1,695 research outputs found
Escape of black holes from the brane
TeV-scale gravity theories allow the possibility of producing small black
holes at energies that soon will be explored at the LHC or at the Auger
observatory. One of the expected signatures is the detection of Hawking
radiation, that might eventually terminate if the black hole, once perturbed,
leaves the brane. Here, we study how the `black hole plus brane' system evolves
once the black hole is given an initial velocity, that mimics, for instance,
the recoil due to the emission of a graviton. The results of our dynamical
analysis show that the brane bends around the black hole, suggesting that the
black hole eventually escapes into the extra dimensions once two portions of
the brane come in contact and reconnect. This gives a dynamical mechanism for
the creation of baby branes.Comment: 4 pages, 6 figure
Branes and Black holes in Collision
We study the collision of a brane with a black hole. Our aim is to explore
the topology changing process of perforation of a brane. The brane is described
as a field theoretical domain wall in the context of an axion-like model
consisting of a complex scalar effective field theory with approximate U(1)
symmetry. We simulate numerically the dynamics of the collision and illustrate
the transition from the configuration without a hole to the pierced one with
the aid of a phase diagram. The process of perforation is found to depend on
the collisional velocity, and, contrary to our expectation, we observe that
above a critical value of the velocity, the black hole has no chance to
perforate the wall. That is: high energy collisions do not assist piercing. We
also show that, only when the model parameters are fine-tuned so that the
energy scale of the string is very close to that of the domain wall, the
collision of the wall with the black hole has a possibility to provide a
mechanism to erase domain walls, if the hole expands. However, in such cases,
domain walls will form with many holes edged by a string and therefore
disappear eventually. Therefore this mechanism is unlikely to be a solution to
the cosmological domain wall problem, although it may cause some minor effects
on the evolution of a domain wall network.Comment: 14 pages; 9 figure
Supergravity and Superstring Signatures of the One-Parameter Model at LHC
Many string constructions have a classical no-scale structure, resulting in a
one-parameter model (OPM) for the supersymmetry breaking soft terms. As a
highly constrained subset of mSUGRA, the OPM has the potential to be
predictive. Conversely, if the observed superpartner spectrum at LHC is a
subset of the OPM parameter space, then this may provide a clue to the
underlying theory at high energies. We investigate the allowed supersymmetry
parameter space for a generic one-parameter model taking into account the most
recent experimental constraints. We find that in the strict moduli scenario,
there are no regions of the parameter space which may satisfy all constraints.
However, for the dilaton scenario, there are small regions of the parameter
space where all constraints may be satisfied and for which the observed dark
matter density may be generated. We also survey the possible signatures which
may be observable at the Large Hadron Collider (LHC). Finally, we compare
collider signatures of OPM to those from a model with non-universal soft terms,
in particular those of an intersecting D6-brane model. We find that it may be
possible to distinguish between these diverse scenarios at LHC.Comment: 25 pages, 10 figures, accepted for publication in PR
Dynamics of domain walls intersecting black holes
Previous studies concerning the interaction of branes and black holes
suggested that a small black hole intersecting a brane may escape via a
mechanism of reconnection. Here we consider this problem by studying the
interaction of a small black hole and a domain wall composed of a scalar field
and simulate the evolution of this system when the black hole acquires an
initial recoil velocity. We test and confirm previous results, however, unlike
the cases previously studied, in the more general set-up considered here, we
are able to follow the evolution of the system also during the separation, and
completely illustrate how the escape of the black hole takes place.Comment: 4 pages, 6 figure
Zeta Determinant for Laplace Operators on Riemann Caps
The goal of this paper is to compute the zeta function determinant for the
massive Laplacian on Riemann caps (or spherical suspensions). These manifolds
are defined as compact and boundaryless dimensional manifolds deformed by a
singular Riemannian structure. The deformed spheres, considered previously in
the literature, belong to this class. After presenting the geometry and
discussing the spectrum of the Laplacian, we illustrate a method to compute its
zeta regularized determinant. The special case of the deformed sphere is
recovered as a limit of our general formulas.Comment: 19 pages, 1 figur
Evaluation of in-farm versus weather station data for use as heat stress indicator in dairy sheep
AbstractHeat stress is a limiting factor in dairy production in hot climates impairing growth, milk production and reproduction. The most widely investigated climatic factors related with heat stress are: air temperature and relative humidity. Previously dairy sheep studies of heat tolerance depended on measurements of physiological functions on individual animals such as rectal temperatures, respiration rates or volumes of air inhaled; unfortunately, such measurements are costly and not feasible on a large scale. This study aims to evaluate in-farm (IF) versus weather station (WS) data to be used as heat stress indicator in dairy sheep. Data were collected in three farms in November 2002 till July 2003. Maximum temperature (T) and relative humidity (RH) were monitored by means of thermo-hygrographs placed in the farms at a height of 1.5m above the ground. Both IF and WS data were taken 24 h before milk recording. The data contained 1,059 test-day records belonging to 275 Valle del Belice ewes. The correl..
Pair production in a strong slowly varying magnetic field: the effect of a background gravitational field
The production probability of an pair in the presence of a strong,
uniform and slowly varying magnetic field is calculated by taking into account
the presence of a background gravitational field. The curvature of the
spacetime metric induced by the gravitational field not only changes the
transition probabilities calculated in the Minkowski spacetime but also primes
transitions that are strictly forbidden in absence of the gravitational field.Comment: 56 pages, no figure
A critical comparison between DWT and Hilbert-Huang-based methods for the diagnosis of rotor bar failures in induction machines
(c) 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] In this paper, a cutting-edge time-frequency decomposition tool, i.e., the Hilbert-Huang transform (HHT), is applied to the stator startup current to diagnose the presence of rotor asymmetries in induction machines. The objective is to extract the evolution during the startup transient of the left sideband harmonic (LSH) caused by the asymmetry, which constitutes a reliable evidence of the presence of the fault. The validity of the diagnosis methodology is assessed through several tests developed using real experimental signals. Moreover, in this paper, an analytical comparison with an alternative time-frequency decomposition tool, i.e., the discrete wavelet transform (DWT), is carried out. This tool was applied in previous works to the transient extraction of fault-related components, with satisfactory results, even in cases in which the classical Fourier approach does not lead to correct results. The results of the application of the HHT and DWT are analyzed and compared, obtaining novel conclusions about their respective suitability for the transient extraction of asymmetry-related components, as well as the equivalence, with regard to the LSH extraction, between their basic components, namely: 1) intrinsic mode function, for the HHT, and 2) approximation signal for the DWT.This work was supported in part by the Spanish “Ministerio de Educación y Ciencia,” in the framework of the “Programa Nacional de proyectos de Investigación Fundamental,” project reference DPI2008-06583/DPI and in part by “Vicerrectorado de Investigación, Desarrollo e Innovación of the Universidad Politécnica de Valencia” through
the Programa de Apoyo a la Investigación y Desarrollo under Contract PAID-06-07.Antonino-Daviu, J.; Riera-Guasp, M.; Pineda-Sanchez, M.; Pérez, RB. (2009). A critical comparison between DWT and Hilbert-Huang-based methods for the diagnosis of rotor bar failures in induction machines. IEEE Transactions on Industry Applications. 45(5):1794-1803. https://doi.org/10.1109/TIA.2009.2027558S1794180345
Coarse Grained Density Functional Theories for Metallic Alloys: Generalized Coherent Potential Approximations and Charge Excess Functional Theory
The class of the Generalized Coherent Potential Approximations (GCPA) to the
Density Functional Theory (DFT) is introduced within the Multiple Scattering
Theory formalism for dealing with, ordered or disordered, metallic alloys. All
GCPA theories are based on a common ansatz for the kinetic part of the
Hohenberg-Kohn functional and each theory of the class is specified by an
external model concerning the potential reconstruction. The GCPA density
functional consists of marginally coupled local contributions, does not depend
on the details of the charge density and can be exactly rewritten as a function
of the appropriate charge multipole moments associated with each lattice site.
A general procedure based on the integration of the 'qV' laws is described that
allows for the explicit construction the same function. The coarse grained
nature of the GCPA density functional implies great computational advantages
and is connected with the O(N) scalability of GCPA algorithms. Moreover, it is
shown that a convenient truncated series expansion of the GCPA functional leads
to the Charge Excess Functional (CEF) theory [E. Bruno, L. Zingales and Y.
Wang, Phys. Rev. Lett. {\bf 91}, 166401 (2003)] which here is offered in a
generalized version that includes multipolar interactions. CEF and the GCPA
numerical results are compared with status of art LAPW full-potential density
functional calculations for 62, bcc- and fcc-based, ordered CuZn alloys, in all
the range of concentrations. These extensive tests show that the discrepancies
between GCPA and CEF are always within the numerical accuracy of the
calculations, both for the site charges and the total energies. Furthermore,
GCPA and CEF very carefully reproduce the LAPW site charges and the total
energy trends.Comment: 19 pages, 11 figure
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