The semi-classical approximation at high temperature revisited

Abstract

Abstract We revisit the semi-classical calculation of the size distribution of instantons at finite temperature in non-abelian gauge theories in four dimensions. The relevant functional determinants were first calculated in the seminal work of Gross, Pisarski and Yaffe and the results were used for a wide variety of applications including axions most recently. In this work we show that the uncertainty on the numerical evaluations and semi-analytical expressions are two orders of magnitude larger than claimed. As a result various quantities computed from the size distribution need to be reevaluated, for instance the resulting relative error on the topological susceptibility at arbitrarily high temperatures is about 5% for QCD and about 10% for SU(3) Yang-Mills theory. With higher rank gauge groups this discrepancy is even higher. We also provide a simple semi-analytical formula for the size distribution with absolute error 2 · 10−4. In addition we also correct the over-all constant of the instanton size distribution in the $$ \overline{\mathrm{MS}} $$ MS ¯ scheme which was widely used incorrectly in the literature if non-trivial fermion content is present.