As the hunt for the elusive dark matter progresses, an impressive series of null results has severely limited options for DM that freezes out via standard model interactions. A hidden sector containing the dark matter particle and an unstable mediator can freezeout independently of the sector's very weak connection to the standard model fields, opening opportunities for phenomenology. I will present two minimal simplified models for hidden sector freezeout (through the vector and scalar portal), discuss the existing constraints on these parameter spaces from a wide array of complementary experimental approaches, and address how the features of these models survive in extensions beyond the minimal case.
A Weyl semimetal is a new topological phase of matter that extends the topological classification beyond insulators, exhibits quantum anomalies, possess exotic surface Fermi arc electron states and provides the first ever realization of Weyl fermions in physics. In a Weyl semimetal, the chirality of the Weyl nodes give rise to topological charges, which can be understood as monopoles and anti-monopoles of Berry flux in momentum space. They are separated in momentum space and are connected only through the crystal boundary by an unusual topological surface state, a Fermi arc.
Electrons in single atomic layer of crystals of graphene possess a new degree of freedom for designing nonlinear and optoelectronic devices. Zero bandgap of graphene leads to dominating metallic behavior for carrier conduction and broadband light absorption. The limited density of states in graphene also leads to semiconductor-like behavior, such as Pauli blocking and absorption saturation. In this talk, we will be focusing on using integrated nanophotonic devices to confine and localize photon for enhanced light-matter interaction in subwavelength scale.