38,818 research outputs found
Vacuum tunneling in gravity
Topologically non-trivial vacuum structure in gravity models with Cartan
variables (vielbein and contortion) is considered. We study the possibility of
vacuum space-time tunneling in Einstein gravity assuming that the vielbein may
play a fundamental role in quantum gravitational phenomena. It has been shown
that in the case of RP3 space topology the tunneling between non-trivial
topological vacuums can be realized by means of Eguchi-Hanson gravitational
instanton. In Riemann-Cartan geometric approach to quantum gravity the vacuum
tunneling can be provided by means of contortion quantum fluctuations. We
define double self-duality condition for the contortion and give explicit
self-dual configurations which can contribute to vacuum tunneling amplitude.Comment: 11 pages, 1 fig. is added, final versio
Cho and Pak reply to Lamm et al. comment on "A Convergent Series for the QED Effective Action"
Cho and Pak reply to Lamm et al. [hep-th/0007108] comment on "A Convergent
Series for the Effective Action of QED" [hep-th/0006057].Comment: 1 pag
Spin diffusion of correlated two-spin states in a dielectric crystal
Reciprocal space measurements of spin diffusion in a single crystal of
calcium fluoride (CaF) have been extended to dipolar ordered states. The
experimental results for the component of the spin diffusion parallel with the
external field are cm/s for the
[001] direction and cm/s for the
[111] direction. The diffusion rates for dipolar order are significantly faster
than those for Zeeman order and are considerably faster than predicted by
simple theoretical models. It is suggested that constructive interference in
the transport of the two spin state is responsible for this enhancement. As
expected the anisotropy in the diffusion rates is observed to be significantly
less for dipolar order compared to the Zeeman case.Comment: 4 pages, 2 figures. Resubmitted to PRL - new figure added /
discussion expande
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
- …