arXiv subjects

O. Pisanti

Publications and source records attributed to O. Pisanti.

At least 37 records · Page 2Linked to original sources

arXiv2008

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.

astro-ph↗

arXiv2008

Enrico Fermi and the Physics and Engineering of a nuclear pile: the retrieval of novel documents

We give a detailed account of the recent retrieval of a consistent amount (about 600 pages) of documents written by Enrico Fermi and/or his collaborators, coming from different sources previously unexplored. These documents include articles, patents, reports, notes on scientific and technical meetings and other papers, mainly testifying Fermi's activity in the 1940s about nuclear pile physics and engineering. All of them have been carefully described, pointing out the relevance of the given papers for their scientific or even historical content. From the analysis of these papers, a number of important scientific and technical points comes out, putting a truly new light on the Fermi's (and others') scientific activity about nuclear piles and their applications. Quite unexpectedly intriguing historical remarks, such as those regarding the relationships between U.S. and Britain, just after the end of the war, about nuclear power for pacific and/or military use, or even regarding long term physics research and post-war research policy, emerge as well.

physics.hist-ph↗

arXiv2007

Disentangling neutrino-nucleon cross section and high energy neutrino flux with a km^3 neutrino telescope

The energy--zenith angular event distribution in a neutrino telescope provides a unique tool to determine at the same time the neutrino-nucleon cross section at extreme kinematical regions, and the high energy neutrino flux. By using a simple parametrization for fluxes and cross sections, we present a sensitivity analysis for the case of a km^3 neutrino telescope. In particular, we consider the specific case of an under-water Mediterranean telescope placed at the NEMO site, although most of our results also apply to an under-ice detector such as IceCube. We determine the sensitivity to departures from standard values of the cross sections above 1 PeV which can be probed independently from an a-priori knowledge of the normalization and energy dependence of the flux. We also stress that the capability to tag downgoing neutrino showers in the PeV range against the cosmic ray induced background of penetrating muons appears to be a crucial requirement to derive meaningful constraints on the cross section.

astro-ph↗

arXiv2007

Ultrahigh energy neutrinos with a mediterranean neutrino telescope

A study of the ultra high energy neutrino detection performances of a km^3 Neutrino Telescope sitting at the three proposed sites for "ANTARES", "NEMO" and "NESTOR" in the Mediterranean sea is here performed. The detected charged leptons energy spectra, entangled with their arrival directions, provide an unique tool to both determine the neutrino flux and the neutrino-nucleon cross section.

astro-ph↗

arXiv2007

High Energy Neutrinos with a Mediterranean Neutrino Telescope

The high energy neutrino detection by a km^3 Neutrino Telescope placed in the Mediterranean sea provides a unique tool to both determine the diffuse astrophysical neutrino flux and the neutrino-nucleon cross section in the extreme kinematical region, which could unveil the presence of new physics. Here is performed a brief analysis of possible NEMO site performances.

astro-ph↗

arXiv2007

The path to metallicity: synthesis of CNO elements in standard BBN

We perform a reanalysis of the production of CNO elements in a standard Big Bang Nucleosynthesis scenario. The CNO yields in BBN are suppressed by the low density of the plasma, Coulomb barrier effects and the short time scales involved. Yet, the inclusion of nuclides and reactions traditionally disregarded may lead to an increase relevant enough to affect the pristine Population III stars. After a critical reanalysis and upgrade of the nuclear network our results show no major discrepancies with the ones obtained using a smaller nuclear network. The robustness of the standard predictions-the early generation of star developed in a metal-free environment-is confirmed.

astro-ph↗

arXiv2007

Ultra High Energy Neutrinos in the Mediterranean: detecting nu_tau and nu_mu with a km^3 Telescope

We perform a study of the ultra high energy neutrino detection performances of a km^3 Neutrino Telescope sitting at the three proposed sites for ANTARES, NEMO and NESTOR in the Mediterranean sea. We focus on the effect of the underwater surface profile on the total amount of yearly expected tau and mu crossing the fiducial volume in the limit of full detection efficiency and energy resolution. We also emphasize the possible enhancement of matter effect by a suitable choice of the geometry of the Telescope.

astro-ph↗

arXiv2004

Ultra High Energy nu_tau detection at Pierre Auger Observatory

Earth--skimming UHE tau neutrinos have a chance to be detected by the Fluorescence Detector (FD) of Pierre Auger Observatory if their astrophysical flux is large enough. A detailed evaluation of the expected number of events is here performed for a wide class of neutrino flux models.

astro-ph↗

arXiv2004

Earth-skimming UHE Tau Neutrinos at the Fluorescence Detector of Pierre Auger Observatory

Ultra high energy neutrinos are produced by the interaction of hadronic cosmic rays with the cosmic radiation background. More exotic scenarios like topological defects or new hadrons predict even larger fluxes. In particular, Earth-skimming tau neutrinos could be detected by the Fluorescence Detector (FD) of Pierre Auger Observatory. A detailed evaluation of the expected number of events has been performed for a wide class of neutrino flux models. An updated computation of the neutrino-nucleon cross section and of the tau energy losses has been carried out. For the most optimistic theoretical models, about one Earth-skimming neutrino event is expected in several years at FD.

astro-ph↗

arXiv2004

Present status of primordial nucleosynthesis after WMAP: results from a new BBN code

We report on the status of primordial nucleosynthesis in light of recent results on CMB anisotropies from WMAP experiment. Theoretical estimates for nuclei abundances, along with the corresponding uncertainties, are evaluated using a new numerical code, where all nuclear rates usually considered have been updated using the most recent available data. Moreover, additional processes, neglected in previous calculations, have been included. The combined analysis of CMB and primordial nucleosynthesis prediction for Deuterium gives an effective number of relativistic degrees of freedom in good agreement with the simplest scenario of three non degenerate neutrinos. Our findings seem to point out possible systematics affecting 4He mass fraction measurements, or the effect of exotic physics, like a slightly degenerate relic neutrino background.

astro-ph↗

arXiv2003

Evolution and nucleosynthesis of primordial low mass stars

We discuss in detail the evolutionary properties of low mass stars M< 1 M(Solar) having metallicity lower than Z=10^(-6) from the pre- main sequence up to (almost) the end of the Asymptotic Giant Branch phase. We also discuss the possibility that the large [C,N/Fe] observed on the surface of the most Iron poor star presently known, HE0107-5240, may be attributed to the autopollution induced by the penetration of the He convective shell into the H rich mantle during the He core flash of a low mass, very low metallicity star. On the basis of a quite detailed analysis, we conclude that the autopollution scenario cannot be responsible for the observed chemical composition of HE0107-5240.

astro-ph↗

arXiv2003

Corsika+Herwig Monte Carlo Simulation of Neutrino Induced Atmospheric Air Showers

High-energy neutrino astronomy represents an open window both on astrophysical mechanisms of particle acceleration and on fundamental interactions. The possibility of detecting them in large earth-based apparatus, like AUGER, AMANDA, ANTARES, is quite challenging. In view of this, the capability of generating reliable simulations of air showers induced by neutrinos is mandatory in the analysis of experimental data. In this paper we describe preliminary results towards the development of a new version of the Monte Carlo CORSIKA, capable of handling neutrinos too as primary particles. In our approach the first interaction of the primary neutrino is simulated in CORSIKA with a call to the HERWIG event generator.

astro-ph↗

arXiv2003

Neutrino energy loss rate in a stellar plasma

We review the purely leptonic neutrino emission processes, contributing to the energy loss rate of the stellar plasma. We perform a complete analysis up to the first order in the electromagnetic coupling constant. In particular the radiative electromagnetic corrections, at order $α$, to the process $e^+ e^- -> ν\barν$ at finite density and temperature have been computed. This process gives one of the main contributions to the cooling of stellar interior in the late stages of star evolution. As a result of the analysis we find that the corrections affect the energy loss rate, computed at tree level, by a factor $(-4 ÷1) %$ in the temperature and density region where the pair annihilation is the most efficient cooling mechanism.

astro-ph↗

arXiv2002

Radiative corrections to neutrino energy loss rate in stellar interiors

We consider radiative electromagnetic corrections, at order α, to the process $e^+ e^- \to ν\barν$ at finite density and temperature. This process represents one of the main contributions to the cooling of stellar environments in the late stages of star evolution. We find that these corrections affect the energy loss rate by a factor $(-4 ÷1) %$ with respect to the tree level estimate, in the temperature and density ranges where the neutrino pair production via e^+ e^- annihilation is the most efficient cooling mechanism.

astro-ph↗

arXiv2001

Early-universe constraints on a time-varying fine structure constant

Higher-dimensional theories have the remarkable feature of predicting a time (and hence redshift) dependence of the `fundamental' four dimensional constants on cosmological timescales. In this paper we update the bounds on a possible variation of the fine structure constant alpha at the time of BBN (z =10^10) and CMB (z=10^3). Using the recently-released high-resolution CMB anisotropy data and the latest estimates of primordial abundances of 4He and D, we do not find evidence for a varying alpha at more than one-sigma level at either epoch.

astro-ph↗

arXiv2001

Constraining neutrino physics with BBN and CMBR

We perform a likelihood analysis of the recent results on the anisotropy of Cosmic Microwave Background Radiation from the BOOMERanG and DASI experiments to show that they single out an effective number of neutrinos in good agreement with standard Big Bang Nucleosynthesis. We also consider degenerate Big Bang Nucleosynthesis to provide new bounds on effective relativistic degrees of freedom $N_ν$ and, in particular, on neutrino chemical potential $ξ_α$. When including Supernova Ia data we find, at $2σ$, $N_ν\leq 7$ and $-0.01 \leq ξ_e \leq 0.22$, $|ξ_{μ,τ}|\leq 2.6$.

astro-ph↗

arXiv2000

Primordial Nucleosynthesis, Cosmic Microwave Background and Neutrinos

We report the results of a recent likelihood analysis combining the primordial nucleosynthesis and the BOOMERanG and MAXIMA-1 data on cosmic microwave background radiation anisotropies. We discuss the possible implications for relic neutrino background of a high value for the baryonic matter content of the universe, larger than what is expected in a standard nucleosynthesis scenario.

astro-ph↗

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↗