Showing papers by "Phil Arras published in 1998"

Can Parity Violation in Neutrino Transport Lead to Pulsar Kicks

Abstract: In magnetized proto-neutron stars, neutrino cross sections depend asymmetrically on the neutrino momenta due to parity violation. However, these asymmetric opacities do not induce any asymmetric flux in the bulk interior of the star where neutrinos are nearly in thermal equilibrium. Consequently, parity violation in neutrino absorption and scattering can only give rise to asymmetric neutrino flux above the neutrino-matter decoupling layer. The kick velocity is substantially reduced from previous estimates, requiring a dipole field $B \sim 10^{16}$~G to get $v_{kick}$ of order a few hundred km~s$^{-1}$.

Canaries in a Coal Mine: Using Globular Clusters to Place Limits on Massive Black Holes in the Galactic Halo

Abstract: We explore the possibility that massive black holes comprise a significant fraction of the dark matter of our galaxy by studying the dissolution of galactic globular clusters bombarded by them. In our simulations, we evolve the clusters along a sequence of King models determined by changes of state resulting from collisions with the black holes. The results divide naturally into regimes of `small' and `large' black hole mass. `Small' black holes do not destroy clusters in single collisions; their effect is primarily cumulative, leading to a relation between $\mbh$ and $\fhalo$, the fraction of the halo in black holes of mass $\mbh$, which is $\fhalo\mbh < $ constant (up to logarithmic corrections). For $\fhalo=1$, we find $\mbh \simless 10^{3} \msun$ by requiring survival of the same clusters studied by Moore (1993), who neglected cluster evolution, mass loss, and stochasticity of energy inputs in his estimates, but reached a similar conclusion. `Large' black holes may not penetrate a cluster without disrupting it; their effect is mainly catastrophic (close collisions), but also partly cumulative (distant collisions). In the large $\mbh$ limit, $\fhalo$ (but not $\mbh$) can be constrained by computing the probability that a cluster survives a combination of close, destructive encounters and distant, nondestructive encounters. We find that it is unlikely that $\fhalo \simgreat 0.3$ by requiring 50 per cent survival probability for Moore's clusters over $10^{10}$ years.