22,584 research outputs found
Quantum Nucleation of Vortex String Loops
We investigate quantum nucleation of vortex string loops in the relativistic
quantum field theory of a complex scalar field by using the Euclidean path
integral. Our initial metastable homogeneous field dominated by the
symmetric bounce solution. The nucleation rate and the critical vortex loop
size are obtained approximately. Gradually the initial current will be reduced
to zero as the induced current inside vortex loops is opposite to the initial
current. We also discuss a similar process in Maxwell-Higgs systems and
possible physical implications.Comment: phyzzx.tex, 13 pages: A correction to the final state of the
nucleation of local vortex string
Cosmic String Loop Microlensing
Cosmic superstring loops within the galaxy microlens background point sources
lying close to the observer-string line of sight. For suitable alignments,
multiple paths coexist and the (achromatic) flux enhancement is a factor of
two. We explore this unique type of lensing by numerically solving for
geodesics that extend from source to observer as they pass near an oscillating
string. We characterize the duration of the flux doubling and the scale of the
image splitting. We probe and confirm the existence of a variety of fundamental
effects predicted from previous analyses of the static infinite straight
string: the deficit angle, the Kaiser-Stebbins effect, and the scale of the
impact parameter required to produce microlensing. Our quantitative results for
dynamical loops vary by O(1) factors with respect to estimates based on
infinite straight strings for a given impact parameter. A number of new
features are identified in the computed microlensing solutions. Our results
suggest that optical microlensing can offer a new and potentially powerful
methodology for searches for superstring loop relics of the inflationary era.Comment: 20 pages, 19 figure
The use of Pauli-Villars' regularization in string theory
The proper-time regularization of bosonic string reproduces the results of
canonical quantization in a special scaling limit where the length in target
space has to be renormalized. We repeat the analysis for the Pauli-Villars
regularization and demonstrate the universality of the results. In the
mean-field approximation we compute the susceptibility anomalous dimension and
show it equals 1/2. We discuss the relation with the previously known results
on lattice strings.Comment: 1+22 p
Semiclassical Equations for Weakly Inhomogeneous Cosmologies
The in-in effective action formalism is used to derive the semiclassical
correction to Einstein's equations due to a massless scalar quantum field
conformally coupled to small gravitational perturbations in spatially flat
cosmological models. The vacuum expectation value of the stress tensor of the
quantum field is directly derived from the renormalized in-in effective action.
The usual in-out effective action is also discussed and it is used to compute
the probability of particle creation. As one application, the stress tensor of
a scalar field around a static cosmic string is derived and the backreaction
effect on the gravitational field of the string is discussed.Comment: 35 pages, UAB-FT 316, Latex (uses a4wide.sty, a4.sty included in the
file)(replaced due to tex problems
Sub-subleading Soft Graviton Theorem in Generic Theories of Quantum Gravity
We analyze scattering amplitudes with one soft external graviton and
arbitrary number of other finite energy external states carrying arbitrary mass
and spin to sub-subleading order in the momentum of the soft graviton. Our
result can be expressed as the sum of a universal part that depends only on the
amplitude without the soft graviton and not the other details of the theory and
a non-universal part that depends on the amplitude without the soft graviton,
and the two and three point functions of the theory. For tree amplitudes our
results are valid in all space-time dimensions while for loop amplitudes,
infrared divergences force us to restrict our analysis to space time dimensions
five or more. With this restriction the results are valid to all orders in
perturbation theory. Our results agree with known results in quantum field
theories and string theory.Comment: 52 pages, 7 figures v2: Proved that the non-universal sub-subleading
corrections depend only on on-shell 3-point function
String Theoretical Interpretation for Finite N Yang-Mills Theory in Two-Dimensions
We discuss the equivalence between a string theory and the two-dimensional
Yang-Mills theory with SU(N) gauge group for finite N. We find a sector which
can be interpreted as a sum of covering maps from closed string world-sheets to
the target space, whose covering number is less than N. This gives an
asymptotic expansion of 1/N whose large N limit becomes the chiral sector
defined by D.Gross and W.Taylor. We also discuss that the residual part of the
partition function provides the non-perturbative corrections to the
perturbative expansion.Comment: 15 pages, no figures, LaTeX2e, typos corrected, final version to
appear in Modern Physics Letters
Thermal history of the string universe
Thermal history of the string universe based on the Brandenberger and Vafa's
scenario is examined. The analysis thereby provides a theoretical foundation of
the string universe scenario. Especially the picture of the initial oscillating
phase is shown to be natural from the thermodynamical point of view. A new tool
is employed to evaluate the multi state density of the string gas. This
analysis points out that the well-known functional form of the multi state
density is not applicable for the important region , and derives a
correct form of it.Comment: 39 pages, no figures, use revtex.sty, aps.sty, aps10.sty &
preprint.st
Asymptotic Analysis of the Boltzmann Equation for Dark Matter Relics
This paper presents an asymptotic analysis of the Boltzmann equations
(Riccati differential equations) that describe the physics of thermal
dark-matter-relic abundances. Two different asymptotic techniques are used,
boundary-layer theory, which makes use of asymptotic matching, and the delta
expansion, which is a powerful technique for solving nonlinear differential
equations. Two different Boltzmann equations are considered. The first is
derived from general relativistic considerations and the second arises in
dilatonic string cosmology. The global asymptotic analysis presented here is
used to find the long-time behavior of the solutions to these equations. In the
first case the nature of the so-called freeze-out region and the
post-freeze-out behavior is explored. In the second case the effect of the
dilaton on cold dark-matter abundances is calculated and it is shown that there
is a large-time power-law fall off of the dark-matter abundance. Corrections to
the power-law behavior are also calculated.Comment: 15 pages, no figure
On Consistent Boundary Conditions for c=1 String Theory
We introduce a new parametrisation for the Fermi sea of the matrix
model. This leads to a simple derivation of the scattering matrix, and a
calculation of boundary corrections in the corresponding --dimensional
string theory. The new parametrisation involves relativistic chiral fields,
rather than the non-relativistic fields of the usual formulations. The
calculation of the boundary corrections, following recent work of Polchinski,
allows us to place restrictions on the boundary conditions in the matrix model.
We provide a consistent set of boundary conditions, but believe that they need
to be supplemented by some more subtle relationship between the space-time and
matrix model. Inspired by these boundary conditions, some thoughts on the black
hole in string theory are presented.Comment: 13 pages, 2 postscript figures include
Post-Wick theorems for symbolic manipulation of second-quantized expressions in atomic many-body perturbation theory
Manipulating expressions in many-body perturbation theory becomes unwieldily
with increasing order of the perturbation theory. Here I derive a set of
theorems for efficient simplification of such expressions. The derived rules
are specifically designed for implementing with symbolic algebra tools. As an
illustration, we count the numbers of Brueckner-Goldstone diagrams in the first
several orders of many-body perturbation theory for matrix elements between two
states of a mono-valent system.Comment: J. Phys. B. (in press); Mathematica packages available from
http://wolfweb.unr.edu/homepage/andrei/WWW-tap/mathematica.htm
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