(Dys)Zphilia or a custodial breaking Higgs at the LHC

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.

Figures (10)

• Figure 1: $(a)$ Diagrams giving a logarithmic divergence in $T$ when $a\neq 1\,$. This is the leading correction in the custodial-preserving case. $(b)$ Diagrams giving a quadratic divergence in $T$ when $a_{cb}\neq 1\,$, see Eq. \ref{['quad_div']}.
• Figure 2: Isocontours in the $(a,a_{cb})$ plane of $|\Delta\epsilon_{1}^{UV}/\epsilon_{1}^{exp}|^{-1}\,$ (solid, black) and of $|\Delta\epsilon_{1}^{TL}/\epsilon_{1}^{exp}|^{-1}\,$ (red, dashed), roughly representing the amount of tuning needed to satisfy EWPT.
• Figure 3: Summary table of the experimental results that we included in our analysis. The signal strengths for all CMS and Tevatron channels, as well as for the ATLAS $WW$ and $\gamma \gamma_{FP}$ are taken at $m_{h}=125\,\mathrm{GeV}$. On the other hand, for the ATLAS $ZZ$ and $\gamma \gamma$ channels we use the peak signal strength. We report the leading scaling with the parameters $(a,a_{cb},c)$ both for production cross section and partial decay width in the various channels. The predictions of the best fit points are also shown in orange.
• Figure 4: Left panel: best-fit region in the $(a,a_{cb})$ plane from LHC results, as in Fig. 3, at $68,95,99\%$ C.L. after marginalization. Dashed lines represent the analogous contours in the case $c=1$. The two best fit points with (without) marginalization are shown as black dots (crosses), while the star is the SM point corresponding to $(a,a_{cb})=(1,0)$. All the observables involved are insensitive to the sign of $a+a_{cb}$, implying the symmetry under $(a,a_{cb})\to (a,-(2a+a_{cb}))$. Right panel: isocontours of $|\Delta\epsilon_{1}^{UV}/\epsilon_{1}^{exp}|^{-1}\,$ (dotted, black) and of $|\Delta\epsilon_{1}^{TL}/\epsilon_{1}^{exp}|^{-1}\,$ (red, dashed), indicating the level of tuning needed to satisfy EWPT, are superimposed to the LHC best fit region.
• Figure 5: The colored regions show the range of $\mu_{ZZ}/\mu_{WW}$ (left panel) and $\mu_{\gamma\gamma jj}/\mu_{ZZ}$ (right panel) as a function of $a$, obtained varying $a_{cb}$ within the $68\%$ CL region of the LHC fit, whereas the full line corresponds to choosing the best-fit value of $a_{cb}$ for the given $a\,$.