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Graciela Gelmini

Publications and source records attributed to Graciela Gelmini.

At least 19 recordsLinked to original sources
arXiv2026

Unfolding the low-energy reactor neutrino flux from CE$\nu$NS data with a finite Dirac sum

We present a novel method to analyze coherent elastic neutrino--nucleus scattering (CE$\nu$NS) data to extract the reactor antineutrino spectrum below the inverse beta decay threshold of 1.8 MeV, where it remains unmeasured. Adapting halo-independent analysis techniques developed for direct dark matter detection, we show how to obtain a best-fit and a pointwise confidence band for the integrated neutrino flux, without assuming a parametric form or smoothness prior for the spectrum. In our approach, which follows from convex geometry arguments, the differential neutrino rate is written as a linear combination of Dirac delta functions -- a finite Dirac sum (FDS) -- with a maximum number of terms determined by the number of data points. We apply our ``FDS method'' to mock CE$\nu$NS data for a low-threshold Ge detector and compare it with Tikhonov-regularized unfolding.

hep-ph↗
arXiv2010

DM production mechanisms

We review the mechanism of production of dark matter particles in the early Universe, both in standard and non-standard pre-Big Bang Nucleosynthesis cosmologies. We concentrate mostly on the production of WIMPs.

astro-ph.CO↗
arXiv2010

XENON10/100 dark matter constraints in comparison with CoGeNT and DAMA: examining the Leff dependence

We consider the compatibility of DAMA/LIBRA, CoGeNT, XENON10 and XENON100 results for spin-independent (SI) dark matter Weakly Interacting Massive Particles (WIMPs), particularly at low masses (~ 10 GeV), assuming a standard dark matter halo. The XENON bounds depend on the scintillation efficiency factor Leff for which there is considerable uncertainty. Thus we consider various extrapolations for Leff at low energy. With the Leff measurements we consider, XENON100 results are found to be insensitive to the low energy extrapolation. We find the strongest bounds are from XENON10, rather than XENON100, due to the lower energy threshold. For reasonable choices of Leff and for the case of SI elastic scattering, XENON10 is incompatible with the DAMA/LIBRA 3$σ$ region and severely constrains the 7-12 GeV WIMP mass region of interest published by the CoGeNT collaboration.

astro-ph.CO↗
arXiv2010

Muon Fluxes and Showers from Dark Matter Annihilation in the Galactic Center

We calculate contained and upward muon flux and contained shower event rates from neutrino interactions, when neutrinos are produced from annihilation of the dark matter in the Galactic Center. We consider model-independent direct neutrino production and secondary neutrino production from the decay of taus, W bosons and bottom quarks produced in the annihilation of dark matter. We illustrate how muon flux from dark matter annihilation has a very different shape than the muon flux from atmospheric neutrinos. We also discuss the dependence of the muon fluxes on the dark matter density profile and on the dark matter mass and of the total muon rates on the detector threshold. We consider both the upward muon flux, when muons are created in the rock below the detector, and the contained flux when muons are created in the (ice) detector. We also calculate the event rates for showers from neutrino interactions in the detector and show that the signal dominates over the background for $150 {\rm GeV} <m_χ< 1$ TeV for $E_{sh}^{th} = 100$ GeV.

hep-ph↗
arXiv2009

Compatibility of DAMA/LIBRA dark matter detection with other searches

The DAMA/NaI and DAMA/LIBRA annual modulation data, which may be interpreted as a signal for the existence of weakly interacting dark matter (WIMPs) in our galactic halo, are examined in light of null results from other experiments. We use the energy spectrum of the combined DAMA modulation data given in 36 bins, and include the effect of channeling. Several statistical tools are implemented in our study: likelihood ratio with a global fit and with raster scans in the WIMP mass and goodness-of-fit (g.o.f.). These approaches allow us to differentiate between the preferred (global best fit) and allowed (g.o.f.) parameter regions. It is hard to find WIMP masses and couplings consistent with all existing data sets. For spin-independent (SI) interactions, the best fit DAMA regions are ruled out to the 3$σ$ C.L., even with channeling taken into account. However, for WIMP masses of ~8 GeV some parameters outside these regions still yield a moderately reasonable fit to the DAMA data and are compatible with all 90% C.L. upper limits from negative searches, when channeling is included. For spin-dependent (SD) interactions with proton-only couplings, a range of masses below 10 GeV is compatible with DAMA and other experiments, with and without channeling, when SuperK indirect detection constraints are included; without the SuperK constraints, masses as high as ~20 GeV are compatible. For SD neutron-only couplings we find no parameters compatible with all the experiments. Mixed SD couplings are examined: e.g. ~8 GeV mass WIMPs with a_n = +/- a_p are found to be consistent with all experiments. In short, there are surviving regions at low mass for both SI and SD interactions; if indirect detection limits are relaxed, some SD proton-only couplings at high masses also survive.

astro-ph↗
arXiv2008

MeV sterile neutrinos in low reheating temperature cosmological scenarios

It is commonly assumed that the cosmological and astrophysical bounds on the mixings of sterile with active neutrinos are much more stringent than those obtained from laboratory measurements. We point out that in scenarios with a very low reheating temperature T_RH << 100 MeV at the end of (the last episode of) inflation or entropy creation, the abundance of sterile neutrinos becomes largely suppressed with respect to that obtained within the standard framework. Thus, in this case cosmological bounds become much less stringent than usually assumed, allowing sterile neutrinos to be ``visible'' in future experiments. Here, we concentrate on massive (mostly sterile) neutrinos heavier than 1 MeV.

astro-ph↗
arXiv2007

GZK Photons in the Minimal Ultra High Energy Cosmic Rays Model

In a recently proposed model the cosmic rays spectrum at energies above 10^{18} eV 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 ~E^{-alpha} and alpha~2.6. Within this minimal model, after fitting the observed HiRes spectrum with four parameters (proton injection spectrum power law index and maximum energy, minimum distance to sources and evolution parameter) we compute the flux of ultra-high energy photons due to photon-pion production, the GZK photons, for several radio background models and average extragalactic magnetic fields with amplitude between 10^{-11} G and 10^{-9} G. We find the photon fraction to be between 10^{-4} and 10^{-3} in cosmic rays at energies above 10^{19} eV. These small fluxes could only be detected in future experiments like Auger North plus South and EUSO.

astro-ph↗
arXiv2006

Constraints on Minimal SUSY models with warm dark matter neutralinos

If the energy density of the Universe before nucleosynthesis is dominated by a scalar field $ϕ$ that decays and reheats the plasma to a low reheating temperature $T_{RH}$, neutralinos may be warm dark matter particles. We study this possibility and derive the conditions on the production mechanism and on the supersymmetric spectrum for which it is viable. Large values of the $μ$ parameter and of the slepton masses are characteristic features of these models. We compute the expected direct detection cross sections and point out that Split-SUSY provides a natural framework for neutralino warm dark matter

hep-ph↗
arXiv2006

The effect of a late decaying scalar on the neutralino relic density

If the energy density of the Universe before nucleosynthesis is dominated by a scalar field phi that decays and reheats the plasma to a temperature T_{RH} smaller than the standard neutralino freeze out temperature, the neutralino relic density differs from its standard value. In this case, the relic density depends on two additional parameters: T_{RH}, and the number of neutralinos produced per phi decay per unit mass of the phi field. In this paper, we numerically study the neutralino relic density as a function of these reheating parameters within minimal supersymmetric standard models and show that the dark matter constraint can almost always be satisfied.

hep-ph↗
arXiv2005

Compatibility of DAMA Dark Matter Detection with Other Searches

We present two examples of velocity distributions for light dark matter particles that reconcile the annual modulation signal observed by DAMA with all other negative results from dark matter searches. They are: (1) a conventional Maxwellian distribution for particle masses around 5 to 9 GeV; (2) a dark matter stream coming from the general direction of Galactic rotation (not the Sagittarius stream). Our idea is based on attributing the DAMA signal to scattering off Na, instead of I, and can be tested in the immediate future by detectors using light nuclei, such as CDMS-II (using Si) and CRESST-II (using O).

hep-ph↗
arXiv2004

Detectability of the Sgr Dwarf Leading Tidal Stream with Auger, EUSO or OWL

We point out that if heavy metastable particles composing the dark matter of our galaxy are responsible for the ultra-high energy cosmic rays (UHECR) then the leading tidal stream of the Sagittarius dwarf galaxy could be detected through UHECR. The signal would be an anisotropy in the UHECR flux smaller than the telltale anisotropy towards the galactic center that would first establish unstable dark matter as the origin of the UHECR.

hep-ph↗
arXiv2004

DAMA Dark Matter Detection Compatible with Other Searches

We present two examples of velocity distributions for light dark matter particles that reconcile the annual modulation signal observed by DAMA with all other negative results from dark matter searches. They are: (1) a conventional Maxwellian distribution for particle masses of 6 to 9 GeV; (2) a dark matter stream coming from the general direction of Galactic rotation (not the Sagittarius stream). Our idea is based on having a signal in Na, instead of I, in DAMA, and can be tested in the immediate future by CDMS-II (using Si) and CRESST-II (using O).

hep-ph↗
arXiv2004

Bounds on Relic Neutrino Masses in the Z-burst Model

Neutrinos from far-away sources annihilating at the Z resonance on relic neutrinos may give origin to the extreme-energy cosmic rays (EECR). If ``Z-bursts'' are responsible for the EECR events, then we show that the non-observation of cosmic ray events at energies above 2 x 10^20 eV by the AGASA Collaboration implies a lower bound around 0.3 eV on the relic neutrino mass. Since this mass exceeds the mass-squared differences inferred from oscillation physics, the bound in fact applies to all three neutrino masses. Together with the upper bound provided by comparisons of the CMB anisotropy with large-scale structure, this bound leaves only a small interval for neutrino masses around 0.3 eV, if Z-bursts are to explain the existing EECR events.

hep-ph↗
arXiv2002

Indirect detection of a subdominant density component of cold dark matter

We examine the detectability through indirect means of weakly interacting dark matter candidates that may constitute not all but only a subdominant component of galactic cold dark matter. We show that the possibility of indirect detection of neutralinos from their annihilations in the Earth and Sun is not severely hampered by decreasing neutralino relic density. Upward-going muon fluxes in underground detectors from neutralino annihilations in the Sun can remain above the threshold of detectability of 10 muons/km^2/yr for neutralinos composing 1% or more of the halo dark matter. Similarly, signals from neutralino annihilations in the Earth can also remain high for neutralino densities of 1% of the halo and actually would only be observable close to this low density for neutralinos lighter than 150 GeV. We also show that there are many models which simultaneously have high direct and indirect detection rates making some model discrimination possible if a signal is seen in any of the current dark matter searches.

hep-ph↗
arXiv2002

Measuring the prompt atmospheric neutrino flux with down-going muons in neutrino telescopes

In the TeV energy region and above, the uncertainty in the level of prompt atmospheric neutrinos would limit the search for diffuse astrophysical neutrinos. We suggest that neutrino telescopes may provide an empirical determination of the flux of prompt atmospheric electron and muon neutrinos by measuring the flux of prompt down-going muons. Our suggestion is based on the consideration that prompt neutrino and prompt muon fluxes at sea level are almost identical.

hep-ph↗
arXiv2002

Experimental identification of non-pointlike dark-matter candidates

We show that direct dark matter detection experiments can distinguish between pointlike and non-pointlike dark-matter candidates. The shape of the nuclear recoil energy spectrum from pointlike dark-matter particles, e.g., neutralinos, is determined by the velocity distribution of dark matter in the galactic halo and by nuclear form factors. In contrast, typical cross sections of non-pointlike dark matter, for example, Q-balls, have a new form factor, which decreases rapidly with the recoil energy. Therefore, a signal from non-pointlike dark matter is expected to peak near the experimental threshold and to fall off rapidly at higher energies. Although the width of the signal is practically independent of the dark matter velocity dispersion, its height is expected to exhibit an annual modulation due to the changes in the dark matter flux.

hep-ph↗