arXiv subjects

G. Mignola

Publications and source records attributed to G. Mignola.

17 recordsLinked to original sources

arXiv1996

Exploring the supersymmetric parameter space by direct search for WIMPs

It is shown that the new data of the DAMA/NaI detector, combined with recent calculations of nuclear structure functions, provide the most stringent upper bounds on the WIMP-nucleon cross-section both for spin-dependent and for scalar interactions. It is proved that, for the first time, data from an experiment of direct search for WIMPs allow the exploration of a region of the supersymmetric parameter space not yet fully investigated at accelerators.

hep-ph↗

arXiv1996

Cosmic Antiprotons from Neutralino Annihilation in the Galactic halo

We investigate the possibility that the antiproton-to-proton flux ratio which is measured in cosmic rays may be generated by neutralino-neutralino annihilation in the galactic halo. We study the most general compositions for the relic neutralinos. We compare our results with the present experimental sensitivity and find that the theoretical predictions are at the level of the current experimental limits for some regions in the parameter space of the model.We expect that the future measurements of the pbar/p will provide very useful information, complementary to the ones obtainable with other experimental means.

astro-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

On neutralino stars as microlensing objects

The microlensing objects, Machos, recently observed in the halo of our Galaxy, can be interpreted as dense neutralino objects, neutralino stars, produced by the gravitational instability of neutralino gas. Taking the mass and radius of these objects from microlensing observations we calculated the diffuse gamma-ray flux produced in neutralino--neutralino annihilation inside the objects. The resulting flux is many orders of magnitude higher than the observed one.

astro-ph↗

arXiv1996

Galactic diffusion and the antiprotron signal of supersymmetric dark matter

The leaky box model is now ruled out by measurements of a cosmic ray gradient throughout the galactic disk. It needs to be replaced by a more refined treatment which takes into account the diffusion of cosmic rays in the magnetic fields of the Galaxy. We have estimated the flux of antiprotons on the Earth in the framework of a two-zone diffusion model. Those species are created by the spallation reactions of high-energy nuclei with the interstellar gas. Another potential source of antiprotons is the annihilation of supersymmetric particles in the dark halo that surrounds our Galaxy. In this letter, we investigate both processes. Special emphasis is given to the antiproton signature of supersymmetric dark matter. The corresponding signal exceeds the conventional spallation flux below 300 MeV, a domain that will be thoroughly explored by the Antimatter Spectrometer experiment. The propagation of the antiprotons produced in the remote regions of the halo back to the Earth plays a crucial role. Depending on the energy, the leaky box estimates are wrong by a factor varying from 0.5 up to 3.

astro-ph↗

arXiv1996

Relic neutralinos in a best-fitted MSSM

We examine the properties of relic neutralinos in the regions of the parameter space selected by recent fits to all the electroweak observables within the Minimal Supersymmetric Standard Model. We discuss the relic neutralino cosmic abundance and the direct detection rates for these most likely supersymmetric configurations. We employ the relevant experimental bounds to constrain the set of the best-fit configurations and discuss the discovery potential of the direct search for relic neutralinos.

hep-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↗

arXiv1996

Non--Baryonic Dark Matter

The best particle candidates for non--baryonic cold dark matter are reviewed, namely, neutralino, axion, axino and Majoron. These particles are considered in the context of cosmological models with the restrictions given by the observed mass spectrum of large scale structures, data on clusters of galaxies, age of the Universe etc.

astro-ph↗

arXiv1995

Limits on the Neutrino Mass and Mixing Angle from Pion and Lepton Decays

Motivated by a recent rather surprising conclusion based on the 1992 PDG data on the pion, kaon and lepton decays that if three generations of neutrinos are assumed to be massive and mixed, the heaviest neutrino, $ν_3$, could have a mass in the range, $155~\mbox{MeV} \lsim m_3 \lsim 225~\mbox{MeV}$, we have analyzed the latest 1995 data on the leptonic decays of pion, $μ$ and $τ$ with the assumption that three generations of neutrinos are massive and mixed. It is shown that when the radiative corrections are included and the constraint {}from partial decay widths is imposed, the 1995 data are consistent with three massless neutrinos with no mixing. Various limits on the neutrino mass and mixing angle implied by the 1995 data are presented together with a critique of the previous analysis.

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↗

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↗