Unitarity and Positivity Constraints on C- or P-odd Anomalous Quartic Couplings

Abstract

In this work, we provide a comprehensive study of partial-wave unitarity and positivity constraints in the dimension-eight genuine anomalous quartic gauge coupling (aQGC) sector of the Standard Model Effective Field Theory (SMEFT). We extend previous partial-wave unitarity analyses to include all C- or P-odd operators, thereby completing the coverage of the full basis of 34 operators. We also derive an analytical set of necessary forward-limit positivity bounds that include all CP-odd Wilson coefficients. We demonstrate that non-vanishing CP-odd Wilson coefficients require non-vanishing contributions from the CP-even sector to satisfy the derived positivity conditions. Combining the positivity conditions with partial-wave unitarity, we obtain stronger bounds on twenty-three of the thirty-four Wilson coefficients in this sector of the SMEFT.