1,341,609 research outputs found
Some considerations about NS5 and LST Hawking radiation
We have studied the Hawking radiation corresponding to the NS5 and Little
String Theory (LST) black hole models using two semi-classical methods: the
complex path method and a gravitational anomaly. After summarizing some known
concepts about the thermodynamics of these theories, we have computed the
emission rates for the two black hole models. The temperature calculated from,
e.g. the well-known surface gravity expression, is shown to be identical to
that obtained from both the computation of the gravitational anomaly and the
complex path method. Moreover, the two semi-classical methods show that NS5
exhibits non-thermal behavior that contrasts with the thermal behavior of LST.
We remark that energy conservation is the key factor leading to a non-thermal
profile for NS5. In contrast, LST keeps a thermal profile even when energy
conservation is considered because temperature in this model does not depend on
energy.Comment: 18 pages, acknowledgments included, some concepts clarified, typos
corrected, journal reference include
String Cosmology: Concepts and Consequences
After recalling a few basic concepts from cosmology and string theory, I will
discuss the main ideas/assumptions underlying string cosmology and show how
these lead to a two-parameter family of ``minimal" models. I will then explain
how to compute, in terms of those parameters, the spectrum of scalar, tensor
and electromagnetic perturbations, point at their ( and -type) duality
symmetries, and mention their most relevant physical consequences.Comment: 21p, latex, epsf, 3 figures in uuencoded fil
Formal deformations, contractions and moduli spaces of Lie algebras
Jump deformations and contractions of Lie algebras are inverse concepts, but
the approaches to their computations are quite different. In this paper, we
contrast the two approaches, showing how to compute jump deformations from the
miniversal deformation of a Lie algebra, and thus arrive at the contractions.
We also compute contractions directly. We use the moduli spaces of real
3-dimensional and complex 3 and 4-dimensional Lie algebras as models for
explaining a deformation theory approach to computation of contractions.Comment: 27 page
The non-unique Universe
The purpose of this paper is to elucidate, by means of concepts and theorems
drawn from mathematical logic, the conditions under which the existence of a
multiverse is a logical necessity in mathematical physics, and the implications
of Godel's incompleteness theorem for theories of everything.
Three conclusions are obtained in the final section: (i) the theory of the
structure of our universe might be an undecidable theory, and this constitutes
a potential epistemological limit for mathematical physics, but because such a
theory must be complete, there is no ontological barrier to the existence of a
final theory of everything; (ii) in terms of mathematical logic, there are two
different types of multiverse: classes of non-isomorphic but elementarily
equivalent models, and classes of model which are both non-isomorphic and
elementarily inequivalent; (iii) for a hypothetical theory of everything to
have only one possible model, and to thereby negate the possible existence of a
multiverse, that theory must be such that it admits only a finite model
Marshallian vs. Walrasian Stability in an Experimental Market
The experiments discussed below are an attempt to examine concepts of
stability as found in economic textbooks. Two concepts of stability, which stem
from two different concepts of market adjustment, seem to have dominated
thinking. Whilst these two concepts are typically called Walras stability and
Marshall stability, some controversy exists over the extent to which these two
models represent their respective thinking. No doubt the current formal
statements of the theories reflect an evolution of the ideas through the work of
many theorists. The terminology is retained for convenience. Regardless of
their origins, these two concepts lead to competing hypotheses about the
conditions under which market instability will be observed so the subject is a
natural one for experimental investigation. Furthermore, since this is the first
experimental examination of the stability of equilibria, the strategy is to inquire
about stability in the context of these two classical models and to avoid the
temptation to attempt to extend them or integrate them with more modern
theory. The old models have not been checked. They seem to be an appropriate
place to start
Rational Trust Modeling
Trust models are widely used in various computer science disciplines. The
main purpose of a trust model is to continuously measure trustworthiness of a
set of entities based on their behaviors. In this article, the novel notion of
"rational trust modeling" is introduced by bridging trust management and game
theory. Note that trust models/reputation systems have been used in game theory
(e.g., repeated games) for a long time, however, game theory has not been
utilized in the process of trust model construction; this is where the novelty
of our approach comes from. In our proposed setting, the designer of a trust
model assumes that the players who intend to utilize the model are
rational/selfish, i.e., they decide to become trustworthy or untrustworthy
based on the utility that they can gain. In other words, the players are
incentivized (or penalized) by the model itself to act properly. The problem of
trust management can be then approached by game theoretical analyses and
solution concepts such as Nash equilibrium. Although rationality might be
built-in in some existing trust models, we intend to formalize the notion of
rational trust modeling from the designer's perspective. This approach will
result in two fascinating outcomes. First of all, the designer of a trust model
can incentivise trustworthiness in the first place by incorporating proper
parameters into the trust function, which can be later utilized among selfish
players in strategic trust-based interactions (e.g., e-commerce scenarios).
Furthermore, using a rational trust model, we can prevent many well-known
attacks on trust models. These two prominent properties also help us to predict
behavior of the players in subsequent steps by game theoretical analyses
Random Matrices and Chaos in Nuclear Physics
The authors review the evidence for the applicability of random--matrix
theory to nuclear spectra. In analogy to systems with few degrees of freedom,
one speaks of chaos (more accurately: quantum chaos) in nuclei whenever
random--matrix predictions are fulfilled. An introduction into the basic
concepts of random--matrix theory is followed by a survey over the extant
experimental information on spectral fluctuations, including a discussion of
the violation of a symmetry or invariance property. Chaos in nuclear models is
discussed for the spherical shell model, for the deformed shell model, and for
the interacting boson model. Evidence for chaos also comes from random--matrix
ensembles patterned after the shell model such as the embedded two--body
ensemble, the two--body random ensemble, and the constrained ensembles. All
this evidence points to the fact that chaos is a generic property of nuclear
spectra, except for the ground--state regions of strongly deformed nuclei.Comment: 54 pages, 28 figure
String Cosmology: Basic Ideas and General Results
After recalling a few basic concepts from cosmology and string theory, I will
outline the main ideas/assumptions underlying (our own group's approach to)
string cosmology and show how these lead to the definition of a two-parameter
family of ``minimal" models. I will then briefly explain how to compute, in
terms of those parameters, the spectrum of scalar, tensor and electromagnetic
perturbations, and mention their most relevant physical consequences. More
details on the latter part of this talk can be found in Maurizio Gasperini's
contribution to these proceedings.Comment: Latex file + 3 figures. Talk presented at the 3rd Colloque
Cosmologie, Paris, 7-9 June 9
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