5,118 research outputs found
Improved Hamiltonian for Minkowski Yang-Mills Theory
I develop an improved Hamiltonian for classical, Minkowski Yang-Mills theory,
which evolves infrared fields with corrections from lattice spacing
beginning at . I use it to investigate the response of Chern-Simons
number to a chemical potential, and to compute the maximal Lyapunov exponent.
Both quantities have small limits, in both cases within of the
limit found using the unimproved (Kogut Susskind) Hamiltonian. For the maximal
Lyapunov exponent the limits differ by about , significant at about , indicating that while a small limit exists, its value is corrupted
by lattice artefacts. For the response of Chern-Simons number the statistics
are not good enough to resolve differences, but it seems possible in
analogy with the Lyapunov exponent that the final answer depends on the lattice
regulation.Comment: Latex, 33 pages plus 2 .epsi figures included with psfig. Revised to
include new data which weakens some original conclusion
Gravity and BF theory defined in bounded regions
We study Einstein gravity in a finite spatial region. By requiring a
well-defined variational principle, we identify all local boundary conditions,
derive surface observables, and compute their algebra. The observables arise as
induced surface terms, which contribute to a non-vanishing Hamiltonian. Unlike
the asymptotically flat case, we find that there are an infinite number of
surface observables. We give a similar analysis for SU(2) BF theory.Comment: References adde
The perturbed universe in the deformed algebra approach of Loop Quantum Cosmology
Loop quantum cosmology is a tentative approach to model the universe down to
the Planck era where quantum gravity settings are needed. The quantization of
the universe as a dynamical space-time is inspired by Loop Quantum Gravity
ideas. In addition, loop quantum cosmology could bridge contact with
astronomical observations, and thus potentially investigate quantum cosmology
modellings in the light of observations. To do so however, modelling both the
background evolution and its perturbations is needed. The latter describe
cosmic inhomogeneities that are the main cosmological observables. In this
context, we present the so-called deformed algebra approach implementing the
quantum corrections to the perturbed universe at an effective level by taking
great care of gauge issues. We particularly highlight that in this framework,
the algebra of hypersurface deformation receives quantum corrections, and we
discuss their meaning. The primordial power spectra of scalar and tensor
inhomogeneities are then presented, assuming initial conditions are set in the
contracting phase preceding the quantum bounce and the well-known expanding
phase of the cosmic history. These spectra are subsequently propagated to
angular power spectra of the anisotropies of the cosmic microwave background.
It is then shown that regardless of the choice for the initial conditions
inside the effective approach for the background evolution (except that they
are set in the contracting phase), the predicted angular power spectra of the
polarized B-modes exceed the upper bound currently set by observations. The
exclusion of this specific version of loop quantum cosmology establishes the
falsifiability of the approach, though one shall not conclude here that either
loop quantum cosmology or loop quantum gravity is excluded.Comment: Invited paper for a special issue of IJMPD on Loop Quantum Cosmolog
-Term and Cosmological Constant from CJD Action
In the gravity without metric formalism of Capovilla, Jacobson and Dell, the
topological -term appears through a canonical transformation.The origin
of this canonical transformation is probed here. It is shown here that when
-term appears cosmological -term also appears simultaneously.Comment: 5 page
Boundary conditions in first order gravity: Hamiltonian and Ensemble
In this work two different boundary conditions for first order gravity,
corresponding to a null and a negative cosmological constant respectively, are
studied. Both boundary conditions allows to obtain the standard black hole
thermodynamics. Furthermore both boundary conditions define a canonical
ensemble. Additionally the quasilocal energy definition is obtained for the
null cosmological constant case.Comment: To be published in Phys, Rev.
A cross-cultural re-evaluation of the Exercise Addiction Inventory (EAI) in five countries
Research into the detrimental effects of excessive exercise has been conceptualized in a number of similar ways, including âexercise addictionâ , âexercise dependenceâ , âobligatory exercisingâ, âexercise abuseâ, and âcompulsive exerciseâ. Among the most currently used (and psychometrically valid and reliable) instruments is the Exercise Addiction Inventory (EAI). The present study aimed to further explore the psychometric properties of the EAI by combining the datasets of a number of surveys carried out in five different countries (Denmark, Hungary, Spain, UK, and US) that have used the EAI with a total sample size of 6,031 participants. A series of multigroup confirmatory factor analyses (CFAs) were carried out examining configural invariance, metric invariance, and scalar invariance. The CFAs using the combined dataset supported the configural invariance and metric invariance but not scalar invariance. Therefore, EAI factor scores from five countries are not comparable because the use or interpretation of the scale was different in the five nations. However, the covariates of exercise addiction can be studied from a cross-cultural perspective because of the metric invariance of the scale. Gender differences among exercisers in the interpretation of the scale also emerged. The implications of the results are discussed, and it is concluded that the studyâs findings will facilitate a more robust and reliable use of the EAI in future research
Multicanonical Recursions
The problem of calculating multicanonical parameters recursively is
discussed. I describe in detail a computational implementation which has worked
reasonably well in practice.Comment: 23 pages, latex, 4 postscript figures included (uuencoded
Z-compressed .tar file created by uufiles), figure file corrected
Multi-word expression-sensitive word alignment
This paper presents a new word alignment method which incorporates knowledge about Bilingual Multi-Word Expressions (BMWEs). Our method of word alignment first extracts such BMWEs in a bidirectional way for a given corpus and then starts conventional word alignment,
considering the properties of BMWEs in their grouping as well as their alignment links. We give partial annotation of alignment links as prior knowledge to the word
alignment process; by replacing the maximum likelihood estimate in the M-step of the IBM Models with the Maximum A
Posteriori (MAP) estimate, prior knowledge about BMWEs is embedded in the prior in this MAP estimate. In our experiments, we saw an improvement of 0.77 Bleu points absolute in JPâEN. Except for one case, our method gave better results than the method using only BMWEs grouping. Even though this paper does not directly address the issues in Cross-Lingual Information Retrieval (CLIR), it
discusses an approach of direct relevance to the field. This approach could be viewed as the opposite of current trends in CLIR on semantic space that incorporate a notion of order in the bag-of-words model (e.g. co-occurences)
Loop Quantum Cosmology corrections on gravity waves produced during primordial inflation
Loop Quantum Gravity (L.Q.G.) is one of the two most promising tentative
theory for a quantum description of gravity. When applied to the entire
universe, the so-called Loop Quantum Cosmology (L.Q.C.) framework offers
microscopical models of the very early stages of the cosmological history,
potentially solving the initial singularity problem via bouncing solutions or
setting the universe in the appropriate initial conditions for inflation to
start, via a phase of super-inflation. More interestingly, L.Q.C. could leave a
footprint on cosmological observables such as the Cosmic Microwave Background
(CMB) anisotropies. Focusing on the modified dispersion relation when holonomy
and inverse-volume corrections arising from the L.Q.C. framework are
considered, it is shown that primordial gravity waves generated during
inflation are affected by quantum corrections. Depending on the type of
corrections, the primordial tensor power spectrum is either suppressed or
boosted at large length scales, and strongly departs from the power-law
behavior expected in the standard scenario.Comment: to be published in the AIP Proceedings of the 'Invisible Universe
International Conference', UNESCO-Paris, June 29-July 3, 2009; 9 pp., 4 Fig
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