arXiv subjects

A. Bottino

Publications and source records attributed to A. Bottino.

83 records · Page 5Linked to original sources

arXiv1995

Neutrino Oscillations in the Framework of Three-Generation Mixings with Mass Hierarchy

We have analyzed the results of reactor and accelerator neutrino oscillation experiments in the framework of a general model with mixing of three neutrino fields and a neutrino mass hierarchy that can accommodate the results of the solar neutrino experiments. It is shown that $ ν_μ\leftrightarrows ν_e $ oscillations with $ 0.6 \le Δm^2 \le 100 \, \mathrm{eV}^2 $ and amplitude larger than $ 2 \times 10^{-3} $ are not compatible with the existing limits on neutrino oscillations if the non-diagonal elements of the mixing matrix $ \left| U_{e3} \right| $ and $ \left| U_{\mu3} \right| $ are small. Thus, if the excess of electron events recently observed in the LSND experiment is due to $ ν_μ\leftrightarrows ν_e $ oscillations, the mixing in the lepton sector is basically different from the CKM mixing of quarks. If this type of mixing is realized in nature, the observation of $ ν_μ\leftrightarrows ν_e $ oscillations would not influence $ ν_μ\leftrightarrows ν_τ$ oscillations that are being searched for in the CHORUS and NOMAD experiments.

hep-ph↗

arXiv1995

Neutralino dark matter in supersymmetric models with non--universal scalar mass terms

Neutralino dark matter is studied in the context of a supergravity scheme where the scalar mass terms are not constrained by universality conditions at the grand unification scale. We analyse in detail the consequences of the relaxation of this universality assumption on the supersymmetric parameter space, on the neutralino relic abundance and on the event rate for the direct detection of relic neutralinos.

hep-ph↗

arXiv1995

Some Remarks on Nu(mu)-Nu(e) Oscillations of Terrestrial Neutrinos and Atmospheric Neutrino Oscillations

We present the results of an analysis of the data of reactor and accelerator neutrino oscillation experiments in the framework of a model with mixing of three massive neutrino fields and a neutrino mass hierarchy. The results of the LSND experiment are commented. Taking into account future long-baseline neutrino oscillation experiments, we have also analyzed the atmospheric neutrino data in the framework of the model.

hep-ph↗

arXiv1995

Effects of the Running Gravitational Constant on the Amount of Dark Matter

The amount of dark matter in the Milky Way and beyond is examined by taking into account the possible running of the gravitational constant $G$ as a function of distance scale. If the running of $G$, as suggested by the Asymptotically-Free Higher-Derivative quantum gravity, is incorporated into the calculation of the total dark matter in the galactic halo, the amount of dark matter that is necessary to explain the rotation curve is shown to be reduced by one third compared with the standard calculations. However, this running of $G$ alone cannot reproduce the observed flat behavior of the rotation curve. It is also shown that the running of $G$ cannot explain away the presence of most of the dark matter beyond the scale of $ \sim 10$ Mpc in the Universe. We also present a pedagogical explanation for the running of $G(r)$ in the region of large scales which is clearly a classical domain.

astro-ph↗

arXiv1994

Searching for Relic Neutralinos

Theoretical expectations for direct and indirect searches for relic neutralinos are presented. Complementarity among various investigation means is discussed in connection with the values of the neutralino relic abundance.

hep-ph↗

arXiv1994

Amount of Antiprotons in Cosmic Rays due to Halo Neutralino Annihilation

We evaluate the antiproton--to--proton flux ratio which can be generated by neutralino--neutralino annihilation in the galactic halo, considering the most general compositions for the relic neutralinos and modelling the neutralino local density according to its relic abundance. We find that in the case of mixed neutralino compositions this $\bar p/p$ ratio is higher than for pure higgsinos or gauginos. It is shown how the expected improvements in sensitivity for the new measurements of the $\bar p/p$ may provide very useful information, complementary to the one obtainable with other experimental means.

hep-ph↗

arXiv1994

Signals of Neutralino Dark Matter from Earth and Sun

We evaluate the fluxes of up--going muons detectable in a neutrino telescope and due to the annihilation of relic neutralinos in the Earth and in the Sun, taking realistically into account the fact that neutralinos might provide only a fraction of the local (solar neighbourhood) dark matter (DM). We determine the relation between the exposure $A t$ of the neutrino telescope ($A$ being the telescope area, $t$ the live time) and the explorable range of the neutralino mass and composition, when the signal--to--background ratio is optimized by an appropriate angular selection.

hep-ph↗

arXiv1994

Neutralinos as Dark Matter Candidates

We review some properties of the neutralino as a candidate for dark matter in the Universe. After presentation of evaluations for the neutralino relic abundance, possibilities for its direct and indirect detections are discussed, with emphasis for measurements at neutrino telescopes.

hep-ph↗

arXiv1994

High Energy Gamma--Radiation from the Galactic Center due to Neutralino Annihilation

We study the NGS (Non--dissipative Gravitational Singularity) model, which successfully describes the non--linear stage of evolution of perturbations (see [1], [2] and references therein). This model predicts DM density distribution $ρ(r) \sim r^{-α}$ with $α\simeq 1.8$ which holds from very small distances $r_{\rm min} \simeq 0.01~{\rm pc}$ up to very large distances $r_{\rm max} \simeq 5~{\rm Mpc}$. Assuming the neutralino to be a CDM particle, we calculate the annihilation of neutralinos in the vicinity of the singularity (Galactic Center). If neutralinos are the dominant component of DM in our Galaxy, the produced energy is enough to provide the whole observed activity of the GC. Neutralinos of the most general composition and of mass in the range $20~{\rm GeV} \leq m_\c \leq 1~{\rm TeV}$ are considered. We find the neutralino compositions which give the relic density needed for the Mixed Dark Matter (MDM) model and we evaluate for these compositions the high--energy ($E_γ > 100 ~{\rm MeV}$) gamma--ray flux under the constraint that the radio flux is lower than the observational limit. The compositions with the detectable gamma--ray flux which we found are provided by a set of almost pure gaugino states with the neutralino mass between $100$ and $500$ GeV. We demonstrate that a detectable high--energy gamma--ray flux is produced by the neutralino annihilation also in the case when neutralinos provide a small fraction (down to $0.1 \%$) of the DM in our Galaxy. The predicted flux is $F_γ\sim 10^{-7}-10^{-8}~{\rm cm}^{-2}~{\rm s}^{-1}$ for $E_γ\gsim 300~{\rm MeV}$

hep-ph↗

arXiv1993

On the Neutralino as Dark Matter Candidate - I. Relic Abundance

The neutralino relic abundance is evaluated for a wide range of the neutralino mass, ${\rm 20\ GeV} \leq m_χ\leq {\rm 1\ TeV}$, by taking into account the full set of final states in the neutralino-neutralino annihilation. The analysis is performed in the Minimal SuSy Standard Model; it is not restricted by stringent GUT assumptions but only constrained by present experimental bounds. We also discuss phenomenological aspects which are employed in the companion paper (II. Direct Detection) where the chances for a successful search for dark matter neutralino are investigated.

hep-ph↗

arXiv1993

On the Neutralino as Dark Matter Candidate - II. Direct Detection

Evaluations of the event rates relevant to direct search for dark matter neutralino are presented for a wide range of neutralino masses and for various detector materials of preeminent interest. Differential and total rates are appropriately weighted over the local neutralino density expected on theoretical grounds.

hep-ph↗