Abstract
We study in detail the impact of anomalous Higgs couplings in angular asymmetries of the crossing-symmetric processes H --> Zl+l- and e+e- --> HZ. Beyond Standard Model physics is parametrized in terms of the SU(3)xSU(2)_LxU(1)_Y dimension-six effective Lagrangian. In the light of present bounds on d = 6 interactions we study how angular asymmetries can reveal non-standard CP-even and CP-odd couplings. We provide approximate expressions to all observables of interest making transparent their dominant dependence on anomalous couplings. We show that some asymmetries may reveal BSM effects that are hidden in other observables. In particular, CP-even and CP-odd d = 6 HZgamma couplings as well as (to a lesser extent) HZll contact interactions can generate asymmetries at the several percent level, while having small or no effects on the di-lepton invariant mass spectrum of H --> Zl+l-. Finally, the higher di-lepton invariant mass probed in e+e- --> HZ leads to interesting differences in the asymmetries with respect to those of H --> Zl+l- that may lead to complementary anomalous coupling searches at the LHC and e+e- colliders.
Highlights
In the spirit of an EFT — assuming the characteristic scale Λ of BSM physics to be much larger than the electroweak scale — the SM should be supplemented with all operators compatible with its symmetries
We study in detail the impact of anomalous Higgs couplings in angular asymmetries of the crossing-symmetric processes H → Z + − and e+e− → HZ
The higher di-lepton invariant mass probed in e+e− → HZ leads to interesting differences in the asymmetries with respect to those of H → Z + − that may lead to complementary anomalous coupling searches at the LHC and e+e− colliders
Summary
In order to parametrize BSM effects in a general way, we resort to the linear realization of the SU(2)L × U(1)Y SM electroweak symmetry. The operators OΦW B and OΦD give tree-level contributions to S and T , respectively (for the explicit expressions in our basis, see [36]) Experimental values for these two parameters [40] constrain αΦW B and αΦD to be at the permille level. One-loop corrections to the SM amplitude give contributions to the H → Z + − and e+e− → HZ processes studied in this paper that can be of the same order of d = 6 terms They have been computed in the past [46,47,48,49] and should eventually be included in a quantitative extraction of the anomalous couplings from data. The three types of diagrams are depicted in figure 1
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