R. F. Sawyer

Speed-up of neutrino transformations in a supernova environment

When the neutral current neutrino-neutrino interaction is treated completely, rather than as an interaction among angle-averaged distributions, or as a set of flavor-diagonal effective potentials, the result can be flavor mixing at a speed orders of magnitude faster than that one would anticipate from the measured neutrino oscillation parameters. It is possible that the energy spectra of the three active species of neutrinos emerging from a supernova are nearly identical.

Damping of vibrations and of the secular instability in quark stars

We calculate the bulk viscosity of hot quark matter, or “strange” matter, which could be present in neutron stars. In the temperature range characteristic of young neutron stars, the bulk viscosity arising from non-leptonic strangeness-changing quark-quark interactions is orders of magnitude larger than that which has been calculated for ordinary nuclear matter. The gravitational wave secular instability should be completely suppressed for quark stars, and the damping times for pulsations will be very short.

NEUTRINO PROPAGATION IN DENSE ASTROPHYSICAL SYSTEMS

▪ Abstract Even the elusive neutrinos are trapped in matter, albeit transiently, in several astrophysical circumstances. Their interactions with the ambient matter not only reveal the properties of such exotic matter, but also shed light on the fundamental properties of the neutrinos. The physical sites of interest include the early universe, supernovae, and newly born neutron stars. Detection of neutrinos from these vastly different eras using the new generation of neutrino detectors holds great promise for enhancing our understanding of neutrino-matter interactions and astrophysical phenomena.

Neutrino transport in accretion disks

We test approximate approaches to solving a neutrino transport problem that presents itself in the analysis of some accretion-disk models. Approximation #1 consists of replacing the full, angular- dependent, distribution function by a two-stream simulation, where the streams are respectively outwardly and inwardly directed, with angles

Speed-up through entanglement—many-body effects in neutrino processes

\cos \theta=\pm 1/\sqrt{3}

Entanglement and quantal coherence: Study of two limiting cases of rapid system-bath interactions

to the vertical. In this approximation the full energy dependence of the distribution function is retained, as are the energy and temperature dependences of the scattering rates. Approximation #2, used in recent works on the subject, replaces the distribution function by an intensity function and the scattering rates by temperature-energy-averaged quantities. We compare the approximations to the results of solving the full Boltzmann equation. Under some interesting conditions, approximation #1 passes the test; approximation #2 does not. We utilize the results of our analysis to construct a toy model of a disc at a temperature and density such that relativistic particles are more abundant than nucleons, and dominate both the opacity and pressure. The nucleons will still provide most of the energy density. In the toy model we take the rate of heat generation (which drives the radiative transfer problem) to be proportional to the nucleon density. The model allows the simultaneous solution of the neutrino transport and hydrostatic equilibrium problems in a disk in which the nucleon density decreases approximately linearly as one moves from the median plane of the disk upwards, reaching zero on the upper boundary.

Do neutrinos have mass only within matter

We study a system containing many particles of identical kinematics with a zero range interaction that scatters one from the other, and with the possible exchange of an attribute. Taking an initial condition in which the attribute is asymmetrically distributed in the regions of momentum space occupied by the particles, we study the rate at which it becomes uniformly distributed, through collisions. We find, in some circumstances, a rate that is much faster than that which would be estimated from cross-sections. This behavior is attributable in some general sense to N-particle entanglement. We suggest applications to neutrino physics, where the attribute is neutrino flavor.

Mesonic wakes in nuclear matter, with application to meson production in nuclear collisions

In this paper, we consider the dynamics of a system coupled to a thermal bath, going beyond the standard two-level system through the addition of an energy excitation degree of freedom. Further extensions are to systems containing many fermions, with the master equations modified to take Fermi-Dirac statistics into account, and to potentials with a time-dependent bias that induce resonant avoided crossing transitions. The limit Q→∞, where the interaction rate with the bath is much greater than all free oscillation rates for the system, is investigated. Two behaviors are possible: freezing (quantum Zeno effect) or synchronization (motional narrowing). We clarify the conditions that give rise to each possibility, making an explicit connection with quantum-measurement theory. We compare the evolution of quantal coherence for the two cases as a function of Q, noting that full coherence is restored as Q→∞. Using an extended master equation, the effect of system-bath interactions on entanglement in bipartite system states is computed. In particular, we show that the sychronization case sees bipartite system entanglement fully preserved in the large Q limit.

Effects of ion and electron correlations on neutrino scattering in the infall phase of a supernova

Abstract We look at the possibility that appreciable neutrino masses and flavor mixing occur only within material media, driven by an interaction between leptons and a very light scalar particle. Limits are placed on the scalar particle mass and coupling constants from a number of experimental and astrophysical considerations.

The meson propagator in nuclear matter

Abstract The process of meson production by a source moving uniformly through infinite nuclear matter is studied in field theoretic models in which a source-meson coupling is assumed, and in which the only effect of the nuclear medium is to modify the propagator of the mesons. If the meson dispersion relation, ω ( k ), in the medium becomes space-like in some region of k , k > ω ( k ), there is, for relativistic source velocities, energy loss to the mesonic excitations. Models of the pion propagator in nuclear matter lead to such a space-like region. Rates of pion production are calculated in the lowest order of the pion-source coupling. Consideration of higher order terms leads to an interesting class of problems which we designate as those of “non-Abelian Cherenkov radiation.” Brief consideration is given to the excitation of nuclear collective modes and to the problems of treating meson production in finite nuclei.