Pushing Higgs effective theory to its limits

Abstract

At the LHC, an effective theory of the Higgs sector allows us to analyze kinematic distributions in addition to inclusive rates, although there is no clear hierarchy of scales. We systematically analyze how well dimension-6 operators describe LHC observables in comparison to the full theory, and in a range where the LHC will be sensitive. The key question is how the breakdown of the dimension-6 description affects Higgs measurements during the upcoming LHC run for weakly interacting models. We cover modified Higgs sectors with a singlet and doublet extension, new top partners, and a vector triplet. First, weakly interacting models only generate small relevant subsets of dimension-6 operators. Second, the dimension-6 description tends to be justified at the LHC. Scanning over model parameters, significant discrepancies can nevertheless arise; their main source is the matching procedure in the absence of a well-defined hierarchy of scales. While these issues require vigilance, they should not present a major problem for future LHC analyses.

The gauge-Higgs legacy of the LHC Run I

“…One caveat applies to these results the same way it applies to the Higgs analyses alone [6,7,[79][80][81][82][83][84][85]. 1 If we consider the dimension-six Lagrangian of eq.…”

“…Com- puting the effects of dimension-eight operators appears to be one way of estimating the theoretical uncertainties which enter the translation of our dimension-six results into actual models. However, detailed studies in the Higgs sector [79][80][81][82][83][84][85] indicate that individual dimension-eight contributions are not necessarily a good measure for these uncertainties. Therefore, the effective theory interpretation of the results on the truncated dimension-six Lagrangian shown in figure 4 should be done with care.…”

“…The dashed lines illustrate the effects from individual dimension-six operators, suggesting that we should be able to derive powerful constraints from the ATLAS measurements. The fact that the last bin extends to large transverse momenta also suggests that we have to be careful interpreting our dimension-six analysis in terms of an effective field theory expansion [6,7,[79][80][81][82][83][84][85].…”

Low energy behaviour of standard model extensions

“…One problem in dealing with BSM models is the absence of a well-defined hierarchy of scales, see ref. [4,5] for a discussion. A second problem, as observed in ref.…”

“…−i k−1 . The term L SM is the SM Lagrangian and ∆L (4) contains light fields only and it is proportional to non-SM couplings (i.e. corrections to SM-couplings, due to the new interactions).…”