## Journal Club

Seminar Room, Mondays at 14:00

### Wednesday 6th of March, 2013

**Presented by Chala**

# Measuring Higgs Couplings at a Linear Collider

(Submitted on 7 Jan 2013 (v1), last revised 25 Feb 2013 (this version, v2))

Higgs couplings can be measured at a linear collider with high precision. We estimate the uncertainties of such measurements, including theoretical errors. Based on these results we show an extrapolation for a combined analysis at a linear collider and a high-luminosity LHC.

**Presented by Santiago**

# Renormalization of dimension-six operators relevant for the Higgs decay h -> γ γ

(Submitted on 22 Feb 2013)

The discovery of the Higgs boson has opened a new window to test the SM through the measurements of its couplings. Of particular interest is the measured Higgs coupling to photons which arises in the SM at the one-loop level, and can then be significantly affected by new physics. We calculate the one-loop renormalization of the dimension-six operators relevant for h -> {\gamma} {\gamma}, which can be potentially important since it could, in principle, give log-enhanced contributions from operator mixing. We find however that there is no mixing from any current-current operator that could lead to this log-enhanced effect. We show how the right choice of operator basis can make this calculation simple. We then conclude that h -> {\gamma} {\gamma} (and also h -> {\gamma} Z) can only be affected by RG mixing from operators whose Wilson coefficients are expected to be of one-loop size, among them fermion dipole-moment operators which we have also included.

**Presented by Lizana**

# "Super"-Dilatation Symmetry of the Top-Higgs System

(Submitted on 6 Feb 2013 (v1), last revised 12 Feb 2013 (this version, v2))

The top-Higgs system, consisting of top quark (LH doublet, RH singlet) and Higgs boson kinetic terms, with gauge fields set to zero, has an exact (modulo total divergences) symmetry where both fermion and Higgs fields are shifted and mixed in a supersymmetric fashion. The full Higgs-Yukawa interaction and Higgs-potential, including additional \sim 1/\Lambda^2 NJL-like interactions, also has this symmetry to O(1/\Lambda^4), up to null-operators. Thus the interaction lagrangian can be viewed as a power series in 1/\Lambda^2. The symmetry involves interplay of the Higgs quartic interaction with the Higgs-Yukawa interaction and implies the relationship, \lambda = \half g^2 between the top--Yukawa coupling, g, and Higgs quartic coupling, \lambda, at a high energy scale \Lambda >= few TeV. We interpret this to be a new physics scale. The top quark is massless in the symmetric phase, satisfying the Nambu-Goldstone theorem. The fermionic shift part of the current is \propto (1-H^\dagger H/v^2), owing to the interplay of \lambda and g, and vanishes in the broken phase. Hence the Nambu-Goldstone theorem is trivially evaded in the broken phase and the top quark becomes heavy (it is not a Goldstino). We have m_t=m_h, subject to radiative corrections that can in principle pull the Higgs into concordance with experiment.