2,614 research outputs found
A grid-based infrastructure for distributed retrieval
In large-scale distributed retrieval, challenges of latency, heterogeneity, and dynamicity emphasise the importance of infrastructural support in reducing the development costs of state-of-the-art solutions. We present a service-based infrastructure for distributed retrieval which blends middleware facilities and a design framework to âliftâ the resource sharing approach and the computational services of a European Grid platform into the domain of e-Science applications. In this paper, we give an overview of the DILIGENT Search Framework and illustrate its exploitation in the ïŹeld of Earth Science
Semileptonic and rare B meson decays into a light pseudoscalar meson
In the framework of a QCD relativistic potential model we evaluate the form
factors describing the exclusive decays B => \pi l nu and B => K l+ l-. The
present calculation extends a previous analysis of B meson decays into light
vector mesons. We find results in agreement with the data, when available, and
with the theoretical constraints imposed by the Callan-Treiman relation and the
infinite heavy quark mass limit.Comment: 11 pages LaTeX + 2 figure
The anomaly-free quantization of two-dimensional relativistic string. I
An anomaly-free quantum theory of a relativistic string is constructed in
two-dimensional space-time. The states of the string are found to be similar to
the states of a massless chiral quantum particle. This result is obtained by
generalizing the concept of an ``operator'' in quantum field theory.Comment: LaTeX, 19 pages, no figure
Exact C=1 Boundary Conformal Field Theories
We present a solution of the problem of a free massless scalar field on the
half line interacting through a periodic potential on the boundary. For a
critical value of the period, this system is a conformal field theory with a
non-trivial and explicitly calculable S-matrix for scattering from the
boundary. Unlike all other exactly solvable conformal field theories, it is
non-rational ({\it i.e.} has infinitely many primary fields). It describes the
critical behavior of a number of condensed matter systems, including
dissipative quantum mechanics and of barriers in ``quantum wires''.Comment: harvmac, 10 pages, PUPT-1432/IASSNS-HEP-93/7
Information Loss and Anomalous Scattering
The approach of 't Hooft to the puzzles of black hole evaporation can be
applied to a simpler system with analogous features. The system is
dimensional electrodynamics in a linear dilaton background. Analogues of black
holes, Hawking radiation and evaporation exist in this system. In perturbation
theory there appears to be an information paradox but this gets resolved in the
full quantum theory and there exists an exact -matrix, which is fully
unitary and information conserving. 't Hooft's method gives the leading terms
in a systematic approximation to the exact result.Comment: 18 pages, 3 figures (postscript files available soon on request),
(earlier version got corrupted by mail system
Gravitational Radiation from Travelling Waves on D-Strings
Boundary states that preserve supersymmetry are constructed for fractional
D-strings with travelling waves on a
orbifold. The gravitational radiation emitted between two D-strings with
antiparallel travelling waves is calculated.Comment: improvements and correction
Infinite Lorentz boost along the M-theory circle and non-asymptotically flat solutions in supergravities
Certain non-asymptotically flat but supersymmetric classical solution of the
type IIA supergravity can be interpreted as the infinitely-boosted version of
the D-particle solution along the M-theory circle. By a chain of T-dual
transformations, this analysis also applies to yield non-asymptotically flat
solutions from the asymptotically flat and (non)-extremal solutions with
intersecting D-strings and D five-branes of the type IIB supergravity
compactified on a five-torus. Under S-duality, the non-asymptotically flat
solutions in this context can in particular be used to describe the
(1+1)-dimensional CGHS type black holes via spontaneous compactifications.Comment: 14 pages, Revte
SO(10) Cosmic Strings and Baryon Number Violation
SO(10) cosmic strings formed during the phase transition Spin(10)
SU(5) are studied. Two types of strings ---
one effectively Abelian and one non-Abelian --- are constructed and the string
solutions are calculated numerically. The non-Abelian string can catalyze
baryon number violation via the ``twisting'' of the scalar field which causes
mixing of leptons and quarks in the fermion multiplet. The non-Abelian string
is also found to have the lower energy possibly for the entire range of the
parameters in the theory. Scattering of fermions in the fields of the strings
is analyzed, and the baryon number violation cross section is calculated. The
role of the self-adjoint parameters is discussed and the values are computed.Comment: LaTex (RevTex), 36 pages, 6 figures (available upon request),
MIT-CTP#215
Improved superposition schemes for approximate multi-caloron configurations
Two improved superposition schemes for the construction of approximate
multi-caloron-anticaloron configurations, using exact single (anti)caloron
gauge fields as underlying building blocks, are introduced in this paper. The
first improvement deals with possible monopole-Dirac string interactions
between different calorons with non-trivial holonomy. The second one, based on
the ADHM formalism, improves the (anti-)selfduality in the case of small
caloron separations. It conforms with Shuryak's well-known ratio-ansatz when
applied to instantons. Both superposition techniques provide a higher degree of
(anti-)selfduality than the widely used sum-ansatz, which simply adds the
(anti)caloron vector potentials in an appropriate gauge. Furthermore, the
improved configurations (when discretized onto a lattice) are characterized by
a higher stability when they are exposed to lattice cooling techniques.Comment: New version accepted for publication in Nucl. Phys. B. Text partly
shortened, changes in the introduction, new results added on the comparison
with exact solution
Ramond-Ramond (boundary) states
The description of D-branes as boundary states for type II string theories
(in the covariant formulation) requires particular care in the R-R sector. Also
the vertices for R-R potentials that can couple to D-branes need a careful
handling. As an illustration of this, the example of the D0-D8 system is
reviewed, where a ``microscopic'' description of the interaction via exchange
of R-R potentials becomes possible.Comment: 8 pages, LaTeX, no figures. Talk presented at the 2nd Conference on
Quantum aspects of Gauge Theories, Supersymmetry and Unification, Corfu,
Greece, 21-26 September 199
- âŠ