77,123 research outputs found
Chiral Vortons and Cosmological Constraints on Particle Physics
We investigate the cosmological consequences of particle physics theories
that admit stable loops of current-carrying string - vortons. In particular, we
consider chiral theories where a single fermion zero mode is excited in the
string core, such as those arising in supersymmetric theories with a D-term.
The resulting vortons formed in such theories are expected to be more stable
than their non-chiral cousins. General symmetry breaking schemes are considered
in which strings formed at one symmetry breaking scale become current-carrying
at a subsequent phase transition. The vorton abundance is estimated and
constraints placed on the underlying particle physics theories from
cosmological observations. Our constraints on the chiral theory are
considerably more stringent than the previous estimates for more general
theories.Comment: minor corrections made. This version will appear in PR
Configurations of Handles and the Classification of Divergences in the String Partition Function
The divergences that arise in the regularized partition function for closed
bosonic string theory in flat space lead to three types of perturbation series
expansions, distinguished by their genus dependence. This classification of
infinities can be traced to geometrical characteristics of the string
worldsheet. Some categories of divergences may be eliminated in string theories
formulated on compact manifolds.Comment: 24 pages, DAMTP-R/94/1
Prolongation of Friction Dominated Evolution for Superconducting Cosmic Strings
This investigation is concerned with cosmological scenarios based on particle
physics theories that give rise to superconducting cosmic strings (whose
subsequent evolution may produce stable loop configurations known as vortons).
Cases in which electromagnetic coupling of the string current is absent or
unimportant have been dealt with in previous work. The purpose of the present
work is to provide quantitative estimates for cases in which electromagnetic
interaction with the surrounding plasma significantly affects the string
dynamics. In particular it will be shown that the current can become
sufficiently strong for the initial period of friction dominated string motion
to be substantially prolonged, which would entail a reinforcement of the short
length scale end of the spectrum of the string distribution, with potentially
observable cosmological implications if the friction dominated scenario lasts
until the time of plasma recombination.Comment: 10 pages Late
Linear analysis of a force reflective teleoperator
Complex force reflective teleoperation systems are often very difficult to analyze due to the large number of components and control loops involved. One mode of a force reflective teleoperator is described. An analysis of the performance of the system based on a linear analysis of the general full order model is presented. Reduced order models are derived and correlated with the full order models. Basic effects of force feedback and position feedback are examined and the effects of time delays between the master and slave are studied. The results show that with symmetrical position-position control of teleoperators, a basic trade off must be made between the intersystem stiffness of the teleoperator, and the impedance felt by the operator in free space
First excited band of a spinor Bose-Einstein condensate
The analytical expression of the fractional parentage coefficients for the
total spin-states of a spinor N-boson system has been derived. Thereby an
S-conserved theory for the spinor Bose-Einstein condensation has been proposed.
A set of equations has been established to describe the first excited band of
the condensates. Numerical solution for Na has been given as an example.Comment: 6 pages, 3 figure
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