Astrophysical sources of high energy neutrinos

Several high energy, >100 GeV, neutrino telescopes are currently operating or under construction. Their main motivation is the extension of the horizon of neutrino astronomy to cosmological scales. We show that general, model independent, arguments imply that ~1 Gton detectors are required to detect cosmic high energy neutrino sources. Predictions of models of some of the leading candidate sources, gamma-ray bursts and micro-quasars, are discussed, and the question of what can be learned from neutrino observations is addressed.Comment: Invited talk, Neutrino 2002 (Munich

Implications of long tails in the distribution of mutant effects

Long-tailed distributions possess an in nite variance, yet a nite sample that is drawn from such a distribution has a nite variance. In this work we consider a model of a population subject to mutation, selection and drift. We investigate the implications of a long-tailed distribution of mutant allelic e¤ects on the distribution of genotypic e¤ects in a model with a continuum of allelic e¤ects. While the analysis is confined to asexual populations, it does also have implications for sexual populations. We obtain analytical results for a selectively neutral population as well as one subject to selection. We supplement these analytical results with numerical simulations, to take into account genetic drift. We nd that a long-tailed distribution of mutant e¤ects may a¤ect both the equilibrium and the evolutionary adaptive behaviour of a population

High energy cosmic-rays and neutrinos from cosmological gamma-ray burst fireballs

The recent detection of delayed, low energy emission from Gamma-Ray Burst (GRB) sources confirmed the cosmological origin of the bursts and provided support for models where GRBs are produced by the dissipation of the kinetic energy of relativistic fireballs. In this review, ultra high energy, >10^{19} eV, cosmic-ray and high energy, 100 TeV, neutrino production in GRBs is discussed in the light of recent GRB and cosmic-ray observations. Emphasis is put on model predictions that can be tested with operating and planned cosmic-ray and neutrino detectors. The predicted neutrino intensity, E^2 dN/dE=3\times 10^{-9} GeV/(cm^2 s sr) for 10^{14} eV<E<10^{16} eV, implies that a km^2 neutrino detector would observe tens of events per year correlated with GRBs, and will be able to test for neutrino properties with an accuracy many orders of magnitude better than is currently possible. The predicted production rate of high-energy protons, which is consistent with that required to account for the observed ultra-high-energy cosmic-ray (UHECR) flux, implies that operating and planned cosmic-ray detectors can test the GRB model for UHECR production. If the predicted sources are found, cosmic-ray detectors will provide us with a technique to investigate the inter-galactic magnetic field.Comment: Physica Scripta, in press; Talk presented at the Nobel Symposium: Particle Physics and The Universe (Sweden, August 1998

Fisher's geometrical model of evolutionary adaptation - beyond spherical geometry

Fisher's geometrical model of evolutionary adaptation has recently been used in a variety of contexts of interest to evolutionary biologists. The renewed interest in this model strongly motivates generalizations that make it a more realistic description of evolutionary adaptation. Previously, the distribution of mutant effects has, for analytical tractability, rather than biological realism, been taken as spherically symmetric. Here we substantially extend Fisher's model, by allowing a wider class of mutational distributions that incorporate mutational bias and more general deviations from spherical symmetry such as correlations between mutant effects. We also incorporate work on generalized fitness landscapes, thereby reducing the number of artificial assumptions underlying the model. The generalized model exhibits a substantially increased flexibility and a far richer underlying geometry. We find that the distribution characterizing selection coefficients of new mutations is expressed in terms of a number of geometrical invariants associated with mutation, selection and the parental phenotype