162 research outputs found
Closed forms and multi-moment maps
We extend the notion of multi-moment map to geometries defined by closed
forms of arbitrary degree. We give fundamental existence and uniqueness results
and discuss a number of essential examples, including geometries related to
special holonomy. For forms of degree four, multi-moment maps are guaranteed to
exist and are unique when the symmetry group is (3,4)-trivial, meaning that the
group is connected and the third and fourth Lie algebra Betti numbers vanish.
We give a structural description of some classes of (3,4)-trivial algebras and
provide a number of examples.Comment: 36 page
Gauge symmetry and the EMC spin effect
We emphasise the EMC spin effect as a problem of symmetry and discuss the
renormalisation of the axial tensor operators. This involves the
generalisation of the Adler-Bell-Jackiw anomaly to each of these operators. We
find that the contribution of the axial anomaly to the spin dependent structure
function scales at . This means that the anomaly
can be a large effect in . Finally we discuss the jet signature of the
anomaly.Comment: 17 pages, Latex, Cavendish preprint HEP 93/
On the characteristic connection of gwistor space
We give a brief presentation of gwistor space, which is a new concept from
G_2 geometry. Then we compute the characteristic torsion T^c of the gwistor
space of an oriented Riemannian 4-manifold with constant sectional curvature k
and deduce the condition under which T^c is \nabla^c-parallel; this allows for
the classification of the G_2 structure with torsion and the characteristic
holonomy according to known references. The case with the Einstein base
manifold is envisaged.Comment: Many changes since first version, including title; Central European
Journal of Mathematics, 201
Rigid upper bounds for the angular momentum and centre of mass of non-singular asymptotically anti-de Sitter space-times
We prove upper bounds on angular momentum and centre of mass in terms of the
Hamiltonian mass and cosmological constant for non-singular asymptotically
anti-de Sitter initial data sets satisfying the dominant energy condition. We
work in all space-dimensions larger than or equal to three, and allow a large
class of asymptotic backgrounds, with spherical and non-spherical conformal
infinities; in the latter case, a spin-structure compatibility condition is
imposed. We give a large class of non-trivial examples saturating the
inequality. We analyse exhaustively the borderline case in space-time dimension
four: for spherical cross-sections of Scri, equality together with completeness
occurs only in anti-de Sitter space-time. On the other hand, in the toroidal
case, regular non-trivial initial data sets saturating the bound exist.Comment: improvements in the presentation; some statements correcte
Leading and higher twists in the proton polarized structure function at large Bjorken x
A phenomenological parameterization of the proton polarized structure
function has been developed for x > 0.02 using deep inelastic data up to ~ 50
(GeV/c)**2 as well as available experimental results on both photo- and
electro-production of proton resonances. According to the new parameterization
the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a
zero-crossing point at Q**2 = 0.16 +/- 0.04 (GeV/c)**2. Then, low-order
polarized Nachtmann moments have been estimated and their Q**2-behavior has
been investigated in terms of leading and higher twists for Q**2 > 1
(GeV/c)**2. The leading twist has been treated at NLO in the strong coupling
constant and the effects of higher orders of the perturbative series have been
estimated using soft-gluon resummation techniques. In case of the first moment
higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and
the singlet axial charge has been determined to be a0[10 (GeV/c)**2] = 0.16 +/-
0.09. In case of higher order moments, which are sensitive to the large-x
region, higher-twist effects are significantly reduced by the introduction of
soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2
at variance with the case of the unpolarized transverse structure function of
the proton. Our finding suggests that spin-dependent correlations among partons
may have more impact than spin-independent ones. As a byproduct, it is also
shown that the Bloom-Gilman local duality is strongly violated in the region of
polarized electroproduction of the Delta(1232) resonance.Comment: revised version to appear in Phys. Rev. D; extended discussion on the
generalized DHG sum rul
SPIN-DEPENDENT NUCLEAR STRUCTURE FUNCTIONS: GENERAL APPROACH WITH APPLICATION TO THE DEUTERON
We study deep-inelastic scattering from polarized nuclei within a covariant
framework. A clear connection is established between relativistic and
non-relativistic limits, which enables a rigorous derivation of convolution
formulae for the spin-dependent nuclear structure functions g_1^A and g_2^A in
terms of off-mass-shell extrapolations of polarized nucleon structure
functions, g_1^N and g_2^N. Approximate expressions for g_{1,2}^A are obtained
by expanding the off-shell g_{1,2}^N about their on-shell limits. As an
application of the formalism we consider nuclear effects in the deuteron,
knowledge of which is necessary to obtain accurate information on the
spin-dependent structure functions of the neutron.Comment: 26 pages RevTeX, 9 figures available upon reques
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Island tourism and sustainability: a case study of the Lakshadweep Islands
Lakshadweep archipelago, off the southwestern coast of India, is a relatively little known island tourism destination. With a very fragile environment, traditional society and marginal economy, and almost entirely dependent on the mainland, Lakshadweep has been developing tourism as an important economic activity. With its geographical and environmental limitations, sustainability is a major issue in Lakshadweep tourism. However, the islands seem to have turned these limitations to their advantage by developing and managing tourism in a controlled manner. This paper considers the development of tourism in Lakshadweep islands within the context of sustainability. Examining the structural and developmental features of Lakshadweep tourism, the paper aims to identify specific development and management patterns, and explores potential strategies for promoting sustainability-oriented tourism in Lakshadweep
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