Testing heavy scale seesaw models at future colliders

Abstract

In this thesis, we introduce the Standard Model (SM) and give motivations for extending it. Amongst the many possible Beyond SM (BSM) scenarios, Supersymmetry (SUSY) combined with a seesaw mechanism is a promising portal to new physics able to remedy several flaws of the SM, which we highlight. Specifically, we discuss SUSY models with high scale seesaw from a phenomenological perspective and test these at future colliders. We start by studying the Next-to-Minimal Supersymmetric Standard Model with right-handed neutrinos (NMSSMr) at the International Linear Collider (ILC) when the lightest right-handed sneutrino is the Dark Matter (DM) candidate. By exploiting a ‘dijet + dilepton + Missing Transverse Energy (MET or /ET)’ signature, we estimate the size of the neutrino Yukawa coupling. In addition, we show that, in some SUSY scenarios combined with selected seesaw models, the large Yukawa couplings produced can leave their fingerprints in Higgs-slepton couplings entering hadro-production processes. For example, in Type-I and Type-III seesaw, we can potentially observe ̃ν₂ → ν₁h and ℓ^±₂ → ℓ^±₁ h decays, respectively. Unfortunately, the current exclusion bounds make it impossible to observe a significant signal of these even at the High-Luminosity Large Hadron Collider (HL-LHC), with luminosity L = 1 ab⁻¹. Thus, we highlight that the High-Energy LHC (HE-LHC), with energy √s = 27 TeV, could provide some sensitivity to such signals in the single lepton channel. The final part of this thesis is instead focused on CP-violation effect in the B-L Supersymmetric Standard Model (BLSSM) with inverse seesaw by measuring Triple Product Asymmetries (TPAs) in ‘lepton + jet’ final states induced by Z′ state at the Future Circular Collider operating in hadron-hadron mode (FCC-hh), with √s = 80 TeV.

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Identifiers

ORCID for Yi Liu: orcid.org/0009-0005-0466-743X

ORCID for Stefano Moretti: orcid.org/0000-0002-8601-7246

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