The role of differential rotation in the evolution of the r-mode instability

We discuss the role of differential rotation in the evolution of the l=2 r-mode instability of a newly born, hot, rapidly-rotating neutron star. It is shown that the amplitude of the r-mode saturates in a natural way at a value that depends on the amount of differential rotation at the time the instability becomes active. It is also shown that, independently of the saturation amplitude of the mode, the star spins down to a rotation rate that is comparable to the inferred initial rotation rates of the fastest pulsars associated with supernova remnants.Comment: 4 pages, 2 figures, in Proceedings of the 5th International Workshop "New Worlds in Astroparticle Physics", Faro, Portugal, 8-10 January 200

Polytropic stars in three-dimensional spacetime

We investigate three-dimensional perfect fluid stars with polytropic equation of state, matched to the exterior three-dimensional black hole geometry of Banados, Teitelboim and Zanelli. A new class of exact solutions for a generic polytropic index is found and analysed.Comment: 3 pages, revte

Stationary Black Holes in a Generalized Three-Dimensional Theory of Gravity

We consider a generalized three-dimensional theory of gravity which is specified by two fields, the graviton and the dilaton, and one parameter. This theory contains, as particular cases, three-dimensional General Relativity and three-dimensional String Theory. Stationary black hole solutions are generated from the static ones using a simple coordinate transformation. The stationary black holes solutions thus obtained are locally equivalent to the corresponding static ones, but globally distinct. The mass and angular momentum of the stationary black hole solutions are computed using an extension of the Regge and Teitelboim formalism. The causal structure of the black holes is described.Comment: 12 pages, Late

Two loops calculation in chiral perturbation theory and the unitarization program of current algebra

In this paper we compare two loop Chiral Perturbation Theory (ChPT) calculation of pion-pion scattering with the unitarity second order correction to the current algebra soft-pion theorem. It is shown that both methods lead to the same analytic structure for the scattering amplitude.Comment: 13 pages, Revtex 3.0, no figures, submitted to Phys. Lett.

Analytical r-mode solution with gravitational radiation reaction force

We present and discuss the analytical r-mode solution to the linearized hydrodynamic equations of a slowly rotating, Newtonian, barotropic, non-magnetized, perfect-fluid star in which the gravitational radiation reaction force is present.Comment: 3 pages, in Proceedings of the 5th International Workshop "New Worlds in Astroparticle Physics", Faro, Portugal, 8-10 January 200

Magnetoresistive Effects in Ferromagnet-Superconductor Multilayers

We consider a nanoscale system consisting of Manganite-ferromagnet and Cuprate-superconductor multilayers in a spin valve configuration. The magnetization of the bottom Manganite-ferromagnet is pinned by a Manganite-antiferromagnet. The magnetization of the top Manganite-ferromagnet is coupled to the bottom one via indirect exchange through the superconducting layers. We study the behavior of the critical temperature and the magnetoresistance as a function of an externally applied parallel magnetic field, when the number of Cuprate-superconductor layers are changed. There are two typical behaviors in the case of a few monolayers of the Cuprates: a) For small magnetic fields, the critical temperature and the magnetoresistance change abruptly when the flipping field of the top Manganite-ferromagnet is reached. b) For large magnetic fields, the multilayered system re-enters the zero-resistance (superconducting) state after having become resistive (normal).Comment: 3 pages, 3 figures. 2004 Magnetism and Magnetic Materials Conferenc

Nonlinear evolution of r-modes: the role of differential rotation

Recent work has shown that differential rotation, producing large scale drifts of fluid elements along stellar latitudes, is an unavoidable feature of r-modes in the nonlinear theory. We investigate the role of this differential rotation in the evolution of the l=2 r-mode instability of a newly born, hot, rapidly rotating neutron star. It is shown that the amplitude of the r-mode saturates a few hundred seconds after the mode instability sets in. The saturation amplitude depends on the amount of differential rotation at the time the instability becomes active and can take values much smaller than unity. It is also shown that, independently of the saturation amplitude of the mode, the star spins down to rotation rates that are comparable to the inferred initial rotation rates of the fastest pulsars associated with supernova remnants. Finally, it is shown that, when the drift of fluid elements at the time the instability sets in is significant, most of the initial angular momentum of the star is transferred to the r-mode and, consequently, almost none is carried away by gravitational radiation.Comment: 10 pages, 5 figure

Generation of Superposition States and Charge-Qubit Relaxation Probing in a Circuit

We demonstrate how a superposition of coherent states can be generated for a microwave field inside a coplanar transmission line coupled to a single superconducting charge qubit, with the addition of a single classical magnetic pulse for chirping of the qubit transition frequency. We show how the qubit dephasing induces decoherence on the field superposition state, and how it can be probed by the qubit charge detection. The character of the charge qubit relaxation process itself is imprinted in the field state decoherence profile.Comment: 6 pages, 4 figure

Two-band superfluidity from the BCS to the BEC limit

We analyze the evolution of two-band superfluidity from the weak coupling Bardeen-Cooper-Schrieffer (BCS) to the strong coupling Bose-Einstein condensation (BEC) limit. When the interband interaction is tuned from negative to positive values, a quantum phase transition occurs from a 0-phase to a $\pi$-phase state, depending on the relative phase of two order parameters. Furthermore, population imbalances between the two bands can be created by tuning the intraband or interband interactions. We also find two undamped low energy collective excitations corresponding to in-phase and out-of-phase modes. Lastly, we derive the coupled Ginzburg-Landau equations, and show that they reduce to coupled Gross-Pitaevskii equations for two types of bosons in the BEC limit.Comment: 4 pages and 3 figure