Scalar-tensor theory with EGB term from Einstein Chern-Simons gravity

It is shown that the compactification a la Randall Sundrum of the so called, five dimensional Einstein Chern Simons action gravity leads to an action for a four dimensional scalar tensor gravity that includes a Gauss Bonnet term, which belongs to a particular case of the action of the Horndeski theory. The five dimensional action includes new gravitational degrees of freedom that were introduced requiring that the action be invariant under symmetries greater than the usual Poincare or (A)dS symmetries, namely the so called generalized Poincare algebras B5.Comment: To be published in Nucl. Phys.

Higher dimensional gravity invariant under the Poincare group

It is shown that the Stelle-West Grignani-Nardelli-formalism allows, both when odd dimensions and when even dimensions are considered, constructing actions for higher dimensional gravity invariant under local Lorentz rotations and under local Poincar\`{e} translations. It is also proved that such actions have the same coefficients as those obtained by Troncoso and Zanelli in ref. Class. Quantum Grav. 17 (2000) 4451.Comment: 7 pages, Latex, accepted in Phys. Rev.

Numerical Modelling of Industrial Induction

Induction heating is a physical process extensively used in the metallurgical industry for different applications involving metal melting. The main components of an induction heating system are an induction coil connected to a power-supply providing an alternating electric current and a conductive workpiece to be heated, placed inside the coil. The alternating current traversing the coil generates eddy currents in the workpiece and by means of ohmic losses the workpiece is heate

Quadrupole moments of rotating neutron stars

Numerical models of rotating neutron stars are constructed for four equations of state using the computer code RNS written by Stergioulas. For five selected values of the star's gravitational mass (in the interval between 1.0 and 1.8 solar masses) and for each equation of state, the star's angular momentum is varied from J=0 to the Keplerian limit J=J_{max}. For each neutron-star configuration we compute Q, the quadrupole moment of the mass distribution. We show that for given values of M and J, |Q| increases with the stiffness of the equation of state. For fixed mass and equation of state, the dependence on J is well reproduced with a simple quadratic fit, Q \simeq - aJ^2/M c^2, where c is the speed of light, and a is a parameter of order unity depending on the mass and the equation of state.Comment: ReVTeX, 7 pages, 5 figures, additional material, and references adde

Precursor Plerionic Activity and High Energy Gamma-Ray Emission in the Supranova Model of Gamma-Ray Bursts

The supranova model of gamma-ray bursts (GRBs), in which the GRB event is preceded by a supernova (SN) explosion by a few months to years, has recently gained support from Fe line detections in X-ray afterglows. A crucial ingredient of this model yet to be studied is the fast-rotating pulsar that should be active during the time interval between the SN and the GRB, driving a powerful wind and a luminous plerionic nebula. We discuss some observational consequences of this precursor plerion, which should provide important tests for the supranova model: 1) the fragmentation of the outlying SN ejecta material by the plerion and its implications for Fe line emission; and 2) the effect of inverse Compton cooling and emission in the GRB external shock due to the plerion radiation field. The plerion-induced inverse Compton emission can dominate in the GeV-TeV energy range during the afterglow, being detectable by GLAST from redshifts $z \lesssim 1.5$ and distinguishable from self-Compton emission by its spectrum and light curve. The prospects for direct detection and identification of the precursor plerion emission are also briefly considered.Comment: ApJ vol.583, in pres

The Cauchy problem of scalar-tensor theories of gravity

The 3+1 formulation of scalar-tensor theories of gravity (STT) is obtained in the physical (Jordan) frame departing from the 4+0 covariant field equations. Contrary to the common belief (folklore), the new system of ADM-like equations shows that the Cauchy problem of STT is well formulated (in the sense that the whole system of evolution equations is of first order in the time-derivative). This is the first step towards a full first order (in time and space) formulation from which a subsequent hyperbolicity analysis (a well-posedness determination) can be performed. Several gauge (lapse and shift) conditions are considered and implemented for STT. In particular, a generalization of the harmonic gauge for STT allows us to prove the well posedness of the STT using a second order analysis which is very similar to the one used in general relativity. Some spacetimes of astrophysical and cosmological interest are considered as specific applications. Several appendices complement the ideas of the main part of the paper.Comment: 29 pages Revtex; typos corrected; references added and updated; a shorter version of this paper was published in Classical and Quantum Gravit

Initial State: Theory Status

I present a brief discussion of the different approaches to the study initial state effects in heavy ion collisions in view of the recent results from Pb+Pb and p+p collisions at the LHC.Comment: 8 pages, 6 figures. Contribution to the proceedings of the XXII International Conference on Ultrarelativistic Nucleus-Nucleus Collisions, QM2011. Annecy, France, 22-28 May 201

Medium-induced gluon radiation and jet quenching in heavy ion collisions

In this brief review, I summarize the new developments on the description of gluon radiation by energetic quarks traversing a medium as well as the observable consequences in high-energy heavy ion collisions. Information about the initial state is essential for a reliable interpretation of the experimental results and will also be reviewed. Comparison with experimental data from RHIC and expectation for the future LHC will be given.Comment: 16 pages, 9 postscript figures. Invited brief review for Modern Physics Letters