124 research outputs found
Non-Singular Stationary Global Strings
A field-theoretical model for non-singular global cosmic strings is
presented. The model is a non-linear sigma model with a potential term for a
self-gravitating complex scalar field. Non-singular stationary solutions with
angular momentum and possibly linear momentum are obtained by assuming an
oscillatory dependence of the scalar field on t, phi and z. This dependence has
an effect similar to gauging the global U(1) symmetry of the model, which is
actually a Kaluza-Klein reduction from four to three spacetime dimensions. The
method of analysis can be regarded as an extension of the
gravito-electromagnetism formalism beyond the weak field limit. Some D=3
self-dual solutions are also discussed.Comment: 20 pages Latex, 12 PS figures included. Minor corrections. Version to
appear in Phys.Rev.
Cosmological Sphaleron from Real Tunneling and Its Fate
We show that the cosmological sphaleron of Einstein-Yang-Mills system can be
produced from real tunneling geometries. The sphaleron will tend to roll down
to the vacuum or pure gauge field configuration, when the universe evolves in
the Lorentzian signature region with the sphaleron and the corresponding
hypersurface being the initial data for the Yang-Mills field and the universe,
respectively. However, we can also show that the sphaleron, although unstable,
can be regarded as a pseudo-stable solution because its lifetime is even much
greater than those of the universe.Comment: 20 pages, LaTex, article 12pt style, TIT/HEP-242/COSMO-3
Localizing Gravity on a String-Like Defect in Six Dimensions
We present a metric solution in six dimensions where gravity is localized on
a four-dimensional singular string-like defect. The corrections to
four-dimensional gravity from the bulk continuum modes are suppressed by . No tuning of the bulk cosmological constant to the brane tension is
required in order to cancel the four-dimensional cosmological constant.Comment: 9 pages, LaTeX ; v2: several equations corrected; v3: minor typos
corrected, reference added, version to be published in Phys.Rev.Lett; v4:
Eq.(16) modifie
Exciton spin relaxation in single semiconductor quantum dots
We study the relaxation of the exciton spin (longitudinal relaxation time
) in single asymmetrical quantum dots due to an interplay of the
short--range exchange interaction and acoustic phonon deformation. The
calculated relaxation rates are found to depend strongly on the dot size,
magnetic field and temperature. For typical quantum dots and temperatures below
100 K, the zero--magnetic field relaxation times are long compared to the
exciton lifetime, yet they are strongly reduced in high magnetic fields. We
discuss explicitly quantum dots based on (In,Ga)As and (Cd,Zn)Se semiconductor
compounds.Comment: accepted for Phys. Rev.
Modifications of the BTZ black hole by a dilaton/scalar
We investigate some modifications of the static BTZ black hole solution due
to a chosen asymptotically constant dilaton/scalar. New classes of static black
hole solutions are obtained. One of the solutions contains the Martinez-Zanelli
conformal black hole solution as a special case. Using quasilocal formalism, we
calculate their mass for a finite spatial region that contains the black hole.
Their temperatures are also computed. Finally, using some of the curvature
singularities as examples, we investigate whether a quantum particle behaves
singularly or not.Comment: 18 pages, Latex, in press in Phys. Rev.
Computation of the winding number diffusion rate due to the cosmological sphaleron
A detailed quantitative analysis of the transition process mediated by a
sphaleron type non-Abelian gauge field configuration in a static Einstein
universe is carried out. By examining spectra of the fluctuation operators and
applying the zeta function regularization scheme, a closed analytical
expression for the transition rate at the one-loop level is derived. This is a
unique example of an exact solution for a sphaleron model in spacetime
dimensions.Comment: Some style corrections suggested by the referee are introduced
(mainly in Sec.II), one reference added. To appear in Phys.Rev.D 29 pages,
LaTeX, 3 Postscript figures, uses epsf.st
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