451 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
Cosmic neutrinos at IceCube: , and initial flavor composition
We discuss the prospect of extracting the values of the mixing parameters
and through the detection of cosmic neutrinos in the
planned and forthcoming neutrino telescopes. We take the ratio of the
muon-track to shower-like events, R, as the realistic quantity that can be
measured in the neutrino telescopes. We take into account several sources of
uncertainties that enter the analysis. We then examine to what extent the
deviation of the initial flavor composition from w_e:w_\mu:w_\tau=1:2:0 can be
tested.Comment: 3 pages, 2 figures, Talk given at the TAUP 2009 conference, Rome,
Italy; J. Phys. Conf. Series to appea
Cosmic Neutrino Bound on the Dark Matter Annihilation Rate in the Late Universe
How large can the dark matter self-annihilation rate in the late universe be?
This rate depends on (rho_DM/m_chi)^2 , where rho_DM/m_chi is the
number density of dark matter, and the annihilation cross section is averaged
over the velocity distribution. Since the clustering of dark matter is known,
this amounts to asking how large the annihilation cross section can be.
Kaplinghat, Knox, and Turner proposed that a very large annihilation cross
section could turn a halo cusp into a core, improving agreement between
simulations and observations; Hui showed that unitarity prohibits this for
large dark matter masses. We show that if the annihilation products are
Standard Model particles, even just neutrinos, the consequent fluxes are ruled
out by orders of magnitude, even at small masses. Equivalently, to invoke such
large annihilation cross sections, one must now require that essentially no
Standard Model particles are produced.Comment: 4 pages, 2 figures; to appear in the proceedings of the TeV Particle
Astrophysics II Workshop, Madison, Wisconsin, 28-31 Aug 200
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
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.
Reconstruction of supernova {\nu}_{\mu}, {\nu}_{\tau}, anti-{\nu}_{\mu}, and anti-{\nu}_{\tau} neutrino spectra at scintillator detectors
We present a new technique to directly reconstruct the spectra of mu/tau
neutrinos and antineutrinos from a supernova, using neutrino-proton elastic
scattering events (nu+p to nu+p) at scintillator detectors. These neutrinos,
unlike electron neutrinos and antineutrinos, have only neutral current
interactions, which makes it very challenging, with any reaction, to detect
them and measure their energies. With updated inputs from theory and
experiments, we show that this channel provides a robust and sensitive measure
of their spectra. Given the low yields and lack of spectral information in
other neutral current channels, this is perhaps the only realistic way to
extract such information. This will be indispensable for understanding flavor
oscillations of SN neutrinos, as it is likely to be impossible to disentangle
neutrino mixing from astrophysical uncertainties in a SN without adequate
spectral coverage of all flavors. We emphasize that scintillator detectors,
e.g., Borexino, KamLAND, and SNO+, have the capability to observe these events,
but they must be adequately prepared with a trigger for a burst of low-energy
events. We also highlight the capabilities of a larger detector like LENA.Comment: v3: Typo corrected in Eq.14, and metadata edits. Matches PRD version.
14 pages, 9 figures, 1 tabl
Neutrino Flavor Goniometry by High Energy Astrophysical Beams
It is shown how high energy neutrino beams from very distant sources can be
utilized to learn about many properties of neutrinos such as lifetimes, mass
hierarchy, mixing, minuscule pseudo-Dirac mass splittings; in addition, the
production mechanism of neutrinos in astrophysical sources can also be
elucidated.Comment: 22 pages. Presented at the COSPA 2007, Taipei, November 2007; to be
published in the proceedings. Added reference
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