2,883 research outputs found
Three Flavour Majorana Neutrinos with Magnetic Moments in a Supernova
The resonant transition effects MSW and NSFP for three flavour Majorana
neutrinos in a supernova are considered, where the transition magnetic moments
are likely to play a relevant role in neutrino physics. In this scenario, the
deformed thermal neutrino distributions are obtained for different choices of
the electron-tau mixing angle. Detailed predictions for the future large
neutrino detectors are also given in terms of the ratio between the spectra of
recoil electrons for deformed and undeformed spectra.Comment: 20 pages, LaTeX, 5 figures.p
The standard and degenerate primordial nucleosynthesis versus recent experimental data
We report the results on Big Bang Nucleosynthesis (BBN) based on an updated
code, with accuracy of the order of 0.1% on He4 abundance, compared with the
predictions of other recent similar analysis. We discuss the compatibility of
the theoretical results, for vanishing neutrino chemical potentials, with the
observational data. Bounds on the number of relativistic neutrinos and baryon
abundance are obtained by a likelihood analysis. We also analyze the effect of
large neutrino chemical potentials on primordial nucleosynthesis, motivated by
the recent results on the Cosmic Microwave Background Radiation spectrum. The
BBN exclusion plots for electron neutrino chemical potential and the effective
number of relativistic neutrinos are reported. We find that the standard BBN
seems to be only marginally in agreement with the recent BOOMERANG and MAXIMA-1
results, while the agreement is much better for degenerate BBN scenarios for
large effective number of neutrinos, N_\nu \sim 10.Comment: LaTeX2e, 41 pages, 20 figures. Minor changes and 4 figures slightly
modifie
Identification of transmembrane domains that regulate spatial arrangements and activity of prokineticin receptor 2 dimers
The chemokine prokineticin 2 (PK2) activates its cognate G protein-coupled receptor (GPCR) PKR2 to elicit various downstream signaling pathways involved in diverse biological processes. Many GPCRs undergo dimerization that can modulate a number of functions including membrane delivery and signal transduction. The aim of this study was to elucidate the interface of PKR2 protomers within dimers by analyzing the ability of PKR2 transmembrane (TM) deletion mutants to associate with wild type (WT) PKR2 in yeast using co-immunoprecipitation and mammalian cells using bioluminescence resonance energy transfer. Deletion of TMs 5-7 resulted in a lack of detectable association with WT PKR2, but could associate with a truncated mutant lacking TMs 6-7 (TM1-5). Interestingly, TM1-5 modulated the distance, or organization, between protomers and positively regulated Gαs signaling and surface expression of WT PKR2. We propose that PKR2 protomers form type II dimers involving TMs 4 and 5, with a role for TM5 in modulation of PKR2 function
Radio constraints on dark matter annihilation in the galactic halo and its substructures
Annihilation of Dark Matter usually produces together with gamma rays
comparable amounts of electrons and positrons. The e+e- gyrating in the
galactic magnetic field then produce secondary synchrotron radiation which thus
provides an indirect mean to constrain the DM signal itself. To this purpose,
we calculate the radio emission from the galactic halo as well as from its
expected substructures and we then compare it with the measured diffuse radio
background. We employ a multi-frequency approach using data in the relevant
frequency range 100 MHz-100 GHz, as well as the WMAP Haze data at 23 GHz. The
derived constraints are of the order =10^{-24} cm3 s^{-1} for a DM
mass m_chi=100 GeV sensibly depending however on the astrophysical
uncertainties, in particular on the assumption on the galactic magnetic field
model. The signal from single bright clumps is instead largely attenuated by
diffusion effects and offers only poor detection perspectives.Comment: 12 pages, 7 figures; v2: some references added, some discussions
enlarged; matches journal versio
Modified quasilinearization method for solving nonlinear equations
Modified quasilinearization algorithm for solving nonlinear equation
Maximum Lift-to-drag Ratio of a Slender, Flat-top, Hypersonic Body
Maximum lift-drag ratio of slender, flat top, hypersonic body assuming modified Newtonian pressure distribution and constant surface averaged skin friction coefficien
Constraining neutrino physics with BBN and CMBR
We perform a likelihood analysis of the recent results on the anisotropy of
Cosmic Microwave Background Radiation from the BOOMERanG and DASI experiments
to show that they single out an effective number of neutrinos in good agreement
with standard Big Bang Nucleosynthesis. We also consider degenerate Big Bang
Nucleosynthesis to provide new bounds on effective relativistic degrees of
freedom and, in particular, on neutrino chemical potential
. When including Supernova Ia data we find, at , and , .Comment: 6 pages, 3 figures, some reference adde
Angular Signatures of Annihilating Dark Matter in the Cosmic Gamma-Ray Background
The extragalactic cosmic gamma-ray background (CGB) is an interesting channel
to look for signatures of dark matter annihilation. In particular, besides the
imprint in the energy spectrum, peculiar anisotropy patterns are expected
compared to the case of a pure astrophysical origin of the CGB. We take into
account the uncertainties in the dark matter clustering properties on
sub-galactic scales, deriving two possible anisotropy scenarios. A clear dark
matter angular signature is achieved when the annihilation signal receives only
a moderate contribution from sub-galactic clumps and/or cuspy haloes.
Experimentally, if galactic foregrounds systematics are efficiently kept under
control, the angular differences are detectable with the forthcoming GLAST
observatory, provided that the annihilation signal contributes to the CGB for a
fraction >10-20%. If, instead, sub-galactic structures have a more prominent
role, the astrophysical and dark matter anisotropies become degenerate,
correspondingly diluting the DM signature. As complementary observables we also
introduce the cross-correlation between surveys of galaxies and the CGB and the
cross-correlation between different energy bands of the CGB and we find that
they provide a further sensitive tool to detect the dark matter angular
signatures.Comment: 13 pages, 8 figures; improved discussion; matches published versio
Levantamento sistemático da produção e abate de suÃnos: 2006 e 2007.
bitstream/item/58227/1/doc122.pd
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