NT/RBRC seminar

Abstract: It is well-known that direct lattice QCD calculations at finite baryochemical potential μB are not possible due to the presence of the sign problem. Taylor series expansion bypasses this difficulty since the Taylor coefficients are defined at μB=0. However, the higher order coefficients are difficult to calculate. Resummation of the Taylor series is a well-known approach by which the contribution of the higher-order terms can be estimated from a knowledge of the lower-order coefficients. In this talk, we will describe a new method of resummation known as exponential resummation. We will first discuss the approach and its advantages over the standard Taylor series. In an actual calculation, the Taylor coefficients are calculated stochastically. Because of this, the standard formulas for resummation contain stochastic bias which needs to be subtracted in order to identify the genuine higher-order contributions. We will describe two ways of subtracting this bias. The first method, cumulant expansion, subtracts the bias but loses all-orders resummation as it is a finite series. The second method which we will describe retains all-orders resummation while also simultaneously subtracting the bias up to a certain order in either μΒ or in the cumulant expansion. We will present results for the excess pressure and number density using this new method and conclude with a discussion of the scope and future applications of this new formalism.