77,321 research outputs found

### Exact self-duality in a modified Skyrme model

We propose a modification of the Skyrme model that supports a self-dual
sector possessing exact non-trivial finite energy solutions. The action of such
a theory possesses the usual quadratic and quartic terms in field derivatives,
but the couplings of the components of the Maurer-Cartan form of the Skyrme
model is made by a non-constant symmetric matrix, instead of the usual Killing
form of the SU(2) Lie algebra. The introduction of such a matrix make the
self-duality equations conformally invariant in three space dimensions, even
though it may break the global internal symmetries of the original Skyrme
model. For the case where that matrix is proportional to the identity we show
that the theory possesses exact self-dual Skyrmions of unity topological
charges.Comment: 12 pages, no figure

### Global-String and Vortex Superfluids in a Supersymmetric Scenario

The main goal of this work is to investigate the possibility of finding the
supersymmetric version of the U(1)-global string model which behaves as a
vortex-superfluid. To describe the superfluid phase, we introduce a
Lorentz-symmetry breaking background that, in an approach based on
supersymmetry, leads to a discussion on the relation between the violation of
Lorentz symmetry and explicit soft supersymmetry breakings. We also study the
relation between the string configuration and the vortex-superfluid phase. In
the framework we settle down in terms of superspace and superfields, we
actually establish a duality between the vortex degrees of freedom and the
component fields of the Kalb-Ramond superfield. We make also considerations
about the fermionic excitations that may appear in connection with the vortex
formation.Comment: 9 pages. This version presented the relation between Lorentz symmetry
violation by the background and the appearance of terms that explicitly break
SUS

### On the Benjamini--Hochberg method

We investigate the properties of the Benjamini--Hochberg method for multiple
testing and of a variant of Storey's generalization of it, extending and
complementing the asymptotic and exact results available in the literature.
Results are obtained under two different sets of assumptions and include
asymptotic and exact expressions and bounds for the proportion of rejections,
the proportion of incorrect rejections out of all rejections and two other
proportions used to quantify the efficacy of the method.Comment: Published at http://dx.doi.org/10.1214/009053606000000425 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org

### Hopf solitons and area preserving diffeomorphisms of the sphere

We consider a (3+1)-dimensional local field theory defined on the sphere. The
model possesses exact soliton solutions with non trivial Hopf topological
charges, and infinite number of local conserved currents. We show that the
Poisson bracket algebra of the corresponding charges is isomorphic to that of
the area preserving diffeomorphisms of the sphere. We also show that the
conserved currents under consideration are the Noether currents associated to
the invariance of the Lagrangian under that infinite group of diffeomorphisms.
We indicate possible generalizations of the model.Comment: 6 pages, LaTe

### Charge and CP symmetry breaking in two Higgs doublet models

We show that, for the most generic model with two Higgs doublets possessing a
minimum that preserves the $U(1)_{em}$ symmetry, charge breaking (CB) cannot
occur. If CB does not occur, the potential could have two different minima, and
there is in principle no general argument to show which one is the deepest. The
depth of the potential at a stationary point that breaks CB or CP, relative to
the $U(1)_{em}$ preserving minimum, is proportional to the squared mass of the
charged or pseudoscalar Higgs, respectively

### Exact Self-Dual Skyrmions

We introduce a Skyrme type model with the target space being the 3-sphere S^3
and with an action possessing, as usual, quadratic and quartic terms in field
derivatives. The novel character of the model is that the strength of the
couplings of those two terms are allowed to depend upon the space-time
coordinates. The model should therefore be interpreted as an effective theory,
such that those couplings correspond in fact to low energy expectation values
of fields belonging to a more fundamental theory at high energies. The theory
possesses a self-dual sector that saturates the Bogomolny bound leading to an
energy depending linearly on the topological charge. The self-duality equations
are conformally invariant in three space dimensions leading to a toroidal
ansatz and exact self-dual Skyrmion solutions. Those solutions are labelled by
two integers and, despite their toroidal character, the energy density is
spherically symmetric when those integers are equal and oblate or prolate
otherwise.Comment: 14 pages, 3 figures, a reference adde

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