11,395 research outputs found
Axions - Motivation, limits and searches
The axion solution of the strong CP problem provides a number of possible
windows to physics beyond the standard model, notably in the form of searches
for solar axions and for galactic axion dark matter, but in a broader context
also inspires searches for axion-like particles in pure laboratory experiments.
We briefly review the motivation for axions, astrophysical limits, their
possible cosmological role, and current searches for axions and axion-like
particles.Comment: Contribution to IRGAC 06, Barcelona. New figure for allowed axion
parameters, including hot dark matter limit
Limits on a CP-violating scalar axion-nucleon interaction
Axions or similar hypothetical pseudoscalar bosons may have a small
CP-violating scalar Yukawa interaction g_s(N) with nucleons, causing
macroscopic monopole-dipole forces. Torsion-balance experiments constrain
g_p(e) g_s(N), whereas g_p(N) g_s(N) is constrained by the depolarization rate
of ultra-cold neutrons or spin-polarized nuclei. However, the pseudoscalar
couplings g_p(e) and g_p(N) are strongly constrained by stellar energy-loss
arguments and g_s(N) by searches for anomalous monopole-monopole forces,
together providing the most restrictive limits on g_p(e) g_s(N) and g_p(N)
g_s(N). The laboratory limits on g_s(N) are currently the most restrictive
constraints on CP-violating axion interactions.Comment: 5 pages, 4 figures, small textual changes in v2, matches published
versio
Reconstructing the supernova bounce time with neutrinos in IceCube
Generic model predictions for the early neutrino signal of a core-collapse
supernova (SN) imply that IceCube can reconstruct the bounce to within about
+/- 3.5 ms at 95% CL (assumed SN distance 10 kpc), relevant for coincidence
with gravitational-wave detectors. The timing uncertainty scales approximately
with distance-squared. The offset between true and reconstructed bounce time of
up to several ms depends on the neutrino flavor oscillation scenario. Our work
extends the recent study of Pagliaroli et al. [PRL 103, 031102 (2009)] and
demonstrates IceCube's superb timing capabilities for neutrinos from the next
nearby SN.Comment: 4 pages, 1 figure, some references and caveats added, matches final
version in PR
Synchronization vs. decoherence of neutrino oscillations at intermediate densities
We study collective oscillations of a two-flavor neutrino system with
arbitrary but fixed density. In the vacuum limit, modes with different energies
quickly de-phase (kinematical decoherence), whereas in the limit of infinite
density they lock to each other (synchronization). For intermediate densities,
we find different classes of solutions. There is always a phase transition in
the sense of partial synchronization occurring only above a density threshold.
For small mixing angles, partial or complete decoherence can be induced by a
parametric resonance, introducing a new time scale to the problem, the final
outcome depending on the spectrum and mixing angle. We derive an analytic
relation that allows us to calculate the late-time degree of coherence based on
the spectrum alone.Comment: 11 pages, including 13 figures. Clarifying paragraphs and 2 figures
added; results unchanged. Matches published version in PR
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