168 research outputs found
SO(10) Cosmic Strings and Baryon Number Violation
SO(10) cosmic strings formed during the phase transition Spin(10)
SU(5) are studied. Two types of strings ---
one effectively Abelian and one non-Abelian --- are constructed and the string
solutions are calculated numerically. The non-Abelian string can catalyze
baryon number violation via the ``twisting'' of the scalar field which causes
mixing of leptons and quarks in the fermion multiplet. The non-Abelian string
is also found to have the lower energy possibly for the entire range of the
parameters in the theory. Scattering of fermions in the fields of the strings
is analyzed, and the baryon number violation cross section is calculated. The
role of the self-adjoint parameters is discussed and the values are computed.Comment: LaTex (RevTex), 36 pages, 6 figures (available upon request),
MIT-CTP#215
Chiral symmetry breaking as a consequence of nontrivial spatial topology
A singular configuration of external static magnetic field in the form of a
pointlike vortex polarizes the vacuum of quantized massless spinor field in
2+1-dimensional space-time. This results in an analogue of the Bohm-Aharonov
effect: the chiral symmetry breaking condensate, energy density and current
emerge in the vacuum even in the case when the spatial region of nonvanishing
external field strength is excluded. The dependence of the vacuum
characteristics both on the value of the vortex flux and on the choice of the
boundary condition at the location of the vortex is determined.Comment: LaTeX2e, 14 page
Euclidean thermal spinor Green's function in the spacetime of a straight cosmic string
Within the framework of the quantum field theory at finite temperature on a
conical space, we determine the Euclidean thermal spinor Green's function for a
massless spinor field. We then calculate the thermal average of the
energy-momentum tensor of a thermal bath of massless fermions. In the
high-temperature limit, we find that the straight cosmic string does not
perturb the thermal bathComment: 11 pages, latex, no figure
Time-dependent quantum scattering in 2+1 dimensional gravity
The propagation of a localized wave packet in the conical space-time created
by a pointlike massive source in 2+1 dimensional gravity is analyzed. The
scattering amplitude is determined and shown to be finite along the classical
scattering directions due to interference between the scattered and the
transmitted wave functions. The analogy with diffraction theory is emphasized.Comment: 15 pages in LaTeX with 3 PostScript figure
Path integrals on a flux cone
This paper considers the Schroedinger propagator on a cone with the conical
singularity carrying magnetic flux (``flux cone''). Starting from the operator
formalism and then combining techniques of path integration in polar
coordinates and in spaces with constraints, the propagator and its path
integral representation are derived. "Quantum correction" in the Lagrangian
appears naturally and no a priori assumption is made about connectivity of the
configuration space.Comment: LaTeX file, 9 page
Quantum Hall Ferromagnets: Induced Topological term and electromagnetic interactions
The quantum Hall ground state in materials like GaAs is well known
to be ferromagnetic in nature. The exchange part of the Coulomb interaction
provides the necessary attractive force to align the electron spins
spontaneously. The gapless Goldstone modes are the angular deviations of the
magnetisation vector from its fixed ground state orientation. Furthermore, the
system is known to support electrically charged spin skyrmion configurations.
It has been claimed in the literature that these skyrmions are fermionic owing
to an induced topological Hopf term in the effective action governing the
Goldstone modes. However, objections have been raised against the method by
which this term has been obtained from the microscopics of the system. In this
article, we use the technique of the derivative expansion to derive, in an
unambiguous manner, the effective action of the angular degrees of freedom,
including the Hopf term. Furthermore, we have coupled perturbative
electromagnetic fields to the microscopic fermionic system in order to study
their effect on the spin excitations. We have obtained an elegant expression
for the electromagnetic coupling of the angular variables describing these spin
excitations.Comment: 23 pages, Plain TeX, no figure
Models for Chronology Selection
In this paper, we derive an expression for the grand canonical partition
function for a fluid of hot, rotating massless scalar field particles in the
Einstein universe. We consider the number of states with a given energy as one
increases the angular momentum so that the fluid rotates with an increasing
angular velocity. We find that at the critical value when the velocity of the
particles furthest from the origin reaches the speed of light, the number of
states tends to zero. We illustrate how one can also interpret this partition
function as the effective action for a boosted scalar field configuration in
the product of three dimensional de Sitter space and . In this case, we
consider the number of states with a fixed linear momentum around the as
the particles are given more and more boost momentum. At the critical point
when the spacetime is about to develop closed timelike curves, the number of
states again tends to zero. Thus it seems that quantum mechanics naturally
enforces the chronology protection conjecture by superselecting the causality
violating field configurations from the quantum mechanical phase space.Comment: 20 pages, Late
Negative Energy Densities in Extended Sources Generating Closed Timelike Curves in General Relativity with and without Torsion
Near a spinning point particle in (2+1)-dimensional gravity (or near an
infinitely thin, straight, spinning string in 3+1 dimensions) there is a region
of space-time with closed timelike curves. Exact solutions for extended sources
with apparently physically acceptable energy-momentum tensors, have produced
the same exterior space-time structure. Here it is pointed out that in the case
with torsion, closed timelike curves appear only for spin densities so high
that the spin energy density is higher than the net effective energy density.
In models without torsion, the presence of closed time-like curves is related
to a heat flow of unphysical magnitude. This corroborates earlier arguments
against the possibility of closed timelike curves in space-time geometries
generated by physical sources.Comment: (to be published in Phys. Rev. D), 5 pages, REVTEX 3.0, NORDITA 93/62
A (Sept. 10/Revised Nov. 1, 1993
Non-relativistic quantum systems on topological defects space-times
We study the behavior of non-relativistic quantum particles interacting with
different potentials in the space-times generated by a cosmic string and a
global monopole. We find the energy spectra in the presence of these
topological defects and show how they differ from their free space-time values.Comment: 17 pages, LATEX fil
Simple Quantum Systems in Spacetimes with Closed Timelike Curves
Three simple examples illustrate properties of path integral amplitudes in
fixed background spacetimes with closed timelike curves: non-relativistic
potential scattering in the Born approximation is non-unitary, but both an
example with hard spheres and the exact solution of a totally discrete model
are unitary.Comment: 15 pages, CALT-68-180
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