4,954 research outputs found
Multicomponent Dark Matter in Supersymmetric Hidden Sector Extensions
Most analyses of dark matter within supersymmetry assume the entire cold dark
matter arising only from weakly interacting neutralinos. We study a new class
of models consisting of hidden sector extensions of the MSSM that
includes several stable particles, both fermionic and bosonic, which can be
interpreted as constituents of dark matter. In one such class of models, dark
matter is made up of both a Majorana dark matter particle, i.e., a neutralino,
and a Dirac fermion with the current relic density of dark matter as given by
WMAP being composed of the relic density of the two species. These models can
explain the PAMELA positron data and are consistent with the anti-proton flux
data, as well as the photon data from FERMI-LAT. Further, it is shown that such
models can also simultaneously produce spin independent cross sections which
can be probed in CDMS-II, XENON-100 and other ongoing dark matter experiments.
The implications of the models at the LHC and at the NLC are also briefly
discussed.Comment: Journal: Physical Review D, Latex 32 pages, 4 eps figure
The peculiar velocity field: constraining the tilt of the Universe
A large bulk flow, which is in tension with the Lambda Cold Dark Matter
(CDM) cosmological model, has been observed. In this paper, we provide
a physically plausible explanation of this bulk flow, based on the assumption
that some fraction of the observed dipole in the cosmic microwave background is
due to an intrinsic fluctuation, so that the subtraction of the observed dipole
leads to a mismatch between the cosmic microwave background (CMB) defined rest
frame and the matter rest frame. We investigate a model that takes into account
the relative velocity (hereafter the tilted velocity) between the two frames,
and develop a Bayesian statistic to explore the likelihood of this tilted
velocity.
By studying various independent peculiar velocity catalogs, we find that: (1)
the magnitude of the tilted velocity is around 400 km/s, and its direction
is close to what is found from previous bulk flow analyses; for most catalogs
analysed, u=0 is excluded at about the level;(2) constraints on
the magnitude of the tilted velocity can result in constraints on the duration
of inflation, due to the fact that inflation can neither be too long (no dipole
effect) nor too short (very large dipole effect); (3) Under the assumption of a
super-horizon isocurvature fluctuation, the constraints on the tilted velocity
require that inflation lasts at least 6 e-folds longer (at the 95% confidence
interval) than that required to solve the horizon problem. This opens a new
window for testing inflation and models of the early Universe from observations
of large scale structure.Comment: 7 pages, 7 figures, match the published version in Phys.Rev.
Search for neutrinoless tau decays tau -> 3l and tau -> l K0S
Neutrinoless tau-lepton decays into either three leptons (tau- -> l1- l2 l3)
or one lepton and one K0S meson(tau- -> l- K0S) where lepton l means either an
electron or muon, have been searched for using 48.6 fb^{-1} of data collected
with the Belle detector at the KEKB e+e- collider. No evidence for candidate
decays are found in any channel. Therefore we set 90% confidence level upper
limits on the branching fraction for 8 different decay modes. These limits are
more stringent than those set previously and reach to the 10^{-7} level.Comment: Invited talk at the Seventh International Workshop on Tau Lepton
Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 7 pages, LaTeX, 3 eps
figure
A new method of measuring the cluster peculiar velocity power spectrum
We propose to use spatial correlations of the kinetic Sunyaev-Zeldovich (KSZ)
flux as an estimator of the peculiar velocity power spectrum. In contrast with
conventional techniques, our new method does not require measurements of the
thermal SZ signal or the X-ray temperature. Moreover, this method has the
special advantage that the expected systematic errors are always sub-dominant
to statistical errors on all scales and redshifts of interest. We show that
future large sky coverage KSZ surveys may allow a peculiar velocity power
spectrum estimates of an accuracy reaching ~10%.Comment: 5 pages, 2 figures, MNRAS in Press (doi:
10.1111/j.1365-2966.2008.13454.x
Dark Matter: The Leptonic Connection
Recent observatons of high-energy positrons and electrons by the PAMELA and
ATIC experiments may be an indication of the annihilation of dark matter into
leptons and not quarks. This leptonic connection was foreseen already some
years ago in two different models of radiative neutrino mass. We discuss here
the generic interactions (nu eta^0 - l eta^+) chi and l^c zeta^- chi^c which
allow this to happen, where chi and/or chi^c are fermionic dark-matter
candidates. We point out in particular the importance of chi chi to l^+ l^-
gamma to both positron and gamma-ray signals within this framework.Comment: 4 pages, 5 figures. v2: PLB versio
A comparison of the galaxy peculiar velocity field with the PSCz gravity field-- A Bayesian hyper-parameter method
We constructed a Bayesian hyper-parameter statistical method to quantify the
difference between predicted velocities derived from the observed galaxy
distribution in the \textit{IRAS}-PSC redshift survey and peculiar
velocities measured using different distance indicators. In our analysis we
find that the model--data comparison becomes unreliable beyond 70 \hmpc
because of the inadequate sampling by \textit{IRAS} survey of prominent,
distant superclusters, like the Shapley Concentration. On the other hand, the
analysis of the velocity residuals show that the PSC gravity field provides
an adequate model to the local, \le 70 \hmpc, peculiar velocity field. The
hyper-parameter combination of ENEAR, SN, A1SN and SFI++ catalogues in the
Bayesian framework constrains the amplitude of the linear flow to be
. For an rms density fluctuations in the PSC galaxy
number density , we obtain an estimate of the
growth rate of density fluctuations ,
which is in excellent agreement with independent estimates based on different
techniques.Comment: 14 pages, 32 figures, MNRAS in press, matched the MNRAS published
versio
Pure Leptonic Gauge Symmetry, Neutrino Masses and Dark Matter
A possible extension of the Standard Model to include lepton number as local
gauge symmetry is investigated. In such a model, anomalies are canceled by two
extra fermions doublet. After leptonic gauge symmetry spontaneously broken,
three active neutrinos may acquire non-zero Majorana masses through the
modified Type-II seesaw mechanism. Constraints on the model from electro-weak
precision measurements are studied. Due to the discrete flavor symmetry,
right-handed Majorana neutrinos can serve as cold dark matter candidate of the
Universe. Constraint from dark matter relic abundance is calculated.Comment: 13 pages, 2 figures; typos corrected, comments and references added,
to appear in Phys. Lett.
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