10,607 research outputs found
Complex lapse, complex action and path integrals
Imaginary time is often used in quantum tunnelling calculations. This article
advocates a conceptually sounder alternative: complex lapse. In the ``3+1''
action for the Einstein gravitational field minimally coupled to a Klein-Gordon
field, allowing the lapse function to be complex yields a complex action which
generates both the usual Lorentzian theory and its Riemannian analogue, and in
particular allows a change of signature between the two. The action and
variational equations are manifestly well defined in the Hamiltonian
representation, with the momentum fields consequently being complex. The
complex action interpolates between the Lorentzian and Riemannian actions as
they appear formally in the respective path integrals. Thus the complex-lapse
theory provides a unified basis for a path-integral quantum theory of gravity
involving both Lorentzian and Riemannian aspects. A major motivation is the
quantum-tunnelling scenario for the origin of the universe. Taken as an
explanation for the observed quantum tunnelling of particles, the complex-lapse
theory determines that the argument of the lapse for the universe now is
extremely small but negative.Comment: 12 pages, Te
M{\o}ller Energy for the Kerr-Newman metric
The energy distribution in the Kerr-Newman space-time is computed using the
M{\o}ller energy-momentum complex. This agrees with the Komar mass for this
space-time obtained by Cohen and de Felice. These results support the
Cooperstock hypothesis.Comment: 8 pages, 1 eps figure, RevTex, accepted for publication in Mod. Phys.
Lett.
The Magnetization of Cu_2(C_5H_{12}N_2)_2Cl_4 : A Heisenberg Spin Ladder System
We study the magnetization of a Heisenberg spin ladder using exact
diagonalization techniques, finding three distinct magnetic phases. We consider
the results in relation to the experimental behaviour of the new copper
compound Cu_2(C_5H_{12}N_2)_2Cl_4 and deduce that the compound is well
described by such a model with a ratio of `chain' to `rung' bond strengths
(J/J^\prime) of the order of 0.2, consistent with results from the magnetic
susceptibility. The effects of temperature, spin impurities and additional
diagonal bonds are presented and we give evidence that these diagonal bonds are
indeed of a ferromagnetic nature.Comment: Latex file (4 pages), related figures (encapsulated postscript)
appende
The suppression of superconductivity in MgCNi3 by Ni-site doping
The effects of partial substitution of Cu and Co for Ni in the intermetallic
perovskite superconductor MgCNi3 are reported. Calculation of the expected
electronic density of states suggests that electron (Cu) and hole (Co) doping
should have different effects. For MgCNi3-xCux, solubility of Cu is limited to
approximately 3% (x = 0.1), and Tc decreases systematically from 7K to 6K. For
MgCNi3-xCox, solubility of Co is much more extensive, but bulk
superconductivity disappears for Co doping of 1% (x = 0.03). No signature of
long range magnetic ordering is observed in the magnetic susceptibility of the
Co doped material.Comment: submitted, Solid State Communication
Energy distribution in a BTZ black hole spacetime
We evaluate the energy distribution associated with the (2+1)-dimensional
rotating BTZ black hole. The energy-momentum complexes of Landau-Lifshitz and
Weinberg are employed for this computation. Both prescriptions give exactly the
same form of energy distribution. Therefore, these results provide evidence in
support of the claim that, for a given gravitational background, different
energy-momentum complexes can give identical results in three dimensions, as it
is the case in four dimensions.Comment: 16 pages, LaTeX; v2: comments, clarifications and references added,
version to appear in Int.J.Mod.Phys.
Kerr black holes in horizon-generating form
New coordinates are given which describe non-degenerate Kerr black holes in
dual-null foliations based on the outer (or inner) horizons, generalizing the
Kruskal form for Schwarzschild black holes. The construction involves an area
radius for the transverse surfaces and a generalization of the Regge-Wheeler
radial function, both functions of the original radial coordinate only.Comment: 4 revtex4 page
Periodic Solutions of the Einstein Equations for Binary Systems
This revision includes clarified exposition and simplified analysis.
Solutions of the Einstein equations which are periodic and have standing
gravitational waves are valuable approximations to more physically realistic
solutions with outgoing waves. A variational principle is found which has the
power to provide an accurate estimate of the relationship between the mass and
angular momentum of the system, the masses and angular momenta of the
components, the rotational frequency of the frame of reference in which the
system is periodic, the frequency of the periodicity of the system, and the
amplitude and phase of each multipole component of gravitational radiation.
Examination of the boundary terms of the variational principle leads to
definitions of the effective mass and effective angular momentum of a periodic
geometry which capture the concepts of mass and angular momentum of the source
alone with no contribution from the gravitational radiation. These effective
quantities are surface integrals in the weak-field zone which are independent
of the surface over which they are evaluated, through second order in the
deviations of the metric from flat space.Comment: 18 pages, RevTeX 3.0, UF-RAP-93-1
Construction and enlargement of traversable wormholes from Schwarzschild black holes
Analytic solutions are presented which describe the construction of a
traversable wormhole from a Schwarzschild black hole, and the enlargement of
such a wormhole, in Einstein gravity. The matter model is pure radiation which
may have negative energy density (phantom or ghost radiation) and the
idealization of impulsive radiation (infinitesimally thin null shells) is
employed.Comment: 22 pages, 7 figure
Energy Associated with Schwarzschild Black Hole in a Magnetic Universe
In this paper we obtain the energy distribution associated with the Ernst
space-time (geometry describing Schwarzschild black hole in Melvin's magnetic
universe) in Einstein's prescription. The first term is the rest-mass energy of
the Schwarzschild black hole, the second term is the classical value for the
energy of the uniform magnetic field and the remaining terms in the expression
are due to the general relativistic effect. The presence of the magnetic field
is found to increase the energy of the system.Comment: RevTex, 8 pages, no figures, a few points are clarified, to appear in
Int. J. Mod. Phys. A. This paper is dedicated to Professor G. F. R. Ellis on
the occasion of his 60th birthda
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