Excited hairy black holes: Dynamical construction and level transitions

International audienceWe study the dynamics of unstable Reissner-Nordström anti–de Sitter black holes under charged scalar field perturbations in spherical symmetry. We unravel their general behavior and approach to the final equilibrium state. In the first part of this work, we present a numerical analysis of massive charged scalar field quasinormal modes. We identify the known mode families—superradiant modes, zero-damped modes, AdS modes, and the near-horizon mode—and we track their migration under variation of the black hole and field parameters. We show that the zero-damped modes become superradiantly unstable for large RNAdS with large gauge coupling; the leading unstable mode is identified with the near-horizon condensation instability. In the second part, we present results of numerical simulations of perturbed large RNAdS, showing the nonlinear development of these unstable modes. For generic initial conditions, charge and mass are transferred from the black hole to the scalar field, until an equilibrium solution with a scalar condensate is reached. We use results from the linear analysis, however, to select special initial data corresponding to an unstable overtone mode. We find that these data evolve to produce a new equilibrium state—an excited hairy black hole with the scalar condensate in an overtone configuration. This state is, however, unstable, and the black hole eventually decays to the generic end state. Nevertheless, this demonstrates the potential relevance of overtone modes as transients in black hole dynamics

Scalar Quasi-Normal Modes of a Loop Quantum Black Hole

International audienceWe compute the Quasi-Normal Mode (QNM) frequencies for scalar perturbations for modified Schwarzschild black holes in Loop Quantum Gravity. We study the singularity-free polymerized metric characterised by two parameters encoding loop quantum effects: the minimal area gap $a_0$ and the polymeric deformation parameter $P$. We perform numerical computations using Leaver's continued fraction method and compare our results to other semi-analytical methods and existing literature. We study the effects on the QNM spectrum of variation of both deformation parameters and systematically compare to the standard Schwarzschild case. In particular we find that the scalar fundamental mode is modified from the third decimal for values of $P$ in accordance with the most recent astrophysical constraints. We also show that qualitative differences arise for highly damped modes: on the one hand, a new crossing of the imaginary axis occurs for high values of $a_0$ and, on the other hand, increasing $P$ produces a positive shift of the real part and an increase of the spacing in imaginary part between modes

Gamma spectroscopy of some short-lived fission products with the isotope separator lohengrin

Gamma spectra and half-lives of 100Y, 100Zr, 149Ce, 149Pr, 150Ce, 150Pr, 135 Te, 136Te, 137Te, 85Se, 86Se, 87Se and 88Se have been measured using the unslowed fission product separator Lohengrin. The ground state beta branching has been measured for the decays of 85Se and 88Br.Les spectres gamma et les périodes des noyaux 100Y, 100 Zr, 149Ce, 149Pr, 150Ce, 150 Pr, 135Te, 136Te, 137Te, 85Se, 86Se, 87Se et 88Se, sont mesurés à l'aide du séparateur de fragments de fission Lohengrin. Les intensités gamma absolues ont été mesurées pour 85Se et 88Br