Gauge Coupling β Functions to Four-Loop Order in the Standard Model

We compute the beta functions of the three standard model gauge couplings to four-loop order in the modified minimal subtraction scheme. At this order a proper definition of gamma(5) in D = 4 - 2 epsilon space-time dimensions is required; however, in our calculation we determine the gamma(5)-dependent terms by exploiting relations with beta function coefficients at lower loop orders.