The electroweak chiral Lagrangian with a light Higgs - systematics & application

por Claudius Krause (Munich University)

jueves 19 may. 2016 12:00 → 13:00 Europe/Madrid

1001-Primera-1-1-1 - Paterna. Seminario (Universe)

I consider the Standard Model as an effective field theory (EFT) at the electroweak scale v. At the scale f >= v I assume a new, strong interaction that breaks the electroweak symmetry dynamically. The Higgs boson arises as a composite pseudo-Nambu-Goldstone boson in these scenarios and is therefore naturally light (m_h ~ v). Based on these assumptions and the value of \xi= v^2 / f^2, I explain the systematics that governs the effective expansion: For \xi = O(1) the effective theory is given by a loop expansion, equivalent to an expansion in chiral dimensions (similar to chiral perturbation theory). I will briefly discuss the operators that arise at next-to-leading order [O(f^2 / \Lambda^2) ~ O(1/16\pi^2)]. On the other hand, in the decoupling limit where \xi -> 0, an expansion in canonical dimension is recovered. The case where \xi is small but non-zero is of phenomenological interest. It leads to a double expansion in \xi and 1/16\pi^2, which captures the expected corrections of a strongly-interacting light Higgs to the Standard Model in a systematic way. Further, I will apply the leading order chiral Lagrangian to current LHC Higgs data. I will show that this gives a QFT justification of the kappa-framework, which is currently used as phenomenological signal-strength parametrization by the experiments at the LHC. I will also present a fit of the leading order chiral Lagrangian to the LHC Higgs data.