Sparse modeling approach to obtaining the shear viscosity from smeared correlation functions

Understand

We propose the sparse modeling method to estimate the spectral function from the smeared correlation functions.

• We give a description of how to obtain the shear viscosity from the correlation function of the renormalized energy-momentum tensor (EMT) measured by the gradient flow method ($C(t,\tau)$) for the quenched QCD at finite temperature.
• The measurement of the renormalized EMT in the gradient flow method reduces a statistical uncertainty thanks to its property of the smearing.
• However, the smearing breaks the sum rule of the spectral function and the over-smeared data in the correlation function may have to be eliminated from the analyzing process of physical observables.