557 research outputs found
Gravitational Field of a Spinning Cosmic String
We study the effect of internal space rotation on the gravitational
properties of infinite straight and stationary cosmic string. From the
approximate solution of Einsten equations for the spinning Q-lump string we
obtain long range gravitational accelleration resembling that of a rotating
massive cylindrical shell. We also compute the angular velocity of the inertial
frame dragging and the angle of light deflection by the Q-lump string. Matter
accretion on to spinning strings can play a role in galaxy formation when the
angular velocity times the string width is comparable to the speed of light.Comment: 14 page
MEASURING GRAVITOMAGNETIC EFFECTS BY MEANS OF RING LASERS
Light is a good probe for general relativistic effects. Exploiting the asymmetry of the propagation in the vicinity of a central rotating mass it is possible to use a ring laser in order to measure the frame dragging of the reference frames by the gravitational field of the Earth (Lense-Thirring effect). I shall present the G-GranSasso experiment whose objective is precisely to measure the Lense-Thirring and the de Sitter effects in a terrestrial laboratory. The experimental apparatus will be made of a set of at least three, differently oriented, ring lasers rigidly attached to a central "monument". The signal will be in the form of the beat frequency produced in the annular cavity of each laser by the rotational anisotropy. The laboratory will be located underground in the Laboratori Nazionali del Gran Sasso facility, in Italy. The required sensitivity is just one order of magnitude below the performance of the best existing instruments and the new design will attain i
Validity and failure of some entropy inequalities for CAR systems
Basic properties of von Neumann entropy such as the triangle inequality and
what we call MONO-SSA are studied for CAR systems.
We show that both inequalities hold for any even state. We construct a
certain class of noneven states giving counter examples of those inequalities.
It is not always possible to extend a set of prepared states on disjoint
regions to some joint state on the whole region for CAR systems.
However, for every even state, we have its `symmetric purification' by which
the validity of those inequalities is shown.
Some (realized) noneven states have peculiar state correlations among
subsystems and induce the failure of those inequalities.Comment: 14 pages, latex, to appear in JMP. Some typos are correcte
Post-Newtonian Approximation in Maxwell-Like Form
The equations of the linearized first post-Newtonian approximation to general
relativity are often written in "gravitoelectromagnetic" Maxwell-like form,
since that facilitates physical intuition. Damour, Soffel and Xu (DSX) (as a
side issue in their complex but elegant papers on relativistic celestial
mechanics) have expressed the first post-Newtonian approximation, including all
nonlinearities, in Maxwell-like form. This paper summarizes that DSX
Maxwell-like formalism (which is not easily extracted from their celestial
mechanics papers), and then extends it to include the post-Newtonian
(Landau-Lifshitz-based) gravitational momentum density, momentum flux (i.e.
gravitational stress tensor) and law of momentum conservation in Maxwell-like
form. The authors and their colleagues have found these Maxwell-like momentum
tools useful for developing physical intuition into numerical-relativity
simulations of compact binaries with spin.Comment: v4: Revised for resubmission to Phys Rev D, 6 pages. v3: Reformulated
in terms of DSX papers. Submitted to Phys Rev D, 6 pages. v2: Added
references. Changed definitions & convention
Beyond Gravitoelectromagnetism: Critical Speed in Gravitational Motion
A null ray approaching a distant astronomical source appears to slow down,
while a massive particle speeds up in accordance with Newtonian gravitation.
The integration of these apparently incompatible aspects of motion in general
relativity is due to the existence of a critical speed. Dynamics of particles
moving faster than the critical speed could then be contrary to Newtonian
expectations. Working within the framework of gravitoelectromagnetism, the
implications of the existence of a critical speed are explored. The results are
expected to be significant for high energy astrophysics.Comment: 13 pages, to appear in the Special December 2005 Issue of Int. J.
Mod. Phys.
Electromagnetic and gravitational responses and anomalies in topological insulators and superconductors
One of the defining properties of the conventional three-dimensional
("-", or "spin-orbit"-) topological insulator is its
characteristic magnetoelectric effect, as described by axion electrodynamics.
In this paper, we discuss an analogue of such a magnetoelectric effect in the
thermal (or gravitational) and the magnetic dipole responses in all symmetry
classes which admit topologically non-trivial insulators or superconductors to
exist in three dimensions. In particular, for topological superconductors (or
superfluids) with time-reversal symmetry which lack SU(2) spin rotation
symmetry (e.g. due to spin-orbit interactions), such as the B phase of He,
the thermal response is the only probe which can detect the non-trivial
topological character through transport. We show that, for such topological
superconductors, applying a temperature gradient produces a thermal- (or mass-)
surface current perpendicular to the thermal gradient. Such charge, thermal, or
magnetic dipole responses provide a definition of topological insulators and
superconductors beyond the single-particle picture. Moreover we find, for a
significant part of the 'ten-fold' list of topological insulators found in
previous work in the absence of interactions, that in general dimensions the
effective field theory describing the space-time responses is governed by a
field theory anomaly. Since anomalies are known to be insensitive to whether
the underlying fermions are interacting or not, this shows that the
classification of these topological insulators is robust to adiabatic
deformations by interparticle interactions in general dimensionality. In
particular, this applies to symmetry classes DIII, CI, and AIII in three
spatial dimensions, and to symmetry classes D and C in two spatial dimensions.Comment: 16 pages, 2 figure
Black string and velocity frame dragging
We investigate velocity frame dragging with the boosted Schwarzschild black
string solution and the boosted Kaluza-Klein bubble solution, in which a
translational symmetry along the boosted -coordinate is implemented. The
velocity frame dragging effect can be nullified by the motion of an observer
using the boost symmetry along the coordinate if it is not compact.
However, in spacetime with the compact coordinate, we show that the effect
cannot be removed since the compactification breaks the global Lorentz boost
symmetry. As a result, the comoving velocity is dependent on and the
momentum parameter along the coordinate becomes an observer independent
characteristic quantity of the black string and bubble solutions. The dragging
induces a spherical ergo-region around the black string.Comment: 8 pages, no figure, some correction
Spin Dynamics of the LAGEOS Satellite in Support of a Measurement of the Earth's Gravitomagnetism
LAGEOS is an accurately-tracked, dense spherical satellite covered with 426
retroreflectors. The tracking accuracy is such as to yield a medium term (years
to decades) inertial reference frame determined via relatively inexpensive
observations. This frame is used as an adjunct to the more difficult and data
intensive VLBI absolute frame measurements. There is a substantial secular
precession of the satellite's line of nodes consistent with the classical,
Newtonian precession due to the non-sphericity of the earth. Ciufolini has
suggested the launch of an identical satellite (LAGEOS-3) into an orbit
supplementary to that of LAGEOS-1: LAGEOS-3 would then experience an equal and
opposite classical precession to that of LAGEOS-1. Besides providing a more
accurate real-time measurement of the earth's length of day and polar wobble,
this paired-satellite experiment would provide the first direct measurement of
the general relativistic frame-dragging effect. Of the five dominant error
sources in this experiment, the largest one involves surface forces on the
satellite, and their consequent impact on the orbital nodal precession. The
surface forces are a function of the spin dynamics of the satellite.
Consequently, we undertake here a theoretical effort to model the spin
ndynamics of LAGEOS. In this paper we present our preliminary results.Comment: 16 pages, RevTeX, LA-UR-94-1289. (Part I of II, postscript figures in
Part II
Cosmological gravitomagnetism and Mach's principle
The spin axes of gyroscopes experimentally define local non-rotating frames.
But what physical cause governs the time-evolution of gyroscope axes? We
consider linear perturbations of Friedmann-Robertson-Walker cosmologies with
k=0. We ask: Will cosmological vorticity perturbations exactly drag the spin
axes of gyroscopes relative to the directions of geodesics to quasars in the
asymptotic unperturbed FRW space? Using Cartan's formalism with local
orthonormal bases we cast the laws of linear cosmological gravitomagnetism into
a form showing the close correspondence with the laws of ordinary magnetism.
Our results, valid for any equation of state for cosmological matter, are: 1)
The dragging of a gyroscope axis by rotational perturbations of matter beyond
the Hubble-dot radius from the gyroscope is exponentially suppressed, where dot
is the derivative with respect to cosmic time. 2) If the perturbation of matter
is a homogeneous rotation inside some radius around a gyroscope, then exact
dragging of the gyroscope axis by the rotational perturbation is reached
exponentially fast as the rotation radius grows beyond the H-dot radius. 3) For
the most general linear cosmological perturbations the time-evolution of all
gyroscope spin axes exactly follow a weighted average of the energy currents of
cosmological matter. The weight function is the same as in Ampere's law except
that the inverse square law is replaced by the Yukawa force with the Hubble-dot
cutoff. Our results demonstrate (in first order perturbation theory for FRW
cosmologies with k = 0) the validity of Mach's hypothesis that axes of local
non-rotating frames precisely follow an average of the motion of cosmic matter.Comment: 18 pages, 1 figure. Comments and references adde
Celestial mechanics in Kerr spacetime
The dynamical parameters conventionally used to specify the orbit of a test
particle in Kerr spacetime are the energy , the axial component of the
angular momentum, , and Carter's constant . These parameters are
obtained by solving the Hamilton-Jacobi equation for the dynamical problem of
geodesic motion. Employing the action-angle variable formalism, on the other
hand, yields a different set of constants of motion, namely, the fundamental
frequencies , and associated with
the radial, polar and azimuthal components of orbital motion. These
frequencies, naturally, determine the time scales of orbital motion and,
furthermore, the instantaneous gravitational wave spectrum in the adiabatic
approximation. In this article, it is shown that the fundamental frequencies
are geometric invariants and explicit formulas in terms of quadratures are
derived. The numerical evaluation of these formulas in the case of a rapidly
rotating black hole illustrates the behaviour of the fundamental frequencies as
orbital parameters such as the semi-latus rectum , the eccentricity or
the inclination parameter are varied. The limiting cases of
circular, equatorial and Keplerian motion are investigated as well and it is
shown that known results are recovered from the general formulas.Comment: 25 pages (LaTeX), 5 figures, submitted to Class. Quantum Gra
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