ETD

• bulk transition
• chiral
• conformal window
• conformality
• eight-flavor QCD
• infrared
• LQCD
• QCD
• Roberge-Weiss
• Roberge–Weiss transition
• symmetry
• transition

This thesis investigates phase transitions in eight-flavor QCD using lattice simulations at purely imaginary chemical potential, placing the theory on the symmetry-protected Roberge–Weiss (RW) transition line where a genuine finite-temperature transition exists already at nonzero quark mass. The RW transition is expected at higher temperature than the zero-chemical-potential (pseudo-)critical temperature, offering a cleaner setting to study whether eight-flavor QCD is chirally broken or infrared-conformal when approaching the continuum chiral limit.
Using staggered fermions, the phase structure is mapped in the plane of bare coupling and mass. The simulations reveal two essentially temperature-independent bulk transitions that bound a nonphysical exotic phase originating from spontaneous breaking of the single-site shift symmetry specific to staggered fermions. At light masses, the RW thermal transition line intersects and overlaps with this bulk region, raising doubts about the survival of a genuine finite-temperature transition in the continuum chiral limit.
Instead of fixing a physical mass scale across lattice spacings, the analysis first approaches the chiral limit at fixed lattice spacing and then extrapolates towards the continuum, using the remnant chiral symmetry of staggered fermions as heuristic support. While this strategy cannot establish definitive physical results, it provides preliminary evidence on whether a finite-temperature RW transition persists in the chiral limit of eight-flavor QCD and clarifies how bulk lattice artifacts shape its apparent realization, with direct implications for distinguishing spontaneous symmetry breaking from conformal dynamics in this theory.