Photonic crystals have provided a controllable platform to examine excitingly new topological states in open systems. In this work, we reveal photonic topological corner states in a photonic graphene with mirror-symmetrically patterned gain and loss. Such a nontrivial Wannier-type higherorder topological phase is achieved through solely tuning on-site gain/loss strengthes, which leads to annihilation of the two valley Dirac cones at time-reversal-symmetric point, as the gain and loss change the effective tunneling between adjacent sites. We find that the symmetry-protected photonic corner modes exhibit purely imaginary energies and the role of Wannier center as topological invariant is illustrated. For experimental considerations, we also examine the topological interface states near a domain wall. Our work introduces an interesting platform for non-Hermiticity-induced photonic higher-order topological insulators, to which, with current experimental technologies, can be readily accessed.

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Radiative transition decay width for was calculated by using twisted mass lattice quantum chromodynamics gauge configurations in this preliminary study. The simulation has been performed on lattices with lattice spacings and lattice size (Ens.C 1), and and lattice size (Ens.B 1) respectively. In this simulation, we have considered the parity mixing effect by using variational method. The calculated central value for the decay width is closer to the experimental data than that in previous lattice studies.

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Recent studies have discovered local potentials can induce nontrivial eigenmodes responding to the bulk topology for the system. While previous studies focused on conventional first-order topological states emerging from vacancy superlattice, here we study higher-order topological properties of the vacancy superlattice on a two-dimensional Chern insulator with particle-hole symmetry. The vacancy superlattice with alternate lattice spacings exhibits an emergent second-order topological phase characterized by the nontrivial edge polarization. This topological phase is robust against particle-hole symmetry-preserved perturbations as long as the energy gap remains open for the mid-gap sates. Our work generalizes the nontrivial higher-order topological properties to a Chern insulator with local defect vacancies and provides a controllable platform for engineering higher-order topological corner states.

The relationship between the elastic scattering phase shifts of the [Formula: see text] system and the two-particle energy spectrum in elongated boxes is established in center-of-mass frame under periodic boundary conditions. The formulas are also extended to cubic boxes to confirm the results in elongated boxes. Our analytical results will be helpful to the study of [Formula: see text] interaction on lattice by using Lüscher’s finite volume method.