3,304 research outputs found
Initial States: IR and Collinear Divergences
The standard approach to the infra-red problem is to use the Bloch-Nordsieck
trick to handle soft divergences and the Lee-Nauenberg (LN) theorem for
collinear singularities. We show that this is inconsistent in the presence of
massless initial particles. Furthermore, we show that using the LN theorem with
such initial states introduces a non-convergent infinite series of diagrams at
any fixed order in perturbation theory.Comment: 4 pages, talk given at Montpellier meeting QCD'06 (to appear in the
proceedings
Effects of Mass Media and Cultural Drift in a Model for Social Influence
In the context of an extension of Axelrod's model for social influence, we
study the interplay and competition between the cultural drift, represented as
random perturbations, and mass media, introduced by means of an external
homogeneous field. Unlike previous studies [J. C. Gonz\'alez-Avella {\it et
al}, Phys. Rev. E {\bf 72}, 065102(R) (2005)], the mass media coupling proposed
here is capable of affecting the cultural traits of any individual in the
society, including those who do not share any features with the external
message. A noise-driven transition is found: for large noise rates, both the
ordered (culturally polarized) phase and the disordered (culturally fragmented)
phase are observed, while, for lower noise rates, the ordered phase prevails.
In the former case, the external field is found to induce cultural ordering, a
behavior opposite to that reported in previous studies using a different
prescription for the mass media interaction. We compare the predictions of this
model to statistical data measuring the impact of a mass media vasectomy
promotion campaign in Brazil.Comment: 10 pages, 3 figures; minor changes; added references. To appear in
IJMP
Intracultural diversity in a model of social dynamics
We study the consequences of introducing individual nonconformity in social
interactions, based on Axelrod's model for the dissemination of culture. A
constraint on the number of situations in which interaction may take place is
introduced in order to lift the unavoidable ho mogeneity present in the final
configurations arising in Axelrod's related models. The inclusion of this
constraint leads to the occurrence of complex patterns of intracultural
diversity whose statistical properties and spatial distribution are
characterized by means of the concepts of cultural affinity and cultural cli
ne. It is found that the relevant quantity that determines the properties of
intracultural diversity is given by the fraction of cultural features that
characterizes the cultural nonconformity of individuals.Comment: 7 pages, 2 tables, 6 figure
Effects of mass media on opinion spreading in the Sznajd sociophysics model
In this work we consider the influence of mass media in the dynamics of the
two-dimensional Sznajd model. This influence acts as an external field, and it
is introduced in the model by means of a probability of the agents to
follow the media opinion. We performed Monte Carlo simulations on square
lattices with different sizes, and our numerical results suggest a change on
the critical behavior of the model, with the absence of the usual phase
transition for . Another effect of the probability is to
decrease the average relaxation times , that are log-normally
distributed, as in the standard model. In addition, the values depend on
the lattice size in a power-law form, , where the
power-law exponent depends on the probability .Comment: 11 pages, 8 figures, to appear in Physica
Topological Symmetry of forms, N=1 Supersymmetry and S-duality on Special Manifolds
We study the quantization of a holomorphic two-form coupled to a Yang-Mills
field on special manifolds in various dimensions, and we show that it yields
twisted supersymmetric theories. The construction determines ATQFT's (Almost
Topological Quantum Field Theories), that is, theories with observables that
are invariant under changes of metrics belonging to restricted classes. For
Kahler manifolds in four dimensions, our topological model is related to N=1
Super Yang-Mills theory. Extended supersymmetries are recovered by considering
the coupling with chiral multiplets. We also analyse Calabi-Yau manifolds in
six and eight dimensions, and seven dimensional G_2 manifolds of the kind
recently discussed by Hitchin. We argue that the two-form field could play an
interesting role for the study of the conjectured S-duality in topological
string. We finally show that in the case of real forms in six dimensions the
partition function of our topological model is related to the square of that of
the holomorphic Chern-Simons theory, and we discuss the uplift to seven
dimensions and its relation with the recent proposals for the topological
M-theory.Comment: v2: NEW results added in the last Section on the relation with
holomorphic Chern Simons and with the topological M theory. References added.
PAR-LPTHE P04-32, SISSA-94/2004/FM, 30 pages, LaTeX fil
Optimal Self-Organization
We present computational and analytical results indicating that systems of
driven entities with repulsive interactions tend to reach an optimal state
associated with minimal interaction and minimal dissipation. Using concepts
from non-equilibrium thermodynamics and game theoretical ideas, we generalize
this finding to an even wider class of self-organizing systems which have the
ability to reach a state of maximal overall ``success''. This principle is
expected to be relevant for driven systems in physics like sheared granular
media, but it is also applicable to biological, social, and economic systems,
for which only a limited number of quantitative principles are available yet.Comment: This is the detailled revised version of a preprint on
``Self-Organised Optimality'' (cond-mat/9903319). For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.html and
http://angel.elte.hu/~vicsek
First Results From The Taiwanese-American Occultation Survey (TAOS)
Results from the first two years of data from the Taiwanese-American
Occultation Survey (TAOS) are presented. Stars have been monitored
photometrically at 4 Hz or 5 Hz to search for occultations by small (~3 km)
Kuiper Belt Objects (KBOs). No statistically significant events were found,
allowing us to present an upper bound to the size distribution of KBOs with
diameters 0.5 km < D < 28 km.Comment: 5 pages, 5 figure, accepted in Ap
The TAOS Project: Statistical Analysis of Multi-Telescope Time Series Data
The Taiwanese-American Occultation Survey (TAOS) monitors fields of up to
~1000 stars at 5 Hz simultaneously with four small telescopes to detect
occultation events from small (~1 km) Kuiper Belt Objects (KBOs). The survey
presents a number of challenges, in particular the fact that the occultation
events we are searching for are extremely rare and are typically manifested as
slight flux drops for only one or two consecutive time series measurements. We
have developed a statistical analysis technique to search the multi-telescope
data set for simultaneous flux drops which provides a robust false positive
rejection and calculation of event significance. In this paper, we describe in
detail this statistical technique and its application to the TAOS data set.Comment: 15 pages, 14 figures. Submitted to PAS
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