564 research outputs found
Semiclassical treatment of matter-enhanced neutrino oscillations for an arbitrary density profile
The matter-enhanced oscillations of two neutrino flavors are studied using a
uniform semiclassical approximation. Unlike some analytic studies which have
focused on certain exactly-solvable densities, this method can be used for an
arbitrary monotonic density profile. The method is applicable to a wider range
of mixing parameters than previous approximate methods for arbitrary densities.
The approximation is excellent in the adiabatic regime and up to the extreme
nonadiabatic limit. In particular, the range of validity for this approximation
extends farther into the nonadiabatic regime than for the linear Landau-Zener
result. This method also allows calculation of the source- and
detector-dependent terms in the unaveraged survival probability, and analytic
results for these terms are given. These interference terms may be important in
studying neutrino mixing in the sun or in supernovae.Comment: 29 REVTeX pages plus 3 included Postscript figures (uses the epsf
macro); submitted to Phys. Rev. D; also available at
http://nucth.physics.wisc.edu/preprints/mad-nt-96-02.tar.g
Black hole formation in core-collapse supernovae and time-of-flight measurements of the neutrino masses
In large stars that have exhausted their nuclear fuel, the stellar core collapses to a hot and dense proto-neutron star that cools by the radiation of neutrinos and antineutrinos of all flavors. Depending on its final mass, this may become either a neutron star or a black hole. Black hole formation may be triggered by mass accretion or a change in the high-density equation of state. We consider the possibility that black hole formation happens when the flux of neutrinos is still measurably high. If this occurs, then the neutrino signal from the supernova will be terminated abruptly (the transition takes ≲0.5 ms). The properties and duration of the signal before the cutoff are important measures of both the physics and astrophysics of the cooling proto-neutron star. For the event rates expected in present and proposed detectors, the cutoff will generally appear sharp, thus allowing model-independent time-of-flight mass tests for the neutrinos after the cutoff. If black hole formation occurs relatively early, within a few (∼1) seconds after core collapse, then the expected luminosities are of order LBH=1052 erg/s per flavor. In this case, the neutrino mass sensitivity can be extraordinary. For a supernova at a distance D=10 kpc, SuperKamiokande can detect a ν̅e mass down to 1.8 eV by comparing the arrival times of the high-energy and low-energy neutrinos in ν̅e+p→e++n. This test will also measure the cutoff time, and will thus allow a mass test of νμ and ντ relative to ν̅e. Assuming that νμ and ντ are nearly degenerate, as suggested by the atmospheric neutrino results, masses down to about 6 eV can be probed with a proposed lead detector of mass MD=4 kton (OMNIS). Remarkably, the neutrino mass sensitivity scales as (D/LBHMD)1/2. Therefore, direct sensitivity to all three neutrino masses in the interesting few-eV range is realistically possible; there are no other known techniques that have this capability
Thermal neutrinos from pre-supernova
We would like to discuss prospects for neutrino observations of the
core-collapse supernova progenitor during neutrino-cooled stage. We will
present new theoretical results on thermal neutrino and antineutrino spectra
produced deep inside the pre-supernova core. Three competing processes: pair-,
photo and plasma-neutrino production, are taken into account. The results will
be used to estimate signal in existing and future neutrino detectors. Chance
for supernova prediction is estimated, with possible aid to core-collapse
neutrino and gravitational wave detectors in the form of early warning.Comment: 1 page, Contribution to the Proceedings of Neutrino 2006 Conferenc
Neutrinos from supernovae: experimental status and perspectives
I discuss the state of the art in the search for neutrinos from galactic
stellar collapses and the future perspectives of this field. The implications
for the neutrino physics of a high statistics supernova neutrino burst
detection by the network of detectors operating around the world are also
reviewed.Comment: 19 pages, 12 figures. Extended version of talk given at IInd
International Workshop on Matter, Anti-Matter and Dark Matter, Trento
(Italy), 29-30 October 2001. A reduced version will appear in Int. J. of Mod.
Phys.
Leveraging the London 2012 Paralympic Games: What legacy for people with disabilities?
The International Paralympic Committee, U.K. Government, and the Organizing Committee for the London 2012 Olympic and Paralympic Games all contended that the London 2012 Paralympic Games would positively impact the lives of disabled people in the United Kingdom, particularly with regard to changing nondisabled attitudes toward disability. All three have claimed partial success during the course of the 4-year period (Olympiad) separating the London and Rio Paralympic Games. However, this is at odds with the findings of Disabled People’s Organizations (DPOs) and the experiences of disabled individuals. This article considers the claims of both sides against a backdrop of public policies that are targeting large-scale benefit cuts, the media coverage of which actually appears to be hardening attitudes toward anyone on benefits and negating any positive impacts from the Games themselves. It argues that the continued predominance of “ableist” perspectives on disability underpins many of the challenges faced by disabled people. The article adopts a historical perspective on the development of legacy-based foundations upon which the disability sport and Paralympic movements originated. It contends that the gradual move toward an elite “Olympic” sports model of competition has actually served to undermine these foundations
Public Diplomacy and the International Paralympic Committee: reconciling the roles of disability advocate and sports regulator
Whilst the link between international diplomacy and the Olympic movement has been the subject of extensive academic and journalistic enquiry, the experience of diplomatic discourse relating to the relatively youthful Paralympic movement has received little attention. It occurs not just in the context of state diplomacy, where for example the Paralympic Games may provide a conduit for the pursuit of specific policy objectives, but also in relation to the engagement of the International Paralympic Committee [IPC] as an evolving non-state actor in the diplomatic process. The idea of the IPC as an advocacy body engaged through public diplomacy in promoting disability rights needs exploration as an element of the contemporary politics of disability. This analysis considers the relationship between the activities of the IPC and wider lobbying by disabled people’s organisations as a means of leveraging change in domestic and international policy toward disability. In relation to the global development agenda, it also assesses IPC responses to the gulf in resourcing for para-sport – as well as related health and education provision - between high- and low-resource regions. It considers the response of the organisation from the perspective of public diplomacy and locates that response within the wider diplomacy of development
Neutrino Constraints on the Dark Matter Total Annihilation Cross Section
In the indirect detection of dark matter through its annihilation products,
the signals depend on the square of the dark matter density, making precise
knowledge of the distribution of dark matter in the Universe critical for
robust predictions. Many studies have focused on regions where the dark matter
density is greatest, e.g., the Galactic Center, as well as on the cosmic signal
arising from all halos in the Universe. We focus on the signal arising from the
whole Milky Way halo; this is less sensitive to uncertainties in the dark
matter distribution, and especially for flatter profiles, this halo signal is
larger than the cosmic signal. We illustrate this by considering a dark matter
model in which the principal annihilation products are neutrinos. Since
neutrinos are the least detectable Standard Model particles, a limit on their
flux conservatively bounds the dark matter total self-annihilation cross
section from above. By using the Milky Way halo signal, we show that previous
constraints using the cosmic signal can be improved on by 1-2 orders of
magnitude; dedicated experimental analyses should be able to improve both by an
additional 1-2 orders of magnitude.Comment: 8 pages, 4 figures; Matches version published in Phys. Rev.
Potential for Supernova Neutrino Detection in MiniBooNE
The MiniBooNE detector at Fermilab is designed to search for oscillation appearance at and to make a
decisive test of the LSND signal. The main detector (inside a veto shield) is a
spherical volume containing 0.680 ktons of mineral oil. This inner volume,
viewed by 1280 phototubes, is primarily a \v{C}erenkov medium, as the
scintillation yield is low. The entire detector is under a 3 m earth
overburden. Though the detector is not optimized for low-energy (tens of MeV)
events, and the cosmic-ray muon rate is high (10 kHz), we show that MiniBooNE
can function as a useful supernova neutrino detector. Simple trigger-level cuts
can greatly reduce the backgrounds due to cosmic-ray muons. For a canonical
Galactic supernova at 10 kpc, about 190 supernova
events would be detected. By adding MiniBooNE to the international network of
supernova detectors, the possibility of a supernova being missed would be
reduced. Additionally, the paths of the supernova neutrinos through Earth will
be different for MiniBooNE and other detectors, thus allowing tests of
matter-affected mixing effects on the neutrino signal.Comment: Added references, version to appear in PR
Weak proton capture on 3He
The astrophysical S-factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to realistic Hamiltonians consisting of the Argonne v14 or
Argonne v18 two-nucleon and Urbana-VIII or Urbana-IX three-nucleon
interactions. The nuclear weak charge and current operators have vector and
axial-vector components, that include one- and many-body terms. All possible
multipole transitions connecting any of the p 3He S- and P-wave channels to the
4He bound state are considered. The S-factor at a p 3He center-of-mass energy
of 10 keV, close to the Gamow-peak energy, is predicted to be 10.1 10^{-20} keV
b with the AV18/UIX Hamiltonian, a factor of about 4.5 larger than the value
adopted in the standard solar model. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor. The energy
dependence is rather weak: the AV18/UIX zero-energy S-factor is 9.64 10^{-20}
keV b, only 5 % smaller than the 10 keV result quoted above. The model
dependence is also found to be weak: the zero-energy S-factor is calculated to
be 10.2 10^{-20} keV b with the older AV14/UVIII model, only 6 % larger than
the AV18/UIX result. Our best estimate for the S-factor at 10 keV is therefore
(10.1 \pm 0.6) 10^{-20} keV b, when the theoretical uncertainty due to the
model dependence is included. This value for the calculated S-factor is not as
large as determined in fits to the Super-Kamiokande data in which the hep flux
normalization is free. However, the precise calculation of the S-factor and the
consequent absolute prediction for the hep neutrino flux will allow much
greater discrimination among proposed solar neutrino oscillation solutions.Comment: 54 pages RevTex file, 6 PostScript figures, submitted to Phys. Rev.
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