25 research outputs found
Neutrino emission in neutron matter from magnetic moment interactions
Neutrino emission drives neutron star cooling for the first several hundreds
of years after its birth. Given the low energy ( keV) nature of this
process, one expects very few nonstandard particle physics contributions which
could affect this rate. Requiring that any new physics contributions involve
light degrees of freedom, one of the likely candidates which can affect the
cooling process would be a nonzero magnetic moment for the neutrino. To
illustrate, we compute the emission rate for neutrino pair bremsstrahlung in
neutron-neutron scattering through photon-neutrino magnetic moment coupling. We
also present analogous differential rates for neutrino scattering off nucleons
and electrons that determine neutrino opacities in supernovae. Employing
current upper bounds from collider experiments on the tau magnetic moment, we
find that the neutrino emission rate can exceed the rate through neutral
current electroweak interaction by a factor two, signalling the importance of
new particle physics input to a standard calculation of relevance to neutron
star cooling. However, astrophysical bounds on the neutrino magnetic moment
imply smaller effects.Comment: 9 pages, 1 figur
Neutrino-induced nucleosynthesis of A>64 nuclei: The nu p-process
We present a new nucleosynthesis process, that we denote nu p-process, which
occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino
fluxes create proton-rich ejecta. In this process, antineutrino absorptions in
the proton-rich environment produce neutrons that are immediately captured by
neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with
mass numbers A >64. Making this process a possible candidate to explain the
origin of the solar abundances of 92,94Mo and 96,98Ru. This process also offers
a natural explanation for the large abundance of Sr seen in an hyper-metal-poor
star.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Synoptic Sky Surveys and the Diffuse Supernova Neutrino Background: Removing Astrophysical Uncertainties and Revealing Invisible Supernovae
The cumulative (anti)neutrino production from all core-collapse supernovae
within our cosmic horizon gives rise to the diffuse supernova neutrino
background (DSNB), which is on the verge of detectability. The observed flux
depends on supernova physics, but also on the cosmic history of supernova
explosions; currently, the cosmic supernova rate introduces a substantial
(+/-40%) uncertainty, largely through its absolute normalization. However, a
new class of wide-field, repeated-scan (synoptic) optical sky surveys is coming
online, and will map the sky in the time domain with unprecedented depth,
completeness, and dynamic range. We show that these surveys will obtain the
cosmic supernova rate by direct counting, in an unbiased way and with high
statistics, and thus will allow for precise predictions of the DSNB. Upcoming
sky surveys will substantially reduce the uncertainties in the DSNB source
history to an anticipated +/-5% that is dominated by systematics, so that the
observed high-energy flux thus will test supernova neutrino physics. The
portion of the universe (z < 1) accessible to upcoming sky surveys includes the
progenitors of a large fraction (~ 87%) of the expected 10-26 MeV DSNB event
rate. We show that precision determination of the (optically detected) cosmic
supernova history will also make the DSNB into a strong probe of an extra flux
of neutrinos from optically invisible supernovae, which may be unseen either
due to unexpected large dust obscuration in host galaxies, or because some
core-collapse events proceed directly to black hole formation and fail to give
an optical outburst.Comment: 11 pages, 6 figure
Fluorine Abundances in the Orion Nebula Cluster
This study uses cool dwarfs as sources with which to probe fluorine
abundances via HF. This molecule is detected for the first time in young K-M
dwarf members of an OB association. Fluorine, oxygen, and carbon abundances
were derived from the HF(1--0) R9 line along with samples of OH and CO
vibration-rotation lines present in high-resolution infrared spectra observed
with the Phoenix spectrograph on the Gemini South Telescope. The fluorine and
oxygen results obtained for these targets, still in the pre-main-sequence stage
of evolution, agree well with the general trend defined for the Milky Way disk;
the latter being deduced from observations of more evolved giant stars. In
addition, the carbon and oxygen abundances obtained for the studied stars
overlap results from previous studies of the more massive OB stars and FG dwarf
members of the Orion Nebula Cluster. We conclude from this agreement that the
fluorine abundances derived for the Orion K-M dwarfs (when there is no
conspicuous evidence of disks) can be considered a good representation of the
current fluorine abundance value for the Milky Way disk.Comment: 18 pages, including 2 tables and 3 figures. Accepted for publication
in The Astrophysical Journa
Neutrino Spectrum from SN 1987A and from Cosmic Supernovae
The detection of neutrinos from SN 1987A by the Kamiokande-II and
Irvine-Michigan-Brookhaven detectors provided the first glimpse of core
collapse in a supernova, complementing the optical observations and confirming
our basic understanding of the mechanism behind the explosion. One
long-standing puzzle is that, when fitted with thermal spectra, the two
independent detections do not seem to agree with either each other or typical
theoretical expectations. We assess the compatibility of the two data sets in a
model-independent way and show that they can be reconciled if one avoids any
bias on the neutrino spectrum stemming from theoretical conjecture. We
reconstruct the neutrino spectrum from SN 1987A directly from the data through
non-parametric inferential statistical methods and present predictions for the
Diffuse Supernova Neutrino Background based on SN 1987A data. We show that this
prediction cannot be too small (especially in the 10-18 MeV range), since the
majority of the detected events from SN 1987 were above 18 MeV (including 6
events above 35 MeV), suggesting an imminent detection in operational and
planned detectors.Comment: 9 pages, 4 figures; Matches version published in Phys. Rev.
Neutrino-induced neutron spallation and supernova r-process nucleosynthesis
In order to explore the consequences of the neutrino irradiation for the
supernova r-process nucleosynthesis, we calculate the rates of charged-current
and neutral-current neutrino reactions on neutron-rich heavy nuclei, and
estimate the average number of neutrons emitted in the resulting spallation.
Our results suggest that charged-current captures can be important in
breaking through the waiting-point nuclei at N=50 and 82, while still allowing
the formation of abundance peaks. Furthermore, after the r-process freezes out,
there appear to be distinctive neutral-current and charged-current
postprocessing effects. A subtraction of the neutrino postprocessing effects
from the observed solar r-process abundance distribution shows that two mass
regions, A=124-126 and 183-187, are inordinately sensitive to neutrino
postprocessing effects. This imposes very stringent bounds on the freeze-out
radii and dynamic timescales governing the r-process. Moreover, we find that
the abundance patterns within these mass windows are entirely consistent with
synthesis by neutrino interactions. This provides a strong argument that the
r-process must occur in the intense neutrino flux provided by a core-collapse
supernova.Comment: 34 pages, 4 PostScript figures, RevTe
Testing neutrino magnetic moment in ionization of atoms by neutrino impact
The atomic ionization processes induced by scattering of neutrinos play key
roles in the experimental searches for a neutrino magnetic moment. Current
experiments with reactor (anti)neutrinos employ germanium detectors having
energy threshold comparable to typical binding energies of atomic electrons,
which fact must be taken into account in the interpretation of the data. Our
theoretical analysis shows that the so-called stepping approximation to the
neutrino-impact ionization is well applicable for the lowest bound Coulomb
states, and it becomes exact in the semiclassical limit. Numerical evidence is
presented using the Thomas-Fermi model for the germanium atom.Comment: 5 pages, 1 figur
A New Upper Limit for the Tau-Neutrino Magnetic Moment
Using a prompt neutrino beam in which a nu_tau component was identified for
the first time, the nu_tau magnetic moment was measured based on a search for
an anomalous increase in the number of neutrino-electron interactions. One such
event was observed when 2.3 were expected from background processes, giving an
upper 90% confidence limit of 3.9x10^-7 Bohr magnetons.Comment: 9 pages; 1 figur