Anomalous character of the axion-photon coupling in a magnetic field distorted by a pp-wave gravitational background

We study the problem of axion-photon coupling in the magnetic field influenced by gravitational radiation. We focus on exact solutions to the equations for axion electrodynamics in the pp-wave gravitational background for two models with initially constant magnetic field. The first model describes the response of an initially constant magnetic field in a gravitational-wave vacuum with unit refraction index; the second model is characterized by a non-unit refraction index prescribed to the presence of ordinary and/or dark matter. We show that both models demonstrate anomalous behavior of the electromagnetic field generated by the axion-photon coupling in the presence of magnetic field, evolving in the gravitational wave background. The role of axionic dark matter in the formation of the anomalous response of this electrodynamic system is discussed.Comment: 26 pages, no figure

Exceptional points in topological edge spectrum of PT symmetric domain walls

We demonstrate that the non-Hermitian parity-time (PT) symmetric interfaces formed between amplifying and lossy crystals support dissipationless edge states. These PT edge states exhibit gapless spectra in the complex band structure interconnecting complex-valued bulk bands as long as exceptional points (EPs) of edge states exist. As a result, regimes exist where the edge states can spectrally overlap with the bulk continuum without hybridization, and leakage into the bulk states is suppressed due to the PT symmetry. Two exemplary PT symmetric systems, based on valley and quantum hall topological phases, are investigated, and the connection with the corresponding Hermitian systems is established. We find that the edge states smoothly transit to the valley edge states found in Hermitian systems if the magnitude of gain/loss vanishes. The topological nature of the PT edge states can be established within the non-Hermitian Haldane model, where the topological invariance is found to be unaffected by gain or loss. Nonreciprocal PT edge states are discovered at the interfaces between PT-Haldane phases, indicating the interplay between the gain/loss and the magnetic flux. The proposed systems are experimentally feasible to realize in photonics. This has been verified by our rigorous full-wave simulations of edge states in PT-symmetric silicon-based photonic graphene.Comment: 24 pages, 9 figures, 2 table

Single molecule fluorescent in situ hybridization (smFISH) of C. elegans worms and embryos

In C. elegans, the expression pattern of a gene provides important clues to understanding its biological function. To accurately depict endogenous transcriptional activity, a highly sensitive method is required to measure transcript levels in the intact tissue across various developmental stages. Conventional RNA in situ hybridization methods using hapten- (biotin or digoxygenin) labeled RNA probes rely on antibody binding for visualization, and are thus only semi-quantitative at best (Raap et al. 1995; Levsky et al. 2003). Additionally, hapten-labeled probes are prone to diffuse localization (when conjugated with alkaline phosphatase), low sensitivity (when conjugated with fluorescent molecules), and non-specific probe binding. Here, we introduce a recently developed mRNA in situ hybridization method (Raj et al. 2008) that circumvents the above difficulties to give single molecule resolution of transcript detection