Effective route beyond the extended scalar sectors of the standard model

Abstract

The Standard Model (SM) of particle physics explains the strong, weak and elec- tromagnetic interactions of the matter particles (quarks and leptons) and the me- diators of these interactions (gluon, W ;Z; photon) based on gauge symmetries SU(3)c SU(2)L U(1)Y . There are three generations of all types of quarks and leptons within the SM. Among the matter particles, only quarks have strong in- teractions, which give rise to bound states like mesons and baryons. Through the discovery of W ;Z bosons to electroweak precision tests, the understanding of the electroweak sector is now rather well-established. The discovery of a Higgs-like par- ticle with mass 125 GeV at the Large Hadron Collider (LHC) completes the hunt for the SM particle spectrum [1, 2]. This discovery con rms that the mechanism of electroweak symmetry breaking is indeed responsible for the masses of the SM parti- cles. The couplings of this Higgs-like particle to the SM gauge bosons and fermions have been measured to be at par with the corresponding SM values up to some uncertainties that are expected to decrease in future. For instance, in HL-LHC the couplings of the Higgs to W, Z bosons will be measured with a precision of < 2% [3]. Some of the open questions of the Universe, for which there exist many convincing cosmological/astrophysical evidence, cannot be addressed within the framework of SM, such as matter-antimatter asymmetry, dark matter, dark energy. Moreover, the issue of Higgs mass hierarchy, non-zero neutrino mass, patterns of mass and mix- ing of SM fermions across generations, etc. also remain unexplained. These open questions point toward the existence of new physics beyond Standard Model (BSM). The problem of Higgs mass hierarchy has been a key guiding principle in construct- ing BSM theories: For instance, supersymmetry solves this problem by introduc-ing additional degrees of freedoms which nullify/soften the quadratic divergence in Higgs mass correction. Neutrino mass can be obtained at the tree-level in the so-called see-saw mechanism, which might also explain matter-antimatter asymmetry via leptogenesis. Several flavour symmetries can be deployed to explain the observed pattern of masses and mixing angles of SM fermions of different generations.