Showing papers by "Olga Mena published in 2007"
TL;DR: In this paper, the relativistic energy density in the universe was parametrized in terms of the effective number of neutrinos Nνeff using the most recent cosmological data on cosmic microwave background (CMB) temperature anisotropies and polarization, large scale galaxy clustering from the Sloan Digital Sky Survey (SDSS) and 2dF, luminosity distances of type Ia supernovae, Lyman-α absorption clouds (Ly-α), the baryonic acoustic oscillations (BAO) detected in the luminous red
Abstract: We discuss the present bounds on the relativistic energy density in the Universe parametrized in terms of the effective number of neutrinos Nνeff using the most recent cosmological data on cosmic microwave background (CMB) temperature anisotropies and polarization, large scale galaxy clustering from the Sloan Digital Sky Survey (SDSS) and 2dF, luminosity distances of type Ia supernovae, Lyman-α absorption clouds (Ly-α), the baryonic acoustic oscillations (BAO) detected in the luminous red galaxies of the SDSS and, finally, big bang nucleosynthesis (BBN) predictions for 4He and deuterium abundances. We find Nνeff = 5.2−2.2+2.7 from CMB and large scale structure data, while adding Ly-α and BAO we obtain Nνeff = 4.6−1.5+1.6 at 95% c.l. These results show some tension with the standard value Nνeff = 3.046 as well as with the BBN range Nνeff = 3.1−1.2+1.4 at 95% c.l., though the discrepancy is slightly below the 2-σ level. In general, considering a smaller set of data weakens the constraints on Nνeff. We emphasize the impact of an improved upper limit (or measurement) of the primordial value of 3He abundance in clarifying the issue of whether the value of Nνeff at early (BBN) and more recent epochs coincide.
62 citations
TL;DR: In this article, a low energy neutrino factory, with peak energy in the few GeV range, was proposed to explore CP-violation and the neutrinos mass hierarchy.
Abstract: If the value of {theta}{sub 13} is within the reach of the upcoming generation of long-baseline experiments, T2K and NOvA, they show that a low-energy neutrino factory, with peak energy in the few GeV range, would provide a sensitive tool to explore CP-violation and the neutrino mass hierarchy. They consider baselines with typical length 1000-1500 km. The unique performance of the low energy neutrino factory is due to the rich neutrino oscillation pattern at energies between 1 and 4 GeV at baselines {Omicron}(1000) km. They perform both a semi-analytical study of the sensitivities and a numerical analysis to explore how well this setup can measure {theta}{sub 13}, CP-violation, and determine the type of mass hierarchy and the {theta}{sub 23} quadrant. A low energy neutrino factory provides a powerful tool to resolve ambiguities and make precise parameter determinations, for both large and fairly small values of the mixing parameter {theta}{sub 13}.
56 citations
TL;DR: In this paper, a suppression in the spectrum of ultra-high-energy (UHE, 10,sup 18, eV) neutrinos was observed in extra-dimensional scenarios, due to enhanced neutrino-antineutrino annihilation processes.
Abstract: A suppression in the spectrum of ultrahigh-energy (UHE, {ge} 10{sup 18} eV) neutrinos will be present in extra-dimensional scenarios, due to enhanced neutrino-antineutrino annihilation processes with the supernova relic neutrinos. In this scenario, neutrinos can not be responsible for the highest energy events observed in the UHE cosmic ray spectrum. A direct implication of these extra-dimensional interactions would be the absence of UHE neutrinos in ongoing and future neutrino telescopes.
12 citations