1,378 research outputs found
Neutrino propagation in a random magnetic field
The active-sterile neutrino conversion probability is calculated for neutrino
propagating in a medium in the presence of random magnetic field fluctuations.
Necessary condition for the probability to be positive definite is obtained.
Using this necessary condition we put constraint on the neutrino magnetic
moment from active-sterile electron neutrino conversion in the early universe
hot plasma and in supernova.Comment: 11 page
Semileptonic B Decays and Determination of |Vub|
Semileptonic decays of the B mesons provide an excellent probe for the weak
and strong interactions of the bottom quark. The large data samples collected
at the B Factories have pushed the experimental studies of the semileptonic B
decays to a new height and stimulated significant theoretical developments. I
review recent progresses in this fast-evolving field, with an emphasis on the
determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element
|Vub|.Comment: 16 pages, 4 figures, accepted by Mod. Phys. Lett.
Matter effects on neutrino oscillations in gravitational and magnetic fields
When neutrinos propagate in a background, their gravitational couplings are
modified by their weak interactions with the particles in the background. In a
medium that contains electrons but no muons or taons, the matter-induced
gravitational couplings of neutrinos are different for the various neutrino
flavors, and they must be taken into account in describing the phenomena
associated with the neutrino oscillations in the presence of strong
gravitational fields. Here we incorporate those couplings in that description,
including also the effects of a magnetic field, and consider the implications
that they have for the emission of high energy neutrinos in the vicinity of
Active Galactic Nuclei.Comment: Latex, 12 page
Radiative decays of the Y (1S) to a pair of charged hadrons
Using data obtained with the CLEO III detector, running at the Cornell Electron Storage Ring (CESR), we report on a new study of exclusive radiative Υ(1S) decays into the final states γπ^+π^-, γK^+K^-, and γpp̅ . We present branching ratio measurements for the decay modes Υ(1S)→γf_2(1270), Υ(1S)→γf′_2(1525), and Υ(1S)→γK^+K^-; helicity production ratios for f_2(1270) and f′_2(1525); upper limits for the decay Υ(1S)→γf_J(2200), with f_J(2220)→π^+π^-, K^+K^-, pp̅ ; and an upper limit for the decay Υ(1S)→γX(1860), with X(1860)→γpp̅
The factorizable amplitude in
Using the measured spectrum shape for , the rate for , information on the Cabibbo-Kobayashi-Maskawa (CKM) matrix
element , and theoretical inputs from factorization and lattice gauge
theory, we obtain an improved estimate of the ``tree'' contribution to . We find the branching ratio \b(B^0 \to \pi^+ \pi^-)|_{\rm tree}
= (5.25^{+1.67}_{-0.50}) \times 10^{-6}, to be compared with the experimental
value \b(B^0 \to \pi^+ \pi^-) = (4.55 \pm 0.44) \times 10^{-6}. The fit
implies . Implications for
tree-penguin interference in and for other charmless
decays are discussed.Comment: 11 pages, LaTeX, 3 figures, to be submitted to Phys. Rev.
Spin-Flavour Oscillations and Neutrinos from SN1987A
The neutrino signal from SN1987A is analysed with respect to spin-flavour
oscillations between electron antineutrinos, , and muon
neutrinos, , by means of a maximum likelihood analysis.
Following Jegerlehner et al. best fit values for the total energy released in
neutrinos, , and the temperature of the electron antineutrino,
, for a range of mixing parameters and progenitor models are
calculated. In particular the dependence of the inferred quantities on the
metallicity of the supernova is investigated and the uncertainties involved in
using the neutrino signal to determine the neutrino magnetic moment are pointed
out.Comment: 14 pages, RevTeX, 4 figures, to appear in Physical Review
High-energy neutrino conversion and the lepton asymmetry in the universe
We study matter effects on oscillations of high-energy neutrinos in the
Universe. Substantial effect can be produced by scattering of the neutrinos
from cosmological sources (z\gta 1) on the relic neutrino background,
provided that the latter has large CP-asymmetry: \eta\equiv
(n_\nu-n_{\bar{\nu}})/n_\gamma\gta 1, where , and
are the concentrations of neutrinos, antineutrinos and photons. We
consider in details the dynamics of conversion in the expanding neutrino
background. Applications are given to the diffuse fluxes of neutrinos from
GRBs, AGN, and the decay of super-heavy relics. We find that the vacuum
oscillation probability can be modified by and in extreme cases
allowed by present bounds on the effect can reach .
Signatures of matter effects would consist (i) for both active-active and
active-sterile conversion, in a deviation of the numbers of events produced in
a detector by neutrinos of different flavours,
, and of their ratios from the values given by
vacuum oscillations; such deviations can reach , (ii) for
active-sterile conversion, in a characteristic energy dependence of the ratios
. Searches for these matter
effects will probe large CP and lepton asymmetries in the universe.Comment: 32 pages, RevTeX, 16 figures. Substantial changes in the treatment of
conversion effects in the relic neutrino background and of active-active
oscillations of high-energy neutrinos. Figures and references added;
conclusions partially modifie
A comprehensive study of neutrino spin-flavour conversion in supernovae and the neutrino mass hierarchy
Resonant spin-flavour (RSF) conversions of supernova neutrinos, which is
induced by the interaction between the nonzero neutrino magnetic moment and
supernova magnetic fields, are studied for both normal and inverted mass
hierarchy. As the case for the pure matter-induced neutrino oscillation
(Mikheyev--Smirnov--Wolfenstein (MSW) effect), we find that the RSF transitions
are strongly dependent on the neutrino mass hierarchy as well as the value of
. Flavour conversions are solved numerically for various neutrino
parameter sets, with presupernova profile calculated by Woosley and Weaver. In
particular, it is very interesting that the RSF-induced
\nu_\rme\to\bar\nu_\rme transition occurs, if the following conditions are
all satisfied: the value of ( is the neutrino magnetic
moment, and is the magnetic field strength) is sufficiently strong, the
neutrino mass hierarchy is inverted, and the value of is large
enough to induce adiabatic MSW resonance. In this case, the strong peak due to
original \nu_\rme emitted from neutronization burst would exist in time
profile of the neutrino events detected at the Super-Kamiokande detector. If
this peak were observed in reality, it would provide fruitful information on
the neutrino properties. On the other hand, characters of the neutrino spectra
are also different between the neutrino models, but we find that there remains
degeneracy among several models. Dependence on presupernova models is also
discussed.Comment: 23 pages, 11 figures, corrected minor typos, added references. Final
version to appear in Journal of Cosmology and Astroparticle Physic
Tracing very high energy neutrinos from cosmological distances in ice
Astrophysical sources of ultrahigh energy neutrinos yield tau neutrino fluxes
due to neutrino oscillations. We study in detail the contribution of tau
neutrinos with energies above PeV relative to the contribution of the other
flavors. We consider several different initial neutrino fluxes and include tau
neutrino regeneration in transit through the Earth and energy loss of charged
leptons. We discuss signals of tau neutrinos in detectors such as IceCube, RICE
and ANITA.Comment: 27 pages, 19 figure
Resonant Spin-Flavor Conversion of Supernova Neutrinos and Deformation of the Electron Antineutrino Spectrum
The neutrino spin-flavor conversion of \bar\nu_e and \nu_\mu which is induced
by the interaction of the Majorana neutrino magnetic moment and magnetic fields
in the collapse-driven supernova is investigated in detail. We calculate the
conversion probability by using the latest precollapse models of Woosley and
Weaver (1995), and also those of Nomono and Hashimoto (1988), changing the
stellar mass and metallicity in order to estimate the effect of the
astrophysical uncertainties. Contour maps of the conversion probability are
given for all the models as a function of neutrino mass squared difference and
the neutrino magnetic moment times magnetic fields. It is shown that in the
solar metallicity models some observational effects are expected with \Delta
m^2 = 10^{-5}--10^{-1} [eV^2] and \mu_\nu >~ 10^{-12} (10^9 G / B_0) [\mu_B],
where B_0 is the strength of the magnetic fields at the surface of the iron
core. We also find that although the dependence on the stellar models or
stellar mass is not so large, the metallicity of precollapse stars has
considerable effects on this conversion. Such effects may be seen in a
supernova in the Large or Small Magellanic Clouds, and should be taken into
account when one considers an upper bound on \mu_\nu from the SN1987A data.Comment: 19 pages, LaTeX, using revtex. To appear in Phys. Rev. D. 16 figures
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