross Section, and Impact of New (g-2)_{mu} Measurement
We derive the allowed ranges of the spin--independent interaction cross
section \sigsip for the elastic scattering of neutralinos on proton for wide
ranges of parameters of the general Minimal Supersymmetric Standard Model. We
investigate the effects of the lower limits on Higgs and superpartner masses
from colliders, as well as the impact of constraints from \bsgamma and the
new measurement of \gmtwo on the upper and lower limits on \sigsip. We
further explore the impact of the neutralino relic density, including
coannihilation, and of theoretical assumptions about the largest allowed values
of the supersymmetric parameters. For , requiring the latter to lie
below 1\tev leads to \sigsip\gsim 10^{-11}\pb at \mchi\sim100\gev and
\sigsip\gsim 10^{-8}\pb at \mchi\sim1\tev. When the supersymmetric
parameters are allowed above 1\tev, for 440\gev \lsim \mchi\lsim 1020 \gev
we derive a {\em parameter--independent lower limit} of \sigsip \gsim 2\times
10^{-12}\pb. (No similar lower limits can be set for nor for
1020\gev\lsim\mchi\lsim2.6\tev.) Requiring \abundchi<0.3 implies a {\em
parameter--independent upper limit} \mchi\lsim2.6\tev. The new \epem--based
measurement of restricts \mchi\lsim 350\gev at CL
and \mchi\lsim515\gev at CL, and implies . The largest
allowed values of \sigsip have already become accessible to recent
experimental searches.Comment: LaTeX, 17 pages, 9 eps figures. Version to appear in JHE
The Suppression of Neutralino Annihilation into Zh
The Indirect Detection of neutralino Dark Matter is most promising through
annihilation channels producing a hard energy spectrum for the detected
particles, such as the neutralino annihilation into . A cancellation
however makes this particular annihilation channel generically subdominant in
the huge parameter space of supersymmetric models. This cancellation requires
non-trivial relations between neutralino mixings and masses, which we derive
from gauge independence and unitarity of the MSSM. To show how the cancellation
overshoots leaving only a subdominant result, we use a perturbative expansion
in powers of the electroweak/supersymmetry breaking ratio .Comment: 10 pages, 5 figures 10 pages, 5 figure
Scalar-Tensor Gravity in Two 3-brane System
We derive the low-energy effective action of four-dimensional gravity in the
Randall-Sundrum scenario in which two 3-branes of opposite tension reside in a
five-dimensional spacetime. The dimensional reduction with the Ansatz for the
radion field by Charmousis et al., which solves five-dimensional linearized
field equations, results in a class of scalar-tensor gravity theories. In the
limit of vanishing radion fluctuations, the effective action reduces to the
Brans-Dicke gravity in accord with the results of Garriga and Tanaka:
Brans-Dicke gravity with the corresponding Brans-Dicke parameter (for positive tension brane) and (for negative
tension brane). In general the gravity induced a brane belongs to a class of
scalar-tensor gravity with the Brans-Dicke parameter which is a function of the
interval and the radion. In particular, gravity on a positive tension brane
contains an attractor mechanism toward the Einstein gravity.Comment: 8 pages, discussion expanded, references adde
Effective Gauss-Bonnet Interaction in Randall-Sundrum Compactification
The effective gravitational interaction below the Planck scale in the
Randall-Sundrum world is shown to be the Gauss-Bonnet term. In this theory we
find that there exists another static solution with a positive bulk
cosmological constant. Also, there exist solutions for positive visible sector
cosmological constant, which are needed for a later Friedman-Robertson-Walker
universe.Comment: 10 pages, including 1 eps figur
Various Modified Solutions of the Randall-Sundrum Model with the Gauss-Bonnet Interaction
The Gauss-Bonnet interaction is the only consistent quadratic interaction
below the Planck scale in the Randall-Sundrum compactification. We study
various static and inflationary solutions including this Gauss-Bonnet
interaction.Comment: 23 pages including 1 eps figur
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