Constraints on coloured scalars from global fits

Abstract

We consider a simple extension of the electroweak theory, incorporating one SU(2)L doublet of colour-octet scalars with Yukawa couplings satisfying the principle of minimal flavour violation. Using the HEPfit package, we perform a global fit to the available data, including all relevant theoretical constraints, and extract the current bounds on the model parameters. Coloured scalars with masses below 1.05 TeV are already excluded, provided they are not fermiophobic. The mass splittings among the different (charged and CP-even and CP-odd neutral) scalars are restricted to be smaller than 20 GeV. Moreover, for scalar masses smaller than 1.5 TeV, the Yukawa coupling of the coloured scalar multiplet to the top quark cannot exceed the one of the SM Higgs doublet by more than 80%. These conclusions are quite generic and apply in more general frameworks (without fine tunings). The theoretical requirements of perturbative unitarity and vacuum stability enforce relevant constraints on the quartic scalar potential parameters that are not yet experimentally tested.

W-boson mass and electric dipole moments from colour-octet scalars

“…Indeed, using these theoretical constraints the mass splitting is reduced to be smaller than 30 GeV for masses of the scalars of around 1 TeV, as shown in Ref. [25]. The combination of the oblique parameters with the theoretical restrictions reduce the parameter space of the theory to the blue regions (oblique parameters) between the red lines (theoretical constraints).…”

“…The allowed region of mass splittings is shown in Figure 2 (left), where we see that the case of totally degenerate masses is strongly disfavoured (at 6 σ level) with the CDF measurement of the W mass. In addition to the experimental constraints from the oblique parameters, restrictions on the mass splittings of the colour-octet scalars are also obtained from imposing perturbative unitarity and renormalization-group stability [23,24,25]. Indeed, using these theoretical constraints the mass splitting is reduced to be smaller than 30 GeV for masses of the scalars of around 1 TeV, as shown in Ref.…”

The top quark electro-weak couplings after LHC Run 2

“…The fit to data is performed using the open source HEPfit package [54,55]. HEPfit is a general tool designed to combine direct and indirect constraints in the SM [56], in EFT [6,57] or in particular BSM extensions [58,59]. Its flexibility allows to easily implement any BSM model or observable.…”

On long-lived electroweak-singlet coloured scalars

“…Recent reviews that highlight different theoretical scenarios that may give rise to such long-lived particles and the experimental strategies to search for them are, for example, Refs. [1][2][3].…”