830 research outputs found
Cosmological Lower Bound on Dark Matter Masses from the Soft Gamma-ray Background
Motivated by a recent detection of 511 keV photons from the center of our
Galaxy, we calculate the spectrum of the soft gamma-ray background of the
redshifted 511 keV photons from cosmological halos. Annihilation of dark matter
particles into electron-positron pairs makes a substantial contribution to the
gamma-ray background. Mass of such dark matter particles must be <~ 100 MeV so
that resulting electron-positron pairs are on-relativistic. On the other hand,
we show that in order for the annihilation not to exceed the observed
background, the dark matter mass needs to be >~ 20 MeV. We include the
contribution from the active galactic nuclei and supernovae. The halo
substructures may increase the lower bound to >~ 60 MeV.Comment: 5 pages, 5 figures; accepted for publication in PRD, Rapid
Communicatio
Note on tree-level unitarity in the General Two Higgs Doublet Model
Tree-level unitarity constraints on the masses of the Higgs bosons in the
general Two Higgs Doublet Model (THDM) are studied. We first consider the case
where the Higgs potential is invariant under a discrete symmetry
transformation, and derive strong constraints on the mass of the lightest
CP-even Higgs boson () as a function of . We then show that the
inclusion of the discrete symmetry breaking term weakens the mass bounds
considerably. It is suggested that a measurement of and may
enable discrimination between the two Higgs potentials.Comment: 10 pages, LaTeX, 2 PostScript figure
About the measurements of the hard X-ray background
We analyze uncertainties in the cosmic X-ray background measurements
performed by the INTEGRAL observatory. We find that the most important effect
limiting the accuracy of the measurements is related to the intrinsic
background variation in detectors. Taking into account all of the uncertainties
arising during the measurements we conclude that the X-ray background intensity
obtained in the INTEGRAL observations is compatible with the historic X-ray
background observations performed by the HEAO-1 satellite.Comment: 20 pages, 4 figures, accepted for publication in Astrophysics and
Space Scienc
Role of lepton flavor violating (LFV) muon decay in Seesaw model and LSND
The aim of the work is to study LFV in a newly proposed Seesaw model of
neutrino mass and to see whether it could explain LSND excess. The motivation
of this Seesaw model was that there was no new physics beyond the TeV scale. By
studying \mu \to 3e in this model, it is shown that the upper bound on the
branching ratio requires Higgs mass m_{h} of a new scalar doublet with lepton
number L=-1 needed in the model has to be about 9 TeV. The predicted branching
ratio for \mu \to e\nu_{l}\bar{\nu}_{l} is too small to explain the LSND. PACS:
11.30.Hv, 14.60.PqComment: 05 pages, three figures, the version to appear in PR
Generating Neutrino Mass in the 331 Model
A mechanism for generating small tree-level Majorana mass for neutrinos is
implemented in the 331 Model. No additional fermions or scalars need to be
added, and no mass scale greater than a few TeV is invoked.Comment: LaTex, 7 pages, no figures. Revised version to appear in Phys. Rev.
EXTRA SPINDLE POLES (Separase) controls anisotropic cell expansion in Norway spruce (Picea abies) embryos independently of its role in anaphase progression
The caspase-related protease separase (EXTRA SPINDLE POLES, ESP) plays a major role in chromatid disjunction and cell expansion in Arabidopsis thaliana. Whether the expansion phenotypes are linked to defects in cell division in Arabidopsis ESP mutants remains elusive. Here we present the identification, cloning and characterization of the gymnosperm Norway spruce (Picea abies, Pa) ESP. We used the P. abies somatic embryo system and a combination of reverse genetics and microscopy to explore the roles of Pa ESP during embryogenesis. Pa ESP was expressed in the proliferating embryonal mass, while it was absent in the suspensor cells. Pa ESP associated with kinetochore microtubules in metaphase and then with anaphase spindle midzone. During cytokinesis, it localized on the phragmoplast microtubules and on the cell plate. Pa ESP deficiency perturbed anisotropic expansion and reduced mitotic divisions in cotyledonary embryos. Furthermore, whilst Pa ESP can rescue the chromatid nondisjunction phenotype of Arabidopsis ESP mutants, it cannot rescue anisotropic cell expansion. Our data demonstrate that the roles of ESP in daughter chromatid separation and cell expansion are conserved between gymnosperms and angiosperms. However, the mechanisms of ESP-mediated regulation of cell expansion seem to be lineage-specific
Linear and cooperative signaling: roles for Stat proteins in the regulation of cell survival and apoptosis in the mammary epithelium
The mammary epithelium undergoes cyclical periods of cellular proliferation, differentiation and regression. These processes are under the control of the hormones secreted during pregnancy, lactation and involution. Signaling pathways have been identified that connect the hormonal stimuli with the transcription of genes responsible for the determination of the cellular fate. The kinetics of induction and deinduction have suggested that cytokine-activated Stat proteins play a crucial role. Stat5 is strongly activated towards the end of pregnancy, persists in an activated state during pregnancy and is rapidly inactivated after cessation of suckling. Stat3 activation is hardly detectable during lactation, but is strongly induced at the onset of involution. The phenotypes of mice in which these genes have been inactivated through homologous recombination corroborate some of the functional assignments deducted from the activation pattern. Stat3 activation seems to be a driving force in the induction of apoptosis early in the involution period
A High Statistics Search for Electron-Neutrino --> Tau-Neutrino Oscillations
We present new limits on nu_e to nu_tau and nu_e to nu_sterile oscillations
by searching for electron neutrino dissappearance in the high-energy wide-band
CCFR neutrino beam. Sensitivity to nu_tau appearance comes from tau decay modes
in which a large fraction of the energy deposited is electromagnetic. The beam
is composed primarily of muon neutrinos but this analysis uses the 2.3%
electron neutrino component of the beam. Electron neutrino energies range from
30 to 600 GeV and flight lengths vary from 0.9 to 1.4 km. This limit improves
the sensitivity of existing limits and obtains a lowest 90% confidence upper
limit in sin**2(2*alpha) of 9.9 x 10**(-2) at delta-m**2 of 125 eV**2.Comment: submitted to Phys. Rev. D. Rapid Com
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