Oblique S and T constraints on electroweak strongly-coupled models with a light Higgs

Abstract

Using a general effective Lagrangian implementing the chiral symmetry breaking SU(2) L ⊗ SU(2) R → SU(2) L+R , we present a one-loop calculation of the oblique S and T parameters within electroweak strongly-coupled models with a light scalar. Imposing a proper ultraviolet behaviour, we determine S and T at next-to-leading order in terms of a few resonance parameters. The constraints from the global fit to electroweak precision data force the massive vector and axial-vector states to be heavy, with masses above the TeV scale, and suggest that the W + W − and ZZ couplings of the Higgs-like scalar should be close to the Standard Model value. Our findings are generic, since they only rely on soft requirements on the short-distance properties of the underlying strongly-coupled theory, which are widely satisfied in more specific scenarios.

Fingerprints of heavy scales in electroweak effective Lagrangians

“…Comparing the experimental bounds on the S parameter [105][106][107] with the one-loop resonance calculation [44,45], one then obtains the determination of F 1 [0] in terms of M V shown in figure 1 [12]. One can also derive positivity constraints, based on generic properties such as unitarity, analyticity and crossing, which get translated into restrictions on the LECs [108][109][110].…”

“…Since parity interchanges left and right, leaving SU(2) L+R invariant, the compensating transformation g h (ϕ, g) is the same in the two chiral sectors. We will adopt the canonical choice of coset representative u L (ϕ) = u † R (ϕ) = u(ϕ) [44,45], 3 which transforms like 4) with the exponential representation u(ϕ) = exp{i σ ϕ/(2v)}. Its relation with the matrix U(ϕ) in eq.…”

“…Obvious extensions of this analysis, to be investigated in future works, include spin-2 bosons, coloured heavy states and massive fermions. A first necessary step is to complete our minimal basis of EWET operators with the additional terms involving [12,45]. The experimental bounds on the S parameter [105][106][107] restrict the allowed region to the black narrow area.…”

Updates on fits to electroweak parameters

“…probability), expected for example in composite Higgs models. This problem can be alleviated by adding extra contributions to the oblique parameters [75][76][77][78]. In the right plot of fig.…”

Vector and axial-vector resonances in composite models of the Higgs boson

“…As a result, potential cancellations have been observed that can relax the constraints from EW precision tests [84,85], including loop contributions from light top partners: these results, however, are not generic. Loop corrections can be considered a modelling of the contribution of the strong dynamics (see also [86,87]). In principle, improved calculability in ref.…”