Nonperturbative investigations of SU(3) gauge theory with eight dynamical flavors

摘要

We present our lattice studies of SU(3) gauge theory with N_f = 8 degenerate fermions in the fundamental representation. Using nHYP-smeared staggered fermions we study finite-temperature transitions on lattice volumes as large as L~3 × N_t = 48~3 × 24, and the zero-temperature composite spectrum on lattice volumes up to 64~3 × 128. The spectrum indirectly indicates spontaneous chiral symmetry breaking, but finite-temperature transitions with fixed N_t ≤ 24 enter a strongly coupled lattice phase as the fermion mass decreases, which prevents a direct confirmation of spontaneous chiral symmetry breaking in the chiral limit. In addition to the connected spectrum we focus on the lightest flavor-singlet scalar particle.We find it to be degenerate with the pseudo-Goldstone states down to the lightest masses reached so far by nonperturbative lattice calculations. Using the same lattice approach, we study the behavior of the composite spectrum when the number of light fermions is changed from eight to four. A heavy flavor-singlet scalar in the 4-flavor theory affirms the contrast between QCD-like dynamics and the low-energy behavior of the 8-flavor theory.