Higgs coupling measurements and the scale of new physics

Abstract

A primary goal of present and future colliders is measuring the Higgs couplings to Standard Model (SM) particles. Any observed deviation from the SM predictions for these couplings is a sign of new physics whose energy scale can be bounded from above by requiring tree-level unitarity. In this paper, we extend previous work on unitarity bounds from the Higgs cubic coupling to Higgs couplings to vector bosons and top quarks. We find that HL-LHC measurements of these couplings compatible with current experimental bounds may point to a scale that can be explored at the HL-LHC or a next-generation collider. Our approach is completely model-independent: we assume only that there are no light degrees of freedom below the scale of new physics, and allow arbitrary values for the infinitely many couplings beyond the SM as long as they are in agreement with current measurements. We also extend and clarify the methodology of this analysis, and show that if the scale of new physics is above the TeV scale, then the deviations can be described by the leading higher-dimension gauge invariant operator, as in the SM effective field theory.

Matching to Higgs-Compositeness and Renormalization of the Higgs-Electroweak Chiral Lagrangian extended by a Scalar Singlet

“…Since the couplings of the gauge bosons are measured to a high precision, the measurement of the Higgs couplings will hopefully serve as portal to new physics. The Higgs couplings are within a few percent as in the Standard Model [31,32]. Any deviation from the SM is an indirect hint to new physics lying behind.…”

Unitarity Bounds on Effective Field Theories at the LHC

“…In this paper, we focus on the s-wave component for simplicity. It is somewhat tedious to keep track of all the S-matrix components corresponding to the various spin configurations when fermions are involved in the scattering (see example calculations in [23,25,47,110,138] and [75,80] for recent reviews). Minimizing this technical complication is the reason for studying the scalar toy models introduced in Sec.…”

“…Our notation for the normalized s-wave amplitude M here follows that in[75,80], which differs from the a 0 notation in e.g [139]. by a factor of two: M = 2a 0 .…”

The Scale of New Physics from the Higgs Couplings to $γγ$ and $γZ$

“…This leaves ample room for physics BSM to be probed at the High Luminosity (HL) LHC. This argument was used in [12,13] in order to probe the scale of new physics in Higgs potential, as well as the Higgs couplings to the top quark and the W and Z. In this study, we seek to extend this argument to the hγγ and hγZ sectors.…”

“…Previous studies in the literature utilized the SM Effective Field Theory (SMEFT) to investigate the couplings hγγ [15,16] and hγZ [17]. However, in this paper, we adopt the completely model-independent bottom-up approach that was used in [12,13], which does not rely on power counting, but parametrizes the scale of new physics as deviations from the SM predictions. We do not make any assumptions regarding the deviations and the infinitly many unconstrained higher-order couplings, other than that they are compatible with expertimental measurements.…”