Patrick Crotty

Current cosmological bounds on neutrino masses and relativistic relics

We combine the most recent observations of large-scale structure (2dF and SDSS galaxy surveys) and cosmic microwave anisotropies (WMAP and ACBAR) to put constraints on flat cosmological models where the number of massive neutrinos and of massless relativistic relics are both left arbitrary. We discuss the impact of each dataset and of various priors on our bounds. For the standard case of three thermalized neutrinos, we find an upper bound on the total neutrino mass sum m_nu < 1.0 (resp. 0.6) eV (at 2sigma), using only CMB and LSS data (resp. including priors from supernovae data and the HST Key Project), a bound that is quite insensitive to the splitting of the total mass between the three species. When the total number of neutrinos or relativistic relics N_eff is left free, the upper bound on sum m_nu (at 2sigma, including all priors) ranges from 1.0 to 1.5 eV depending on the mass splitting. We provide an explanation of the parameter degeneracy that allows larger values of the masses when N_eff increases. Finally, we show that the limit on the total neutrino mass is not significantly modified in the presence of primordial gravitational waves, because current data provide a clear distinction between the corresponding effects.

Does the small CMB quadrupole moment suggest new physics

Motivated by WMAPs confirmation of an anomalously low value of the quadrupole moment of the CMB temperature fluctuations, we investigate the effects on the CMB of cutting off the primordial power spectrum P(k) at low wave numbers. This could arise, for example, from a break in the inflaton potential, a prior period of matter or radiation domination, or an oscillating scalar field which couples to the inflaton. We reanalyse the full WMAP parameter space supplemented by a low-k cutoff for P(k). The temperature correlations by themselves are better fit by a cutoff spectrum, but including the TE temperature-polarization spectrum reduces this preference to a 1.4σ effect. Inclusion of large scale structure data does not change the conclusion. If taken seriously, the low-k cutoff is correlated with optical depth so that reionization occurs even earlier than indicated by the WMAP analysis.

Gravitational production of superheavy dark matter

The dark matter in the universe can be in the form of a superheavy matter species (wimpzilla). Several mechanisms have been proposed for the production of wimpzilla particles during or immediately following the inflationary epoch. Perhaps the most attractive mechanism is through gravitational particle production, where particles are produced simply as a result of the expansion of the universe. In this paper we present a detailed numerical calculation of wimpzilla gravitational production in hybrid-inflation models and natural-inflation models. Generalizing these findings, we also explore the dependence of the gravitational production mechanism on various models of inflation. We show that superheavy dark matter production seems to be robust, with {Omega}{sub X}h{sup 2}{approx}(M{sub X}/10{sup 11}GeV){sup 2}(T{sub RH}/10{sup 9}GeV), so long as M{sub X}<H{sub I}, where M{sub X} is the wimpzilla mass, T{sub RH} is the reheat temperature, and H{sub I} is the expansion rate of the universe during inflation.

Measuring the cosmological background of relativistic particles with the Wilkinson Microwave Anisotropy Probe

We show that the first year results of the Wilkinson Microwave Anisotropy Probe (WMAP) constrain very efficiently the energy density in relativistic particles in the universe. We derive new bounds on additional relativistic degrees of freedom expressed in terms of an excess in the effective number of light neutrinos Delta N_eff. Within the flat LambdaCDM scenario, the allowed range is Delta N_eff<6 (95% CL) using WMAP data only, or -2.6<Delta N_eff<4 with the prior H_0= 72 \pm 8 km/s/Mpc. When other cosmic microwave background and large scale structure experiments are taken into account, the window shrinks to -1.6<Delta N_eff<3.8. These results are in perfect agreement with the bounds from primordial nucleosynthesis. Non-minimal cosmological models with extra relativistic degrees of freedom are now severely restricted.

Enhanced signal of astrophysical tau neutrinos propagating through Earth

Earth absorbs

High-energy neutrino fluxes from supermassive dark matter

{\ensuremath{\nu}}_{e}

Effects of Na+ channel inactivation kinetics on metabolic energy costs of action potentials

and

Energy-efficient interspike interval codes

{\ensuremath{\nu}}_{\ensuremath{\mu}}

Optimization of the leak conductance in the squid giant axon.

of energies above about 100 TeV. As is well known, although

Synchronization dynamics on the picosecond timescale in coupled Josephson junction neurons

{\ensuremath{\nu}}_{\ensuremath{\tau}}