A self-consistent phase-space distribution function for the anisotropic dark matter halo of the Milky Way

Dark Matter (DM) direct detection experiments usually assume the simplest possible ‘Standard Halo Model’ for the Milky Way (MW) halo in which the velocity distribution is Maxwellian. This model assumes that the MW halo is an isotropic, isothermal sphere, hypotheses that are unlikely to be valid in reality. An alternative approach is to derive a self-consistent solution for a particular mass model of the MW (i.e. obtained from its gravitational potential) using the Eddington formalism, which assumes isotropy. In this paper we extend this approach to incorporate an anisotropic phase-space distribution function. We perform Bayesian scans over the parameters defining the mass model of the MW and parameterising the phase-space density, implementing constraints from a wide range of astronomical observations. The scans allow us to estimate the precision reached in the reconstruction of the velocity distribution (for different DM halo profiles). As expected, allowing for an anisotropic velocity tensor increases the uncertainty in the reconstruction of f (v), but the distribution can still be determined with a precision of a factor of 4-5. The mean velocity distribution resembles the isotropic case, however the amplitude of the high-velocity tail is up to a factor of 2 larger. Our results agree with the phenomenological parametrization proposed in Mao et al. (2013) as a good fit to N-body simulations (with or without baryons), since their velocity distribution is contained in our 68% credible interval

A prospective randomized trial of content expertise versus process expertise in small group teaching

Article deposited according to agreement with BMC, December 6, 2010.YesFunding provided by the Open Access Authors Fund

Steady free-surface flow at the stern of a ship

New solutions for steady two-dimensional free-surface flow past a curved plate are considered here. They can be interpreted as approximations to the flow locally at the stern of a ship. Weakly nonlinear solutions are derived analytically and nonlinear solutions are computed by boundary integral equation methods. Analysis in the phase plane provides a way to determine the geometries of hulls that give rise to wave-free stern flows. These waveless flows are desirable as they reduce ship-drag

Cosmological Black Holes as Seeds of Voids in Galaxy Distribution

Deep surveys indicate a bubbly structure of cosmological large scale which should be the result of evolution of primordial density perturbations. Several models have been proposed to explain origin and dynamics of such features but, till now, no exhaustive and fully consistent theory has been found. We discuss a model where cosmological black holes, deriving from primordial perturbations, are the seeds for large-scale-structure voids. We give details of dynamics and accretion of the system voids-cosmological black holes from the epochs $(z\simeq10^{3})$ till now finding that void of $40h^{-1}Mpc$ of diameter and under-density of -0.9 will fits the observations without conflicting with the homogeneity and isotropy of cosmic microwave background radiation.Comment: to appear in Astronomy & Astrophysic

Event Texture Search for Phase Transitions in Pb+Pb Collisions

NA44 uses a 512 channel Si pad array covering $1.5 <\eta < 3.3$ to study charged hadron production in 158 A GeV Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a Discrete Wavelet Transformation, to probe the texture of particle distributions event-by-event, allowing simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we search for signals of clustering and of critical behavior in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy ion event generators, and with a reference sample created via event mixing. An upper limit is set on the probability and magnitude of dynamical fluctuations