Vector Boson Scattering Processes: Status and Prospects

Insight into the electroweak (EW) and Higgs sectors can be achieved through measurements of vector boson scattering (VBS) processes. The scattering of EW bosons are rare processes that are precisely predicted in the Standard Model (SM) and are closely related to the Higgs mechanism. Modifications to VBS processes are also predicted in models of physics beyond the SM (BSM), for example through changes to the Higgs boson couplings to gauge bosons and the resonant production of new particles. In this review, experimental results and theoretical developments of VBS at the Large Hadron Collider, its high luminosity upgrade, and future colliders are presented.

Anatomy of inclusive $toverline{t}W$ production at hadron colliders

In LHC searches for new and rare phenomena the top-associated channel $pp to toverline{t}W^pm +X$ is a challenging background that multilepton analyses must overcome. Motivated by sustained measurements of enhanced rates of same-sign and multi-lepton final states, we reexamine the importance of higher jet multiplicities in $pp to toverline{t}W^pm +X$ that enter at $mathcal{O}(alpha_s^3alpha)$ and $mathcal{O}(alpha_s^4alpha)$, i.e., that contribute at NLO and NNLO in QCD in inclusive $toverline{t}W^pm$ production. Using fixed-order computations, we estimate that a mixture of real and virtual corrections at $mathcal{O}(alpha_s^4alpha)$ in well-defined regions of phase space can arguably increase the total $toverline{t}W^pm$ rate at NLO by at least $10%-14%$. However, by using non-unitary NLO multi-jet matching, we estimate that these same corrections are at most $10%-12%$, and at the same time exhibit the enhanced jet multiplicities that are slightly favored by data. This seeming incongruity suggests a need for the full NNLO result. We comment on implications for the $toverline{t}Z$ process.

Automated Predictions from Polarized Matrix Elements

The anticipated experimental resolution and data cache of the High Luminosity Large Hadron Collider will enable precision investigations of polarization in multiboson processes. This includes, for the first time, vector boson scattering. To facilitate such studies, we report the automation of polarized matrix element computations in the publicly available Monte Carlo tool suite, MadGraph5_aMC@NLO. This enables scattering and decay simulations involving helicity-polarized asymptotic or intermediate states, preserving both spin-correlation and off-shell effects. As demonstrations of the method, we investigate the leading order production and decay of polarized weak gauge bosons in the process $pp to j j W^+_lambda W^-_{lambda}$, with helicity eigenstates $(lambda,lambda)$ defined in various reference frames. We consider the Standard Model at both $mathcal{O}(alpha^4)$ and $mathcal{O}(alpha^2 alpha_s^2)$ as well as a benchmark composite Higgs scenario. We report good agreement with polarization studies based on the On-Shell Projection (OSP) technique. Future capabilities are discussed.

Lepton Number Violation and W Chiral Couplings at the LHC

We study the observability for a heavy Majorana neutrino N along with a new charged gauge boson W at the LHC. We emphasize the complementarity of these two particles in their production and decay to unambiguously determine their properties. We show that the Majorana nature of N can be verified by the lepton-number violating like-sign dilepton process, and by polar and azimuthal angular distributions. The chirality of the W coupling to leptons and to quarks can be determined by a polar angle distribution in the reconstructed frame and an azimuthal angle distribution.