Large-$N$ Pion Scattering, Finite-Temperature Effects and the   Relationship of the $f_{0}(500)$ with Chiral Symmetry Restoration
  In this work, we review how the mass and the width of the $f_{0}(500)$ pole behave in a regime where temperature is below the critical chiral transition value. This is attained by considering a large-$N$ $O(N + 1)/O(N)$ invariant Non-Linear Sigma Model (NLSM) such that we can study the dynamical generation of a $f_{0}(500)$ resonance. Introducing thermal effects via the imaginary time formalism allows us to study the behavior of the pole and relate it to chiral restoration. 
Santiago Cortes, Angel Gomez Nicola, John Morales
hep-ph