8,538 research outputs found
Folded Strings Falling into a Black Hole
We find all the classical solutions (minimal surfaces) of open or closed
strings in {\it any} two dimensional curved spacetime. As examples we consider
the SL(2,R)/R two dimensional black hole, and any 4D black hole in the
Schwarzschild family, provided the motion is restricted to the time-radial
components. The solutions, which describe longitudinaly oscillating folded
strings (radial oscillations in 4D), must be given in lattice-like patches of
the worldsheet, and a transfer operation analogous to a transfer matrix
determines the future evolution. Then the swallowing of a string by a black
hole is analyzed. We find several new features that are not shared by particle
motions. The most surprizing effect is the tunneling of the string into the
bare singularity region that lies beyond the black hole that is classically
forbidden to particles.Comment: 28 pages plus 4 figures, LaTeX, USC-94/HEP-B
Quasinormal frequencies of asymptotically flat two-dimensional black holes
We discuss whether the minimally coupled massless Klein-Gordon and Dirac
fields have well defined quasinormal modes in single horizon, asymptotically
flat two-dimensional black holes. To get the result we solve the equations of
motion in the massless limit and we also calculate the effective potentials of
Schrodinger type equations. Furthermore we calculate exactly the quasinormal
frequencies of the Dirac field propagating in the two-dimensional uncharged
Witten black hole. We compare our results on its quasinormal frequencies with
other already published.Comment: 12 pages. Accepted for publication in Gen. Rel. and Gra
Planetoid String Solutions in 3 + 1 Axisymmetric Spacetimes
The string propagation equations in axisymmetric spacetimes are exactly
solved by quadratures for a planetoid Ansatz. This is a straight
non-oscillating string, radially disposed, which rotates uniformly around the
symmetry axis of the spacetime. In Schwarzschild black holes, the string stays
outside the horizon pointing towards the origin. In de Sitter spacetime the
planetoid rotates around its center. We quantize semiclassically these
solutions and analyze the spin/(mass) (Regge) relation for the planetoids,
which turns out to be non-linear.Comment: Latex file, 14 pages, two figures in .ps files available from the
author
String Quantization in Curved Spacetimes: Null String Approach
We study quantum strings in strong gravitational fields. The relevant small
parameter is , where is the curvature of the spacetime
and is the string tension. Within our systematic expansion we obtain to
zeroth order the null string (string with zero tension), while the first order
correction incorporates the string dynamics. We apply our formalism to quantum
null strings in de Sitter spacetime. After a reparametrization of the
world-sheet coordinates, the equations of motion are simplified. The quantum
algebra generated by the constraints is considered, ordering the momentum
operators to the right of the coordinate operators. No critical dimension
appears. It is anticipated however that the conformal anomaly will appear when
the first order corrections proportional to , are introduced.Comment: 6 pages, plain Tex, no figure
Strings Next To and Inside Black Holes
The string equations of motion and constraints are solved near the horizon
and near the singularity of a Schwarzschild black hole. In a conformal gauge
such that ( = worldsheet time coordinate) corresponds to the
horizon () or to the black hole singularity (), the string
coordinates express in power series in near the horizon and in power
series in around . We compute the string invariant size and
the string energy-momentum tensor. Near the horizon both are finite and
analytic. Near the black hole singularity, the string size, the string energy
and the transverse pressures (in the angular directions) tend to infinity as
. To leading order near , the string behaves as two dimensional
radiation. This two spatial dimensions are describing the sphere in the
Schwarzschild manifold.Comment: RevTex, 19 pages without figure
On the difference between proton and neutron spin-orbit splittings in nuclei
The latest experimental data on nuclei at Sn permit us for the first
time to determine the spin-orbit splittings of neutrons and protons in
identical orbits in this neutron-rich doubly-magic region and compare the case
to that of Pb. Using the new results, which are now consistent for the
two neutron-rich doubly magic regions, a theoretical analysis defines the
isotopic dependence of the mean field spin-orbit potential and leads to a
simple explicit expression for the difference between the spin-orbit splittings
of neutrons and protons. The isotopic dependence is explained in the framework
of different theoretical approaches.Comment: 8 pages, revte
Impurity in a granular gas under nonlinear Couette flow
We study in this work the transport properties of an impurity immersed in a
granular gas under stationary nonlinear Couette flow. The starting point is a
kinetic model for low-density granular mixtures recently proposed by the
authors [Vega Reyes F et al. 2007 Phys. Rev. E 75 061306]. Two routes have been
considered. First, a hydrodynamic or normal solution is found by exploiting a
formal mapping between the kinetic equations for the gas particles and for the
impurity. We show that the transport properties of the impurity are
characterized by the ratio between the temperatures of the impurity and gas
particles and by five generalized transport coefficients: three related to the
momentum flux (a nonlinear shear viscosity and two normal stress differences)
and two related to the heat flux (a nonlinear thermal conductivity and a cross
coefficient measuring a component of the heat flux orthogonal to the thermal
gradient). Second, by means of a Monte Carlo simulation method we numerically
solve the kinetic equations and show that our hydrodynamic solution is valid in
the bulk of the fluid when realistic boundary conditions are used. Furthermore,
the hydrodynamic solution applies to arbitrarily (inside the continuum regime)
large values of the shear rate, of the inelasticity, and of the rest of
parameters of the system. Preliminary simulation results of the true Boltzmann
description show the reliability of the nonlinear hydrodynamic solution of the
kinetic model. This shows again the validity of a hydrodynamic description for
granular flows, even under extreme conditions, beyond the Navier-Stokes domain.Comment: 23 pages, 11 figures; v2: Preliminary DSMC results from the Boltzmann
equation included, Fig. 11 is ne
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