763 research outputs found
Supergravity with a Gravitino LSP
We investigate supergravity models in which the lightest supersymmetric
particle (LSP) is a stable gravitino. We assume that the next-lightest
supersymmetric particle (NLSP) freezes out with its thermal relic density
before decaying to the gravitino at time t ~ 10^4 s - 10^8 s. In contrast to
studies that assume a fixed gravitino relic density, the thermal relic density
assumption implies upper, not lower, bounds on superpartner masses, with
important implications for particle colliders. We consider slepton, sneutrino,
and neutralino NLSPs, and determine what superpartner masses are viable in all
of these cases, applying CMB and electromagnetic and hadronic BBN constraints
to the leading two- and three-body NLSP decays. Hadronic constraints have been
neglected previously, but we find that they provide the most stringent
constraints in much of the natural parameter space. We then discuss the
collider phenomenology of supergravity with a gravitino LSP. We find that
colliders may provide important insights to clarify BBN and the thermal history
of the Universe below temperatures around 10 GeV and may even provide precise
measurements of the gravitino's mass and couplings.Comment: 24 pages, updated figures and minor changes, version to appear in
Phys.Rev.
Effect of River Levee with Geosynthetic-Reinforced Soil against Overflow Erosion and Infiltration
Overflows from huge floods have caused levee breaches in a great number of places, including Japan. To prevent such destruction and thereby increase the resistance of armored levees to overflow erosion, in this study, we examined the performances of Geosynthetic-Reinforced Soil (GRS) levees against overflow erosion under various conditions, such as reinforcement, back slopes, and geo-grid layers. In addition, we investigated the effect of geo-grid layers on the infiltration of levees. The model tests revealed that 1) with scour protection in front of the toe of the back slope, the GRS levee exhibits much higher resistance against overflow erosion than the armored levee; 2) the armored levee with a steep back slope (= 1:0.5) collapsed faster than that with a normal slope (= 1:2). However, the GRS levee with a steep back slope of 1:0.5 maintained high resistance against overflow erosion after the target time. 3) The GRS levee with partial and full reinforcements had a comparably high resistance against overflow erosion. 4) The GRS levee using a small-sized geo-grid maintained a high residual ratio of the cross-sectional area over a long period. 5) The infiltration discharge of the GRS levee was lesser than that of the levee with no reinforcement due to the reduction in infiltration erosion in the GRS levee. These facts suggest that the GRS levee with partial reinforcement can be applied to the reinforcement of existing levees, and appropriately sized geo-grid layers should be selected
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
Flavor mixing in the gluino coupling and the nucleon decay
Flavor mixing in the quark-squark-gluino coupling is studied for the minimal
SU(5) SUGRA-GUT model and applied to evaluation of the nucleon lifetime. All
off-diagonal (generation mixing) elements of Yukawa coupling matrices and of
squark/slepton mass matrices are included in solving numerically one-loop
renormalization group equations for MSSM parameters, and the parameter region
consistent with the radiative electroweak symmetry breaking condition is
searched. It is shown that the flavor mixing in the gluino coupling for a large
is of the same order of magnitude as the corresponding
Kobayashi-Maskawa matrix element in both up-type and down-type sector. There
exist parameter regions where the nucleon decay amplitudes for charged lepton
modes are dominated by the gluino dressing process, while for all the examined
regions the neutrino mode amplitudes are dominated by the wino dressing over
the gluino dressing.Comment: 24 pages, LaTeX, figures are available upon request.
ICRR-Report-317-94-1
Continuum limit of proton decay matrix elements in quenched lattice QCD
We present a lattice QCD calculation of the parameters \alpha and \beta which
are necessary in the theoretical estimation of the proton lifetime in grand
unified theories (GUTs) using chiral lagrangian approach. The simulation is
carried out using the Wilson quark action at three gauge coupling constants in
the quenched approximation. We obtain
|\alpha(2GeV)|=0.0091(08)(^{+10}_{-19})GeV^3 and
|\beta(2GeV)|=0.0098(08)(^{+10}_{-20})GeV^3 in the continuum limit where the
first error is statistical and the second one is due to scale setting.Comment: 3 pages, 2 figures, talk presented at Lattice2003(matrix
Kuiper Belt Object Occultations: Expected Rates, False Positives, and Survey Design
A novel method of generating artificial scintillation noise is developed and
used to evaluate occultation rates and false positive rates for surveys probing
the Kuiper Belt with the method of serendipitous stellar occultations. A
thorough examination of survey design shows that: (1) diffraction-dominated
occultations are critically (Nyquist) sampled at a rate of 2 Fsu^{-1},
corresponding to 40 s^{-1} for objects at 40 AU, (2) occultation detection
rates are maximized when targets are observed at solar opposition, (3) Main
Belt Asteroids will produce occultations lightcurves identical to those of
Kuiper Belt Objects if target stars are observed at solar elongations of: 116
deg < epsilon < 125 deg, or 131 deg < epsilon < 141 deg, and (4) genuine KBO
occultations are likely to be so rare that a detection threshold of >7-8 sigma
should be adopted to ensure that viable candidate events can be disentangled
from false positives.Comment: Accepted AJ, 12 pages, 12 figure
Particle Horizon and Warped Phenomenology
Giant resonances of gravity Kaluza-Klein modes (with tensor couplings) in
high energy collisions are expected in the Randall-Sundrum orbifold model that
incorporates a plausible solution to the hierarchy problem. When the model is
extended to incorporate an exponentially small 4-D cosmological constant, the
KK spectrum becomes continuous, even in the compactified case. This is due to
the presence of a particle horizon, which provides a way to evade Weinberg's
argument of the need of fine-tuning to get a very small cosmological constant.Comment: 10 pages, 1 figure, REVTE
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