9,625 research outputs found
Minimally Extended Left-Right Symmetric Model for Dark Matter with U(1) Portal
A minimal extension of the left-right symmetric model for neutrino masses
that includes a vector-like singlet fermion dark matter (DM) is presented with
the DM connected to the visible sector via a gauged U(1) portal. We discuss the
symmetry breaking in this model and calculate the mass and mixings of the extra
heavy neutral gauge boson at the TeV scale. The extra gauge boson can decay to
both standard model particles as well to dark matter. We calculate the relic
density of the singlet fermion dark matter and its direct detection cross
section and use these constraints to obtain the allowed parameter range for the
new gauge coupling and the dark matter mass.Comment: 19 pages, 8 figure
Dynamical replica theoretic analysis of CDMA detection dynamics
We investigate the detection dynamics of the Gibbs sampler for code-division
multiple access (CDMA) multiuser detection. Our approach is based upon
dynamical replica theory which allows an analytic approximation to the
dynamics. We use this tool to investigate the basins of attraction when phase
coexistence occurs and examine its efficacy via comparison with Monte Carlo
simulations.Comment: 18 pages, 2 figure
Simulations of slow positron production using a low energy electron accelerator
Monte Carlo simulations of slow positron production via energetic electron
interaction with a solid target have been performed. The aim of the simulations
was to determine the expected slow positron beam intensity from a low energy,
high current electron accelerator. By simulating (a) the fast positron
production from a tantalum electron-positron converter and (b) the positron
depth deposition profile in a tungsten moderator, the slow positron production
probability per incident electron was estimated. Normalizing the calculated
result to the measured slow positron yield at the present AIST LINAC the
expected slow positron yield as a function of energy was determined. For an
electron beam energy of 5 MeV (10 MeV) and current 240 A (30 A)
production of a slow positron beam of intensity 5 10 s is
predicted. The simulation also calculates the average energy deposited in the
converter per electron, allowing an estimate of the beam heating at a given
electron energy and current. For low energy, high-current operation the maximum
obtainable positron beam intensity will be limited by this beam heating.Comment: 11 pages, 15 figures, submitted to Review of Scientific Instrument
Effective actions on the squashed three-sphere
The effective actions of a scalar and massless spin-half field are determined
as functions of the deformation of a symmetrically squashed three-sphere. The
extreme oblate case is particularly examined as pertinant to a high temperature
statistical mechanical interpretation that may be relevant for the holographic
principle. Interpreting the squashing parameter as a temperature, we find that
the effective `free energies' on the three-sphere are mixtures of thermal
two-sphere scalars and spinors which, in the case of the spinor on the
three-sphere, have the `wrong' thermal periodicities. However the free energies
do have the same leading high temperature forms as the standard free energies
on the two-sphere. The next few terms in the high-temperature expansion are
also explicitly calculated and briefly compared with the Taub-Bolt-AdS bulk
result.Comment: 23 pages, JyTeX. Conclusion slightly amended, one equation and minor
misprints correcte
Probing Left-handed Slepton Flavor Mixing at Future Lepton Colliders
It has been argued in the literature that the search for the slepton
oscillation phenomenon can be a powerful probe of intergenerational mixing
between sleptons, once sleptons are found at future colliders. In this article
we estimate possible reach of future lepton colliders in probing left-handed
slepton flavor mixing, especially mixing between the first and third
generations, on which constraints imposed by other processes like are very weak. collider is suitable for this purpose, since it
can produce, if kinematically allowed, sleptons of the first generation via
t-channel, in addition to s-channel. Utilizing e^+e^- \to \tau e + 4jets + \E
signal at linear collider with integrated luminosity L=50 fb^{-1}(500
fb^{-1}) it may be possible to reach mixing angle and mass difference GeV for sneutrinos in the first and third generations at the
statistical significance of 5 \sigma.Comment: 27 pages, 6 figures. A new section added. Conclusion unchanged. To
appear in Phys. Rev.
A Solution for Little Hierarchy Problem and b --> s gamma
We show that all the parameters which destabilize the weak scale can be taken
around the weak scale in the MSSM without conflicting with the SM Higgs mass
bound set by LEP experiment. The essential point is that if the lightest
CP-even Higgs h in the MSSM has only a small coupling to Z boson, g_{ZZh}, LEP
cannot generate the Higgs sufficiently. In the scenario, the SM Higgs mass
bound constrains the mass of the heaviest CP-even Higgs H which has the SM like
g_{ZZH} coupling. However, it is easier to make the heaviest Higgs heavy by the
effect of off-diagonal elements of the mass matrix of the CP-even Higgs because
the larger eigenvalue of 2 times 2 matrix becomes larger by introducing
off-diagonal elements. Thus, the smaller stop masses can be consistent with the
LEP constraints. Moreover, the two excesses observed at LEP Higgs search can
naturally be explained as the signals of the MSSM Higgs h and H in this
scenario. One of the most interesting results in the scenario is that all the
Higgs in the MSSM have the weak scale masses. For example, the charged Higgs
mass should be around 130 GeV. This looks inconsistent with the lower bound
obtained by the b --> s gamma process as m_{H^\pm}>350GeV. However, we show
that the amplitude induced by the charged Higgs can naturally be compensated by
that of the chargino if we take the mass parameters by which the little
hierarchy problem can be solved. The point is that the both amplitudes have the
same order of magnitudes when all the fields in the both loops have the same
order of masses.Comment: 14 pages, 5 figures, input parameter slightly changed, figures
replaced, references correcte
Measurement of the analyzing power of proton-carbon elastic scattering in the CNI region at RHIC
The single transverse spin asymmetry, A_N, of the p-carbon elastic scattering
process in the Coulomb Nuclear Interference (CNI) region was measured using an
ultra thin carbon target and polarized proton beam in the Relativistic Heavy
Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were
collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100
GeV). A_N was obtained as a function of momentum transfer -t. The results were
fit with theoretical models which allow us to assess the contribution from a
hadronic spin flip amplitude.Comment: Contribution to the proceedings of the 16th International Spin
Physics Symposium, spin2004 (Trieste
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