QCD phase diagram at strong coupling including auxiliary field fluctuations

We investigate the phase diagram and the mechanism for the sign problem to appear in finite density QCD at strong coupling in a combined framework of the auxiliary field Monte-Carlo (AFMC) and the chiral angle fixing (CAF) methods. When bosonizing meson hopping terms in the effective action, we need to introduce imaginary number coefficients, which leads to a complex phase in numerical simulations. By using the cut-off technique, we quantitatively show that high momentum modes of auxiliary fields mainly contribute to the weight cancellation; Cutting-off high-momentum auxiliary field modes does not modify order parameters but suppresses statistical weight cancellation, when we choose the cut-off parameter appropriately.