Chiral EW Lagrangian

  • Rafael Delgado LópezEmail author
Part of the Springer Theses book series (Springer Theses)


The ATLAS and CMS collaborations at LHC have found a new boson compatible with the SM Higgs, with a mass of nearly \(M_h\simeq 125\,\mathrm{GeV}\). Furthermore, the most probable \(J^P\) quantum numbers are \(0^+\), and couplings with other particles are in agreement with the SM Higgs, although with moderate precision. Moreover, there is a mass gap for the presence of new physics until an energy of about 600-700 GeV, or even higher for the presence of new vector resonances. However, the data is still compatible with either an elementary or a composite Higgs: this last possibility will be considered in this work. The mass gap between the \(M_W\), \(M_Z\) and \(M_h\) masses, all of \(\mathcal {O}(100\,\mathrm{GeV})\), and the new physics scale (if there is one within reach), suggests that the Higgs boson and the would-be Goldstone bosons \(\omega ^\pm \) and z could be (pseudo) Goldstone Boson, related with a global spontaneous symmetry breaking extending the \(SU(2)_L\times SU(2)_R\rightarrow SU(2)_{L+R}\) global symmetry breaking of the SM. There are several models with specific implementations for the relevant global symmetry breaking pattern: the (Minimal) Composite Higgs Model based on the coset SO(5)/SO(4), dilaton models and others. In this chapter, the old electroweak chiral Lagrangian (ECL) is extended to include the new Higgs-like particle found at the LHC. The non-linear Electroweak Chiral Lagrangian (EWChPT) is considered as a low-energy parameterization of the new physics at the TeV scale, within the limits of the Equivalence Theorem: \(M_W,M_h\ll \sqrt{s}\ll 3\,\mathrm{TeV}\). Couplings to \(\gamma \gamma \) and \(t\bar{t}\) states are also providen.


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© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.Facultad de Ciencias Físicas, Theoretical Physics I DepartmentComplutense University of MadridMadridSpain

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