Numerical Mass Estimates from Correlation Functions in a 4D SU(2) Higgs Model

In lattice gauge theory one estimates masses from correlation functions in Euclidean time to which superselection rules may apply. The correlation functions are a superposition of exponential functions of the energy levels, and the mass to be estimated is that associated with the ground state in our investigation. We discuss and implement three such estimators. The first is obtained by taking the logarithm of the ratios of consecutive values of the correlation function and estimating the asymptotic value. Another estimator involves fitting a 2-parameter exponential function to the correlation function and trying to eliminate higher mass contributions. The third estimator involves fitting a 4-parameter function of the sum of two exponentials to the correlation function. Various features and quirks of the different estimators are described. A comparison of the three estimators shows consistency indicating that all three are reliable methods, supplementing one another, for numerically estimating masses from correlation functions.