49,783 research outputs found
Implications of Color Gauge Symmetry For Nucleon Spin Structure
We study the chromodynamical gauge symmetry in relation to the internal spin
structure of the nucleon. We show that 1) even in the helicity eigenstates the
gauge-dependent spin and orbital angular momentum operators do not have
gauge-independent matrix element; 2) the evolution equations for the gluon spin
take very different forms in the Feynman and axial gauges, but yield the same
leading behavior in the asymptotic limit; 3) the complete evolution of the
gauge-dependent orbital angular momenta appears intractable in the light-cone
gauge. We define a new gluon orbital angular momentum distribution
which {\it is} an experimental observable and has a simple scale evolution.
However, its physical interpretation makes sense only in the light-cone gauge
just like the gluon helicity distribution y.Comment: Minor corrections are made in the tex
Collective modes and ballistic expansion of a Fermi gas in the BCS-BEC crossover
We evaluate the frequencies of collective modes and the anisotropic expansion
rate of a harmonically trapped Fermi superfluid at varying coupling strengths
across a Feshbach resonance driving a BCS-BEC crossover. The equations of
motion for the superfluid are obtained from a microscopic mean-field expression
for the compressibility and are solved within a scaling ansatz. Our results
confirm non-monotonic behavior in the crossover region and are in quantitative
agreement with current measurements of the transverse breathing mode by Kinast
{\it et al.} [Phys. Rev. Lett. {\bf 92}, 150402 (2004)] and of the axial
breathing mode by Bartenstein {\it et al.} [Phys. Rev. Lett. {\bf 92}, 203201
(2004)].Comment: 4 pages and 4 figures; proof version with more extensive discussions
on the comparison between theoretical results and experimental findings; to
appear in Phys. Rev. Lett. (Nov. 2004
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Tailored gamification and serious game framework based on fuzzy logic for saving energy in connected thermostats
Connected thermostats (CTs) often save less energy than predicted because consumers may not know how to use them and may not be engaged in saving energy. Additionally, several models perform contrary to consumers’ expectations and are thus not used the way they are intended to. As a result, CTs save less energy and are underused in households. This paper reviews aspects of gamification and serious games focused on engaging consumers. A gamification and serious games framework is proposed for saving energy that is tailored by a fuzzy logic system to motivate connected thermostat consumers. This intelligent gamification framework can be used to customize the gamification and serious game strategy to each consumer so that fuzzy logic systems can be adapted according to the requirements of each consumer. The framework is designed to teach, engage, and motivate consumers while helping them save electrical energy when using their thermostats. It is described the proposed framework as well as a mockup that can be run on a cellphone. Although this framework is designed to be implemented in CTs, it can be translated to their energy devices in smart homes
Quark Orbital-Angular-Momentum Distribution in the Nucleon
We introduce gauge-invariant quark and gluon angular momentum distributions
after making a generalization of the angular momentum density operators. From
the quark angular momentum distribution, we define the gauge-invariant and
leading-twist quark {\it orbital} angular momentum distribution . The
latter can be extracted from data on the polarized and unpolarized quark
distributions and the off-forward distribution in the forward limit. We
comment upon the evolution equations obeyed by this as well as other orbital
distributions considered in the literature.Comment: 8 pages, latex, no figures, minor corrections mad
Chiral-Odd and Spin-Dependent Quark Fragmentation Functions and their Applications
We define a number of quark fragmentation functions for spin-0, -1/2 and -1
hadrons, and classify them according to their twist, spin and chirality. As an
example of their applications, we use them to analyze semi-inclusive
deep-inelastic scattering on a transversely polarized nucleon.Comment: 19 pages in Plain TeX, MIT CTP #221
Disentangling positivity constraints for generalized parton distributions
Positivity constraints are derived for the generalized parton distributions
(GPDs) of spin-1/2 hadrons. The analysis covers the full set of eight twist-2
GPDs. Several new inequalities are obtained which constrain GPDs by various
combinations of usual (forward) unpolarized and polarized parton distributions
including the transversity distribution.Comment: 9 pages (REVTEX), typos correcte
Solution of the off-forward leading logarithmic evolution equation based on the Gegenbauer moments inversion
Using the conformal invariance the leading-log evolution of the off-forward
structure function is reduced to the forward evolution described by the
conventional DGLAP equation. The method relies on the fact that the anomalous
dimensions of the Gegenbauer moments of the off-forward distribution are
independent on the asymmetry, or skewedness, parameter and equal to the DGLAP
ones. The integral kernels relating the forward and off-forward functions with
the same Mellin and Gegenbauer moments are presented for arbitrary asymmetry
value.Comment: 11 pages, LaTeX, no figures, revised version, references adde
One-Loop Factorization of the Nucleon g_2-Structure Function in the Non-Singlet Case
We consider the one-loop factorization of the simplest twist-three process:
inclusive deep-inelastic scattering of longitudinally-polarized leptons on a
transversely-polarized nucleon target. By studying the Compton amplitudes for
certain quark and gluon states at one loop, we find the coefficient functions
for the non-singlet twist-three distributions in the factorization formula of
g_2(x_B,Q^2). The result marks the first step towards a next-to-leading order
(NLO) formalism for this transverse-spin-dependent structure function of the
nucleon.Comment: 14 pages, revtex4, four figures included, minor change
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