47,044 research outputs found
Quasi-local energy for cosmological models
First we briefly review our covariant Hamiltonian approach to quasi-local
energy, noting that the Hamiltonian-boundary-term quasi-local energy
expressions depend on the chosen boundary conditions and reference
configuration. Then we present the quasi-local energy values resulting from the
formalism applied to homogeneous Bianchi cosmologies. Finally we consider the
quasi-local energies of the FRW cosmologies. Our results do not agree with
certain widely accepted quasi-local criteria.Comment: Contributed to International Symposium on Cosmology and Particle
Astrophysics (CosPA 2006), Taipei, Taiwan, 15-17 Nov 200
Local Energy Statistics in Directed Polymers
Recently, Bauke and Mertens conjectured that the local statistics of energies
in random spin systems with discrete spin space should, in most circumstances,
be the same as in the random energy model. We show that this conjecture holds
true as well for directed polymers in random environment. We also show that,
under certain conditions, this conjecture holds for directed polymers even if
energy levels that grow moderately with the volume of the system are
considered
Unlocking Local Energy Markets
This is the final version. Freely available from University of Exeter Energy Policy Group via the link in this recordEuropean Regional Development FundCentric
Quasi-local Energy for Spherically Symmetric Spacetimes
We present two complementary approaches for determining the reference for the
covariant Hamiltonian boundary term quasi-local energy and test them on
spherically symmetric spacetimes. On the one hand, we isometrically match the
2-surface and extremize the energy. This can be done in two ways, which we call
programs I (without constraint) and II (with additional constraints). On the
other hand, we match the orthonormal 4-frames of the dynamic and the reference
spacetimes. Then, if we further specify the observer by requiring the reference
displacement to be the timelike Killing vector of the reference, the result is
the same as program I, and the energy can be positive, zero, or even negative.
If, instead, we require that the Lie derivatives of the two-area along the
displacement vector in both the dynamic and reference spacetimes to be the
same, the result is the same as program II, and it satisfies the usual
criteria: the energies are non-negative and vanish only for Minkowski (or
anti-de Sitter) spacetime.Comment: 16 pages, no figure
Quantum reading under a local energy constraint
Nonclassical states of light play a central role in many quantum information
protocols. Their quantum features have been exploited to improve the readout of
information from digital memories, modelled as arrays of microscopic beam
splitters [S. Pirandola, Phys. Rev. Lett. 106, 090504 (2011)]. In this model of
quantum reading, a nonclassical source of light with Einstein-Podolski-Rosen
correlations has been proven to retrieve more information than any classical
source. In particular, the quantum-classical comparison has been performed
under a global energy constraint, i.e., by fixing the mean total number of
photons irradiated over each memory cell. In this paper we provide an
alternative analysis which is based on a local energy constraint, meaning that
we fix the mean number of photons per signal mode irradiated over the memory
cell. Under this assumption, we investigate the critical number of signal modes
after which a nonclassical source of light is able to beat any classical source
irradiating the same number of signals.Comment: REVTeX. Published versio
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