arXiv subjects

N. Fornengo

Publications and source records attributed to N. Fornengo.

At least 91 records · Page 5Linked to original sources

arXiv1999

On the Interpretation of the Atmospheric Neutrino Data in Terms of Flavor Changing Neutrino Interactions

Flavour changing (FC) neutrino-matter interactions have been proposed as a solution to the atmospheric neutrino anomaly. Here we perform the analysis of the full set of the recent 52 kTy Super-Kamiokande atmospheric neutrino data, including the zenith angle distribution of the contained events as well as the higher energy upward-going stopping and through-going muon events. Our results show that the FC mechanism can describe the full data sample with a chi^2_{min}=44/(33 d.o.f) which is acceptable at the 90% confidence level. The combined analysis confines the amount of FC to be either close to maximal or to the level of about (10-50)%.

hep-ph↗

arXiv1999

Implications for relic neutralinos of the theoretical uncertainties in the neutralino-nucleon cross-section

We discuss the effect induced on the neutralino-nucleon cross-section by the present uncertainties in the values of the quark masses and of the quark scalar densities in the nucleon. We examine the implications of this aspect on the determination of the neutralino cosmological properties, as derived from measurements of WIMP direct detection. We show that, within current theoretical uncertainties, the DAMA annual modulation data are compatible with a neutralino as a major dark matter component, to an extent which is even larger than the one previously derived. We also comment on implications of the mentioned uncertainties for experiments of indirect dark matter detection.

hep-ph↗

arXiv1999

Antideuterons as a Signature of Supersymmetric Dark Matter

Once the energy spectrum of the secondary component is well understood, measurements of the antiproton cosmic-ray flux at the Earth will be a powerful way to indirectly probe for the existence of supersymmetric relics in the galactic halo. Unfortunately, it is still spoilt by considerable theoretical uncertainties. As shown in this work, searches for low-energy antideuterons appear in the mean time as a plausible alternative, worth being explored. Above a few GeV/n, a dozen spallation antideuterons should be collected by the future AMS experiment on board ISSA. For energies less than about 3 GeV/n, the antideuteron spallation component becomes negligible and may be supplanted by a potential supersymmetric signal. If a few low-energy antideuterons are discovered, this should be seriously taken as a clue for the existence of massive neutralinos in the Milky Way.

hep-ph↗

arXiv1999

Dark Matter and its Particle Candidates

In these lectures we first briefly review the main observational facts which imply that most part of matter in the Universe is not visible and some recent intriguing experimental data which would point to a significant contribution to Omega due to a cosmological constant. We subsequently discuss some particle candidates for dark matter, with particular emphasis for the neutralino. We present the main properties of this particle, also in the light of the most recent experimental results in direct search for relic particles; furthermore, we discuss the perspectives for their indirect searches.

hep-ph↗

arXiv1999

Extending the DAMA annual-modulation region by inclusion of the uncertainties in the astrophysical velocities

The original annual-modulation region, singled out by the DAMA/NaI experiment for direct detection of WIMPs, is extended by taking into account the uncertainties in the galactic astrophysical velocities. Also the effect due to a possible bulk rotation for the dark matter halo is considered. We find that the range for the WIMP mass becomes 30 GeV < m_chi < 130 GeV at 1-sigma C.L. with a further extension in the upper bound, when a possible bulk rotation of the dark matter halo is taken into account. We show that the DAMA results, when interpreted in the framework of the Minimal Supersymmetric extension of the Standard Model, are consistent with a relic neutralino as a dominant component of cold dark matter (on the average in our universe and in our galactic halo). It is also discussed the discovery potential for the relevant supersymmetric configurations at accelerators of present generation.

hep-ph↗

arXiv1998

Combining the data of annual modulation effect in WIMP direct detection with measurements of WIMP indirect searches

In previous papers we showed that the data of the DAMA/NaI experiment for WIMP direct detection, which indicate a possible annual modulation effect, are widely compatible with an interpretation in terms of a relic neutralino as the major component of dark matter in the Universe. In the present note we discuss the detectability of the relevant supersymmetric neutralino configurations by two of the most promising methods of indirect search for relic particles: measurement of cosmic-ray antiprotons and measurement of neutrino fluxes from Earth and Sun.

hep-ph↗

arXiv1998

Neutralino properties in the light of a further indication of an annual modulation effect in WIMP direct search

We demonstrate that the further indication of a possible annual modulation effect, singled out by the DAMA/NaI experiment for WIMP direct detection, is widely compatible with an interpretation in terms of a relic neutralino as the major component of dark matter in the Universe. We discuss the supersymmetric features of this neutralino in the Minimal Supersymmetric extension of the Standard Model (MSSM) and their implications for searches at accelerators.

hep-ph↗

arXiv1998

Compatibility of the new DAMA/NaI data on an annual modulation effect in WIMP direct search with a relic neutralino in supergravity schemes

Recent results of the DAMA/NaI experiment for WIMP direct detection point to a possible annual modulation effect in the detection rate. We show that these results, when interpreted in terms of a relic neutralino, are compatible with supergravity models. Together with the universal SUGRA scheme, we also consider SUGRA models where the unification condition in the Higgs mass parameters at GUT scale is relaxed.

hep-ph↗

arXiv1998

Supersymmetric candidates for dark matter

Direct and indirect detection rates of relic neutralinos are reviewed in the framework of the Minimal Supersymmetric Standard Model. The theoretical estimates are compared with the most recent experimental limits from low-background detectors and neutrino telescopes. The properties of neutralino under the hypothesis that preliminary experimental results of the DAMA/NaI Collaboration may be indicative of a yearly modulation effect are examined.

astro-ph↗

arXiv1998

Which fraction of the measured cosmic-ray antiprotons might be due to neutralino annihilation in the galactic halo?

We analyze the data of low-energy cosmic-ray antiproton spectrum, recently published by the BESS Collaboration, in terms of newly calculated fluxes for secondary antiprotons and for a possible contribution of an exotic signal due to neutralino annihilation in the galactic halo. We single out the relevant supersymmetric configurations and discuss their explorability with experiments of direct search for particle dark matter and at accelerators. We discuss how future measurements with the Alpha Magnetic Spectrometer (AMS) on the Shuttle flight may disentangle the possible neutralino-induced contribution from the secondary one.

astro-ph↗

arXiv1998

Effects of galactic dark halo rotation on WIMP direct detection

The effects of a possible rotation of the galactic dark halo on the calculation of the direct detection rates for particle dark matter are analyzed, with special attention to the extraction of the upper limits on the WIMP--nucleon scalar cross section from the experimental data. We employ a model of dark halo rotation which describes the maximal possible effects. For WIMP masses above 50 GeV, the upper limit exclusion plot is modified by less than a factor of two when rotation is included. For lighter masses the effect can be stronger, suggesting the necessity to develop specific models of halo rotation in order to provide more accurate conclusions.

hep-ph↗

arXiv1997

Gravitational effects on the neutrino oscillation in vacuum

The propagation of neutrinos in a gravitational field is studied by developing a method of calculating a covariant quantum-mechanical phase in a curved space-time. The result is applied to neutrino propagation in the Schwarzschild metric.

hep-ph↗

arXiv1997

Extending a previous analysis on a possible modulation effect in WIMP direct search

In this note we present an extension of our previous analysis of some preliminary experimental results of the DAMA/NaI Collaboration which might be indicative of a yearly modulation effect. Here we present a direct way for obtaining from the experimental data the relevant cosmological implications for relic neutralinos. We find that some of the configurations singled out by the DAMA/NaI results would have cosmological properties compatible with a neutralino as a dominant component of cold dark matter (on the average in the Universe and in our galactic halo).

hep-ph↗

arXiv1997

Pinning down neutralino properties from a possible modulation signal in WIMP direct search

We analyze the properties of neutralino under the hypothesis that some preliminary experimental results of the DAMA/NaI Collaboration may be indicative of a yearly modulation effect. We examine which supersymmetric configurations would be singled out by the DAMA/NaI data. We also discuss the possibility to investigate these configurations by means of experimental searches for relic neutralinos other than direct searches. We finally discuss the possibility to probe these configurations by accelerator searches.

hep-ph↗

arXiv1997

Finite temperature effects on the neutrino decoupling in the early Universe

Leading finite temperature effects on the neutrino decoupling temperature in the early Universe have been studied. We have incorporated modifications of the dispersion relation and the phase space distribution due to the presence of particles in the heat bath at temperature around MeV. Since both the expansion rate of the Universe and the interaction rate of a neutrino are reduced by finite temperature effects, it is necessary to calculate thermal corrections as precisely as possible in order to find the net effect on the neutrino decoupling temperature. We have performed such a calculation by using the finite temperature field theory. It has been shown that the finite temperature effects increase the neutrino decoupling temperature by 4.4%, the largest contribution coming from the modification of the phase space due to the thermal bath.

hep-ph↗

arXiv1996

Gravitational Effects on the Neutrino Oscillation

The propagation of neutrinos in a gravitational field is studied. A method of calculating a covariant quantum-mechanical phase in a curved space-time is presented. The result is used to calculate gravitational effects on the neutrino oscillation in the presence of a gravitational field. We restrict our discussion to the case of the Schwartzschild metric. Specifically, the cases of the radial propagation and the non-radial propagation are considered. A possible application to gravitational lensing of neutrinos is also suggested.

hep-ph↗

arXiv1996

Perspectives for Detection of a Higgsino-like Relic Neutralino

It has been conjectured by Ambrosanio, Kane, Kribs, Martin and Mrenna (AKM) that the CDF event $p \bar p \to e^+ e^- γγ+ missing E_T$ is due to a decay chain involving two neutralino states (the lightest and the next-to-lightest ones). The lightest neutralino ($χ_{AKM}$) has been further considered by Kane and Wells as a candidate for cold dark matter. In this paper we examine the properties of relic $χ_{AKM}$'s in their full parameter space, and examine the perspectives for detection by comparing theoretical predictions to sensitivities of various experimental searches. We find that for most regions of the parameter space the detectability of a relic $χ_{AKM}$ would require quite substantial improvements in current experimental sensitivities. The measurements of neutrino fluxes from the center of the Earth and of an excess of $\bar{p}/p$ in cosmic rays are shown to offer some favorable perspectives for investigating a region of the $χ_{AKM}$ parameter space around the maximal $\tan β$ value allowed by the model.

astro-ph↗

arXiv1996

Searching for Relic Neutralinos using Neutrino Telescopes

Neutrino telescopes of large area offer the possibility of searching for indirect signals of relic neutralinos in the galactic halo, due to annihilations in the Sun or the Earth. Here we investigate the sensitivity, using a supergravity scheme where the soft scalar mass terms are not constrained by universality conditions at the grand unification scale. We first discuss in which regions of the supersymmetric parameter space the neutralino may be considered as a good candidate for cold dark matter. The discovery potential of the search using neutrino telescopes is then compared to that of the direct search for relic neutralinos.

hep-ph↗