arXiv subjects

N. Fornengo

Publications and source records attributed to N. Fornengo.

At least 73 records · Page 4Linked to original sources

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

Probing neutrino non-standard interactions with atmospheric neutrino data

We have reconsidered the atmospheric neutrino anomaly in light of the laetst data from Super-Kamiokande contained events and from Super-Kamiokande and MACRO up-going muons. We have reanalysed the proposed solution to the atmospheric neutrino anomaly in terms of non-standard neutrino-matter interactions (NSI) as well as the standard nu_mu -> nu_tau oscillations (OSC). Our statistical analysis shows that a pure NSI mechanism is now ruled out at 99%, while the standard nu_mu -> nu_tau OSC mechanism provides a quite remarkably good description of the anomaly. We therefore study an extended mechanism of neutrino propagation which combines both oscillation and non-standard neutrino-matter interactions, in order to derive limits on flavour-changing (FC) and non-universal (NU) neutrino interactions. We obtain that the off-diagonal flavour-changing neutrino parameter epsilon and the diagonal non-universality neutrino parameter epsilon' are confined to -0.03 < epsilon < 0.02 and |epsilon'| < 0.05 at 99.73% CL. These limits are model independent and they are obtained from pure neutrino-physics processes. The stability of the neutrino oscillation solution to the atmospheric neutrino anomaly against the presence of non-standard neutrino interactions establishes the robustness of the near-maximal atmospheric mixing and massive-neutrino hypothesis. The best agreement with the data is obtained for Delta_m^2 = 2.3*10^{-3} eV^2, sin^2(2*theta) = 1, epsilon = 6.7*10^{-3} and epsilon' = 1.1*10^{-3}, although the chi^2 function is quite flat in the epsilon and epsilon' directions for epsilon, epsilon' -> 0.

hep-ph↗

arXiv2003

Temporal distortion of annual modulation at low recoil energies

We show that the main features of the annual modulation of the signal expected in a WIMP direct detection experiment, i.e. its sinusoidal dependence with time, the occurrence of its maxima and minima during the year and (under some circumstances) even the one-year period, may be affected by relaxing the isothermal sphere hypothesis in the description of the WIMP velocity phase space. The most relevant effect is a distortion of the time-behaviour at low recoil energies for anisotropic galactic halos. While some of these effects turn out to be relevant at recoil energies below the current detector thresholds, some others could already be measurable, although some degree of tuning between the WIMP mass and the experimental parameters would be required. Either the observation or non-observation of these effects could provide clues on the phase space distribution of our galactic halo.

hep-ph↗

arXiv2003

Light Relic Neutralinos

The relic abundance and the scalar cross-section off nucleon for light neutralinos (of mass below about 45 GeV) are evaluated in an effective MSSM model without GUT-inspired relations among gaugino masses. It is shown that these neutralinos may provide a sizeable contribution to the matter density in the Universe and produce measurable effects in WIMP direct detection experiments. These properties are elucidated in terms of simple analytical arguments.

hep-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

Supersymmetric Dark Matter and the Reheating Temperature of the Universe

Since the thermal history of the Universe is unknown before the epoch of primordial nucleosynthesis, the largest temperature of the radiation dominated phase (the reheating temperature) might have been as low as 1 MeV. We perform a quantitative study of supersymmetric dark matter relic abundance in cosmological scenarios with low reheating temperature. We show that, for values of the reheating temperature smaller than about 30 GeV, the domains of the supergravity parameter space which are compatible with the hypothesis that dark matter is composed by neutralinos are largely enhanced. We also find a lower bound on the reheating temperature: if the latter is smaller than about 1 GeV neutralinos cannot be efficiently produced in the early Universe and then they are not able to explain the present amount of dark matter.

hep-ph↗

arXiv2002

Does Solar Physics Provide Constraints to Weakly Interacting Massive Particles?

We investigate whether present data on helioseismology and solar neutrino fluxes may constrain WIMP--matter interactions in the range of WIMP parameters under current exploration in WIMP searches. We find that, for a WIMP mass of 30 GeV, once the effect of the presence of WIMPs in the Sun's interior is maximized, the squared isothermal sound speed is modified, with respect to the standard solar model, by at most 0.4% at the Sun's center. The maximal effect on the Boron-8 solar neutrino flux is a reduction of 4.5%. Larger masses lead to smaller effects. These results imply that present sensitivities in the measurements of solar properties, though greatly improved in recent years, do not provide information or constraints on WIMP properties of relevance for dark matter. Furthermore, we show that, when current bounds from direct WIMP searches are taken into account, the effect induced by WIMPs with dominant coherent interactions are drastically reduced as compared to the values quoted above. The case of neutralinos in the minimal supersymmetric standard model is also discussed.

hep-ph↗

arXiv2002

Effect of the galactic halo modeling on the DAMA/NaI annual modulation result: an extended analysis of the data for WIMPs with a purely spin-independent coupling

The DAMA/NaI Collaboration has observed a 4-sigma C.L. model independent effect investigating the annual modulation signature in the counting rate of an NaI(Tl) set-up (total exposure of 57986 kg day) and the implications of this effect have been studied under different model-dependent assumptions. In this paper we extend one of the previous analyses, the case of a WIMP with a purely spin-independent coupling, by discussing in detail the implications on the results of the uncertainties on the dark matter galactic velocity distribution. We study in a systematic way possible departures from the isothermal sphere model, which is the parameterization usually adopted to describe the halo. We specifically consider modifications arising from various matter density profiles, effects due to anisotropies of the velocity dispersion tensor and rotation of the galactic halo. The hypothesis of WIMP annual modulation, already favoured in the previous analysis using an isothermal sphere, is confirmed in all the investigated scenarios, and the effects of the different halo models on the determination of the allowed maximum-likelihood region in the WIMP mass and WIMP-nucleon cross-section are derived and discussed.

hep-ph↗

arXiv2002

Cold Dark Matter and Neutralinos

Neutralinos are natural candidates for cold dark matter in many realizations of supersymmetry. We briefly review our recent results in the evaluation of neutralino relic abundance and direct detection rates in a class of supergravity models.

hep-ph↗

arXiv2001

Relic neutralinos

Phenomenology of relic neutralinos is analyzed in an effective supersymmetric scheme at the electroweak scale. It is shown that current direct experiments for WIMPs, when interpreted in terms of relic neutralinos, are indeed probing regions of supersymmetric parameter space compatible with all present experimental bounds.

hep-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

Particle candidates for dark matter: a case for (dominant or subdominant) relic neutralinos

After a short introduction on particle candidates for dark matter within possible extensions of the standard model, we concentrate on Weakly Interacting Massive Particles, and on one of their most interesting physical realizations: the neutralino. We analyze how detectability of relic neutralinos by direct and indirect means is related to their local and cosmological densities; we use simple general arguments to discusss different scenarios where relic neutralinos make up the dominant bulk of dark matter or only a small fraction of it. Our general arguments are further corroborated by specific numerical results. We show to which extent the present experiments of direct searches for WIMPs, when interpreted in terms of relic neutralinos, probe interesting regions of the supersymmetric parameter space. Our analysis is performed in a number of different supersymmetric schemes.

hep-ph↗

arXiv2001

Implications of a possible 115 GeV supersymmetric Higgs boson on detection and cosmological abundance of relic neutralinos

We show that a supersymmetric neutral Higgs boson with a mass of about 115 GeV and with the other prerequisites required by the LEP Higgs events would be compatible with the detection of relic neutralinos in current set-ups for WIMP direct search. Thus this putative Higgs would fit remarkably well in an interpretation in terms of relic neutralinos of the annual-modulation effect recently measured in a WIMP direct experiment. We also show that the cosmological abundance of the relevant neutralinos reaches values of cosmological interest.

hep-ph↗

arXiv2001

Probing the supersymmetric parameter space by WIMP direct detection

We discuss to which extent the present experiments of direct search for WIMPs, when interpreted in terms of relic neutralinos, probe interesting regions of the supersymmetric parameter space, which are also being progressively explored at accelerators. Our analysis is performed in a number of different supersymmetric schemes. We derive the relevant neutralino cosmological properties, locally and on the average in the universe. We prove that part of the susy configurations probed by current WIMP experiments entail relic neutralinos of cosmological interest. The main astrophysical and particle physics uncertainties, relevant for a proper comparison between theory and experimental data, are stressed and taken into account.

hep-ph↗

arXiv2000

Updated Global Analysis of the Atmospheric Neutrino Data in terms of neutrino oscillations

A global analysis of all the available atmospheric neutrino data is presented in terms of neutrino oscillations in the nu_mu -> nu_tau and nu_mu -> nu_s channels, where nu_s denotes a sterile neutrino. We perform our analysis of the contained events data as well as the upward-going neutrino-induced muon fluxes. In addition to the previous data samples of Frejus, Nusex, IMB and Kamioka experiments, we include the full data set of the 52 kton-yr of Super-Kamiokande, the recent 4.6 kton-yr contained events of Soudan2 and the results on upgoing muons from the MACRO and Baksan detectors. From the statistical analysis it emerges that the nu_mu -> nu_tau channel provides the best agreement with the combined data, with a best fit point of sin^2(2 theta) = 0.99 and Delta m^2 = 3.0 * 10^{-3} eV^2. Although somehow disfavoured, the nu_mu -> nu_s channels cannot be ruled out on the basis of the global fit to the full set of observables.

hep-ph↗

arXiv2000

Further investigation of a relic neutralino as a possible origin of an annual-modulation effect in WIMP direct search

We analyze the annual-modulation effect, measured by the DAMA Collaboration with the new implementation of a further two-years running, in the context of a possible interpretation in terms of relic neutralinos. We impose over the set of supersymmetric configurations, selected by the annual-modulation data, the constraints derived from WIMP indirect measurements, and discuss the features of the ensuing relic neutralinos. We critically discuss the sources of the main theoretical uncertainties in the analysis of event rates for direct and indirect WIMP searches.

hep-ph↗