8,051 research outputs found
Gravitino dark matter from increased thermal relic particles
We investigate the so-called superWIMP scenario with gravitino as the
lightest supersymmetric particle (LSP) in the context of non-standard
cosmology, in particular, brane world cosmology. As a candidate of the
next-to-LSP (NLSP), we examine slepton and sneutrino. Brane world cosmological
effects dramatically enhance the relic density of the slepton or sneutrino
NLSP, so that the NLSP with mass of order 100 GeV can provide the correct
abundance of gravitino dark matter through its decay. We find that with an
appropriate five dimensional Planck mass, this scenario can be realized
consistently with the constraints from Big Bang Nucleosynthesis (BBN) for both
NLSP candidates of slepton and sneutrino. The BBN constraints for slepton NLSP
are more stringent than that for sneutrino, as the result, the gravitino must
be rather warm in the slepton NLSP case. The energy density of gravitino
produced by thermal scattering is highly suppressed and negligible due to the
brane world cosmological effects.Comment: 15 pages, discussion and references added, the final versio
Gauss-Bonnet braneworld cosmological effect on relic density of dark matter
In Gauss-Bonnet braneworld cosmology, the Friedmann equation of our
four-dimensional universe on 3-brane is modified in a high energy regime
(Gauss-Bonnet regime), while the standard expansion law is reproduced in low
energies (standard regime). We investigate the Gauss-Bonnet braneworld
cosmological effect on the thermal relic density of cold dark matter when the
freeze-out of the dark matter occurs in the Gaugss-Bonnet regime. We find that
the resultant relic density is considerably reduced when the transition
temperature, which connects the Gauss-Bonnet regime with the standard regime,
is low enough. This result is in sharp contrast with the result previously
obtained in the Randall-Sundrum braneworld cosmology, where the relic density
is enhanced.Comment: 11 pages, 2 figures, new references were added, some typos were
correcte
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
Statistical mechanics of lossy compression using multilayer perceptrons
Statistical mechanics is applied to lossy compression using multilayer
perceptrons for unbiased Boolean messages. We utilize a tree-like committee
machine (committee tree) and tree-like parity machine (parity tree) whose
transfer functions are monotonic. For compression using committee tree, a lower
bound of achievable distortion becomes small as the number of hidden units K
increases. However, it cannot reach the Shannon bound even where K -> infty.
For a compression using a parity tree with K >= 2 hidden units, the rate
distortion function, which is known as the theoretical limit for compression,
is derived where the code length becomes infinity.Comment: 12 pages, 5 figure
Electroweak phase transition in a nonminimal supersymmetric model
The Higgs potential of the minimal nonminimal supersymmetric standard model
(MNMSSM) is investigated within the context of electroweak phase transition. We
investigate the allowed parameter space yielding correct electroweak phase
transitoin employing a high temperature approximation. We devote to
phenomenological consequences for the Higgs sector of the MNMSSM for
electron-positron colliders. It is observed that a future linear
collider with GeV will be able to test the model with regard
to electroweak baryogenesis.Comment: 28 pages, 5 tables, 12 figure
Resonant Leptogenesis in the Minimal B-L Extended Standard Model at TeV
We investigate the resonant leptogenesis scenario in the minimal B-L extended
standard model(SM) with the B-L symmetry breaking at the TeV scale. Through
detailed analysis of the Boltzmann equations, we show how much the resultant
baryon asymmetry via leptogenesis is enhanced or suppressed, depending on the
model parameters, in particular, the neutrino Dirac Yukawa couplings and the
TeV-scale Majorana masses of heavy degenerate neutrinos. In order to consider a
realistic case, we impose a simple ansatz for the model parameters and analyze
the neutrino oscillation parameters and the baryon asymmetry via leptogenesis
as a function of only a single CP-phase. We find that for a fixed CP-phase all
neutrino oscillation data and the observed baryon asymmetry of the present
universe can be simultaneously reproduced.Comment: 25 pages, 15 figures, version to be published in Phys. Rev.
Statistical mechanics of lossy compression for non-monotonic multilayer perceptrons
A lossy data compression scheme for uniformly biased Boolean messages is
investigated via statistical mechanics techniques. We utilize tree-like
committee machine (committee tree) and tree-like parity machine (parity tree)
whose transfer functions are non-monotonic. The scheme performance at the
infinite code length limit is analyzed using the replica method. Both committee
and parity treelike networks are shown to saturate the Shannon bound. The AT
stability of the Replica Symmetric solution is analyzed, and the tuning of the
non-monotonic transfer function is also discussed.Comment: 29 pages, 7 figure
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
The X-ray Properties of the Nearby Star-Forming Galaxy IC 342: The XMM-Newton View
We present the X-ray properties of IC342 using XMM-Newton. Thirty-five
sources are detected coincident with the disk of IC342 (more than tripling the
number known), of which ~31 are likely to be intrinsic to IC342. This
population shows a range of spectral properties and has an X-ray luminosity
function slope and infrared luminosity comparable to that of starburst galaxies
such as M82 and the Antennae, while its relative lack of extended X-ray
emission is similar to the properties of quiescent spirals. We do detect
long-term variability between this observation and the 1991 ROSAT and 1993/2000
ASCA observations for five sources. Notably, the second most luminous source
IC342 X-2 is is found to be in its the lowest luminosity state observed for X-2
to date, although the slope of the spectrum is intermediate between the
previously observed low/hard and high/soft states. IC342 X-1, on the other
hand, is found to be in an identical state to that observed in 2000 with ASCA.
Assuming X-1 is in an anomalous very high (VH) state, then either (1) X-1 has
remained in this state between 2000 and 2002, and is therefore the longest
duration VH-state binary ever observed, or (2) it was simply caught in a VH
state by chance in both the 2000 ASCA and 2002 XMM-Newton observations. We have
also confirmed the ROSAT HRI result that the nucleus of IC342 is made up of
both point-like and extended emission. The relative fluxes of the two spectral
components suggest that the nucleus is complex, with a soft extended component
contributing approximately half of the total luminosity. (Abridged)Comment: AJ in press (December 2003), 9 pages, 7 figures, 2 tables,
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