1,693 research outputs found
A theorem on topologically massive gravity
We show that for three dimensional space-times admitting a hypersurface
orthogonal Killing vector field Deser, Jackiw and Templeton's vacuum field
equations of topologically massive gravity allow only the trivial flat
space-time solution. Thus spin is necessary to support topological mass.Comment: published in Classical and Quantum Gravity 13 (1996) L2
Topologically massive gravito-electrodynamics: exact solutions
We construct two classes of exact solutions to the field equations of
topologically massive electrodynamics coupled to topologically massive gravity
in 2 + 1 dimensions. The self-dual stationary solutions of the first class are
horizonless, asymptotic to the extreme BTZ black-hole metric, and regular for a
suitable parameter domain. The diagonal solutions of the second class, which
exist if the two Chern-Simons coupling constants exactly balance, include
anisotropic cosmologies and static solutions with a pointlike horizon.Comment: 15 pages, LaTeX, no figure
The Random Bit Complexity of Mobile Robots Scattering
We consider the problem of scattering robots in a two dimensional
continuous space. As this problem is impossible to solve in a deterministic
manner, all solutions must be probabilistic. We investigate the amount of
randomness (that is, the number of random bits used by the robots) that is
required to achieve scattering. We first prove that random bits are
necessary to scatter robots in any setting. Also, we give a sufficient
condition for a scattering algorithm to be random bit optimal. As it turns out
that previous solutions for scattering satisfy our condition, they are hence
proved random bit optimal for the scattering problem. Then, we investigate the
time complexity of scattering when strong multiplicity detection is not
available. We prove that such algorithms cannot converge in constant time in
the general case and in rounds for random bits optimal
scattering algorithms. However, we present a family of scattering algorithms
that converge as fast as needed without using multiplicity detection. Also, we
put forward a specific protocol of this family that is random bit optimal ( random bits are used) and time optimal ( rounds are used).
This improves the time complexity of previous results in the same setting by a
factor. Aside from characterizing the random bit complexity of mobile
robot scattering, our study also closes its time complexity gap with and
without strong multiplicity detection (that is, time complexity is only
achievable when strong multiplicity detection is available, and it is possible
to approach it as needed otherwise)
Generally Covariant Conservative Energy-Momentum for Gravitational Anyons
We obtain a generally covariant conservation law of energy-momentum for
gravitational anyons by the general displacement transform. The energy-momentum
currents have also superpotentials and are therefore identically conserved. It
is shown that for Deser's solution and Clement's solution, the energy vanishes.
The reasonableness of the definition of energy-momentum may be confirmed by the
solution for pure Einstein gravity which is a limit of vanishing Chern-Simons
coulping of gravitational anyons.Comment: 12 pages, Latex, no figure
The black holes of topologically massive gravity
We show that an analytical continuation of the Vuorio solution to
three-dimensional topologically massive gravity leads to a two-parameter family
of black hole solutions, which are geodesically complete and causally regular
within a certain parameter range. No observers can remain static in these
spacetimes. We discuss their global structure, and evaluate their mass, angular
momentum, and entropy, which satisfy a slightly modified form of the first law
of thermodynamics.Comment: 10 pages; Eq. (15) corrected, references added, version to appear in
Classical and Quantum Gravit
Hidden symmetry of the three-dimensional Einstein-Maxwell equations
It is shown how to generate three-dimensional Einstein-Maxwell fields from
known ones in the presence of a hypersurface-orthogonal non-null Killing vector
field. The continuous symmetry group is isomorphic to the Heisenberg group
including the Harrison-type transformation. The symmetry of the
Einstein-Maxwell-dilaton system is also studied and it is shown that there is
the transformation between the Maxwell and the dilaton fields.
This transformation is identified with the Geroch
transformation of the four-dimensional vacuum Einstein equation in terms of the
Ka{\l}uza-Klein mechanism.Comment: 5 page
Are eccentricity fluctuations able to explain the centrality dependence of ?
The fourth harmonic of the azimuthal distribution of particles has been
measured for Au-Au collisions at the Relativistic Heavy Ion Collider (RHIC).
The centrality dependence of does not agree with the prediction from
hydrodynamics. In particular, the ratio , where denotes the
second harmonic of the azimuthal distribution of particles, is significantly
larger than predicted by hydrodynamics. We argue that this discrepancy is
mostly due to elliptic flow () fluctuations. We evaluate these
fluctuations on the basis of a Monte Carlo Glauber calculation. The effect of
deviations from local thermal equilibrium is also studied, but appears to be
only a small correction. Combining these two effects allows us to reproduce
experimental data for peripheral and midcentral collisions. However, we are
unable to explain the large magnitude of observed for the most
central collisions.Comment: talk presented at the Strangeness in Quark Matter Conference, Buzios,
Brazil, Sept. 27 - oct. 2, 200
Black hole mass and angular momentum in topologically massive gravity
We extend the Abbott-Deser-Tekin approach to the computation of the Killing
charge for a solution of topologically massive gravity (TMG) linearized around
an arbitrary background. This is then applied to evaluate the mass and angular
momentum of black hole solutions of TMG with non-constant curvature
asymptotics. The resulting values, together with the appropriate black hole
entropy, fit nicely into the first law of black hole thermodynamics.Comment: 20 pages, references added, version to appear in Classical and
Quantum Gravit
Existence and uniqueness of Bowen-York Trumpets
We prove the existence of initial data sets which possess an asymptotically
flat and an asymptotically cylindrical end. Such geometries are known as
trumpets in the community of numerical relativists.Comment: This corresponds to the published version in Class. Quantum Grav. 28
(2011) 24500
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