Robust determination of the Higgs couplings: Power to the data

Abstract

We study the indirect effects of new physics on the phenomenology of the recently discovered "Higgs-like" particle. In a model independent framework these effects can be parametrized in terms of an effective Lagrangian at the electroweak scale. In a theory in which the SU (2)L × U (1)Y gauge symmetry is linearly realized they appear at lowest order as dimension-six operators, containing all the SM fields including the light scalar doublet, with unknown coefficients. We discuss the choice of operator basis which allows us to make better use of all the available data on the new state, triple gauge boson vertex and electroweak precision tests, to determine the coefficients of the new operators. We illustrate our present knowledge of those by performing a global fit to the existing data which allows simultaneous determination of the eight relevant parameters quantifying the Higgs couplings to gluons, electroweak gauge bosons, bottom quarks, and tau leptons. We find that for all scenarios considered the standard model predictions for each individual Higgs coupling and observable are within the corresponding 68% CL allowed range. We finish by commenting on the implications of the results for unitarity of processes at higher energies.Note added: The analysis has been updated with all the public data available by October 2013. Updates of this analysis are provided at the web site http://hep.if.usp.br/Higgs as well as new versions of this manuscript.

Investigating perturbative unitarity in the presence of anomalous couplings

“…Using the best fit values of the combined analysis with Tevatron and LHC data [34], we observe that the unitarity validation scale can be raised upto 9 TeV.…”

“…A global fit to the existing LHC and Tevatron data has been performed in reference [34] allowing simultaneous determination of the parameters quantifying the Higgs boson couplings to the electroweak gauge bosons and the other SM particles. Using their best fit value 1.5 (-1.6) TeV −2 for f W W /Λ 2 (f BB /Λ 2 ), we observe that unitarity is not violated upto energies ∼ 9 (19) TeV.…”

Complete Higgs sector constraints on dimension-6 operators

“…2 Many strong constraints come from electroweak precision tests (EWPT) [94][95][96] at LEP, and from triplegauge coupling (TGC) [91,92,97] measurements at LEP and the LHC. In the case of Higgs observables, aside from operators contributing to couplings that are absent at tree-level in the SM, only weaker limits are available so far.…”

“…Constraints on these operators have been placed for subsets of operators [80][81][82][83][84][85][86][87][88][89] and in full global fits both before [90] and after [91][92][93] the Higgs discovery. 2 Many strong constraints come from electroweak precision tests (EWPT) [94][95][96] at LEP, and from triplegauge coupling (TGC) [91,92,97] measurements at LEP and the LHC.…”

The effective Standard Model after LHC Run I

“…Using the equations of motions reduces the number of independent operators [44][45][46][47][48][49], with a complete non-redundant set first categorised in [50]. This is the effective Standard Model approach adopted in a large number of recent papers 1 , and there have been many analyses of the constraints imposed on new physics via upper limits on the coefficients of a complete dimension-6 operator basis [84][85][86][87][88][89], in particular. Several different classes of measurements make important contributions to these constraints.…”