arXiv subjects

F. L. Villante

Publications and source records attributed to F. L. Villante.

54 records · Page 3Linked to original sources

arXiv2001

A few comments after the charged current measurement at the Sudbury Neutrino Observatory

The comparison of the SNO charged current result with the solar neutrino signal measured by Super-Kamiokande has provided, for the first time, the evidence of a non electron flavour active neutrino component in the solar flux. We remark here that this evidence can be obtained in a model independent way, i.e. without any assumpion about solar models, about the energy dependence of the neutrino oscillation probability and about the presence of sterile neutrinos. Furthermore, from the 8B neutrino flux obtained by combining SNO and Super-Kamiokande, one can determine the central solar temperature, T = 1.57 (1 \pm 1%) 10^7 K, and provide an estimate of the beryllium neutrino flux, Phi_Be = 4.9 (1 \pm 11%) 10^9 cm^{-2} s^{-1}.

hep-ph↗

arXiv2001

Constraints on inflation from CMB and Lyman-alpha forest

We constrain the spectrum of primordial curvature perturbations by using recent Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) data. Specifically, we consider CMB data from the COBE, Boomerang and Maxima experiments, the real space galaxy power spectrum from the IRAS PSCz survey, and the linear matter power spectrum inferred from Ly-alpha forest spectra. We study the case of single field slow roll inflationary models, and we extract bounds on the scalar spectral index, n, the tensor to scalar ratio, r, and the running of the scalar spectral index, dlnk, for various combinations of the observational data. We find that CMB data, when combined with data from Lyman-alpha forest, place strong constraints on the inflationary parameters. Specifically, we obtain n \approx 0.9, r < 0.3 and dlnk \approx 0, indicating that single field hybrid models are ruled out.

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arXiv2001

Atmospheric neutrino flux and muon data

We present a new one-dimensional calculation of low and intermediate energy atmospheric muon and neutrino fluxes, using up-to-date data on primary cosmic rays and hadronic interactions. The existing agreement between calculated muon fluxes and the data of the CAPRICE 94 muon experiment provides an evidence in favor of the validity of our description of hadronic interactions and shower development. This also supports our neutrino fluxes which are essentially lower than those used for the standard analyses of the sub-GeV and multi-GeV neutrino induced events in underground detectors.

hep-ph↗

arXiv2001

Atmospheric neutrino flux supported by recent muon experiments

We present a new one-dimensional calculation of low and intermediate energy atmospheric muon and neutrino fluxes, using up-to-date data on primary cosmic rays and hadronic interactions. We study several sources of uncertainties relevant to our calculations. A comparison with the muon fluxes and charge ratios measured in several modern balloon-borne experiments suggests that the atmospheric neutrino flux is essentially lower than one used for the standard analyses of the sub-GeV and multi-GeV neutrino induced events in underground detectors.

hep-ph↗

arXiv2001

Solar neutrino event spectra: Tuning SNO to equalize Super-Kamiokande

The Super-Kamiokande (SK) and the Sudbury Neutrino Observatory (SNO) experiments are monitoring the flux of B solar neutrinos through the electron energy spectrum from the reactions nu_{e,mu,tau} + e --> nu_{e,mu,tau} + e and nu_e + d --> p + p + e, respectively. We show that the SK detector response to B neutrinos in each bin of the electron energy spectrum (above 8 MeV) can be approximated, with good accuracy, by the SNO detector response in an appropriate electron energy range (above 5.1 MeV). For instance, the SK response in the bin [10,10.5] MeV is reproduced (``equalized'') within 2 percent by the SNO response in the range [7.1,11.75] MeV. As a consequence, in the presence of active neutrino oscillations, the SK and SNO event rates in the corresponding energy ranges turn out to be linearly related, for any functional form of the oscillation probability. Such equalization is not spoiled by the possible contribution of hep neutrinos (within current phenomenological limits). In perspective, when the SK and the SNO spectra will both be measured with high accuracy, the SK-SNO equalization can be used to determine the absolute B neutrino flux, and to cross-check the (non)observation of spectral deviations in SK and SNO. At present, as an exercise, we use the equalization to ``predict'' the SNO energy spectrum, on the basis of the current SK data. Finally, we briefly discuss some modifications or limitations of our results in the case of sterile neutrino oscillations and of relatively large Earth matter effects.

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arXiv2001

Probing the power spectrum bend with recent CMB data

We constrain the primordial fluctuation spectrum P(k) by using the new data on the Cosmic Microwave Background (CMB) from the Boomerang and MAXIMA experiments. Our study is based on slow-roll inflationary models, and we consider the possibility of a running spectral index. Specifically, we expand the power spectrum P(k) to second order in ln(k), thus allowing the power spectrum to ``bend'' in k-space. We show that allowing the power spectrum to bend erases the ability of the present data to measure the tensor to scalar perturbation ratio. Moreover, if the primordial baryon density Ω_b h^2 is as low as found from Big Bang nucleosynthesis (BBN), the data favor a negative bending of the power spectrum, corresponding to a bump-like feature in the power spectrum around a scale of k=0.004 Mpc^-1.

astro-ph↗

arXiv2000

Helioseismology and solar neutrinos: an update

We review recent advances concerning helioseismology, solar models and solar neutrinos. Particularly we address the following points: i) helioseismic tests of recent SSMs; ii) predictions of the Beryllium neutrino flux based on helioseismology; iii) helioseismic tests regarding the screening of nuclear reactions in the Sun.

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arXiv2000

Helioseismology and screening of nuclear reactions in the Sun

We show that models for screening of nuclear reactions in the Sun can be tested by means of helioseismology. As well known, solar models using the weak screening factors are in agreement with data. We find that the solar model calculated with the anti screening factors of Tsytovitch is not consistent with helioseismology, both for the sound speed profile and for the depth of the convective envelope. Moreover, the difference between the no-screening and weak screening model is significant in comparison with helioseismic uncertainty. In other words, the existence of screening can be proved by means of helioseismology.

astro-ph↗

arXiv2000

Decaying neutrino and a high cosmological baryon density

The low second acoustic peak in the recent Boomerang data may indicate a cosmological baryon density which is larger than allowed by standard big bang nucleosynthesis. We show that the decay of the tau-neutrino: nu_tau -> nu_e + phi, where nu_e is the electron neutrino and phi is a scalar, essentially can assure agreement between BBN calculations and light element observations for a large baryon density.

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arXiv2000

Helioseismic determination of Beryllium neutrinos produced in the Sun

We provide a determination of the Beryllium neutrino luminosity directly by means of helioseismology, without using additional assumptions. We have constructed solar models where Beryllium neutrino, ($ν_{Be}$) production is artificially changed by varying in an arbitrary way the zero energy astrophysical S-factor $S_{34}$ for the reaction $^3{\rm He}+^4{\rm He}\to ^7{\rm Be}+ γ$. Next we have compared the properties of such models with helioseismic determinations of photospheric helium abundance, depth of the convective zone and sound speed profile. We find that helioseismology directly confirms the production rate of $ν_{Be}$ as predicted by SSMs to within $\pm 25%$ ($1σ$ error). This constraint is somehow weaker than that estimated from uncertainties of the SSM ($\pm 10%$), however it relies on direct observational data.

astro-ph↗

arXiv1999

Electron capture on ^{8}B nuclei and Superkamiokande results

The energy spectrum of recoil electrons from solar neutrino scattering, as observed by Superkamiokande, is deformed with respect to that expected from SSM calculations. We considered ν-e scattering from neutrinos produced by the electron-capture on ^{8}B nuclei, e^{-}+^{8}B --> ^{8}Be^{*}+ν_{e}, as a possible explanation of the spectral deformation. A flux Φ_{eB}\simeq 10^{4} cm^{-2} s^{-1} could account for Superkamiokande solar neutrino data. However this explanation is untenable, since the theoretical prediction, Φ_{eB}=(1.3+-0.2) cm^{-2} s^{-1}, is smaller by four orders of magnitude.

hep-ph↗

arXiv1999

Big bang nucleosynthesis limit on N_nu

Recently we presented a simple method for determining the correlated uncertainties of the light element abundances expected from big bang nucleosynthesis, which avoids the need for lengthy Monte Carlo simulations. We now extend this approach to consider departures from the Standard Model, in particular to constrain any new light degrees of freedom present in the thermal plasma during nucleosynthesis. Since the observational situation regarding the inferred primordial abundances has not yet stabilized, we present illustrative bounds on the equivalent number of neutrino species N_nu for various combinations of individual abundance determinations. Our 95% C.L. bounds on N_nu range between 2 and 4, and can easily be reevaluated using the technique provided when the abundances are known more accurately.

hep-ph↗

arXiv1999

Helioseismology and Beryllium neutrino

We derive a lower limit on the Beryllium neutrino flux on earth, $Φ(Be)_{min} = 1\cdot 10^9 cm^{-2} s^{-1}$, in the absence of oscillations, by using helioseismic data, the B-neutrino flux measured by Superkamiokande and the hydrogen abundance at the solar center predicted by Standard Solar Model (SSM) calculations. We emphasize that this abundance is the only result of SSMs needed for getting $Φ(Be)_{min}$. We also derive lower bounds for the Gallium signal, $G_{min}=(91 \pm 3) $ SNU, and for the Chlorine signal, $C_{min}=(3.24\pm 0.14)$ SNU, which are about $3σ$ above their corresponding experimental values, $G_{exp}= (72\pm 6)$ SNU and $C_{exp}= (2.56\pm 0.22) $ SNU.

astro-ph↗

arXiv1998

Solar neutrino interactions: Using charged currents at SNO to tell neutral currents at Super-Kamiokande

In the presence of flavor oscillations, muon and tau neutrinos can contribute to the Super-Kamiokande (SK) solar neutrino signal through the neutral current process ν_{μ,τ} e^{-}\to ν_{μ,τ} e^{-}. We show how to separate the ν_e and ν_{μ,τ} event rates in SK in a model independent way, by using the rate of the charged current process ν_e d \to p p e^{-} from the Sudbury Neutrino Observatory (SNO) experiment, with an appropriate choice of the SK and SNO energy thresholds. Under the additional hypothesis of no oscillations into sterile states, we also show how to determine the absolute ^{8}B neutrino flux from the same data set, independently of the ν_e survival probability.

hep-ph↗

arXiv1998

Quantifying uncertainties in primordial nucleosynthesis without Monte Carlo simulations

We present a simple method for determining the (correlated) uncertainties of the light element abundances expected from big bang nucleosynthesis, which avoids the need for lengthy Monte Carlo simulations. Our approach helps to clarify the role of the different nuclear reactions contributing to a particular elemental abundance and makes it easy to implement energy-independent changes in the measured reaction rates. As an application, we demonstrate how this method simplifies the statistical estimation of the nucleon-to-photon ratio through comparison of the standard BBN predictions with the observationally inferred abundances.

astro-ph↗

arXiv1998

Nuclear burning rates and population II stellar models

We discuss theoretical predictions concerning the evolution of globular cluster Pop.II stars vis-a-vis current estimates of standard errors in the determination of nuclear burning rates. Numerical evaluations are given for the dependence of TO and HB luminosity from the rate of the relevant nuclear reactions. We conclude that evolutionary predictions appear rather solid in this respect, with a maximum 3$σ$ error of about 1 Gyr in the evaluation of cluster ages derived from the calibration of the difference in luminosity between HB and TO. However, current evaluation of the original He content, as given on the basis of the R parameter, should wait for a much better determination of the C12($α$,$γ$)O16 reaction before reaching a satisfactory accuracy.

astro-ph↗

arXiv1998

The anisotropy of inverse beta decay and antineutrino detection

The anisotropy of the positrons emitted in the reaction $\barν_{e}+p\to n+e^{+}$ has to be taken into account for extracting an antineutrino signal in Superkamiokande. For the Sun, this effect allows a sensitivity to $ν_{e}\to\barν_{e}$ transition probability at the 3% level already with the statistics collected in the first hundred days. For a supernova in the Galaxy, the effect is crucial for extracting the correct ratio of $ν-e$ to $\barν_{e}-p$ events.

astro-ph↗

arXiv1997

Superkamiokande and solar antineutrinos

We propose to exploit the angular distribution of the positrons emitted in the inverse beta decay to extract a possible antineutrino signal from the Superkamiokande background. From the statistics collected in just 101.9 days one obtains a model independent upper bound on the antineutrino flux (for energy greater than 8.3 MeV) Phi < 9*10^4 cm^-2 s^-1 at the 95% C.L. By assuming the same energy spectrum as for the 8B neutrinos, the 95% C.L. bound is Phi < 6*10^4 cm^-2 s^-1. Within three years of data taking, the sensitivity to neutrino-antineutrino transition probability will reach the 1% level, thus providing a stringent test of hybrid oscillation models.

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