Topic: Revisiting O(N) σ model: with unphysical pion masses and temperatures
Speaker: Prof. Zhi-Guang Xiao
Coordinates: PCFT C1124, 16:00, Thursday, December 26
Abstract: Lattice calculations with unphysical pion masses and hadron physics under finite temperatures provide new information about QCD, which may extend our understanding of QCD and strong interaction. Recent Roy-equation analysis on lattice data of ππ scattering phase shifts at mπ=391 MeV reveals that the lowest f0(σ) state becomes a bound state under this condition. In addition, there is a pair of complex poles below the threshold on the second Riemann sheet of the scattering amplitude. To understand this pole structure, we show that this behavior can be reproduced by utilizing the O(N) σ model at the leading order of 1/N expansion, together with the N/D method. The pole trajectories with varying pion masses are consistent with the Roy-equation analyses. The σ pole trajectory with varying temperature is also discussed and found to be similar to its properties when varying mπ. Finally, we will also discuss the vacuum structure of the O(N) model in the situation when mπ and temperature get large.