138 research outputs found
Analogies between self-duality and stealth matter source
We consider the problem of a self-interacting scalar field nonminimally
coupled to the three-dimensional BTZ metric such that its energy-momentum
tensor evaluated on the BTZ metric vanishes. We prove that this system is
equivalent to a self-dual system composed by a set of two first-order
equations. The self-dual point is achieved by fixing one of the coupling
constant of the potential in terms of the nonminimal coupling parameter. At the
self-dual point and up to some boundary terms, the matter action evaluated on
the BTZ metric is bounded below and above. These two bounds are saturated
simultaneously yielding to a vanishing action for configurations satisfying the
set of self-dual first-order equations.Comment: 6 pages. To be published in Jour. Phys.
Are stealth scalar fields stable?
Non-gravitating (stealth) scalar fields associated with Minkowski space in
scalar-tensor gravity are examined. Analytical solutions for both non-minimally
coupled scalar field theory and for Brans-Dicke gravity are studied and their
stability with respect to tensor perturbations is assessed using a covariant
and gauge-invariant formalism developed for alternative gravity. For
Brans-Dicke solutions, the stability with respect to homogeneous perturbations
is also studied. There are regions of parameter space corresponding to
stability and other regions corresponding to instability.Comment: 10 pages, 1 table, no figures, to appear in Phys. Rev,
Multi-Lagrangians for Integrable Systems
We propose a general scheme to construct multiple Lagrangians for completely
integrable non-linear evolution equations that admit multi- Hamiltonian
structure. The recursion operator plays a fundamental role in this
construction. We use a conserved quantity higher/lower than the Hamiltonian in
the potential part of the new Lagrangian and determine the corresponding
kinetic terms by generating the appropriate momentum map. This leads to some
remarkable new developments. We show that nonlinear evolutionary systems that
admit -fold first order local Hamiltonian structure can be cast into
variational form with Lagrangians which will be local functionals of
Clebsch potentials. This number increases to when the Miura
transformation is invertible. Furthermore we construct a new Lagrangian for
polytropic gas dynamics in dimensions which is a {\it local} functional
of the physical field variables, namely density and velocity, thus dispensing
with the necessity of introducing Clebsch potentials entirely. This is a
consequence of bi-Hamiltonian structure with a compatible pair of first and
third order Hamiltonian operators derived from Sheftel's recursion operator.Comment: typos corrected and a reference adde
BRAF V600E mutations in urine and plasma cell-free DNA from patients with Erdheim-Chester disease.
Erdheim-Chester disease (ECD) is a rare histiocytosis with a high prevalence of BRAF V600E mutation (>50% of patients). Patients with BRAF-mutant ECD can respond to BRAF inhibitors. Unfortunately, the lack of adequate archival tissue often precludes BRAF testing. We hypothesized that cell-free DNA (cfDNA) from plasma or urine can offer an alternative source of biologic material for testing. We tested for BRAF V600E mutation in cfDNA from the plasma and urine of 6 ECD patients. In patients with available archival tissue, the result of BRAF mutation analysis was concordant with plasma and urine cfDNA results in all 3 patients (100% agreement, kappa 1.00). In all 6 patients, BRAF mutation analysis of plasma and urine cfDNA was concordant in 5 of 6 patients (83% agreement, kappa 0.67). Testing for BRAF V600E mutation in plasma and urine cfDNA should be further investigated as an alternative to archival tissue mutation analysis
Holographic Superconductors with Power-Maxwell field
With the Sturm-Liouville analytical and numerical methods, we investigate the
behaviors of the holographic superconductors by introducing a complex charged
scalar field coupled with a Power-Maxwell field in the background of
-dimensional Schwarzschild AdS black hole. We note that the Power-Maxwell
field takes the special asymptotical solution near boundary which is different
from all known cases. We find that the larger power parameter for the
Power-Maxwell field makes it harder for the scalar hair to be condensated. We
also find that, for different , the critical exponent of the system is still
1/2, which seems to be an universal property for various nonlinear
electrodynamics if the scalar field takes the form of this paper.Comment: 14 pages, 1 figure, and 2 table
Transgression forms and extensions of Chern-Simons gauge theories
A gauge invariant action principle, based on the idea of transgression forms,
is proposed. The action extends the Chern-Simons form by the addition of a
boundary term that makes the action gauge invariant (and not just
quasi-invariant). Interpreting the spacetime manifold as cobordant to another
one, the duplication of gauge fields in spacetime is avoided. The advantages of
this approach are particularly noticeable for the gravitation theory described
by a Chern-Simons lagrangian for the AdS group, in which case the action is
regularized and finite for black hole geometries in diverse situations. Black
hole thermodynamics is correctly reproduced using either a background field
approach or a background-independent setting, even in cases with asymptotically
nontrivial topologies. It is shown that the energy found from the thermodynamic
analysis agrees with the surface integral obtained by direct application of
Noether's theorem.Comment: 28 pages, no figures. Minor changes in the introduction, final
comments and reference
Low-temperature properties of monoalcohol glasses and crystals
We review and jointly discuss both earlier and recent experiments conducted by us on simple aliphatic glass-forming monoalcohols at low temperatures, including specific heat, thermal conductivity, Brillouin scattering and x-ray diffraction experiments. The family of simple monoalcohols constitutes an interesting model system to explore different relevant issues concerning molecular glass-forming liquids, low-temperature universal proper-ties of glasses, and even the glass transition phenomenon itself. More specifically, we discuss the role played by the molecular aspect ratio in vitrification/crystallization kinetics, the reported appearance of particular cases of polymorphism (in ethanol) and polyamorphism (in butanol), and especially the influence of position isomerism and the location of the hydrogen bond on the lattice dynamics and hence on the low-temperature universal prop-erties of glasses
Modeling the bremsstrahlung emission from converters
The bremsstrahlung angular and energy theoretical distributions delivered from W and UCx thick converters are reported. This study is focussed on initial kinetic energies of the electron beam included in the range 30-60 MeV, suitable for the production of large radiative yields able to induce the U fission. These results offer the possibility to evaluate the required shielding for a neutron rich nuclei source
The non-linear Schr\"odinger equation and the conformal properties of non-relativistic space-time
The cubic non-linear Schr\"odinger equation where the coefficient of the
nonlinear term is a function only passes the Painlev\'e test of Weiss,
Tabor, and Carnevale only for , where and are constants.
This is explained by transforming the time-dependent system into the
constant-coefficient NLS by means of a time-dependent non-linear
transformation, related to the conformal properties of non-relativistic
space-time. A similar argument explains the integrability of the NLS in a
uniform force field or in an oscillator background.Comment: Thoroughly revised version, in the light of new interest in
non-relativistic conformal tranformation, with a new reference list. 8 pages,
LaTex, no figures. To be published in Int. J. Theor. Phy
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