Bulk viscosity of resonantly interacting fermions in the quantum virial expansion

We consider two-component fermions with a zero-range interaction both in two and three dimensions calculate the bulk viscosity for an arbitrary scattering length high-temperature regime. evaluate Kubo formula using expansion respect to fugacity, which acts as small parameter at high temperatures. In zero-frequency limit of formula, pinch singularities emerge that reduce order fugacity by one. These can turn higher-order vertex corrections nonzero frequencies into leading zero frequency, so all such contributions have be resummed. present exact microscopic computation regime taking account these singularities. For negative lengths, we derive complete second show self-consistent equation resum is identical linearized kinetic equation. positive new type singularity arises bound pairs. pairs leads first-order contribution viscosity, one lower than also provide contributions. propose derives from corrections.