8,549 research outputs found
Isolated vacua in supersymmetric Yang-Mills theories
An explicit proof of the existence of nontrivial vacua in the pure
supersymmetric Yang-Mills theories with higher orthogonal SO(N), N>=7 or the
G_2 gauge group defined on a 3-torus with periodic boundary conditions is
given. Extra vacuum states are separated by an energy barrier from the
perturbative vacuum A_i=0 and its gauge copies.Comment: 8 pages, no figures, late
Machine learning techniques to select Be star candidates. An application in the OGLE-IV Gaia south ecliptic pole field
Statistical pattern recognition methods have provided competitive solutions
for variable star classification at a relatively low computational cost. In
order to perform supervised classification, a set of features is proposed and
used to train an automatic classification system. Quantities related to the
magnitude density of the light curves and their Fourier coefficients have been
chosen as features in previous studies. However, some of these features are not
robust to the presence of outliers and the calculation of Fourier coefficients
is computationally expensive for large data sets. We propose and evaluate the
performance of a new robust set of features using supervised classifiers in
order to look for new Be star candidates in the OGLE-IV Gaia south ecliptic
pole field. We calculated the proposed set of features on six types of variable
stars and on a set of Be star candidates reported in the literature. We
evaluated the performance of these features using classification trees and
random forests along with K-nearest neighbours, support vector machines, and
gradient boosted trees methods. We tuned the classifiers with a 10-fold
cross-validation and grid search. We validated the performance of the best
classifier on a set of OGLE-IV light curves and applied this to find new Be
star candidates. The random forest classifier outperformed the others. By using
the random forest classifier and colour criteria we found 50 Be star candidates
in the direction of the Gaia south ecliptic pole field, four of which have
infrared colours consistent with Herbig Ae/Be stars. Supervised methods are
very useful in order to obtain preliminary samples of variable stars extracted
from large databases. As usual, the stars classified as Be stars candidates
must be checked for the colours and spectroscopic characteristics expected for
them
Remarks on propagating waves in non-linear vacuum electrodynamics
Using the quadratic expansion in the photon fields of Euler-Heisemberg (EH)
non-linear electrodynamics (NLED) Lagrangian model we study relevant vacuum
properties in a scenario involving the propagation of a photon probe in the
presence of a background constant and static magnetic field, . We compute
the gauge invariant, symmetric and conserved energy-momentum tensor (EMT) and
the angular momentum tensor (AMT) for arbitrary magnetic field strength using
the Hilbert method under the soft-photon approximation. We discuss how the
presence of magneto-electric terms in the EH Lagrangian is a source of
anisotropy and induce the non-zero trace in the EMT, the latter being connected
to the non-conformal anomaly of the non-linear Lagrangian and with the
non-conservation of the light cone in Minkowski space-time inducing
birefringence. From the EMT we analyze some quantities of interest such as the
energy density, pressures, Poynting vector, and angular momentum vector and we
compare them with those obtained from the Noether method. The magnetized vacuum
properties are also studied showing that a photon-effective magnetic moment can
be defined for different polarization modes. The calculations are done in terms
of derivatives of the two scalar invariants of electrodynamics hence, extension
to other NLED Lagrangian is straightforward. We discuss further physical
implications and experimental strategies to test magnetization, photon pressure
and efective magnetic moment.Comment: 24 pages, 3 figure
Neutrino mean free paths in spin-polarized neutron Fermi liquids
Neutrino mean free paths in magnetized neutron matter are calculated using
the Hartree-Fock approximation with effective Skyrme and Gogny forces in the
framework of the Landau Fermi Liquid Theory. It is shown that describing
nuclear interaction with Skyrme forces and for magnetic field strengths
, the neutrino mean free paths stay almost unchanged
at intermediate densities but they largely increase at high densities when they
are compared to the field-free case results. However the description with Gogny
forces differs from the previous and mean free paths stay almonst unchanged or
decrease at densities . This different behaviour can be explained
due to the combination of common mild variation of the Landau parameters with
both types of forces and the values of the nucleon effective mass and induced
magnetization of matter under presence of a strong magnetic field as described
with the two parametrizations of the nuclear interaction.Comment: 9 pages, 3 figure
Probing for Instanton Quarks with epsilon-Cooling
We use epsilon-cooling, adjusting at will the order a^2 corrections to the
lattice action, to study the parameter space of instantons in the background of
non-trivial holonomy and to determine the presence and nature of constituents
with fractional topological charge at finite and zero temperature for SU(2). As
an additional tool, zero temperature configurations were generated from those
at finite temperature with well-separated constituents. This is achieved by
"adiabatically" adjusting the anisotropic coupling used to implement finite
temperature on a symmetric lattice. The action and topological charge density,
as well as the Polyakov loop and chiral zero-modes are used to analyse these
configurations. We also show how cooling histories themselves can reveal the
presence of constituents with fractional topological charge. We comment on the
interpretation of recent fermion zero-mode studies for thermalized ensembles at
small temperatures.Comment: 26 pages, 14 figures in 33 part
IntroducciĂłn de las tĂ©cnicas de modelizaciĂłn para el estudio de la fĂsica y de las matemĂĄticas en los primeros cursos de las carreras tĂ©cnicas
In this article we present a program of interdisciplinary practices for a first engineering course. We followed this program during the course 1996-1997, and we give several examples of the kind of exercises that we used. We also present some remarks and conclusions that we have achieved in our experience. Our purpose is to introduce a teaching strategy for Mathematics and Physics at the University level
IntroducciĂłn de las tĂ©cnicas de modelizaciĂłn para el estudio de la fĂsica y de las matemĂĄticas en los primeros cursos de las carreras tĂ©cnicas
In this article we present a program of interdisciplinary practices for a first engineering course. We followed this program during the course 1996-1997, and we give several examples of the kind of exercises that we used. We also present some remarks and conclusions that we have achieved in our experience. Our purpose is to introduce a teaching strategy for Mathematics and Physics at the University level
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