12,092 research outputs found
Unified description of seagull cancellations and infrared finiteness of gluon propagators
We present a generalized theoretical framework for dealing with the important
issue of dynamical mass generation in Yang-Mills theories, and, in particular,
with the infrared finiteness of the gluon propagators, observed in a multitude
of recent lattice simulations. Our analysis is manifestly gauge-invariant, in
the sense that it preserves the transversality of the gluon self-energy, and
gauge-independent, given that the conclusions do not depend on the choice of
the gauge-fixing parameter within the linear covariant gauges. The central
construction relies crucially on the subtle interplay between the Abelian Ward
identities satisfied by the nonperturbative vertices and a special integral
identity that enforces a vast number of 'seagull cancellations' among the one-
and two-loop dressed diagrams of the gluon Schwinger-Dyson equation. The key
result of these considerations is that the gluon propagator remains rigorously
massless, provided that the vertices do not contain (dynamical) massless poles.
When such poles are incorporated into the vertices, under the pivotal
requirement of respecting the gauge symmetry of the theory, the terms
comprising the Ward identities conspire in such a way as to still enforce the
total annihilation of all quadratic divergences, inducing, at the same time,
residual contributions that account for the saturation of gluon propagators in
the deep infrared.Comment: 40 pages, 7 figures; v2: typos corrected, version matching the
published on
Evidence of ghost suppression in gluon mass dynamics
In this work we study the impact that the ghost sector of pure Yang-Mills
theories may have on the generation of a dynamical gauge boson mass, which
hinges on the appearance of massless poles in the fundamental vertices of the
theory, and the subsequent realization of the well-known Schwinger mechanism.
The process responsible for the formation of such structures is itself
dynamical in nature, and is governed by a set of Bethe-Salpeter type of
integral equations. While in previous studies the presence of massless poles
was assumed to be exclusively associated with the background-gauge three-gluon
vertex, in the present analysis we allow them to appear also in the
corresponding ghost-gluon vertex. The full analysis of the resulting
Bethe-Salpeter system reveals that the contribution of the poles associated
with the ghost-gluon vertex are particularly suppressed, their sole discernible
effect being a slight modification in the running of the gluon mass, for
momenta larger than a few GeV. In addition, we examine the behavior of the
(background-gauge) ghost-gluon vertex in the limit of vanishing ghost momentum,
and derive the corresponding version of Taylor's theorem. These considerations,
together with a suitable Ansatz, permit us the full reconstruction of the pole
sector of the two vertices involved.Comment: 30 pages, 10 figure
Going Further with Point Pair Features
Point Pair Features is a widely used method to detect 3D objects in point
clouds, however they are prone to fail in presence of sensor noise and
background clutter. We introduce novel sampling and voting schemes that
significantly reduces the influence of clutter and sensor noise. Our
experiments show that with our improvements, PPFs become competitive against
state-of-the-art methods as it outperforms them on several objects from
challenging benchmarks, at a low computational cost.Comment: Corrected post-print of manuscript accepted to the European
Conference on Computer Vision (ECCV) 2016;
https://link.springer.com/chapter/10.1007/978-3-319-46487-9_5
Transformations of Heun's equation and its integral relations
We find transformations of variables which preserve the form of the equation
for the kernels of integral relations among solutions of the Heun equation.
These transformations lead to new kernels for the Heun equation, given by
single hypergeometric functions (Lambe-Ward-type kernels) and by products of
two hypergeometric functions (Erd\'elyi-type). Such kernels, by a limiting
process, also afford new kernels for the confluent Heun equation.Comment: This version was published in J. Phys. A: Math. Theor. 44 (2011)
07520
Species-people correlations and the need to account for survey effort in biodiversity analyses
Aim Positive regional correlations between biodiversity and human population
have been detected for several taxonomic groups and geographical regions.
Such correlations could have important conservation implications and have
been mainly attributed to ecological factors, with little testing for an artefactual
explanation: more populated regions may show higher biodiversity because they
are more thoroughly surveyed. We tested the hypothesis that the correlation
between people and herptile diversity in Europe is influenced by survey effor
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