arXiv subjects

George B. Field

Publications and source records attributed to George B. Field.

26 records · Page 2Linked to original sources

arXiv1997

Is there evidence for cosmic anisotropy in the polarization of distant radio sources?

Measurements of the polarization angle and orientation of cosmological radio sources may be used to search for unusual effects in the propagation of light through the universe. Recently, Nodland and Ralston (astro-ph/9704196) have claimed to find evidence for a redshift- and direction-dependent rotation effect in existing data. We re-examine these data and argue that there is no statistically significant signal present. We are able to place stringent limits on hypothetical chiral interactions of photons propagating through spacetime.

astro-ph↗

arXiv1996

Relativistic Precessing Jets and Cosmological Gamma Ray Bursts

We discuss the possibility that gamma-ray bursts may result from cosmological relativistic blob emitting neutron star jets that precess past the line of sight. Beaming reduces the energy requirements, so that the jet emission can last longer than the observed burst duration. One precession mode maintains a short duration time scale, while a second keeps the beam from returning to the line of sight, consistent with the paucity of repeaters. The long life of these objects reduces the number required for production as compared to short lived jets. Blobs can account for the time structure of the bursts. Here we focus largely on kinematic and time scale considerations of beaming, precession, and blobs--issues which are reasonably independent of the acceleration and jet collimation mechanisms. We do suggest that large amplitude electro-magnetic waves could be a source of blob acceleration.

astro-ph↗

arXiv1994

Non-thermal Acceleration from Reconnection Shocks

Reconnection shocks in a magnetically dominated plasma must be compressive. Non-thermal ion acceleration can occur across built-in slow shocks, and across outflow fast shocks when the outflow is supermagnetosonic and the field is line-tied. Electron acceleration may be initiated by injection from the dissipation region. Reconnection and shock acceleration thus cooperate and non-thermal acceleration should be a characteristic feature.

astro-ph↗

arXiv1994

Consequences of Propagating Torsion in Connection-Dynamic Theories of Gravity

We discuss the possibility of constraining theories of gravity in which the connection is a fundamental variable by searching for observational consequences of the torsion degrees of freedom. In a wide class of models, the only modes of the torsion tensor which interact with matter are either a massive scalar or a massive spin-1 boson. Focusing on the scalar version, we study constraints on the two-dimensional parameter space characterizing the theory. For reasonable choices of these parameters the torsion decays quickly into matter fields, and no long-range fields are generated which could be discovered by ground-based or astrophysical experiments.

gr-qc↗

arXiv1994

Electroweak String Configurations with Baryon Number

In the context of electroweak strings, the baryon number anomaly equation may be reinterpreted as a conservation law for baryon number minus helicity. Since the helicity is a sum of the link and twist numbers, linked or twisted loops of electroweak string carry baryon number. We evaluate the change in the baryon number obtained by delinking loops of electroweak $Z-$string and show that twisted electroweak string segments may be regarded as extended sphalerons. We also suggest an alternative scenario for electroweak baryogenesis.

hep-ph↗

arXiv1994

Ohm's Law for a Relativistic Pair Plasma

We derive the fully relativistic Ohm's law for an electron-positron plasma. The absence of non-resistive terms in Ohm's law and the natural substitution of the 4-velocity for the velocity flux in the relativistic bulk plasma equations do not require the field gradient length scale to be much larger than the lepton inertial lengths, or the existence of a frame in which the distribution functions are isotropic.

astro-ph↗

arXiv1993

On the Distance Determination and Ionization of the High Velocity Clouds

We present a study of the ionization and thermal structure of neutral hydrogen clouds located in the Galactic halo, immersed in the extragalactic background radiation field, and supposed to be in pressure equilibrium with the surrounding (presumably) hot medium. The problem is solved numerically, but an useful analytical approximation has been derived as well. We discuss the two main parameters of the problem, \ie the radiation field and the halo pressure, in the framework of the current models for the halo/disk interaction. We find a well defined relation between a critical column density at which the cloud starts to develop a cold central core with the cloud linear size. Making use of this relation, we suggest a straightforward method to derive the distance to the cloud. We discuss the possible sources of error in this determination and it is found that the method is particularly suitable for those clouds which are subsonic with respect to the surrounding medium, while for the supersonic ones, the method can only give a lower limit to the distance. The H$α$ emission from the partially ionized edge of the cloud is calculated and compared with the available observations; this measure is a powerful indicator of the possible presence of a shock in the cloud.

astro-ph↗

arXiv1992

Primordial magnetic fields from pseudo-Goldstone bosons

The existence of large-scale magnetic fields in galaxies is well established, but there is no accepted mechanism for generating a primordial field which could grow into what is observed today. We discuss a model which attempts to account for the necessary primordial field by invoking a pseudo-Goldstone boson coupled to electromagnetism. The evolution of this boson during inflation generates a magnetic field; however, it seems difficult on rather general grounds to obtain fields of sufficient strength on astrophysically interesting scales.

hep-ph↗