36,828 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
Evaluating and improving the cluster variation method entropy functional for Ising alloys
The success of the "Cluster Variation Method" (CVM) in reproducing quite
accurately the free energies of Monte Carlo (MC) calculations on Ising models
is explained in terms of identifying a cancellation of errors: We show that the
CVM produces correlation functions that are too close to zero, which leads to
an overestimation of the exact energy, E, and at the same time, to an
underestimation of -TS, so the free energy F=E-TS is more accurate than either
of its parts. This insight explains a problem with "hybrid methods" using MC
correlation functions in the CVM entropy expression: They give exact energies E
and do not give significantly improved -TS relative to CVM, so they do not
benefit from the above noted cancellation of errors. Additionally, "hybrid
methods" suffer from the difficulty of adequately accounting for both ordered
and disordered phases in a consistent way. A different technique, the "Entropic
Monte Carlo" (EMC), is shown here to provide a means for critically evaluating
the CVM entropy. Inspired by EMC results, we find a universal and simple
correction to the CVM entropy which produces individual components of the free
energy with MC accuracy, but is computationally much less expensive than either
MC thermodynamic integration or EMC.Comment: 7 pages, ReVTeX galley format, 4 eps figures embedded using epsf, to
be published in J. Chem. Phy
Dark Matter, Modified Gravity and the Mass of the Neutrino
It has been suggested that Einstein's theory of General Relativity can be
modified to accomodate mismatches between the gravitational field and luminous
matter on a wide range of scales. Covariant theories of modified gravity
generically predict the existence of extra degrees of freedom which may be
interpreted as dark matter. We study a subclass of these theories where the
overall energy density in these extra degrees of freedom is subdominant
relative to the baryon density and show that they favour the presence of
massive neutrinos. For some specific cases (such as a flat Universes with a
cosmological constant) one finds a conservative lower bound on the neutrinos
mass of eV.Comment: 5 pages, 2 figures, 2 tables, submitted to Phys. Rev.
Exploring degeneracies in modified gravity with weak lensing
By considering linear-order departures from general relativity, we compute a
novel expression for the weak lensing convergence power spectrum under
alternative theories of gravity. This comprises an integral over a 'kernel' of
general relativistic quantities multiplied by a theory-dependent 'source' term.
The clear separation between theory-independent and -dependent terms allows for
an explicit understanding of each physical effect introduced by altering the
theory of gravity. We take advantage of this to explore the degeneracies
between gravitational parameters in weak lensing observations.Comment: 17 pages, 7 figures. v2: Minor changes to match version accepted by
PR
A remark on the asymptotic form of BPS multi-dyon solutions and their conserved charges
We evaluate the gauge invariant, dynamically conserved charges, recently
obtained from the integral form of the Yang-Mills equations, for the BPS
multi-dyon solutions of a Yang-Mills-Higgs theory associated to any compact
semi-simple gauge group G. Those charges are shown to correspond to the
eigenvalues of the next-to-leading term of the asymptotic form of the Higgs
field at spatial infinity, and so coinciding with the usual topological charges
of those solutions. Such results show that many of the topological charges
considered in the literature are in fact dynamical charges, which conservation
follows from the global properties of classical Yang-Mills theories encoded
into their integral dynamical equations. The conservation of those charges can
not be obtained from the differential form of Yang-Mills equations.Comment: Version to be published in JHEP, Journal of High Energy Physics (19
pages, no figures, some examples added
Discrete and continuous symmetries in multi-Higgs-doublet models
We consider the Higgs sector of multi-Higgs-doublet models in the presence of
simple symmetries relating the various fields. We construct basis invariant
observables which may in principle be used to detect these symmetries for any
number of doublets. A categorization of the symmetries into classes is
required, which we perform in detail for the case of two and three Higgs
doublets.Comment: 13 pages, RevTex, references adde
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