Systematizing and addressing theory uncertainties of unitarization with the Inverse Amplitude Method

Effective Field Theories (EFTs) constructed as derivative expansions in powers of momentum, the spirit Chiral Perturbation Theory (ChPT), are a controllable approximation to strong dynamics long energy interacting particles remains small, they do not respect exact elastic unitarity. This limits their predictive power towards new physics at higher scale if small separations from Standard Model found LHC or elsewhere. Unitarized chiral perturbation theory techniques have been devised extend reach EFT regimes where partial waves saturating unitarity, but uncertainties hitherto addressed thoroughly. Here we take one best known them, Inverse Amplitude Method (IAM), and carefully following its derivation, quantify uncertainty introduced each step. We compare hadron ChPT electroweak sector Higgs applications. find that relative theoretical IAM mass first resonance encountered partial-wave is same order counting starting near-threshold energies, so unitarized extension should priori be expected reasonably successful. provided check for zeroes wave amplitude carried out and, appear near region, show how modify adequately them into account.