36,211 research outputs found
Quantum stabilization of a hedgehog type of cosmic string
Within a slightly simplified version of the electroweak standard model we
investigate the stabilization of cosmic strings by fermion quantum
fluctuations. Previous studies of quantum energies considered variants of the
Nielsen-Olesen profile embedded in the electroweak gauge group and showed that
configurations are favored for which the Higgs vacuum expectation value drops
near the string core and the gauge field is suppressed. This work found that
the strongest binding was obtained from strings that differ significantly from
Nielsen-Olesen configurations, deforming essentially only the Higgs field in
order to generate a strong attraction without inducing large gradients.
Extending this analysis, we consider the leading quantum correction to the
energy per unit length of a hedgehog type string, which, in contrast to the
Nielsen-Olesen configuration, contains a pseudoscalar field. To employ the
spectral method we develop the scattering and bound state problems for fermions
in the background of a hedgehog string. Explicit occupation of bound state
levels leads to strings that carry the quantum numbers of the bound fermions.
We discuss the parameter space for which stable, hedgehog type cosmic strings
emerge and reflect on phenomenological consequences of these findings.Comment: 34 page
Attractive Electromagnetic Casimir Stress on a Spherical Dielectric Shell
Based on calculations involving an idealized boundary condition, it has long
been assumed that the stress on a spherical conducting shell is repulsive. We
use the more realistic case of a Drude dielectric to show that the stress is
attractive, matching the generic behavior of Casimir forces in
electromagnetism. We trace the discrepancy between these two cases to
interactions between the electromagnetic quantum fluctuations and the
dielectric material.Comment: Five pages, one figure, pdflatex, matches version to be pusblished in
Phys Lett
Stable charged cosmic strings
We study the quantum stabilization of a cosmic string by a heavy fermion
doublet in a reduced version of the standard model. We show that charged
strings, obtained by populating fermionic bound state levels, become stable if
the electro--weak bosons are coupled to a fermion that is less than twice as
heavy as the top quark. This result suggests that extraordinarily large fermion
masses or unrealistic couplings are not required to bind a cosmic string in the
standard model. Numerically we find the most favorable string profile to be a
simple "trough" in the Higgs vev of radius . The
vacuum remains stable in our model, because neutral strings are not
energetically favored.Comment: 5 pages, 3 figures, version to be published in Phys. Rev. Let
Spectral Methods for Coupled Channels with a Mass Gap
We develop a method to compute the vacuum polarization energy for coupled
scalar fields with different masses scattering off a background potential in
one space dimension. As an example we consider the vacuum polarization energy
of a kink-like soliton built from two real scalar fields with different mass
parameters.Comment: 14 pages, 5 figures, matches journal version, references added
(surprisingly many
Casimir Effects in Renormalizable Quantum Field Theories
We review the framework we and our collaborators have developed for the study
of one-loop quantum corrections to extended field configurations in
renormalizable quantum field theories. We work in the continuum, transforming
the standard Casimir sum over modes into a sum over bound states and an
integral over scattering states weighted by the density of states. We express
the density of states in terms of phase shifts, allowing us to extract
divergences by identifying Born approximations to the phase shifts with low
order Feynman diagrams. Once isolated in Feynman diagrams, the divergences are
canceled against standard counterterms. Thus regulated, the Casimir sum is
highly convergent and amenable to numerical computation. Our methods have
numerous applications to the theory of solitons, membranes, and quantum field
theories in strong external fields or subject to boundary conditions.Comment: 27 pp., 11 EPS figures, LaTeX using ijmpa1.sty; email correspondence
to R.L. Jaffe ; based on talks presented by the authors at
the 5th workshop `QFTEX', Leipzig, September 200
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