Anomalous Higgs couplings in angular asymmetries of H →Zℓ⁺ℓ⁻ and e⁺e⁻ →HZ

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) × SU(2)_L × U(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 HZγ couplings as well as (to a lesser extent) HZℓ⁺ℓ⁻ 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.