3,446 research outputs found
Topology Change in (2+1)-Dimensional Gravity
In (2+1)-dimensional general relativity, the path integral for a manifold
can be expressed in terms of a topological invariant, the Ray-Singer torsion of
a flat bundle over . For some manifolds, this makes an explicit computation
of transition amplitudes possible. In this paper, we evaluate the amplitude for
a simple topology-changing process. We show that certain amplitudes for spatial
topology change are nonvanishing---in fact, they can be infrared
divergent---but that they are infinitely suppressed relative to similar
topology-preserving amplitudes.Comment: 19 pages of text plus 4 pages of figures, LaTeX (using epsf),
UCD-11-9
On the gravitational field of static and stationary axial symmetric bodies with multi-polar structure
We give a physical interpretation to the multi-polar Erez-Rozen-Quevedo
solution of the Einstein Equations in terms of bars. We find that each
multi-pole correspond to the Newtonian potential of a bar with linear density
proportional to a Legendre Polynomial. We use this fact to find an integral
representation of the function. These integral representations are
used in the context of the inverse scattering method to find solutions
associated to one or more rotating bodies each one with their own multi-polar
structure.Comment: To be published in Classical and Quantum Gravit
Factorization of Ising correlations C(M,N) for and M+N odd, , and their lambda extensions
We study the factorizations of Ising low-temperature correlations C(M,N) for
and M+N odd, , for both the cases where there are
two factors, and where there are four factors. We find that the two
factors for satisfy the same non-linear differential equation and,
similarly, for M=0 the four factors each satisfy Okamoto sigma-form of
Painlev\'e VI equations with the same Okamoto parameters. Using a Landen
transformation we show, for , that the previous non-linear
differential equation can actually be reduced to an Okamoto sigma-form of
Painlev\'e VI equation. For both the two and four factor case, we find that
there is a one parameter family of boundary conditions on the Okamoto
sigma-form of Painlev\'e VI equations which generalizes the factorization of
the correlations C(M,N) to an additive decomposition of the corresponding
sigma's solutions of the Okamoto sigma-form of Painlev\'e VI equation which we
call lambda extensions. At a special value of the parameter, the
lambda-extensions of the factors of C(M,N) reduce to homogeneous polynomials in
the complete elliptic functions of the first and second kind. We also
generalize some Tracy-Widom (Painlev\'e V) relations between the sum and
difference of sigma's to this Painlev\'e VI framework.Comment: 45 page
Gap Probabilities for Edge Intervals in Finite Gaussian and Jacobi Unitary Matrix Ensembles
The probabilities for gaps in the eigenvalue spectrum of the finite dimension
random matrix Hermite and Jacobi unitary ensembles on some
single and disconnected double intervals are found. These are cases where a
reflection symmetry exists and the probability factors into two other related
probabilities, defined on single intervals. Our investigation uses the system
of partial differential equations arising from the Fredholm determinant
expression for the gap probability and the differential-recurrence equations
satisfied by Hermite and Jacobi orthogonal polynomials. In our study we find
second and third order nonlinear ordinary differential equations defining the
probabilities in the general case. For N=1 and N=2 the probabilities and
thus the solution of the equations are given explicitly. An asymptotic
expansion for large gap size is obtained from the equation in the Hermite case,
and also studied is the scaling at the edge of the Hermite spectrum as , and the Jacobi to Hermite limit; these last two studies make
correspondence to other cases reported here or known previously. Moreover, the
differential equation arising in the Hermite ensemble is solved in terms of an
explicit rational function of a {Painlev\'e-V} transcendent and its derivative,
and an analogous solution is provided in the two Jacobi cases but this time
involving a {Painlev\'e-VI} transcendent.Comment: 32 pages, Latex2
Constructing Integrable Third Order Systems:The Gambier Approach
We present a systematic construction of integrable third order systems based
on the coupling of an integrable second order equation and a Riccati equation.
This approach is the extension of the Gambier method that led to the equation
that bears his name. Our study is carried through for both continuous and
discrete systems. In both cases the investigation is based on the study of the
singularities of the system (the Painlev\'e method for ODE's and the
singularity confinement method for mappings).Comment: 14 pages, TEX FIL
Chaos and Rotating Black Holes with Halos
The occurrence of chaos for test particles moving around a slowly rotating
black hole with a dipolar halo is studied using Poincar\'e sections. We find a
novel effect, particles with angular momentum opposite to the black hole
rotation have larger chaotic regions in phase space than particles initially
moving in the same direction.Comment: 9 pages, 4 Postscript figures. Phys. Rev. D, in pres
Radar detection of a localized 1.4 Hz pulsation in auroral plasma, simultaneous with pulsating optical emissions, during a substorm
Many pulsating phenomena are associated with the auroral substorm.
It has been considered that some of these phenomena involve kilometer-scale
Alfvén waves coupling the magnetosphere and ionosphere. Electric field
oscillations at the altitude of the ionosphere are a signature of
such wave activity that could distinguish it from other sources of
auroral particle precipitation, which may be simply tracers of magnetospheric
activity. Therefore, a ground based diagnostic of kilometer-scale
oscillating electric fields would be a valuable tool in the study
of pulsations and the auroral substorm. In this study we attempt to
develop such a tool in the Poker Flat incoherent scatter radar (PFISR).
The central result is a statistically significant detection of a 1.4 Hz
electric field oscillation associated with a similar oscillating
optical emission, during the recovery phase of a substorm. The optical
emissions also contain a bright, lower frequency (0.2 Hz) pulsation
that does not show up in the radar backscatter. The fact that higher
frequency oscillations are detected by the radar, whereas the bright,
lower frequency optical pulsation is not detected by the radar, serves
to strengthen a theoretical argument that the radar is sensitive to
oscillating electric fields, but not to oscillating particle precipitation.
Although it is difficult to make conclusions as to the physical mechanism,
we do not find evidence for a plane-wave-like Alfvén wave; the detected
structure is evident in only two of five adjacent beams. We emphasize
that this is a new application for ISR, and that corroborating results
are needed
General-relativistic Model of Magnetically Driven Jet
The general scheme for the construction of the general-relativistic model of
the magnetically driven jet is suggested. The method is based on the usage of
the 3+1 MHD formalism. It is shown that the critical points of the flow and the
explicit radial behavior of the physical variables may be derived through the
jet ``profile function."Comment: 12 pages, LaTex, no figure
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