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G. Gelmini

Publications and source records attributed to G. Gelmini.

8 recordsLinked to original sources
arXiv2007

Direct detection of neutralino dark mattter in non-standard cosmologies

We compute the neutralino direct detection rate in non-standard cosmological scenarios where neutralinos account for the dark matter of the Universe. Significant differences are found when such rates are compared with those predicted by the standard cosmological model. For bino-like neutralinos, the main feature is the presence of additional light ($m_χ\lesssim 40\gev$) and heavy ($m_χ\gtrsim 600\gev$) neutralinos with detection rates within the sensitivity of future dark matter experiments. For higgsino- and wino-like neutralinos lighter than $m_χ\sim 1\tev$, enhancements of more than two orders of magnitude in the largest detection rates are observed. Thus, if dark matter is made up of neutralinos, the prospects for their direct detection are in general more promising than in the standard cosmology.

hep-ph↗
arXiv2007

Constraints on secondary 10-100 EeV gamma ray flux in the minimal bottom-up model of Ultra High Energy Cosmic Rays

In a recently proposed model the cosmic rays spectrum at energies above EeV can be fitted with a minimal number of unknown parameters assuming that the extragalactic cosmic rays are only protons with a power law source spectrum. Within this minimal model, after fitting the observed HiRes spectrum with four parameters (proton injection spectrum power law index, maximum energy, minimum distance to sources and evolution parameter) we compute the flux of ultra-high energy photons due to photon-pion production and e+e- pair production by protons for several radio background models and a range of average extragalactic magnetic fields.

astro-ph↗
arXiv2005

Pulsar Kicks from Majoron Emission

We show that Majoron emission from a hot nascent neutron star can be anisotropic in the presence of a strong magnetic field. If Majorons carry a non-negligible fraction of the supernova energy, the resulting recoil velocity of a neutron star can explain the observed velocities of pulsars.

hep-ph↗
arXiv2004

Low reheating temperature and the visible sterile neutrino

We present here a scenario, based on a low reheating temperature T_R << 100 MeV at the end of (the last episode of) inflation, in which the coupling of sterile neutrinos to active neutrinos can be as large as experimental bounds permit (thus making this neutrino ``visible'' in future experiments). In previous models this coupling was forced to be very small to prevent a cosmological overabundance of sterile neutrinos. Here the abundance depends on how low the reheating temperature is. For example, the sterile neutrino required by the LSND result does not have any cosmological problem within our scenario.

astro-ph↗
arXiv2000

WIMP Annual Modulation with Opposite Phase in Late-Infall Halo Models

We show that in the late-infall model of our galactic halo by P. Sikivie the expected phase of the annual modulation of a WIMP halo signal in direct detection experiments is opposite to the one usually expected. If a non-virialized halo component due to the infall of (collisionless) dark matter particles cannot be rejected, an annual modulation in a dark matter signal should be looked for by experimenters without fixing the phase a-priori. Moreover, WIMP streams coming to Earth from directions above and below the galactic plane should be expected, with a characteristic pattern of arrival directions.

hep-ph↗
arXiv1994

Structure Formation with Decaying Neutrinos

We consider the effects of a massive, unstable neutrino on the evolution of large--scale structure and anisotropies in the cosmic microwave background. Comparison with large--scale structure data allows us to rule out a wide range of masses and lifetimes for such neutrinos. We also define a range of masses and lifetimes which delay matter--radiation equality and improve the agreement with the data of Cold Dark Matter models with critical density.

astro-ph↗
arXiv1992

Cosmic Neutrinos from Unstable Relic Particles

We derive constraints on the relic abundance of a generic particle of mass $\sim~1-10^{14}$ TeV which decays into neutrinos at cosmological epochs, using data from the Fréjus and IMB nucleon decay detectors and the Fly's Eye air shower array. The lifetime of such unstable particles which may constitute the dark matter today is bounded to be greater than $\sim~10^{14}-10^{18}$ yr, depending on the mass. For lifetimes shorter than the age of the universe, neutrino energy losses due to scattering and the expansion redshift become important and set limits to the ability of neutrino observatories to probe the early universe.

hep-ph↗