180,555 research outputs found
A decidable subclass of finitary programs
Answer set programming - the most popular problem solving paradigm based on
logic programs - has been recently extended to support uninterpreted function
symbols. All of these approaches have some limitation. In this paper we propose
a class of programs called FP2 that enjoys a different trade-off between
expressiveness and complexity. FP2 programs enjoy the following unique
combination of properties: (i) the ability of expressing predicates with
infinite extensions; (ii) full support for predicates with arbitrary arity;
(iii) decidability of FP2 membership checking; (iv) decidability of skeptical
and credulous stable model reasoning for call-safe queries. Odd cycles are
supported by composing FP2 programs with argument restricted programs
Nondecoupling of Maximal Supergravity from the Superstring
We consider the conditions necessary for obtaining perturbative maximal supergravity in d dimensions as a decoupling limit of type II superstring theory compactified on a (10-d) torus. For dimensions d=2 and d=3, it is possible to define a limit in which the only finite-mass states are the 256 massless states of maximal supergravity. However, in dimensions d>=4, there are infinite towers of additional massless and finite-mass states. These correspond to Kaluza-Klein charges, wound strings, Kaluza-Klein monopoles, or branes wrapping around cycles of the toroidal extra dimensions. We conclude that perturbative supergravity cannot be decoupled from string theory in dimensions >=4. In particular, we conjecture that pure [script N]=8 supergravity in four dimensions is in the Swampland
D-effects in Toroidally Compactified Type II String Theory
We review exact results obtained for R^4 couplings in maximally
supersymmetric type II string theories. These couplings offer a privileged
scene to understand the rules of semiclassical calculus in string theory. Upon
expansion in weak string coupling, they reveal an infinite sum of
non-perturbative e^{-1/g} effects that can be imputed to euclidean D-branes
wrapped on cycles of the compactification manifolds. They also shed light on
the relation between Dp-branes and D-(p-2)branes, D-strings and (p,q) strings,
instanton sums and soliton loops. The latter interpretation takes over in D<=6
in order to account for the e^{-1/g^2} effects, still mysterious from the point
of view of instanton calculus.
[To appear in the proceedings of the conference "Quantum Aspects of Gauge
Theories, Supersymmetry and Unification" held at Neuchatel University,
Switzerland, 18-23 September 1997.]Comment: 1+6 pages, neuchatel.sty include
EFT strings and emergence
We revisit the Emergence Proposal in 4d vector multiplet sectors
that arise from type II string Calabi--Yau compactifications, with emphasis on
the role of axionic fundamental strings, or EFT strings. We focus on
large-volume type IIA compactifications, where EFT strings arise from
NS5-branes wrapping internal four-cycles, and consider a set of
infinite-distance moduli-space limits that can be classified in terms of a
scaling weight . It has been shown before how one-loop threshold
effects of an infinite tower of BPS particles made up of D2/D0-branes generate
the asymptotic behaviour of the gauge kinetic functions along limits with
. We extend this result to limits, by taking into account D2-brane
multi-wrapping numbers. In limits the leading tower involves EFT string
oscillations, and one can reproduce the behaviour of both weakly and
strongly-coupled 's independently on whether the EFT string is critical
or not, by assuming that charged modes dominate the light spectrum.Comment: 33 pages + appendi
Finite-size and correlation-induced effects in Mean-field Dynamics
The brain's activity is characterized by the interaction of a very large
number of neurons that are strongly affected by noise. However, signals often
arise at macroscopic scales integrating the effect of many neurons into a
reliable pattern of activity. In order to study such large neuronal assemblies,
one is often led to derive mean-field limits summarizing the effect of the
interaction of a large number of neurons into an effective signal. Classical
mean-field approaches consider the evolution of a deterministic variable, the
mean activity, thus neglecting the stochastic nature of neural behavior. In
this article, we build upon two recent approaches that include correlations and
higher order moments in mean-field equations, and study how these stochastic
effects influence the solutions of the mean-field equations, both in the limit
of an infinite number of neurons and for large yet finite networks. We
introduce a new model, the infinite model, which arises from both equations by
a rescaling of the variables and, which is invertible for finite-size networks,
and hence, provides equivalent equations to those previously derived models.
The study of this model allows us to understand qualitative behavior of such
large-scale networks. We show that, though the solutions of the deterministic
mean-field equation constitute uncorrelated solutions of the new mean-field
equations, the stability properties of limit cycles are modified by the
presence of correlations, and additional non-trivial behaviors including
periodic orbits appear when there were none in the mean field. The origin of
all these behaviors is then explored in finite-size networks where interesting
mesoscopic scale effects appear. This study leads us to show that the
infinite-size system appears as a singular limit of the network equations, and
for any finite network, the system will differ from the infinite system
Distribution and density of the partition function zeros for the diamond-decorated Ising model
Exact renormalization map of temperature between two successive decorated
lattices is given, and the distribution of the partition function zeros in the
complex temperature plane is obtained for any decoration-level. The rule
governing the variation of the distribution pattern as the decoration-level
changes is given. The densities of the zeros for the first two
decoration-levels are calculated explicitly, and the qualitative features about
the densities of higher decoration-levels are given by conjecture. The Julia
set associated with the renormalization map is contained in the distribution of
the zeros in the limit of infinite decoration level, and the formation of the
Julia set in the course of increasing the decoration-level is given in terms of
the variations of the zero density.Comment: 8 pages,8figure
Wrapped Branes and Supersymmetry
Configurations of two or more branes wrapping different homology cycles of
space-time are considered and the amount of supersymmetry preserved is
analysed, generalising the analysis of multiple branes in flat space. For K3
compactifications, these give the Type II or M theory origin of certain
supersymmetric four-dimensional heterotic string solutions that fit into
spin-3/2 multiplets and which become massless at certain points in moduli
space. The interpretation of these BPS states and the possibility of
supersymmetry enhancement are discussed.Comment: 18 pages, Latex with Revtex, minor corrections and references added,
version to appear in Nuclear Physics
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