24,312 research outputs found
The C-metric as a colliding plane wave space-time
It is explicitly shown that part of the C-metric space-time inside the black
hole horizon may be interpreted as the interaction region of two colliding
plane waves with aligned linear polarization, provided the rotational
coordinate is replaced by a linear one. This is a one-parameter generalization
of the degenerate Ferrari-Ibanez solution in which the focussing singularity is
a Cauchy horizon rather than a curvature singularity.Comment: 6 pages. To appear in Classical and Quantum Gravit
Choice of Consistent Family, and Quantum Incompatibility
In consistent history quantum theory, a description of the time development
of a quantum system requires choosing a framework or consistent family, and
then calculating probabilities for the different histories which it contains.
It is argued that the framework is chosen by the physicist constructing a
description of a quantum system on the basis of questions he wishes to address,
in a manner analogous to choosing a coarse graining of the phase space in
classical statistical mechanics. The choice of framework is not determined by
some law of nature, though it is limited by quantum incompatibility, a concept
which is discussed using a two-dimensional Hilbert space (spin half particle).
Thus certain questions of physical interest can only be addressed using
frameworks in which they make (quantum mechanical) sense. The physicist's
choice does not influence reality, nor does the presence of choices render the
theory subjective. On the contrary, predictions of the theory can, in
principle, be verified by experimental measurements. These considerations are
used to address various criticisms and possible misunderstandings of the
consistent history approach, including its predictive power, whether it
requires a new logic, whether it can be interpreted realistically, the nature
of ``quasiclassicality'', and the possibility of ``contrary'' inferences.Comment: Minor revisions to bring into conformity with published version.
Revtex 29 pages including 1 page with figure
Anomalies of weakened decoherence criteria for quantum histories
The theory of decoherent histories is checked for the requirement of
statistical independence of subsystems. Strikingly, this is satisfied only when
the decoherence functional is diagonal in both its real a n d imaginary parts.
In particular, the condition of consistency (or weak decoherence) required for
the assignment of probabilities appears to be ruled out. The same conclusion is
obtained independently, by claiming a plausible dynamical robustness of
decoherent histories.Comment: 3pp, submitted to Phys. Rev. Let
The Exact Ground State of the Frenkel-Kontorova Model with Repeated Parabolic Potential: II. Numerical Treatment
A procedure is described for efficiently finding the ground state energy and
configuration for a Frenkel-Kontorova model in a periodic potential, consisting
of N parabolic segments of identical curvature in each period, through a
numerical solution of the convex minimization problem described in the
preceding paper. The key elements are the use of subdifferentials to describe
the structure of the minimization problem; an intuitive picture of how to solve
it, based on motion of quasiparticles; and a fast linear optimization method
with a reduced memory requirement. The procedure has been tested for N up to
200.Comment: 9 RevTeX pages, using AMS-Fonts (amssym.tex,amssym.def), 3 Postscript
figures, accepted by Phys.Rev.B to be published together with
cond-mat/970722
Radiation generated by accelerating and rotating charged black holes in (anti-)de Sitter space
Asymptotic behaviour of gravitational and electromagnetic fields of exact
type D solutions from the large Plebanski-Demianski family of black hole
spacetimes is analyzed. The amplitude and directional structure of radiation is
evaluated in cases when the cosmological constant is non-vanishing, so that the
conformal infinities have either de Sitter-like or anti-de Sitter-like
character. In particular, explicit relations between the parameters that
characterize the sources (that is their mass, electric and magnetic charges,
NUT parameter, rotational parameter, and acceleration) and properties of the
radiation generated by them are presented. The results further elucidate the
physical interpretation of these solutions and may help to understand radiative
characteristics of more general spacetimes than those that are asymptotically
flat.Comment: 24 pages, 18 figures. To appear in Classical and Quantum Gravit
Correlation inequalities for noninteracting Bose gases
For a noninteracting Bose gas with a fixed one-body Hamiltonian H^0
independent of the number of particles we derive the inequalities _N <
_{N+1}, _N _N _N for i\neq j, \partial
_N/\partial \beta >0 and ^+_N _N. Here N_i is the occupation
number of the ith eigenstate of H^0, \beta is the inverse temperature and the
superscript + refers to adding an extra level to those of H^0. The results
follow from the convexity of the N-particle free energy as a function of N.Comment: a further inequality adde
Gambling in Great Britain:a response to Rogers
A recent issue of Practice: Social Work in Action featured a paper by Rogers that examined whether the issue of problem gambling was a suitable case for social work. Rogers’ overview was (in various places) out of date, highly selective, contradictory, presented unsupported claims and somewhat misleading. Rogers’ paper is to be commended for putting the issue of problem gambling on the social work agenda. However, social workers need up-to-date information and contextually situated information if they are to make informed decisions in helping problem gamblers
Optimal Eavesdropping in Quantum Cryptography. II. Quantum Circuit
It is shown that the optimum strategy of the eavesdropper, as described in
the preceding paper, can be expressed in terms of a quantum circuit in a way
which makes it obvious why certain parameters take on particular values, and
why obtaining information in one basis gives rise to noise in the conjugate
basis.Comment: 7 pages, 1 figure, Latex, the second part of quant-ph/970103
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