4,132 research outputs found
Revisiting Cosmic No-Hair Theorem for Inflationary Settings
In this work we revisit Wald's cosmic no-hair theorem in the context of
accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing
anisotropic stress tensor and when the fluid energy momentum tensor is of the
form of a cosmological constant term plus a piece which does not respect strong
or dominant energy conditions. Such a fluid is the one appearing in
inflationary models. We show that for such a system anisotropy may grow, in
contrast to the cosmic no-hair conjecture. In particular, for a generic
inflationary model we show that there is an upper bound on the growth of
anisotropy. For slow-roll inflationary models our analysis can be refined
further and the upper bound is found to be of the order of slow-roll
parameters. We examine our general discussions and our extension of Wald's
theorem for three classes of slow-roll inflationary models, generic
multi-scalar field driven models, anisotropic models involving U(1) gauge
fields and the gauge-flation scenario.Comment: 21 pp, 4 .eps figure
Temperature-induced pair correlations in clusters and nuclei
The pair correlations in mesoscopic systems such as -size superconducting
clusters and nuclei are studied at finite temperature for the canonical
ensemble of fermions in model spaces with a fixed particle number: i) a
degenerate spherical shell (strong coupling limit), ii) an equidistantly spaced
deformed shell (weak coupling limit). It is shown that after the destruction of
the pair correlations at T=0 by a strong magnetic field or rapid rotation,
heating can bring them back. This phenomenon is a consequence of the fixed
number of fermions in the canonical ensemble
Effective Feature Selection for Feature Possessing Group Structure
Feature selection has become an interesting research topic in recent years. It is an effective method to tackle the data with high dimension. The underlying structure has been ignored by the previous feature selection method and it determines the feature individually. Considering this we focus on the problem where feature possess some group structure. To solve this problem we present group feature selection method at group level to execute feature selection. Its objective is to execute the feature selection in within the group and between the group of features that select discriminative features and remove redundant features to obtain optimal subset. We demonstrate our method on data sets and perform the task to achieve classification accuracy
Black Hole Statistics from Holography
We study the microstates of the ``small'' black hole in the \half-BPS
sector of AdS, the superstar of Myers and Tafjord, using the
powerful holographic description provided by LLM. The system demonstrates the
inherently statistical nature of black holes, with the geometry of Myer and
Tafjord emerging only after averaging over an ensemble of geometries. The
individual microstate geometries differ in the highly non-trivial topology of a
quantum foam at their core, and the entropy can be understood as a partition of
units of flux among 5-cycles, as required by flux quantization. While the
system offers confirmation of the most controversial aspect of Mathur and
Lunin's recent ``fuzzball'' proposal, we see signs of a discrepancy in
interpreting its details.Comment: 21 pages, 4 figures; References adde
An Arena for Model Building in the Cohen-Glashow Very Special Relativity
The Cohen-Glashow Very Special Relativity (VSR) algebra
[arXiv:hep-ph/0601236] is defined as the part of the Lorentz algebra which upon
addition of CP or T invariance enhances to the full Lorentz group, plus the
space-time translations. We show that noncommutative space-time, in particular
noncommutative Moyal plane, with light-like noncommutativity provides a robust
mathematical setting for quantum field theories which are VSR invariant and
hence set the stage for building VSR invariant particle physics models. In our
setting the VSR invariant theories are specified with a single deformation
parameter, the noncommutativity scale \Lambda_{NC}. Preliminary analysis with
the available data leads to \Lambda_{NC}\gtrsim 1-10 TeV.
This note is prepared for the Proceedings of the G27 Mathematical Physics
Conference, Yerevan 2008, and is based on arXiv:0806.3699[hep-th].Comment: Presented by M.M.Sh-J. in the G27 Mathematical Physics Conference,
Yerevan 2008 as the 4th Weyl Prize Ceremony Tal
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