Precision Higgs coupling analysis at e+e- colliders using Effective Field Theory
One of the goals of future e+e- colliders is to measure the couplings of the Higgs boson with high precision. It is not completely straightforward to go from sigma x BR measurements to absolutely normalized Higgs couplings. A framework is required, even to make "model-independent" statements. In this lecture, I will explore the use of Effective Field Theory for this purpose, parametrizing the most general new physics effects as dimension-6 operators to be added to the Standard Model. This method has less model-dependence than the conventionally-used method of allowing arbitrary rescaling of Higgs couplings, and it is also more powerful, allowing the addition of new constraints from SU(2)xU(1) and new Higgs observables. Using measurements expected at the 250 GeV ILC or other 250 GeV colliders, it is possible to constraint all relevant dimension-6 coefficients (20 in all) in a fit with no significant degeneracies. I will present the expectations that this method gives for Higgs coupling determinations at the 250 GeV ILC and for the full ILC program, and comparisons to expectations from BSM models. I will also discuss the model-independent extraction of the triple Higgs coupling from data and argue that this is possible uniquely at e+e- colliders.