4,222 research outputs found
Causality of black holes in 4-dimensional Einstein-Gauss-Bonnet-Maxwell theory
We study charged black hole solutions in 4-dimensional (4D)
Einstein-Gauss-Bonnet-Maxwell theory to the linearized perturbation level. We
first compute the shear viscosity to entropy density ratio. We then demonstrate
how bulk causal structure analysis imposes a upper bound on the Gauss-Bonnet
coupling constant in the AdS space. Causality constrains the value of
Gauss-Bonnet coupling constant to be bounded by as .Comment: 13 pages, minor revision, references adde
Rotation-induced Asymmetry of Far-field Emission from Optical Microcavities
We study rotation-induced asymmetry of far-field emission from optical
microcavities, based on which a new scheme of rotation detection may be
developed. It is free from the "dead zone" caused by the frequency splitting of
standing-wave resonances at rest, in contrast to the Sagnac effect. A
coupled-mode theory is employed to provide a quantitative explanation and
guidance on the optimization of the far-field sensitivity to rotation. We
estimate that a 10^4 enhancement of the minimal detectable rotation speed can
be achieved by measuring the far-field asymmetry, instead of the Sagnac effect,
in microcavities 5 microns in radius and with distinct emission directions for
clockwise and counterclockwise waves.Comment: 7 pages, 4 figure
- …