66,009 research outputs found
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
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
Board Structure and Price Informativeness
We develop and test the hypothesis that private information incorporated into stock prices affects the structure of corporate boards. Stock price informativeness may be a complement to board monitoring, because the information revealed by prices can be used by directors to monitor management. But price informativeness may also be a substitute for board monitoring, because more informative prices can trigger external monitoring mechanisms, such as takeovers. We find robust evidence for the substitution effect: Stock price informativeness, as measured by the probability of informed trading (PIN), is negatively related to board independence. Consistent with the model's predictions, this relationship is particularly strong for firms exposed to external governance mechanisms and internal governance mechanisms, and firms for which firm-specific knowledge is relatively unimportant. We address endogeneity concerns in a number of different ways and conclude that our results are unlikely to be driven by omitted variables or reverse causality. The results are also robust to using different measures of price informativeness and different proxies for board monitoringCorporate boards, Independent directors, Price informativeness
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