52 research outputs found
Neutrinos and Primordial Nucleosynthesis
The importance of the Big Bang Nucleosynthesis (BBN) as a unique tool for
studying neutrino properties is discussed, and the recent steps towards a
self-consistent and robust handling of the weak reaction decoupling from the
thermal bath as well as of the neutrino reheating following the e+e-
annihilation are summarized. We also emphasize the important role of the Cosmic
Microwave Background (CMB) anisotropy in providing an accurate and independent
determination of the baryon density parameter omegab. The BBN is presently a
powerful parameter-free theory that can test the standard scenario of the
neutrino decoupling in the early Universe. Moreover it can constrain new
physics in the neutrino sector. The perspectives for improvements in the next
years are outlined.Comment: Talk given by G. Mangano at NOW2004, Conca Specchiulla, Otranto
Italy, september 2004. To appear in the Proceedings of the Worksho
PArthENoPE: Public Algorithm Evaluating the Nucleosynthesis of Primordial Elements
We describe a program for computing the abundances of light elements produced
during Big Bang Nucleosynthesis which is publicly available at
http://parthenope.na.infn.it/. Starting from nuclear statistical equilibrium
conditions the program solves the set of coupled ordinary differential
equations, follows the departure from chemical equilibrium of nuclear species,
and determines their asymptotic abundances as function of several input
cosmological parameters as the baryon density, the number of effective
neutrino, the value of cosmological constant and the neutrino chemical
potential. The program requires commercial NAG library routines.Comment: 18 pages, 2 figures. Version accepted by Comp. Phys. Com. The code
(and an updated manual) is publicly available at
http://parthenope.na.infn.it
Recommended from our members
Dark matter annihilation bound from the diffuse gamma ray flux
An upper limit on the total annihilation rate of dark matter (DM) has been recently derived from the observed atmospheric neutrino background. It is a very conservative upper bound based on the sole hypothesis that the DM annihilation products are the least detectable final states in the Standard Model (SM), neutrinos. Any other decay channel into SM particles would lead to stronger constraints. We show that comparable bounds are obtained for DM masses around the TeV scale by observations of the diffuse gamma ray flux by EGRET, because electroweak bremsstrahlung leads to non-negligible electromagnetic branching ratios, even if DM particles only couple to neutrinos at tree level. A better mapping and the partial resolution of the diffuse gamma-ray background into astrophysical sources by the GLAST satellite will improve this bound in the near future
Neutrino decay as a possible interpretation to the MiniBooNE observation with unparticle scenario
In a new measurement on neutrino oscillation , the
MiniBooNE Collaboration observes an excess of electron-like events at low
energy and the phenomenon may demand an explanation which obviously is beyond
the oscillation picuture. We propose that heavier neutrino decaying
into a lighter one via the transition process
where denotes any light products, could be a natural mechanism. The
theoretical model we employ here is the unparticle scenario established by
Georgi. We have studied two particular modes \nu_\mu\to \nu_e+\Un and
. Unfortunately, the number coming out from
the computation is too small to explain the observation. Moreover, our results
are consistent with the cosmology constraint on the neutrino lifetime and the
theoretical estimation made by other groups, therefore we can conclude that
even though neutrino decay seems plausible in this case, it indeed cannot be
the source of the peak at lower energy observed by the MiniBooNE collaboration
and there should be other mechanisms responsible for the phenomenon.Comment: 14 pages, conclusions are changed; published version for EPJ
Constraining the cosmic radiation density due to lepton number with Big Bang Nucleosynthesis
The cosmic energy density in the form of radiation before and during Big Bang
Nucleosynthesis (BBN) is typically parameterized in terms of the effective
number of neutrinos N_eff. This quantity, in case of no extra degrees of
freedom, depends upon the chemical potential and the temperature characterizing
the three active neutrino distributions, as well as by their possible
non-thermal features. In the present analysis we determine the upper bounds
that BBN places on N_eff from primordial neutrino--antineutrino asymmetries,
with a careful treatment of the dynamics of neutrino oscillations. We consider
quite a wide range for the total lepton number in the neutrino sector, eta_nu=
eta_{nu_e}+eta_{nu_mu}+eta_{nu_tau} and the initial electron neutrino asymmetry
eta_{nu_e}^in, solving the corresponding kinetic equations which rule the
dynamics of neutrino (antineutrino) distributions in phase space due to
collisions, pair processes and flavor oscillations. New bounds on both the
total lepton number in the neutrino sector and the nu_e -bar{nu}_e asymmetry at
the onset of BBN are obtained fully exploiting the time evolution of neutrino
distributions, as well as the most recent determinations of primordial 2H/H
density ratio and 4He mass fraction. Note that taking the baryon fraction as
measured by WMAP, the 2H/H abundance plays a relevant role in constraining the
allowed regions in the eta_nu -eta_{nu_e}^in plane. These bounds fix the
maximum contribution of neutrinos with primordial asymmetries to N_eff as a
function of the mixing parameter theta_13, and point out the upper bound N_eff
< 3.4. Comparing these results with the forthcoming measurement of N_eff by the
Planck satellite will likely provide insight on the nature of the radiation
content of the universe.Comment: 17 pages, 9 figures, version to be published in JCA
The Compton-Getting effect on ultra-high energy cosmic rays of cosmological origin
Deviations from isotropy have been a key tool to identify the origin and the
primary type of cosmic rays at low energies. We suggest that the
Compton-Getting effect can play a similar role at ultra-high energies: If at
these energies the cosmic ray flux is dominated by sources at cosmological
distances, then the movement of the Sun relative to the cosmic microwave
background frame induces a dipole anisotropy at the 0.6% level. The energy
dependence and the orientation of this anisotropy provide important information
about the transition between galactic and extragalactic cosmic rays, the charge
of the cosmic ray primaries, the galactic magnetic field and, at the highest
energies, the energy-loss horizon of cosmic rays. A 3-sigma detection of this
effect requires around 10^6 events in the considered energy range and is thus
challenging but not impossible with present detectors. As a corollary we note
that the Compton-Getting effect allows one also to constrain the fraction of
the diffuse gamma-ray background emitted by sources at cosmological distance,
with promising detection possibilities for the GLAST satellite.Comment: v2: 5 pages, no figure. Minor changes, matches published versio
Astrophysical interpretation of the medium scale clustering in the ultra-high energy sky
We compare the clustering properties of the combined dataset of ultra-high
energy cosmic rays events, reported by the AGASA, HiRes, Yakutsk and Sugar
collaborations, with a catalogue of galaxies of the local universe (redshift
z<~0.06). We find that the data reproduce particularly well the clustering
properties of the nearby universe within z <~0.02. There is no statistically
significant cross-correlation between data and structures, although
intriguingly the nominal cross-correlation chance probability drops from ~50%
to ~10% using the catalogue with a smaller horizon. Also, we discuss the impact
on the robustness of the results of deflections in some galactic magnetic field
models used in the literature. These results suggest a relevant role of
magnetic fields (possibly extragalactic ones, too) and/or possibly some heavy
nuclei fraction in the UHECRs. The importance of a confirmation of these hints
by Auger data is emphasized.Comment: 10 pages, 7 figures; one reference adde
Dynamical Dark Energy model parameters with or without massive neutrinos
We use WMAP5 and other cosmological data to constrain model parameters in
quintessence cosmologies, focusing also on their shift when we allow for
non-vanishing neutrino masses. The Ratra-Peebles (RP) and SUGRA potentials are
used here, as examples of slowly or fastly varying state parameter w(a). Both
potentials depend on an energy scale \Lambda. Here we confirm the results of
previous analysis with WMAP3 data on the upper limits on \Lambda, which turn
out to be rather small (down to ~10^{-9} in RP cosmologies and ~10^{-5} for
SUGRA). Our constraints on \Lambda are not heavily affected by the inclusion of
neutrino mass as a free parameter. On the contrary, when the neutrino mass
degree of freedom is opened, significant shifts in the best-fit values of other
parameters occur.Comment: 9 pages, 3 figures, submitted to JCA
Creation of the CMB spectrum: precise analytic solutions for the blackbody photosphere
The blackbody spectrum of CMB was created in the blackbody photosphere at
redshifts z>2x10^6. At these early times, the Universe was dense and hot enough
that complete thermal equilibrium between baryonic matter (electrons and ions)
and photons could be established. Any perturbation away from the blackbody
spectrum was suppressed exponentially. New physics, for example annihilation
and decay of dark matter, can add energy and photons to CMB at redshifts z>10^5
and result in a Bose-Einstein spectrum with a non-zero chemical potential
(). Precise evolution of the CMB spectrum around the critical redshift of
z~2x10^6 is required in order to calculate the -type spectral distortion
and constrain the underlying new physics. Although numerical calculation of
important processes involved (double Compton process, comptonization and
bremsstrahlung) is not difficult, analytic solutions are much faster and easier
to calculate and provide valuable physical insights. We provide precise (better
than 1%) analytic solutions for the decay of , created at an earlier
epoch, including all three processes, double Compton, Compton scattering on
thermal electrons and bremsstrahlung in the limit of small distortions. This is
a significant improvement over the existing solutions with accuracy ~10% or
worse. We also give a census of important sources of energy injection into CMB
in standard cosmology. In particular, calculations of distortions from
electron-positron annihilation and primordial nucleosynthesis illustrate in a
dramatic way the strength of the equilibrium restoring processes in the early
Universe. Finally, we point out the triple degeneracy in standard cosmology,
i.e., the and distortions from adiabatic cooling of baryons and
electrons, Silk damping and annihilation of thermally produced WIMP dark matter
are of similar order of magnitude (~ 10^{-8}-10^{-10})
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