378 research outputs found
Neutrino physics theory
Neutrino physics covers a wide range in theoretical physics. I briefly review the state of the art of neutrino theory, with particular regard to the measure of masses and mixings. Some issues for the future are outlined
On detecting oscillations of gamma rays into axion-like particles in turbulent and coherent magnetic fields
Background radiation fields pervade the Universe, and above a certain energy
any -ray flux emitted by an extragalactic source should be attenuated
due to pair production. The opacity could be alleviated if photons
oscillated into hypothetical axion-like particles (ALPs) in ambient magnetic
fields, leading to a -ray excess especially at high optical depths that
could be detected with imaging air Cherenkov telescopes (IACTs).
Here, we introduce a method to search for such a signal in -ray data
and to estimate sensitivities for future observations. Different magnetic
fields close to the -ray source are taken into account in which photons
can convert into ALPs that then propagate unimpeded over cosmological distances
until they re-convert in the magnetic field of the Milky Way. Specifically, we
consider the coherent field at parsec scales in a blazar jet as well as the
turbulent field inside a galaxy cluster. For the latter, we explicitly derive
the transversal components of a magnetic field with gaussian turbulence which
are responsible for the photon-ALP mixing. To illustrate the method, we apply
it to a mock IACT array with characteristics similar to the Cherenkov Telescope
Array and investigate the dependence of the sensitivity to detect a
-ray excess on the magnetic-field parameters.Comment: 31 pages, 9 figures. Published in JCA
Reionization during the dark ages from a cosmic axion background
Recently it has been pointed out that a cosmic background of relativistic
axion-like particles (ALPs) would be produced by the primordial decays of heavy
fields in the post-inflation epoch, contributing to the extra-radiation content
in the Universe today. Primordial magnetic fields would trigger conversions of
these ALPs into sub-MeV photons during the dark ages. This photon flux would
produce an early reionization of the Universe, leaving a significant imprint on
the total optical depth to recombination . Using the current measurement
of and the limit on the extra-radiation content by
the Planck experiment we put a strong bound on the ALP-photon conversions.
Namely we obtain upper limits on the product of the photon-ALP coupling
constant times the magnetic field strength down to
for
ultralight ALPs.Comment: 23 pages, 6 figures. Minor changes, references added. Prepared for
publication in JCA
Revisiting cosmological bounds on radiative neutrino lifetime
Neutrino oscillation experiments and direct bounds on absolute masses
constrain neutrino mass differences to fall into the microwave energy range,
for most of the allowed parameter space. As a consequence of these recent
phenomenological advances, older constraints on radiative neutrino decays based
on diffuse background radiations and assuming strongly hierarchical masses in
the eV range are now outdated. We thus derive new bounds on the radiative
neutrino lifetime using the high precision cosmic microwave background spectral
data collected by the Far Infrared Absolute Spectrophotometer instrument on
board of Cosmic Background Explorer. The lower bound on the lifetime is between
a few x 10^19 s and 5 x 10^20 s, depending on the neutrino mass ordering and on
the absolute mass scale. However, due to phase space limitations, the upper
bound in terms of the effective magnetic moment mediating the decay is not
better than ~ 10^-8 Bohr magnetons. We also comment about possible improvements
of these limits, by means of recent diffuse infrared photon background data. We
compare these bounds with pre-existing limits coming from laboratory or
astrophysical arguments. We emphasize the complementarity of our results with
others available in the literature.Comment: 7 pages, 3 figures. Minor changes in the text, few references added.
Matches the published versio
Axion-like particles from primordial black holes shining through the Universe
We consider a cosmological scenario in which the very early Universe
experienced a transient epoch of matter domination due to the formation of a
large population of primordial black holes (PBHs) with masses , that evaporate before Big Bang nucleosynthesis. In this
context, Hawking radiation would be a non-thermal mechanism to produce a cosmic
background of axion-like particles (ALPs). We assume the minimal scenario in
which these ALPs couple only with photons. In the case of ultralight ALPs () the cosmic magnetic fields might trigger
ALP-photon conversions, while for masses
spontaneous ALP decay in photon pairs would be effective. We investigate the
impact of these mechanisms on the cosmic X-ray background, on the excess in
X-ray luminosity in Galaxy Clusters, and on the process of cosmic reionization.Comment: (33 pages, 12 pdf figures
Solar neutrino oscillations in the quasi-vacuum regime
Motivated by recent experimental data, we study solar neutrino oscillations
in the range 10^-10 < delta m^2/E < 10^-7 eV^2/MeV. In this range vacuum
oscillations become increasingly affected by (solar and terrestrial) matter
effects for increasing delta m^2, smoothly reaching the MSW regime. A numerical
study of matter effects in such "quasi-vacuum" regime is performed. The results
are applied to the analysis of the recent solar neutrino phenomenology.Comment: 4 pages, 2 figures. Talk given at Europhysics Neutrino Oscillation
Workshop (NOW 2000), Conca Specchiulla, Otranto, Lecce, Italy, 9-16 Sep 2000.
Figure 2 correcte
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