1,941 research outputs found
Cosmic String Spacetime in Dilaton Gravity and Flat Rotation Curves
In dilaton gravity theories, we consider a string-like topological defect
formed during U(1) gauge symmetry-breaking phase transition in the early
Universe, and far from the cosmic string we have vacuum solutions of the
generalized Einstein equation. We discuss how they can be related to the
flatness of galactic rotation curves.Comment: 9 pages, RevTeX4 fil
Instanton solutions mediating tunneling between the degenerate vacua in curved space
We investigate the instanton solution between the degenerate vacua in curved
space. We show that there exist -symmetric solutions not only in de
Sitter but also in both flat and anti-de Sitter space. The geometry of the new
type of solutions is finite and preserves the symmetry. The nontrivial
solution corresponding to the tunneling is possible only if gravity is taken
into account. The numerical solutions as well as the analytic computations
using the thin-wall approximation are presented. We expect that these solutions
do not have any negative mode as in the instanton solution.Comment: Some typos are corrected and references are added with respect to the
published version. 17pages, 11fi
Oscillating instanton solutions in curved space
We investigate oscillating instanton solutions of a self-gravitating scalar
field between degenerate vacua. We show that there exist O(4)-symmetric
oscillating solutions in a de Sitter background. The geometry of this solution
is finite and preserves the symmetry. The nontrivial solution
corresponding to tunneling is possible only if the effect of gravity is taken
into account. We present numerical solutions of this instanton, including the
phase diagram of solutions in terms of the parameters of the present work and
the variation of energy densities. Our solutions can be interpreted as
solutions describing an instanton-induced domain wall or braneworld-like object
rather than a kink-induced domain wall or braneworld. The oscillating instanton
solutions have a thick wall and the solutions can be interpreted as a mechanism
providing nucleation of the thick wall for topological inflation. We remark
that invariant solutions also exist in a flat and anti-de Sitter
background, though the physical significance is not clear.Comment: 25 pages, 11 figues. Some typos corrected, references added, and Ch3.
modified according to referee's comment
A Holographic Model of Strange Metals
We give a review on our recent work arXiv:1006.0779 [hep-th] and
arXiv:1006.1719 [hep-th], in which properties of holographic strange metals
were investigated. The background is chosen to be anisotropic scaling solution
in Einstein-Maxwell-Dilaton theory with a Liouville potential. The effects of
bulk Maxwell field, an extra U(1) gauge field and probe D-branes on the DC
conductivity, the DC Hall conductivity and the AC conductivity are extensively
analyzed. We classify behaviors of the conductivities according to the
parameter ranges in the bulk theory and characterize conditions when the
holographic results can reproduce experimental data.Comment: 34 pages, 15 figures, minor correction
Diffusive Ionization of Relativistic Hydrogen-Like Atom
Stochastic ionization of highly excited relativistic hydrogenlike atom in the
monochromatic field is investigated. A theoretical analisis of chaotic dynamics
of the relativistic electron based on Chirikov criterion is given for the cases
of one- and three-dimensional atoms. Critical value of the external field is
evaluated analitically. The diffusion coefficient and ionization time are
calculated.Comment: 13 pages, latex, no figures, submitted to PR
Dynamics of false vacuum bubbles in Brans-Dicke theory
We study the dynamics of false vacuum bubbles in the Brans-Dicke theory of
gravity by using the thin shell or thin wall approximation. We consider a false
vacuum bubble that has a different value for the Brans-Dicke field between the
inside false vacuum region and the outside true vacuum region. Within a certain
limit of field values, the difference of field values makes the effective
tension of the shell negative. This allows new expanding false vacuum bubbles
to be seen by the outside observer, which are disallowed in Einstein gravity.Comment: 29 pages, 20 figure
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