UvA CMT:Form factor summation in integrable models: local vs semi-local observables(Etienne Granet)
Channel: Yuan Miao
Date: 10/06/2020

UvA CMT seminar

Date: 9 June, 2020

Speaker: Dr. Etienne Granet (Oxford University)

Title: Form factor summation in integrable models: local vs semi-local observables

Abstract: Correlation functions in integrable models can be written as a sum of form factors over all the eigenstates. Although in the past decade this representation has proven very fruitful for zero-temperature correlation functions, much less is known about the computation of this spectral sum for generic eigenstates as encountered at finite temperature. I will show that the nature of the sum crucially depends on the observable considered: for local observables it can be expanded in the number of particle-hole excitations, whereas for semi-local observables it cannot, and instead it necessarily involves an exponential number of states and is more naturally expanded in the density of the eigenstate. These two cases will be illustrated with the density operator in Lieb-Liniger, and the longitudinal magnetization in the Transverse Field Ising model.