2,428 research outputs found
Numerical relativity simulation of GW150914 beyond general relativity
We produce the first astrophysically-relevant numerical binary black hole
gravitational waveform in a higher-curvature theory of gravity beyond general
relativity. We simulate a system with parameters consistent with GW150914, the
first LIGO detection, in order-reduced dynamical Chern-Simons gravity, a theory
with motivations in string theory and loop quantum gravity. We present results
for the leading-order corrections to the merger and ringdown waveforms, as well
as the ringdown quasi-normal mode spectrum. We estimate that such corrections
may be discriminated in detections with signal to noise ratio , with the precise value depending on the dimension of the GR waveform
family used in data analysis.Comment: 7 pages + appendices, 8 figures, Updated to match Phys. D. Rev
articl
On the feasibility of studying vortex noise in 2D superconductors with cold atoms
We investigate the feasibility of using ultracold neutral atoms trapped near
a thin superconductor to study vortex noise close to the
Kosterlitz-Thouless-Berezinskii transition temperature. Alkali atoms such as
rubidium probe the magnetic field produced by the vortices. We show that the
relaxation time of the Zeeman sublevel populations can be conveniently
adjusted to provide long observation times. We also show that the transverse
relaxation times for Zeeman coherences are ideal for studying the vortex
noise. We briefly consider the motion of atom clouds held close to the surface
as a method for monitoring the vortex motion.Comment: 4 pages, 1 figur
Coincident count rates in absorbing dielectric media
A study of the effects of absorption on the nonlinear process of parametric
down conversion is presented. Absorption within the nonlinear medium is
accounted for by employing the framework of macroscopic QED and the Green
tensor quantization of the electromagnetic field. An effective interaction
Hamiltonian, which describes the nonlinear interaction of the electric field
and the linear noise polarization field, is used to derive the quantum state of
the light leaving a nonlinear crystal. The signal and idler modes of this
quantum state are found to be a superpositions of the electric and noise
polarization fields. Using this state, the expression for the coincident count
rates for both Type I and Type II conversion are found. The nonlinear
interaction with the noise polarization field were shown to cause an increase
in the rate on the order of 10^{-12} for absorption of 10% per cm. This
astonishingly small effect is found to be negligible compared to the decay
caused by linear absorption of the propagating modes. From the expressions for
the biphoton amplitude it can be seen the maximally entangled states can still
be produced even in the presence of strong absorption.Comment: Updated to journal version. 10 Pages, 8 figure
On the Casimir entropy between 'perfect crystals'
We give a re-interpretation of an `entropy defect' in the electromagnetic
Casimir effect. The electron gas in a perfect crystal is an electromagnetically
disordered system whose entropy contains a finite Casimir-like contribution.
The Nernst theorem (third law of thermodynamics) is not applicable.Comment: 10 pages, 2 figures, proceedings of "Quantum Field Theory under the
influence of external boundary conditions" QFExt (Oklahoma, Sep 2009
Treating instabilities in a hyperbolic formulation of Einstein's equations
We have recently constructed a numerical code that evolves a spherically
symmetric spacetime using a hyperbolic formulation of Einstein's equations. For
the case of a Schwarzschild black hole, this code works well at early times,
but quickly becomes inaccurate on a time scale of 10-100 M, where M is the mass
of the hole. We present an analytic method that facilitates the detection of
instabilities. Using this method, we identify a term in the evolution equations
that leads to a rapidly-growing mode in the solution. After eliminating this
term from the evolution equations by means of algebraic constraints, we can
achieve free evolution for times exceeding 10000M. We discuss the implications
for three-dimensional simulations.Comment: 13 pages, 9 figures. To appear in Phys. Rev.
Upper bounds on success probabilities in linear optics
We develop an abstract way of defining linear-optics networks designed to
perform quantum information tasks such as quantum gates. We will be mainly
concerned with the nonlinear sign shift gate, but it will become obvious that
all other gates can be treated in a similar manner. The abstract scheme is
extremely well suited for analytical as well as numerical investigations since
it reduces the number of parameters for a general setting. With that we show
numerically and partially analytically for a wide class of states that the
success probability of generating a nonlinear sign shift gate does not exceed
1/4 which to our knowledge is the strongest bound to date.Comment: 8 pages, typeset using RevTex4, 5 EPS figure
Black Hole--Scalar Field Interactions in Spherical Symmetry
We examine the interactions of a black hole with a massless scalar field
using a coordinate system which extends ingoing Eddington-Finkelstein
coordinates to dynamic spherically symmetric-spacetimes. We avoid problems with
the singularity by excising the region of the black hole interior to the
apparent horizon. We use a second-order finite difference scheme to solve the
equations. The resulting program is stable and convergent and will run forever
without problems. We are able to observe quasi-normal ringing and power-law
tails as well an interesting nonlinear feature.Comment: 16 pages, 26 figures, RevTex, to appear in Phys. Rev.
Casimir forces from a loop integral formulation
We reformulate the Casimir force in the presence of a non-trivial background.
The force may be written in terms of loop variables, the loop being a curve
around the scattering sites. A natural path ordering of exponentials take place
when a particular representation of the scattering centres is given. The basic
object to be evaluated is a reduced (or abbreviated) classical pseudo-action
that can be operator valued.Comment: references added, text clarified in place
Black Hole Area in Brans-Dicke Theory
We have shown that the dynamics of the scalar field
in Brans-Dicke theories of gravity makes the surface area of the black hole
horizon {\it oscillatory} during its dynamical evolution. It explicitly
explains why the area theorem does not hold in Brans-Dicke theory. However, we
show that there exists a certain non-decreasing quantity defined on the event
horizon which is proportional to the black hole entropy for the case of
stationary solutions in Brans-Dicke theory. Some numerical simulations have
been demonstrated for Oppenheimer-Snyder collapse in Brans-Dicke theory.Comment: 12 pages, latex, 5 figures, epsfig.sty, some statements clarified and
two references added, to appear in Phys. Rev.
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