149 research outputs found

### Astrophysical Axion Bounds

Axion emission by hot and dense plasmas is a new energy-loss channel for
stars. Observational consequences include a modification of the solar
sound-speed profile, an increase of the solar neutrino flux, a reduction of the
helium-burning lifetime of globular-cluster stars, accelerated white-dwarf
cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We
review and update these arguments and summarize the resulting axion
constraints.Comment: Contribution to Axion volume of Lecture Notes in Physics, 20 pages, 3
figure

### Photon Production From The Scattering of Axions Out of a Solenoidal Magnetic Field

We calculate the total cross section for the production of photons from the
scattering of axions by a strong inhomogeneous magnetic field in the form of a
2D delta-function, a cylindrical step function and a 2D Gaussian distribution,
which can be approximately produced by a solenoidal current. The theoretical
result is used to estimate the axion-photon conversion probability which could
be expected in a reasonable experimental situation. The calculated conversion
probabilities for QCD inspired axions are bigger by a factor of 2.67 (for the
cylindrical step function case) than those derived by applying the celebrated
1D calculation of the (inverse) coherent Primakoff effect. We also consider
scattering at a resonance $E_{axion} \sim m_{axion}$, which corresponds to the
scattering from a delta-function and gives the most enhanced results. Finally,
we analyze the results of this work in the astrophysical extension to suggest a
way in which they may be directed to a solution to some basic solar physics
problems and, in particular, the coronal heating problem.Comment: 19 pages, 1 figure, added analysis of our results in the
astrophysical extensio

### Supernova neutrinos and antineutrinos: ternary luminosity diagram and spectral split patterns

In core-collapse supernovae, the nu_e and anti-nu_e species may experience
collective flavor swaps to non-electron species nu_x, within energy intervals
limited by relatively sharp boundaries ("splits"). These phenomena appear to
depend sensitively upon the initial energy spectra and luminosities. We
investigate the effect of generic variations of the fractional luminosities
(l_e, l_{anti-e}, l_x) with respect to the usual "energy equipartition" case
(1/6, 1/6, 1/6), within an early-time supernova scenario with fixed thermal
spectra and total luminosity. We represent the constraint l_e+l_{anti-e}+4l_x=1
in a ternary diagram, which is explored via numerical experiments (in
single-angle approximation) over an evenly-spaced grid of points. In inverted
hierarchy, single splits arise in most cases, but an abrupt transition to
double splits is observed for a few points surrounding the equipartition one.
In normal hierarchy, collective effects turn out to be unobservable at all grid
points but one, where single splits occur. Admissible deviations from
equipartition may thus induce dramatic changes in the shape of supernova
(anti)neutrino spectra. The observed patterns are interpreted in terms of
initial flavor polarization vectors (defining boundaries for the single/double
split transitions), lepton number conservation, and minimization of potential
energy.Comment: 24 pages, including 14 figures (1 section with 2 figures added).
Accepted for publication in JCA

### New constraints for heavy axion-like particles from supernovae

We derive new constraints on the coupling of heavy pseudoscalar (axion-like)
particles to photons, based on the gamma ray flux expected from the decay of
these particles into photons. After being produced in the supernova core, these
heavy axion-like particles would escape and a fraction of them would decay into
photons before reaching the Earth. We have calculated the expected flux on
Earth of these photons from the supernovae SN 1987A and Cassiopeia A and
compared our results to data from the Fermi Large Area Telescope. This analysis
provides strong constraints on the parameter space for axion-like particles.
For a particle mass of 100 MeV, we find that the Peccei-Quinn constant, f_a,
must be greater than about 10^{15} GeV. Alternatively, for fa=10^{12} GeV, we
exclude the mass region between approximately 100 eV and 1 GeV.Comment: 14 pages, 4 figures. Version published in JCAP. Major changes in the
exposition. Added a figure. Added appendix. Minor changes in the results.
Some changes in the bibliograph

### Flavour-dependent radiative correction to neutrino-neutrino refraction

In the framework of the Standard Model we calculate the flavour non-universal
correction for neutrino refraction in a neutrino background and verify a
similar previous result for the case of ordinary-matter background. The
dominant term arises at loop level and involves tau leptons circulating in the
loop. These O(G_F m_tau^2) corrections to the tree-level potential provide the
dominant refractive difference between nu_mu and nu_tau unless the medium
contains mu or tau leptons. Our results affect the flavour evolution of dense
neutrino gases and may be of interest for collective three-flavour oscillations
of supernova neutrinos. We spell out explicitly how these non-universal
neutrino-neutrino interactions enter the flavour oscillation equations.Comment: 15 pages, 6 figures; updated reference lis

### Fast-time Variations of Supernova Neutrino Fluxes and Detection Perspectives

AbstractIn the delayed explosion scenario of a core-collapse supernova, the accretion phase shows pronounced convective over-turns and a low-multipole hydrodynamic instability, the so-called standing accretion shock instability (SASI). Neutrino signal variations from the first full-scale three-dimensional core-collapse supernova simulations with sophisticated neutrino transport are presented as well as their detection perspectives in IceCube and Hyper-Kamiokande

### On a Light Spinless Particle Coupled to Photons

A pseudoscalar or scalar particle $\phi$ that couples to two photons but not
to leptons, quarks and nucleons would have effects in most of the experiments
searching for axions, since these are based on the $a \gamma \gamma$ coupling.
We examine the laboratory, astrophysical and cosmological constraints on $\phi$
and study whether it may constitute a substantial part of the dark matter. We
also generalize the $\phi$ interactions to possess $SU(2) \times U(1)$ gauge
invariance, and analyze the phenomenological implications.Comment: LaTex, 20p., 6 figures. Changes in sections 4, 5 and figure 2, our
bounds are now more stringent. To be published in Physical Review

### Sterile neutrino production via active-sterile oscillations: the quantum Zeno effect

We study several aspects of the kinetic approach to sterile neutrino
production via active-sterile mixing. We obtain the neutrino propagator in the
medium including self-energy corrections up to $\mathcal{O}(G^2_F)$, from which
we extract the dispersion relations and damping rates of the propagating modes.
The dispersion relations are the usual ones in terms of the index of refraction
in the medium, and the damping rates are $\Gamma_1(k) = \Gamma_{aa}(k)
\cos^2\theta_m(k); \Gamma_2(k) = \Gamma_{aa}(k) \sin^2\theta_m(k)$ where
$\Gamma_{aa}(k)\propto G^2_F k T^4$ is the active neutrino scattering rate and
$\theta_m(k)$ is the mixing angle in the medium. We provide a generalization of
the transition probability in the \emph{medium from expectation values in the
density matrix}: $P_{a\to s}(t) = \frac{\sin^22\theta_m}{4}[e^{-\Gamma_1t} +
e^{-\Gamma_2 t}-2e^{-{1/2}(\Gamma_1+\Gamma_2)t} \cos\big(\Delta E t\big)]$ and
study the conditions for its quantum Zeno suppression directly in real time. We
find the general conditions for quantum Zeno suppression, which for $m_s\sim
\textrm{keV}$ sterile neutrinos with $\sin2\theta \lesssim 10^{-3}$ \emph{may
only be} fulfilled near an MSW resonance. We discuss the implications for
sterile neutrino production and argue that in the early Universe the wide
separation of relaxation scales far away from MSW resonances suggests the
breakdown of the current kinetic approach.Comment: version to appear in JHE

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