The thermal photon emissivity at the QCD chiral crossover from imaginary momentum correlators

The thermal photon emissivity at the QCD chiral crossover is investigated using imaginary momentum correlators. These have been measured on a newly generated 20 × 963 lattice-QCD ensemble with O(a)-improved Wilson quarks and physical up, down and strange quark masses at a temperature T = 154 MeV near the pseudo-critical temperature. In order to realize the photon on-shell condition, the spatially transverse Euclidean correlators have to be evaluated at imaginary spatial momenta. Employing a bounding method, we present a preliminary result on the quantity HE(ω1), which corresponds to an energy-moment of the photon spectral function σ(ω)/ω defined by the weight function 1/(ω2 + ω2n), the ωn being integer multiples of 2πT.