Vacuum Instabilities with a Wrong-Sign Higgs-Gluon-Gluon Amplitude

Abstract

The recently discovered 125 GeV boson appears very similar to a Standard Model Higgs, but with data favoring an enhanced (h \rightarrow \gamma \gamma) rate. A number of groups have found that fits would allow (or, less so after the latest updates, prefer) that the (ht \bar t)coupling have the opposite sign. This can be given meaning in the context of an electroweak chiral Lagrangian, but it might also be interpreted to mean that a new colored and charged particle runs in loops and reinforces the W-loop contribution to hFF, while also producing the opposite-sign hGG amplitude to that generated by integrating out the top. Due to a correlation in sign of the new physics amplitudes, when the SM hFF coupling is enhanced the hGG coupling is decreased. Thus, in order to not suppress the rate of (h \rightarrow WW) and (h \rightarrow Z Z), which appear to be approximately Standard Model-like, one would need the loop to “overshoot,” not only canceling the top contribution but producing an opposite-sign hGG vertex of about the same magnitude as that in the SM. We argue that most such explanations have severe problems with fine-tuning and, more importantly, vacuum stability. In particular, the case of stop loops producing an opposite-sign hGG vertex of the same size as the Standard Model one is ruled out by a combination of vacuum decay bounds and LEP constraints. We also show that scenarios with a sign flip from loops of color octet charged scalars or new fermionic states are highly constrained.