1,337 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
Direct Detection of the Wino- and Higgsino-like Neutralino Dark Matters at One-Loop Level
The neutralino-nucleon (\tilde{\chi}^0-N) scattering is an important process
for direct dark matter searches. In this paper we discuss one-loop
contributions to the cross section in the wino-like and Higgsino-like LSP
cases. The neutralino-nucleon scattering mediated by the Higgs
\tilde{\chi}^0\tilde{\chi}^0 and Z\tilde{\chi}^0\tilde{\chi}^0 couplings at
tree level is suppressed by the gaugino-Higgsino mixing at tree level when the
neutralino is close to a weak eigenstate. The one-loop contribution to the
cross section, generated by the gauge interaction, is not suppressed by any
SUSY particle mass or mixing in the wino- and Higgsino-like LSP cases. It may
significantly alter the total cross section when \sigma_{\tilde{\chi}^0 N}\sim
10^{-45} cm^2 or less.Comment: 26 pages, 9 figures. Version to be published in Physical Review
Quantum Hall States of Gluons in Quark Matter
We have recently shown that dense quark matter possesses a color
ferromagnetic phase in which a stable color magnetic field arises
spontaneously. This ferromagnetic state has been known to be Savvidy vacuum in
the vacuum sector. Although the Savvidy vacuum is unstable, the state is
stabilized in the quark matter. The stabilization is achieved by the formation
of quantum Hall states of gluons, that is, by the condensation of the gluon's
color charges transmitted from the quark matter. The phase is realized between
the hadronic phase and the color superconducting phase. After a review of
quantum Hall states of electrons in semiconductors, we discuss the properties
of quantum Hall states of gluons in quark matter in detail. Especially, we
evaluate the energy of the states as a function of the coupling constant. We
also analyze solutions of vortex excitations in the states and evaluate their
energies. We find that the states become unstable as the gauge coupling
constant becomes large, or the chemical potential of the quarks becomes small,
as expected. On the other hand, with the increase of the chemical potential,
the color superconducting state arises instead of the ferromagnetic state. We
also show that the quark matter produced by heavy ion collisions generates
observable strong magnetic field Gauss when it enters the
ferromagnetic phase.Comment: 11 pages, 2 figure
Sensitivity of T2KK to the non-standard interaction in propagation
Assuming only the non-zero electron and tau neutrino components
, , of the non-standard
matter effect and postulating the atmospheric neutrino constraint
, we study the
sensitivity to the non-standard interaction in neutrino propagation of the T2KK
neutrino long-baseline experiment. It is shown that T2KK can constrain the
parameters , . It is
also shown that if and are large, then T2KK
can determine the Dirac phase and the phase of separately,
due to the information at the two baselines. We also provide an argument that
the components must be small for
the disappearance oscillation probability to be consistent with high-energy
atmospheric neutrino data, which justifies our premise that these quantities
are negligible.Comment: 29 pages, 25 figures, uses revtex4-1. Several places including typos
revised. New references adde
Non-Perturbative Effect on Dark Matter Annihilation and Gamma Ray Signature from Galactic Center
Detection of gamma rays from dark matter annihilation in the galactic center
is one of the feasible techniques to search for dark matter. We evaluate the
gamma ray flux in the case that the dark matter has an electroweak SU(2)_L
charge. Such dark matter is realized in the minimal supersymmetric standard
model (MSSM) when the lightest SUSY particle is the Higgsino- or Wino-like
neutralino. When the dark matter is heavy compared to the weak gauge bosons,
the leading-order calculation of the annihilation cross sections in
perturbation breaks down due to a threshold singularity. We take into account
non-perturbative effects by using the non-relativistic effective theory for the
two-body states of the dark matter and its SU(2)_L partner(s), and evaluate
precise cross sections relevant to the gamma ray fluxes. We find that the
annihilation cross sections may be enhanced by several orders of magnitude due
to resonances when the dark matter mass is larger than 1 TeV. Furthermore, the
annihilation cross sections in the MSSM may be changed by factors even when the
mass is about 500 GeV. We also discuss sensitivities to gamma ray signals from
the galactic center in the GLAST satellite detector and the large Air Cerenkov
Telescope arrays.Comment: 44 pages, 25 figures, some typos in Sec.V-2 (related to fitting
functions) correcte
Foxp1 and lhx1 coordinate motor neuron migration with axon trajectory choice by gating Reelin signalling.
Topographic neuronal maps arise as a consequence of axon trajectory choice correlated with the localisation of neuronal soma, but the identity of the pathways coordinating these processes is unknown. We addressed this question in the context of the myotopic map formed by limb muscles innervated by spinal lateral motor column (LMC) motor axons where the Eph receptor signals specifying growth cone trajectory are restricted by Foxp1 and Lhx1 transcription factors. We show that the localisation of LMC neuron cell bodies can be dissociated from axon trajectory choice by either the loss or gain of function of the Reelin signalling pathway. The response of LMC motor neurons to Reelin is gated by Foxp1- and Lhx1-mediated regulation of expression of the critical Reelin signalling intermediate Dab1. Together, these observations point to identical transcription factors that control motor axon guidance and soma migration and reveal the molecular hierarchy of myotopic organisation
Analytic Model for Advection-Dominated Accretion Flows in a Global Magnetic Field
A model for advection-dominated accretion flows (ADAFs) in a global magnetic
field is proposed. In contrast to the well known ADAF models in which the
viscosity of a fluid determines both angular momentum transfer and energy
dissipation in the flow, the magnetic field and the electric resistivity,
respectively, control them in this model. A manageable set of analytic
solutions for the flow and the magnetic field is obtained to vertically
non-integrated basic equations. This set describes mathematically a fully
advective accretion flow and, in physically plausible situations for most AGNs,
it is also confirmed that the radiation cooling estimated on this solution is
really negligible compared with the internal energy of the flow.Comment: 27pages, 1 figure, to appear in ApJ vol 529, Feb.1, 200
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