Scattering of massless scalar field by charged dilatonic black holes

Wave propagations in the presence of black holes is a significant problem both in theoretical and observational aspects, especially after the discovery of gravitational wave and confirmation of black holes. We study the scattering of massless scalar field by a charged dilatonic black hole in frame of full wave theory. We apply partial wave method to obtain the scattering cross sections of the scalar field, and investigate how the black hole charge affects the scalar scattering cross sections. Furthermore, we investigate the Regge pole approach of the scattering cross section of the dilatonic black hole. We find that in order to obtain results at the same precision, we need more Regge poles as the black hole charge increases. We compare the results in the full wave theory and results in the classical geodesic scattering and the semi-classical glory approximations, and demonstrate the improvements and power of our approach.Comment: 14 pages, 22 figures, published versio

Realization of a three-dimensional photonic topological insulator

Confining photons in a finite volume is in high demand in modern photonic devices. This motivated decades ago the invention of photonic crystals, featured with a photonic bandgap forbidding light propagation in all directions. Recently, inspired by the discoveries of topological insulators (TIs), the confinement of photons with topological protection has been demonstrated in two-dimensional (2D) photonic structures known as photonic TIs, with promising applications in topological lasers and robust optical delay lines. However, a fully three-dimensional (3D) topological photonic bandgap has never before been achieved. Here, we experimentally demonstrate a 3D photonic TI with an extremely wide (> 25% bandwidth) 3D topological bandgap. The sample consists of split-ring resonators (SRRs) with strong magneto-electric coupling and behaves as a 'weak TI', or a stack of 2D quantum spin Hall insulators. Using direct field measurements, we map out both the gapped bulk bandstructure and the Dirac-like dispersion of the photonic surface states, and demonstrate robust photonic propagation along a non-planar surface. Our work extends the family of 3D TIs from fermions to bosons and paves the way for applications in topological photonic cavities, circuits, and lasers in 3D geometries

DAISY filter flow: A generalized discrete approach to dense correspondences

Establishing dense correspondences reliably between a pair of images is an important vision task with many ap-plications. Though significant advance has been made to-wards estimating dense stereo and optical flow fields for two images adjacent in viewpoint or in time, building re-liable dense correspondence fields for two general images still remains largely unsolved. For instance, two given im-ages sharing some content exhibit dramatic photometric and geometric variations, or they depict different 3D scenes of similar scene characteristics. Fundamental challenges to such an image or scene alignment task are often mul-tifold, which render many existing techniques fall short of producing dense correspondences robustly and efficiently. This paper presents a novel approach called DAISY filter flow (DFF) to address this challenging task. Inspired by the recent PatchMatch Filter technique, we leverage and extend a few established methods: 1) DAISY descriptors, 2) filter-based efficient flow inference, and 3) the Patch-Match fast search. Coupling and optimizing these mod-ules seamlessly with image segments as the bridge, the pro-posed DFF approach enables efficiently performing dense descriptor-based correspondence field estimation in a gen-eralized high-dimensional label space, which is augmented by scales and rotations. Experiments on a variety of chal-lenging scenes show that our DFF approach estimates spa-tially coherent yet discontinuity-preserving image align-ment results both robustly and efficiently. 1

Novel black holes in higher derivative gravity

We find a class of novel black holes in higher derivative theory. The novel black holes follow behavior of~\sch\ ones at large mass limit, while dramatically differentiate from ~\sch\ ones for little holes because of the effects which may root in quantum gravity. The temperature of the hole takes maximum for a specific mass, which is related to the new sale introduced in the higher derivative theory, and goes to zero at little mass limit. This property leads to a significant observation that the novel black hole may be a candidate for dark matters evading constraint from $\gamma$-ray burst.Comment: 12 pages, 10 figures, comments welcom