Beam-beam effects at STCF

Beam-beam effects in the Super Tau-Charm Facility (STCF) are studied using both weak-strong and strong-strong simulations, with emphasis on impact of synchro-betatron coupling. The crab-waist scheme is shown to effectively suppress beam-beam-driven betatron resonances, while synchro-betatron resonances remain a key limitation to the accessible working point and thus to the achievable luminosity. Strong-strong simulations reveal that coherent X-Z instabilities significantly broaden the beam blowup regions near resonances, reducing the available stable tune space. The roles of the synchrotron tune and horizontal beam-beam parameter are clarified: the former determines the spacing of resonances, while the latter governs their width. The impact of [Formula: see text] and longitudinal impedance is also investigated, showing that impedance-induced modifications of synchrotron motion can substantially alter the resonance structure. These results provide guidance for optimizing machine parameters and selecting robust operating points for STCF.