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G. Miele

Publications and source records attributed to G. Miele.

At least 55 records · Page 3Linked to original sources
arXiv2000

Non equilibrium spectra of degenerate relic neutrinos

We calculate the exact kinetic evolution of cosmic neutrinos until complete decoupling, in the case when a large neutrino asymmetry exists. While not excluded by present observations, this large asymmetry can have relevant cosmological consequences and in particular may be helpful in reconciling Primordial Nucleosynthesis with a high baryon density as suggested by the most recent observations of the Cosmic Microwave Background Radiation. By solving numerically the Boltzmann kinetic equations for the neutrino distribution functions, we find the momentum-dependent corrections to the equilibrium spectra and briefly discuss their phenomenological implications.

astro-ph↗
arXiv2000

The standard and degenerate primordial nucleosynthesis versus recent experimental data

We report the results on Big Bang Nucleosynthesis (BBN) based on an updated code, with accuracy of the order of 0.1% on He4 abundance, compared with the predictions of other recent similar analysis. We discuss the compatibility of the theoretical results, for vanishing neutrino chemical potentials, with the observational data. Bounds on the number of relativistic neutrinos and baryon abundance are obtained by a likelihood analysis. We also analyze the effect of large neutrino chemical potentials on primordial nucleosynthesis, motivated by the recent results on the Cosmic Microwave Background Radiation spectrum. The BBN exclusion plots for electron neutrino chemical potential and the effective number of relativistic neutrinos are reported. We find that the standard BBN seems to be only marginally in agreement with the recent BOOMERANG and MAXIMA-1 results, while the agreement is much better for degenerate BBN scenarios for large effective number of neutrinos, N_ν\sim 10.

astro-ph↗
arXiv2000

Testing Standard and Degenerate Big Bang Nucleosynthesis with BOOMERanG and MAXIMA-1

We test different Big Bang Nucleosynthesis scenarios using the recent results on the Cosmic Microwave Background Anisotropies provided by the BOOMERanG and MAXIMA-1 experiments versus the observed abundances of 4He, D and 7Li. The likelihood analysis, based on Bayesian approach, shows that, in the case of high deuterium abundance, Y_D=(2.0\pm0.5) 10^{-4}, both standard and degenerate BBN are inconsistent with the CMBR measurement at more than 3 σ. Assuming low deuterium abundance, Y_D=(3.4\pm0.3) 10^{-5}, the standard BBN model is still inconsistent with present observations at 2 σlevel, while the degenerate BBN results to be compatible. Unless systematics effects will be found in nuclide abundances and/or in CMBR data analysis this result may be a signal in favour of new physics like a large chemical potential of the relic neutrino-antineutrino background.

astro-ph↗
arXiv2000

Unstable Heavy Majorana Neutrinos and Leptogenesis

We propose a new mechanism producing a non-vanishing lepton number asymmetry, based on decays of heavy Majorana neutrinos. If they are produced out of equilibrium, as occurs in preheating scenario, and are superpositions of mass eigenstates rapidly decaying, their decay rates contains interference terms provided the mass differences $Δm$ are small compared to widths $Γ$. The resulting lepton asymmetry, which is the analogue of the time-integrated CP asymmetry in $B^0-\bar{B}^0$ system, is found to be proportional to $Δm/Γ$.

hep-ph↗
arXiv1999

New results in primordial nucleosynthesis

We report the results of a new accurate evaluation of light nuclei yields in primordial nucleosynthesis. The relic densities of 4He, D and 7Li have been numerically obtained via a new updated version of the standard BBN code.

astro-ph↗
arXiv1999

Primordial Nucleosynthesis: Accurate Predictions

A new accurate evaluation of primordial light nuclei abundances is presented. The proton to neutron conversion rates have been corrected to take into account radiative effects, finite nucleon mass, thermal and plasma corrections. The theoretical uncertainty on 4He is so reduced to the order of 0.1%.

astro-ph↗
arXiv1999

Big Bang Nucleosynthesis: an accurate determination of light element yields

We report the results of a new accurate evaluation of light nuclei yields in primordial nucleosynthesis. All radiative effects, finite nucleon mass, thermal and plasma corrections are included in the proton to neutron conversion rates. The relic densities of He4, D and Li7 have been numerically obtained via a new updated version of the standard BBN code. In particular the theoretical uncertainty on He4 is reduced to the order of 0.1%.

astro-ph↗
arXiv1999

A direct evaluation of the Lambda_c^+ absolute branching ratios: a new approach

A novel method for a direct measurement of the exclusive Lambda_c^+ branching ratios is here described. The approach is based on the peculiar topology of the quasi-elastic charm neutrino-induced events on nucleons. The intrinsic potentiality of the method is thoroughly discussed using a "perfect detector". As an application, the statistical accuracy reachable with existing data sample has been estimated. From a theoretical point of view, such measurement provides a better understanding of the baryonic b-decays.

hep-ph↗
arXiv1998

Precision Rates for Nucleon Weak Interactions in Primordial Nucleosynthesis and He-4 Abundance

We report the results of a detailed calculation of nucleon weak interactions relevant for the neutron to proton density ratio at the onset of primordial nucleosynthesis. Radiative electromagnetic corrections, finite nucleon mass terms, thermal radiative effects on weak processes and on neutrino temperature are taken into account to reduce the theoretical uncertainty on $n \leftrightarrow p $ rates to 1%. This translates into a sensitivity in $^4 He$ mass fraction $Y_p$ prediction up to $10^{-4}$. We find a positive total correction to the Born prediction $δY_p \simeq 0.004$.

astro-ph↗
arXiv1998

Wave Function Renormalization at Finite Temperature

We present a derivation of the medium dependent wave function renormalization for a spinor field in presence of a thermal bath. We show that, as already pointed out in literature, projector operators are not multiplicatively renormalized and the effect involves a non trivial spinor dependence, which disappears in the zero temperature covariant limit. The results, which differ from what already found in literature, are then applied to the decay of a massive scalar boson into two fermions and to the $β$--decay and crossed related processes relevant for primordial nucleosynthesis.

hep-ph↗
arXiv1997

Hybrid Inflation from Supersymmetric SU(5)

A scheme of hybrid inflation is considered in the framework of the minimal supersymmetric SU(5) model with an extra singlet. The relevant role of the cubic term in the adjoint representation in the renormalizable superpotential is pointed out in order to have a quite wide region of initial conditions compatible with inflation efficiency, monopole density and perturbations constraint.

hep-ph↗
arXiv1997

Mirror Fermions in Noncommutative Geometry

In a recent paper we pointed out the presence of extra fermionic degrees of freedom in a chiral gauge theory based on Connes Noncommutative Geometry. Here we propose a mechanism which provides a high mass to these mirror states, so that they decouple from low energy physics.

hep-th↗
arXiv1997

Three Flavour Majorana Neutrinos with Magnetic Moments in a Supernova

The resonant transition effects MSW and NSFP for three flavour Majorana neutrinos in a supernova are considered, where the transition magnetic moments are likely to play a relevant role in neutrino physics. In this scenario, the deformed thermal neutrino distributions are obtained for different choices of the electron-tau mixing angle. Detailed predictions for the future large neutrino detectors are also given in terms of the ratio between the spectra of recoil electrons for deformed and undeformed spectra.

hep-ph↗
arXiv1996

Supernova Neutrino Energy Spectra and the MSW Effect

The distortions in the thermal energy spectra for neutrinos produced in a supernova when a resonant oscillation, MSW effect, occurs are determined. In order to show this effect for some relevant and representative examples of unified gauge models, we have chosen $SO(10)$, and $SU(5)_{SUSY}$, $SO(10)_{SUSY}$ with a particular scheme for fermion masses (DHR model). The analysis has been performed for two choices of neutrinos parameters, predicted by the above models, and capable to explain the solar neutrino problem. In both cases one observes a strong distortion in the electron neutrino energy spectrum. This effect, computed for a wide range of $SO(10)_{SUSY}$ models has produced the same results of the previous supersymmetric ones.

hep-ph↗
arXiv1996

Fermion Hilbert Space and Fermion Doubling in the Noncommutative Geometry Approach to Gauge Theories

In this paper we study the structure of the Hilbert space for the recent noncommutative geometry models of gauge theories. We point out the presence of unphysical degrees of freedom similar to the ones appearing in lattice gauge theories (fermion doubling). We investigate the possibility of projecting out these states at the various levels in the construction, but we find that the results of these attempts are either physically unacceptable or geometrically unappealing.

hep-th↗
arXiv1996

Quantum Statistical Parton Distributions and the Spin Crisis

Quantum statistical distributions for the partons provide a fair description of deep inelastic scattering data at $Q^2 = 3$ and $10 (GeV/c)^2$. The study of the polarized structure functions seems to suggest an alternative possible solution of the {\it spin crisis} based on the Pauli principle. In this scheme, in fact, the defects of the Gottfried sum rule and Ellis--Jaffe sum rule for proton, result strongly connected. This possibility finds particular evidence from the phenomenological observation that the relation $Δu = 2 \tilde{F} + u - d -1$ seems well satisfied by parton distributions.

hep-ph↗
arXiv1996

Statistical Inspired Parton Distributions and the Violation of QPM Sum Rules

A quantum statistical parametrization of parton distributions has been considered. In this framework, the exclusion Pauli principle connects the violation of the Gottfried sum rule with the Ellis and Jaffe one, and implies a defect in the Bjorken sum rule. However, in terms of standard parametrizations of the polarized distributions a good description of the data is obtained once a large gluon polarization is provided. Interestingly, in this description there is no violation of the Bjorken sum rule.

hep-ph↗