19,633 research outputs found
Projectable Horava-Lifshitz gravity in a nutshell
Approximately one year ago Horava proposed a power-counting renormalizable
theory of gravity which abandons local Lorentz invariance. The proposal has
been received with growing interest and resulted in various different versions
of Horava-Lifshitz gravity theories, involving a colourful potpourri of new
terminology. In this proceedings contribution we first motivate and briefly
overview the various different approaches, clarifying their differences and
similarities. We then focus on a model referred to as projectable
Horava-Lifshitz gravity and summarize the key results regarding its viability.Comment: 8 pages, no figures, to appear in the proceedings of First
Mediterranean Conference on Classical and Quantum Gravity Conference (MCCQG),
Kolymbari (Crete, Greece), September 14-18, 200
On the Power Counting in Effective Field Theories
We discuss the systematics of power counting in general effective field
theories, focussing on those that are nonrenormalizable at leading order. As an
illuminating example we consider chiral perturbation theory gauged under the
electromagnetic symmetry. This theory describes the low-energy
interactions of the octet of pseudo-Goldstone bosons in QCD with photons and
has been discussed extensively in the literature. Peculiarities of the standard
approach are pointed out and it is shown how these are resolved within our
scheme. The presentation follows closely our recent discussion of power
counting for the electroweak chiral Lagrangian. The systematics of the latter
is reviewed and shown to be consistent with the concept of chiral dimensions.
The results imply that naive dimensional analysis (NDA) is incomplete in
general effective field theories, while still reproducing the correct counting
in special cases.Comment: 14 pages, no figure
Area Law Micro-State Entropy from Criticality and Spherical Symmetry
It is often assumed that the area law of micro-state entropy and the
holography are intrinsic properties exclusively of the gravitational systems,
such as black holes. We construct a non-gravitational model that exhibits an
entropy that scales as area of a sphere of one dimension less. It is
represented by a non-relativistic bosonic field living on a d-dimensional
sphere of radius R and experiencing an angular-momentum-dependent attractive
interaction. We show that the system possesses a quantum critical point with
the emergent gapless modes. Their number is equal to the area of a
(d-1)-dimensional sphere of the same radius R. These gapless modes create an
exponentially large number of degenerate micro-states with the corresponding
micro-state entropy given by the area of the same (d-1)-dimensional sphere.
Thanks to a double-scaling limit, the counting of the entropy and of the number
of the gapless modes is made exact. The phenomenon takes place for arbitrary
number of dimensions and can be viewed as a version of holography.Comment: 7 page
More on "Little Lambda" in Ho\v{r}ava-Lifshitz Gravity
We analyze different claims on the role of the coupling constant lambda in
so-called lambda-R models, a minimal generalization of general relativity
inspired by Horava-Lifshitz gravity. The dimensionless parameter lambda appears
in the kinetic term of the Einstein-Hilbert action, leading to a one-parameter
family of classical theories. Performing a canonical constraint analysis for
closed spatial hypersurfaces, we obtain a result analogous to that of Bellorin
and Restuccia, who showed that all non-projectable lambda-R models are
equivalent to general relativity in the asymptotically flat case. However, the
tertiary constraint present for closed boundary conditions assumes a more
general form. We juxtapose this with an earlier finding by Giulini and Kiefer,
who ruled out a range of lambda-R models by a physical, cosmological argument.
We show that their analysis can be interpreted consistently within the
projectable sector of Horava-Lifshitz gravity, thus resolving the apparent
contradiction.Comment: 21 pages, no figure
Towards the Automatic Classification of Documents in User-generated Classifications
There is a huge amount of information scattered on the World Wide Web. As the information flow occurs at a high speed in the WWW, there is a need to organize it in the right manner so that a user can access it very easily. Previously the organization of information was generally done manually, by matching the document contents to some pre-defined categories. There are two approaches for this text-based categorization: manual and automatic. In the manual approach, a human expert performs the classification task, and in the second case supervised classifiers are used to automatically classify resources. In a supervised classification, manual interaction is required to create some training data before the automatic classification task takes place. In our new approach, we intend to propose automatic classification of documents through semantic keywords and building the formulas generation by these keywords. Thus we can reduce this human participation by combining the knowledge of a given classification and the knowledge extracted from the data. The main focus of this PhD thesis, supervised by Prof. Fausto Giunchiglia, is the automatic classification of documents into user-generated classifications. The key benefits foreseen from this automatic document classification is not only related to search engines, but also to many other fields like, document organization, text filtering, semantic index managing
Searching for T-Violating, P-Conserving New Physics with Neutrons
The observance of parity conserving time reversal violation in light quark
systems could signal the presence of physics beyond the Standard Model. I
discuss the implications of low-energy time reversal tests for the existence of
such T-violating, P-conserving (TVPC) interactions. I argue that searches for
permanent electric dipole moments (EDM's) and direct TVPC searches provide
complementary information on P-conserving T-violation. EDM searches yield
constraints only under the assumption that parity symmetry is restored at the
scale Lambda associated with new TVPC physics. If parity remains broken at
short distances, direct searches yield the least ambiguous bounds. In the
latter case, improving the experimental precision of direct TVPC searches in
neutron beta-decay and polarized epithermal neutron transmission at the
Spallation Neutron Source could yield tighter bounds.Comment: To appear in proceedings of Workshop on Fundamental Physics with
Pulsed Neutron Beams, held at the Research Triangle Park, North Carolina,
June 1 -- 3, 2000. Nine page
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