Instituto Superior Técnico

About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.

Model for fermion masses and lepton mixing in SO(10) x A(4)

Abstract: 8 pages.-- PACS nrs.: 11.30.Hv; 12.10.-g; 12.15.Ff; 14.60.Pq.-- ISI Article Identifier: 000246076700079.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0702034

Minimal scenarios for leptogenesis and CP violation

Abstract: The relation between leptogenesis and CP violation at low energies is analyzed in detail in the framework of the minimal seesaw mechanism. Working, without loss of generality, in a weak basis where both the charged lepton and the right-handed Majorana mass matrices are diagonal and real, we consider a convenient generic parametrization of the Dirac neutrino Yukawa coupling matrix and identify the necessary condition which has to be satisfied in order to establish a direct link between leptogenesis and CP violation at low energies. In the context of the LMA solution of the solar neutrino problem, we present minimal scenarios which allow for the full determination of the cosmological baryon asymmetry and the strength of CP violation in neutrino oscillations. Some specific realizations of these minimal scenarios are considered. The question of the relative sign between the baryon asymmetry and CP violation at low energies is also discussed.

Fundamental photon orbits: Black hole shadows and spacetime instabilities

Abstract: The standard black holes (BHs) in general relativity, as well as other ultracompact objects (with or without an event horizon) admit planar circular photon orbits These light rings (LRs) determine several spacetime properties For instance, stable LRs trigger instabilities and, in spherical symmetry, (unstable) LRs completely determine BH shadows In generic stationary, axisymmetric spacetimes, nonplanar bound photon orbits may also exist, regardless of the integrability properties of the photon motion We suggest a classification of these fundamental photon orbits (FPOs) and, using Poincar\'e maps, determine a criterion for their stability For the Kerr BH, all FPOs are unstable (similar to its LRs) and completely determine the Kerr shadow But in non-Kerr spacetimes, stable FPOs may also exist, even when all LRs are unstable, triggering new instabilities We illustrate this for the case of Kerr BHs with Proca hair, wherein, moreover, qualitatively novel shadows with a cuspy edge exist, a feature that can be understood from the interplay between stable and unstable FPOs FPOs are the natural generalization of LRs beyond spherical symmetry and should generalize the LRs key role in different spacetime properties

Quasinormal modes and classical wave propagation in analogue black holes

Abstract: Many properties of black holes can be studied using acoustic analogues in the laboratory through the propagation of sound waves. We investigate in detail sound wave propagation in a rotating acoustic $(2+1)$-dimensional black hole, which corresponds to the ``draining bathtub'' fluid flow. We compute the quasinormal mode frequencies of this system and discuss late-time power-law tails. Because of the presence of an ergoregion, waves in a rotating acoustic black hole can be superradiantly amplified. We also compute superradiant reflection coefficients and instability time scales for the acoustic black hole bomb, the equivalent of the Press-Teukolsky black hole bomb. Finally we discuss quasinormal modes and late-time tails in a nonrotating canonical acoustic black hole, corresponding to an incompressible, spherically symmetric $(3+1)$-dimensional fluid flow.