58,787 research outputs found
The mechanisms of temporal inference
The properties of a temporal language are determined by its constituent elements: the temporal objects which it can represent, the attributes of those objects, the relationships between them, the axioms which define the default relationships, and the rules which define the statements that can be formulated. The methods of inference which can be applied to a temporal language are derived in part from a small number of axioms which define the meaning of equality and order and how those relationships can be propagated. More complex inferences involve detailed analysis of the stated relationships. Perhaps the most challenging area of temporal inference is reasoning over disjunctive temporal constraints. Simple forms of disjunction do not sufficiently increase the expressive power of a language while unrestricted use of disjunction makes the analysis NP-hard. In many cases a set of disjunctive constraints can be converted to disjunctive normal form and familiar methods of inference can be applied to the conjunctive sub-expressions. This process itself is NP-hard but it is made more tractable by careful expansion of a tree-structured search space
An Analysis of Four-quark Energies in SU(2) Lattice Monte Carlo using the Flux-tube Symmetry:
Energies of four-quark systems calculated by the static quenched SU(2)
lattice Monte Carlo method are analyzed in bases for square,
rectangle, tilted rectangle, linear and quadrilateral geometry configurations
and in bases for a non-planar geometry configuration. For small
interquark distances, a lattice effect is taken into account by considering
perimeter dependent terms which are characterized by the cubic symmetry. It is
then found that a parameter - that can be identified as a gluon field
overlap factor - is rather well described by the form , where and are the area and
perimeter mainly defined by the positions of the four quarks, is the
string constant in the 2-quark potentials and are constants.Comment: (19 pages of Latex - 1 page of figures not included - sent on
request). Preprint HU-TFT-94-2
Mass corrections in string theory and lattice field theory
Kaluza-Klein compactifications of higher dimensional Yang-Mills theories
contain a number of four dimensional scalars corresponding to the internal
components of the gauge field. While at tree-level the scalar zero modes are
massless, it is well known that quantum corrections make them massive. We
compute these radiative corrections at 1-loop in an effective field theory
framework, using the background field method and proper Schwinger-time
regularization. In order to clarify the proper treatment of the sum over
KK--modes in the effective field theory approach, we consider the same problem
in two different UV completions of Yang-Mills: string theory and lattice field
theory. In both cases, when the compactification radius is much bigger than
the scale of the UV completion (), we recover a mass
renormalization that is independent of the UV scale and agrees with the one
derived in the effective field theory approach. These results support the idea
that the value of the mass corrections is, in this regime, universal for any UV
completion that respects locality and gauge invariance. The string analysis
suggests that this property holds also at higher loops. The lattice analysis
suggests that the mass of the adjoint scalars appearing in
Super Yang-Mills is highly suppressed due to an interplay between the
higher-dimensional gauge invariance and the degeneracy of bosonic and fermionic
degrees of freedom.Comment: 27 page
Maximal supersymmetry and exceptional groups
The article is a tribute to my old mentor, collaborator and friend Murray
Gell-Mann. In it I describe work by Pierre Ramond, Sung-Soo Kim and myself
where we describe the N = 8 Supergravity in the light-cone formalism. We show
how the Cremmer-Julia E7(7) non-linear symmetry is implemented and how the full
supermultiplet is a representation of the E7(7) symmetry. I also show how the
E7(7) symmetry is a key to understand the higher order couplings in the theory
and is very useful when we discuss possible counterterms for this theory.Comment: Proceedings of Conference in Honour of Murray Gell-Mann's 80th
Birthda
Supersymmetry Constraints on Type IIB Supergravity
Supersymmetry is used to derive conditions on higher derivative terms in the
effective action of type IIB supergravity. Using these conditions, we are able
to prove earlier conjectures that certain modular invariant interactions of
order alpha' **3 relative to the Einstein-Hilbert term are proportional to
eigenfunctions of the Laplace operator on the fundamental domain of SL(2,Z). We
also discuss how these arguments generalize to terms of higher order in alpha',
as well as to compactifications of supergravity.Comment: 31 pages, harvmac (b); minor correction
Perturbative Relations between Gravity and Gauge Theory
We review the relations that have been found between multi-loop scattering
amplitudes in gauge theory and gravity, and their implications for ultraviolet
divergences in supergravity.Comment: LaTex with package axodraw.sty. 10 pages. Presented by L.D. at
Strings 99. Cosmetic changes onl
Newtonian limit of String-Dilaton Gravity
We study the weak-field limit of string-dilaton gravity and derive
corrections to the Newtonian potential which strength directly depends on the
self interaction potential and the nonminimal coupling of the dilaton scalar
field. We discuss also possible astrophysical applications of the results, in
particular the flat rotation curves of spiral galaxies.Comment: 11 pages, LATEX file, to appear in IJMP
A Study of the Production of Neutrons for Boron Neutron Capture Therapy using a Proton Accelerator
Boron Neutron Capture Therapy (BNCT) is a binary cancer therapy particularly well-suited to treating aggressive tumours that exhibit a high degree of infiltration of the surrounding healthy tissue. Such tumours, for example of the brain and lung, provide some of the most challenging problems in oncology. The first element of the therapy is boron-10 which is preferentially introduced into the cancerous cells using a carrier compound. Boron-10 has a very high capture cross-section with the other element of the therapy, thermal neutrons, resulting in the production of a lithium nucleus and an alpha particle which destroy the cell they are created in. However, a large flux of neutrons is required and until recently the only source used was a nuclear reactor. In Birmingham, studies of an existing BNCT facility using a 2.8 MeV proton beam and a solid lithium target have found a way to increase the beam power to a sufficient level to allow clinical trials, while maintaining the target solid. In this paper, we will introduce BNCT, describe the work in Birmingham and compare with other accelerator-driven BNCT projects around the World
Tree Amplitudes and Two-loop Counterterms in D=11 Supergravity
We compute the tree level 4-particle bosonic scattering amplitudes in D=11
supergravity. By construction, they are part of a linearized supersymmetry-,
coordinate- and 3-form gauge-invariant. While this on-shell invariant is
nonlocal, suitable SUSY-preserving differentiations turn it into a local one
with correct dimension to provide a natural lowest (two-loop) order counterterm
candidate. Its existence shows explicitly that no symmetries protect this
ultimate supergravity from the nonrenormalizability of its lower-dimensional
counterparts.Comment: 14 page
- …