Pulsar Kicks With Modified URCA and Electrons in Landau Levels

We derive the energy asymmetry given the proto-neutron star during the time when the neutrino sphere is near the surface of the proto-neutron star, using the modified URCA process. The electrons produced with the anti-neutrinos are in Landau levels due to the strong magnetic field, and this leads to asymmetry in the neutrino momentum, and a pulsar kick. The magnetic field must be strong enough for a large fraction of the eletrons to be in the lowest Landau level, however, there is no direct dependence of our pulsar velocity on the strength of the magnetic field. Our main prediction is that the large pulsar kicks start at about 10 s and last for about 10 s, with the corresponding neutrinos correlated in the direction of the magnetic field. We predict a pulsar velocity of 1.03 $\times 10^{-4} (T/10^{10}K)^7$ km/s, which reaches 1000 km/s if T $\simeq 9.96 \times 10^{10}$ K.Comment: 11 pages, 6 figure

Parity Violation in Neutrino Transport and the Origin of Pulsar Kicks

In proto-neutron stars with strong magnetic fields, the neutrino-nucleon scattering/absorption cross sections depend on the direction of neutrino momentum with respect to the magnetic field axis, a manifestation of parity violation in weak interactions. We study the deleptonization and thermal cooling (via neutrino emission) of proto-neutron stars in the presence of such asymmetric neutrino opacities. Significant asymmetry in neutrino emission is obtained due to multiple neutrino-nucleon scatterings. For an ordered magnetic field threading the neutron star interior, the fractional asymmetry in neutrino emission is about $0.006 (B/10^{14}G)$, corresponding to a pulsar kick velocity of about $200 (B/10^{14}G)$ km/s for a total radiated neutrino energy of $3\times 10^{53}$ erg.Comment: AASTeX, 10 pages including 2 ps figures; ApJ Letter in press (March 10, 1998). Shortened to agree with the published versio

Can Parity Violation in Neutrino Transport Lead to Pulsar Kicks?

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$^{-1}$.Comment: REVTEX, 4 pages, no figures. Submitted to Phys. Rev. Letter

Radiative heat transfer between nanostructures

We simplify the formalism of Polder and Van Hove [Phys.Rev.B {\bf 4}, 3303(1971)], which was developed to calculate the heat transfer between macroscopic and nanoscale bodies of arbitrary shape, dispersive and adsorptive dielectric properties. In the non-retarded limit, at small distances between the bodies, the problem is reduced to the solution of an electrostatic problem. We apply the formalism to the study of the heat transfer between: (a) two parallel semi-infinite bodies, (b) a semi-infinite body and a spherical body, and (c) that two spherical bodies. We consider the dependence of the heat transfer on the temperature $T$, the shape and the separation $d$. We determine when retardation effects become important.Comment: 11 pages, 5 figure

Neutrino Transport in Strongly Magnetized Proto-Neutron Stars and the Origin of Pulsar Kicks: The Effect of Asymmetric Magnetic Field Topology

In proto-neutron stars with strong magnetic fields, the cross section for $\nu_e$ ($\bar\nu_e$) absorption on neutrons (protons) depends on the local magnetic field strength due to the quantization of energy levels for the $e^-$ ($e^+$) produced in the final state. If the neutron star possesses an asymmetric magnetic field topology in the sense that the magnitude of magnetic field in the north pole is different from that in the south pole, then asymmetric neutrino emission may be generated. We calculate the absorption cross sections of \nue and \bnue in strong magnetic fields as a function of the neutrino energy. These cross sections exhibit oscillatory behaviors which occur because new Landau levels for the $e^-$ ($e^+$) become accessible as the neutrino energy increases. By evaluating the appropriately averaged neutrino opacities, we demonstrate that the change in the local neutrino flux due to the modified opacities is rather small. To generate appreciable kick velocity ($\sim 300$ km~s$^{-1}$) to the newly-formed neutron star, the difference in the field strengths at the two opposite poles of the star must be at least $10^{16}$~G. We also consider the magnetic field effect on the spectral neutrino energy fluxes. The oscillatory features in the absorption opacities give rise to modulations in the emergent spectra of $\nu_e$ and $\bar\nu_e$.Comment: AASTeX, 25 pages. Expanded introduction and references. This revised version was accepted by ApJ in April 1998 (to appear in the Oct 1 issue

Pulsar kicks from neutrino oscillations

Neutrino oscillations in a core-collapse supernova may be responsible for the observed rapid motions of pulsars. Given the present bounds on the neutrino masses, the pulsar kicks require a sterile neutrino with mass 2-20 keV and a small mixing with active neutrinos. The same particle can be the cosmological dark matter. Its existence can be confirmed the by the X-ray telescopes if they detect a 1-10 keV photon line from the decays of the relic sterile neutrinos. In addition, one may be able to detect gravity waves from a pulsar being accelerated by neutrinos in the event of a nearby supernova.Comment: invited review article to appear in Int. J. Mod. Phys. (21 pages, 6 figures

The cusp effect in eta' --> eta pi pi decays

Strong final-state interactions create a pronounced cusp in eta' --> eta pi0 pi0 decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of pi pi scattering lengths from K --> 3 pi decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the pi+ pi- threshold.Comment: 11 pages, 8 figures; comment added, typos corrected, version published in Eur. Phys. J.

The Halo Beaming Model for Gamma-Ray Bursts

We consider a model for gamma-ray bursts (GRBs) from high-velocity neutron stars in the galactic halo. In this model, bursters are born in the galactic disk with large recoil velocities V_r, and GRBs are beamed to within emission cones of half-angle \phi centered on V_r. We describe scenarios for magnetically -channeled GRBs that have such beaming characteristics. We then make detailed comparisons of this halo beaming model (HBM) to BATSE and PVO data for GRB intensity & angular position distributions. Acceptable fits to observations of over 1000 bursts are obtained for \phi = 15 - 30 degrees and for a BATSE sampling depth ~ 180 kpc. Present data favor a truly isotropic (cosmological) model over the HBM, but not by a statistically compelling margin. Bursters born in nearby external galaxies, such as M31, are almost entirely undetectable in the HBM because of misdirected beaming. We analyze several refinements of the basic HBM: gamma-ray intensities that vary with angle from the beam axis; non-standard-candle GRB luminosity functions; and models including a subset of bursters that do not escape from the galaxy. We also discuss the energy budgets for the bursters, the origins of their recoils, and the physics of burst beaming and alignment. One possible physical model is based on the magnetar model of soft gamma repeaters (SGRs). Empirical bounds on the rate of formation and peculiar velocities of SGRs imply that there exist ~ 10^4 to ~ 10^7 aged SGRs in the galactic halo within a distance of 100 kpc. The HBM gives an acceptable fit to observations only if it satisfies certain conditions (e.g. \phi ~ 20 deg) which are possible, but for which there exist no clear & compelling theoretical justifications. The cosmological burster hypothesis is more generic and thus more attractive in this sense. (Abbreviated Abstract).Comment: ApJ accepted, 9 figures, AASTE

Detecting sterile dark matter in space

Space-based instruments provide new and, in some cases, unique opportunities to search for dark matter. In particular, if dark matter comprises sterile neutrinos, the x ray detection of their decay line is the most promising strategy for discovery. Sterile neutrinos with masses in the keV range could solve several long-standing astrophysical puzzles, from supernova asymmetries and the pulsar kicks to star formation, reionization, and baryogenesis. The best current limits on sterile neutrinos come from Chandra and XMM-Newton. Future advances can be achieved with a high-resolution x-ray spectrometry in space.Comment: 11 pages, 1 figure, to appear in proceedings "From Quantum to Cosmos: fundametal physics research in space", Washington, DC, May 22-24, 200