arXiv subjects

F. Donato

Publications and source records attributed to F. Donato.

At least 55 records · Page 3Linked to original sources

arXiv2008

Positrons from dark matter annihilation in the galactic halo: theoretical uncertainties

Indirect detection signals from dark matter annihilation are studied in the positron channel. We discuss in detail the positron propagation inside the galactic medium: we present novel solutions of the diffusion and propagation equations and we focus on the determination of the astrophysical uncertainties which affect the positron dark matter signal. We find dark matter scenarios and propagation models that nicely fit existing data on the positron fraction. Finally, we present predictions both on the positron fraction and on the flux for already running or planned space experiments, concluding that they have the potential to discriminate a possible signal from the background and, in some cases, to distinguish among different astrophysical propagation models.

astro-ph↗

arXiv2007

Science with the new generation high energy gamma- ray experiments

This Conference is the fifth of a series of Workshops on High Energy Gamma- ray Experiments, following the Conferences held in Perugia 2003, Bari 2004, Cividale del Friuli 2005, Elba Island 2006. This year the focus was on the use of gamma-ray to study the Dark Matter component of the Universe, the origin and propagation of Cosmic Rays, Extra Large Spatial Dimensions and Tests of Lorentz Invariance.

astro-ph↗

arXiv2007

Zooming in on light relic neutralinos by direct detection and measurements of galactic antimatter

The DAMA Collaboration has recently analyzed its data of the extensive WIMP direct search (DAMA/NaI) which detected an annual modulation, by taking into account the channelling effect which occurs when an ion traverses a detector with a crystalline structure. Among possible implications, this Collaboration has considered the case of a coherent WIMP-nucleus interaction and then derived the form of the annual modulation region in the plane of the WIMP-nucleon cross section versus the WIMP mass, using a specific modelling for the channelling effect. In the present paper we first show that light neutralinos fit the annual modulation region also when channelling is taken into account. To discuss the connection with indirect signals consisting in galactic antimatter, in our analysis we pick up a specific galactic model, the cored isothermal-sphere. In this scheme we determine the sets of supersymmetric models selected by the annual modulation regions and then prove that these sets are compatible with the available data on galactic antiprotons. We comment on implications when other galactic distribution functions are employed. Finally, we show that future measurements on galactic antiprotons and antideuterons will be able to shed further light on the populations of light neutralinos singled out by the annual modulation data.

hep-ph↗

arXiv2007

Positrons from dark matter annihilation in the galactic halo: uncertainties

Indirect detection signals from dark matter annihilation are studied in the positron channel. We discuss in detail the positron propagation inside the galactic medium: we present novel solutions of the diffusion and propagation equations and we focus on the determination of the astrophysical uncertainties which affect the positron dark matter signal. We show that, especially in the low energy tail of the positron spectra at Earth, the uncertainty is sizeable and we quantify the effect. Comparison of our predictions with current available and foreseen experimental data are derived.

astro-ph↗

arXiv2007

Antideuterons from supersymmetric dark matter

We calculate the antideuteron flux expected from dark matter annihilation in the galactic halo. The propagation is treated in a full 2-D propagation model consistent with the results obtained from the propagation of B/C and other galactic species. We discuss the potentials of this indirect dark matter detection means, with special emphasis on the possible sources of uncertainties affecting future measurements

astro-ph↗

arXiv2006

Additional bounds on the pre Big--Bang--Nucleosynthesis Expansion by means of $γ$-rays from the Galactic Center

The possibility to use $γ$--ray data from the Galactic Center (GC) to constrain the cosmological evolution of the Universe in a phase prior to primordial nucleosyntesis, namely around the time of cold dark matter (CDM) decoupling, is analyzed. The basic idea is that in a modified cosmological scenario, where the Hubble expansion rate is enhanced with respect to the standard case, the CDM decoupling is anticipated and the relic abundance of a given dark matter (DM) candidate enhanced. This implies that the present amount of CDM in the Universe may be explained by a Weakly Interacting Massive Particle (WIMP) which possesses annihilation cross section (much) larger than in standard cosmology. This enhanced annihilation implies larger fluxes of indirect detection signals of CDM. We show that the HESS measurements can set bounds for WIMPs heavier than a few hundreds of GeV, depending on the actual DM halo profile. These results are complementary to those obtained in a previous analysis based on cosmic antiprotons. For a Moore DM profile, $γ$--ray data limit the maximal Hubble rate enhancement to be below a factor of 100. Moreover, a WIMP heavier than 1 TeV is not compatible with a cosmological scenario with enhanced expansion rate prior to Big Bang Nucleosynthesis (BBN). Less steep DM profiles provide less stringent bounds, depending of the cosmological scenario.

hep-ph↗

arXiv2005

Do current WIMP direct measurements constrain light relic neutralinos?

New upper bounds on direct detection rates have recently been presented by a number of experimental collaborations working on searches for WIMPs. In this paper we analyze how the constraints on relic neutralinos which can be derived from these results is affected by the uncertainties in the distribution function of WIMPs in the halo. Various different categories of velocity distribution functions are considered, and the ensuing implications for supersymmetric configurations derived. We conservatively conclude that current experimental data do not constrain neutralinos of small mass (below 50 GeV).

hep-ph↗

arXiv2005

Antiproton fluxes from light neutralinos

We analyze how the measurements of the low-energy spectrum of cosmic antiprotons can provide information on relic neutralinos. The analysis is focused on the light neutralinos which emerge in supersymmetric schemes where gaugino-mass unification is not assumed. We determine which ranges of the astrophysical parameters already imply stringent constraints on the supersymmetric configurations and those ranges which make the antiproton flux sensitive to the primary component generated by the neutralino self-annihilation. Our results are derived from some general properties of the antiproton flux proved to be valid for a generic cold dark matter candidate.

hep-ph↗

arXiv2005

Diffusion coefficient and acceleration spectrum from direct measurements of charged cosmic ray nuclei

We discuss the potentials of several experimental configurations dedicated to direct measurements of charged cosmic ray (CR) nuclei at energies $\gsim$ 100 GeV/n. Within a two-zone propagation model for stable CRs, we calculate light primary and secondary nuclei fluxes for different diffusion and acceleration schemes. We show that the new detectors exploiting the long and ultra long duration balloon flights could determine the diffusion coefficient power index $δ$ through the measurement of the boron-to-carbon ratio with an uncertainty of about 10-15 %, if systematic errors are low enough. Only space-based or satellite detectors will be able to determine $δ$ with very high accuracy even in the case of important systematic errors, thanks to the higher energy reach and the less severe limitations in the exposure. We show that no uncertainties other than those on $δ$ affect the determination of the acceleration slope $α$, so that measures of light primary nuclei, such as the carbon one, performed with the same experiments, will provide valuable information on the acceleration mechanisms.

astro-ph↗

arXiv2004

Cores of Dark Matter Halos Correlate with Disk Scale Lengths

We investigate in detail the mass distribution obtained by means of high resolution rotation curves of 25 galaxies of different morphological types. The dark matter contribution to the circular rotation velocity is well-described by resorting to a dark component whose density shows an inner core, i.e. a central constant density region. We find a very strong correlation between the core radius size $R_C$ and the stellar exponential scale length $R_D$: $R_C \simeq 13 (\frac {R_D} {5 {\rm kpc}})^{1.05} {\rm kpc} $, and between $R_C$ and the galaxy dynamical mass at this distance, $M_{dyn}(R_C)$. These relationships would not be expected if the core radii were the product of an incorrect decomposition procedure, or the biased result of wrong or misunderstood observational data. The very strong correlation between the dark and luminous scale lengths found here seems to hold also for different Hubble types and opens new scenarios for the nature of the dark matter in galaxies.

astro-ph↗

arXiv2004

Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification

We examine indirect signals produced by neutralino self-annihilations, in the galactic halo or inside celestial bodies, in the frame of an effective MSSM model without gaugino-mass unification at a grand unification scale. We compare our theoretical predictions with current experimental data of gamma-rays and antiprotons in space and of upgoing muons at neutrino telescopes. Results are presented for a wide range of the neutralino mass, though our discussions are focused on light neutralinos. We find that only the antiproton signal is potentially able to set constraints on very low-mass neutralinos, below 20 GeV. The gamma-ray signal, both from the galactic center and from high galactic latitudes, requires significantly steep profiles or substantial clumpiness in order to reach detectable levels. The up-going muon signal is largely below experimental sensitivities for the neutrino flux coming from the Sun; for the flux from the Earth an improvement of about one order of magnitude in experimental sensitivities (with a low energy threshold) can make accessible neutralino masses close to O, Si and Mg nuclei masses, for which resonant capture is operative.

hep-ph↗

arXiv2004

Antiprotons in cosmic rays from neutralino annihilation

We calculate the antiproton flux due to relic neutralino annihilations, in a two-dimensional diffusion model compatible with stable and radioactive cosmic ray nuclei. We find that the uncertainty in the primary flux induced by the propagation parameters alone is about two orders of magnitude at low energies, and it is mainly determined by the lack of knowledge on the thickness of the diffusive halo. On the contrary, different dark matter density profiles do not significantly alter the flux: a NFW distribution produces fluxes which are at most 20% higher than an isothermal sphere. The most conservative choice for propagation parameters and dark matter distribution normalization, together with current data on cosmic antiprotons, cannot lead to any definitive constraint on the supersymmetric parameter space, neither in a low-energy effective MSSM, or in a minimal SUGRA scheme. However, if the best choice for propagation parameters - corresponding to a diffusive halo of L=4 kpc - is adopted, some supersymmetric configurations with the neutralino mass of about 100 GeV should be considered as excluded. An enhancement flux factor - due for instance to a clumpy dark halo or to a higher local dark matter density - would imply a more severe cut on the supersymmetric parameters.

astro-ph↗

arXiv2003

Lower Bound on the Neutralino Mass from New Data on CMB and Implications for Relic Neutralinos

In the frame of an effective MSSM model without gaugino-mass unification at a grand unification (GUT) scale, we set a lower bound on the neutralino mass based on the new WMAP data on $Ω_{CDM}$. Our lower bound, $m_χ \gsim 6$ GeV, leaves much room for relic neutralinos significantly lighter than those commonly considered ($m_χ \gsim 50$ GeV). We prove that these light neutralinos may produce measurable effects in WIMP direct detection experiments of low energy threshold and large exposure.

hep-ph↗

arXiv2003

Antideuterons as a probe of primordial black holes

In most cosmological models, primordial black holes (PBHs) should have formed in the early Universe. Their Hawking evaporation into particles could eventually lead to the formation of antideuterium nuclei. This paper is devoted to a first computation of this antideuteron flux. The production of these antinuclei is studied with a simple coalescence scheme, and their propagation in the Galaxy is treated with a well-constrained diffusion model. We compare the resulting primary flux to the secondary background, due to the spallation of protons on the interstellar matter. Antideuterons are shown to be a very sensitive probe for primordial black holes in our Galaxy. The next generation of experiments should allow investigators to significantly improve the current upper limit, nor even provide the first evidence of the existence of evaporating black holes.

astro-ph↗

arXiv2002

Supersymmetric Dark Matter

After a short introduction on some general implications of recent cosmological observations, we discuss the properties of relic neutralinos in connection with present experimental strategies for detecting WIMPs.

hep-ph↗

arXiv2002

Antiprotons from primordial black holes

Primordial black holes (PBHs) have motivated many studies since it was shown that they should evaporate and produce all kinds of particles. Recent experimental measurements of cosmic rays with great accuracy, theoretical investigations on the possible formation mechanisms and detailed evaporation processes have revived the interest in such astrophysical objects. This article aims at using the latest developments on antiproton propagation models together with new data from BESS, CAPRICE and AMS experiments to constrain the local amount of PBH dark matter. Depending on the diffusion halo parameters and on the details of emission mechanism, we derive an average upper limit of the order of rho < 1.7E-33 g cm^-3.

astro-ph↗

arXiv2001

Size of the neutralino--nucleon cross--section in the light of a new determination of the pion--nucleon sigma term

We discuss the implications of a new determination of the pion-nucleon sigma term for the evaluation of the neutralino-nucleon cross-section, and, in turn, for detection rates for relic neutralinos in WIMP direct experiments and in some of the indirect searches. It is shown that the new range for the pion-nucleon sigma term, taken at its face value, favours values of the neutralino-nucleon cross-sections which are sizeably larger than some of the current estimates. Implications for neutralino cosmological properties are derived.

hep-ph↗

arXiv2001

Antiprotons from spallations of cosmic rays on interstellar matter

Cosmic ray antiprotons provide an important probe for the study of the galactic Dark Matter, as they could be produced by exotic sources. On the other hand, antiprotons are anyway produced by standard nuclear reactions of cosmic ray nuclei on interstellar matter. This process is responsible for a background flux that must be carefully determined to estimate the detectability of an hypothetical exotic signal. Estimates of this background suffer from potential uncertainties of various origins. The propagation of cosmic antiprotons depends on several physical characteristics of the Galaxy which are poorly known. Antiprotons are created from cosmic protons and helium nuclei whose fluxes were not measured with great accuracy until very recently. Calculations of antiproton fluxes make use of nuclear physics models with their own shortcomings and uncertainties. The goal of this paper is to give a new evaluation of the cosmic antiproton flux along with the associated uncertainties. The propagation parameters were tightly constrained in Maurin et al. 2001 by an analysis of cosmic ray nuclei data in the framework of a two-zone diffusion model and we apply these parameters to the propagation of antiprotons. We use the recently published data on proton and helion fluxes, and we find that this particular source of uncertainty has become negligible. The Monte Carlo program DTUNUC was used to carefully examine nuclear reactions. We find that all the cosmic antiproton fluxes naturally coming out of the calculation are fully compatible with experimental data. Uncertainties in this flux have been strongly reduced. Those related to propagation are less than 25%. All other possible sources of uncertainty have also been studied.

astro-ph↗