Abstract
Abstract Electroweak precision measurements established that custodial symmetry is preserved to a good accuracy in the gauge sector after electroweak symmetry breaking. However, recent LHC results might be interpreted as pointing towards Higgs couplings that do not respect such symmetry. Motivated by this possibility, we reconsider the presence of an explicitly custodial breaking coupling in a generic Higgs parameterization. After briefly commenting on the large UV sensitivity of the T parameter to such a coupling, we perform a fit to results of Higgs searches at LHC and Tevatron, and find that the apparent enhancement of the ZZ channel with respect to WW can be accommodated. Two degenerate best-fit points are present, which we label ‘Zphilic’ and ‘dysZphilic’ depending on the sign of the hZZ coupling. Finally we highlight some measurements at future linear colliders that may remove such degeneracy.
Highlights
T parameterIt is well known that when a = 1 in eq (2.7), a logarithmically divergent contribution to T (as well as to S) arises
Such hints could be just due to statistical fluctuations, or to issues with the modeling of complex backgrounds
We remark that many proposals for physics beyond the SM exist in the literature where the custodial symmetry is not respected: for example, models where the Higgs sector is extended with scalar triplets that get a non-vanishing vacuum expectation value, generic two Higgs doublet models, as well as theories where the Higgs arises as the pseudoGoldstone boson of a coset G/H where H does not contain SO(4) ∼ SU(2) × SU(2), such as SU(3)/(SU(2) × U(1)), fall in this class
Summary
It is well known that when a = 1 in eq (2.7), a logarithmically divergent contribution to T (as well as to S) arises. Such contribution is due to the diagrams, and is computable within the low-energy theory, see ref. In the present case we need to consider the effects of explicit custodial breaking contained in eq (2.8). Even if we set tcb = 0, a quadratic UV sensitivity appears in T , due to the diagrams involving the Higgs shown in figure 1(b).
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