Positivity bounds on vector boson scattering

Searching for deviations in quartic gauge boson couplings (QGCs) is one of the main goals of the electroweak program at the LHC. We consider positivity bounds adapted to the Standard Model EFT, and show that a set of positivity constraints on 18 anomalous QGC couplings can be derived, by requiring that the vector boson scattering amplitudes satisfy the fundamental principles of quantum field theory. We solve the positivityinequalities and find that the allowed parameter space is carved out bythe intersection of pyramids, prisms, and cones. Altogether, the allowedparameter space is reduced to ~2% of total. These bounds provideguidance to future BSM searches and could affect the limits on couplingsby modifying the prior.

Cen Zhang obtained his PhD in University of Illinois atUrbana-Champaign. He then spent time in Louvain-la-Neuve and inBrookhaven National Lab as a postdoctoral researcher, and now he is anassociate professor in the theory division of Institute of High EnergyPhysics, Chinese Academy of Sciences. His main research interests focuson the collider phenomenological aspects of the Standard Model EffectiveField Theory (SMEFT), in particular in its top-quark sector. He has been working on accurate predictions of collider observables via the development of Monte Carlo tools for SMEFT, understanding of signatures and indirect measurements, and global fits to collider data. The talk will be related to his recent research on the application of positivity approach in SMEFT.