[Hybrid RBRC seminar] Lee-Yang zeroes from the functional renormalisation group

by Friederike Ihssen (ITP Heidelberg)

Thursday 10 Nov 2022, 12:30 → 13:30 US/Eastern

2-160 (https://bnl.zoomgov.com/j/1606067399?pwd=am02b0xIUXZ6TDR3d1dWL05TTDdaUT09)

As a precursor for a quantitative study in QCD we discuss the impact of fluctuations in a simple low energy effective theory, the non-linear sigma model. We show that in this model the location of the phase transition can accurately be determined by tracking the Lee-Yang singularities in the complex plane.
For this purpose, we set up a general functional renormalisation group framework for the computation of complex effective actions. We consider both flows the Wilsonian effective action and the one-particle irreducible (1PI) effective action.  In the present implementations of the general approaches, the flow of the Wilsonian effective action has a wider range of applicability and we obtain results for the effective potential of complex fields in φ4-theories from zero up to four dimensions. The complex effective action allows us to determine the location of the Lee-Yang zeros for general parameter values.

RIKENBNL22_Ihssen.pdf