Study of possible ultraviolet zero of the beta function in gauge theories with many fermions
Physical Review D
We study the possibility of an ultraviolet (UV) zero in the n-loop beta function of U(1) and non-Abelian gauge theories with N_f fermions for large N_f. The effect of scheme transformations on the coefficients of different powers of N_f in the n-loop term in the beta function is calculated. A general scheme-independent criterion is given for determining whether or not the n-loop beta function has a UV zero for large N_f. We compare the results with exact integral representations of the leading
... erms in the beta functions for the respective Abelian and non-Abelian theories in the limit N_f →∞ limit with N_f α finite. As part of this study, new analytic and numerical results are presented for certain coefficients, denoted b_n,n-1, that control the large-N_f behavior at n-loop order in the beta function. We also investigate various test functions incorporating a power-law and essential UV zero in the beta function and determine their manifestations in series expansions in powers of coupling and in powers of 1/N_f.