Anomalous Higgs Couplings as a Window to New Physics

TL;DR

This paper investigates how deviations in Higgs boson couplings from the Standard Model could indicate new physics, showing potential unitarity violations and vacuum instability at TeV scales, thus requiring new UV-complete theories.

Contribution

It analyzes the implications of anomalous Higgs couplings on unitarity and vacuum stability, highlighting the need for new physics at TeV energies.

Findings

Unitarity in gauge boson scattering breaks down between 1 and 10 TeV for certain anomalous couplings.

Higgs quartic coupling becomes negative around the same energy scale, indicating vacuum instability.

New ultraviolet physics is required to restore consistency if deviations are confirmed.

Abstract

The initial data on the production and decay of the Higgs boson reported significant deviations from the Standard Model (SM) expectations, prompting much speculation about its couplings to the other particles. Although the latest data has veered towards conformity with the SM, there is yet room for a sizable deviation from the SM values of the coupling of the Higgs boson with $t\bar{t}$, and to a smaller extent, of that with $W^+W^-$ and $ZZ$. Keeping the fluid nature of the data in mind, this opens up an interesting avenue to explore regarding unitarity of gauge boson scattering and the stability of the electroweak vacuum in the presence of anomalous couplings. We show that, for some typical benchmark points, unitarity in gauge boson scattering breaks down between 1 and 10 TeV. We also show that if there are no new light degrees of freedom, the Higgs quartic coupling becomes negative at around the same point, making the electroweak vacuum unstable. Thus, some new ultraviolet completing new physics is demanded at that scale to cancel both these anomalous behaviours if such deviations from the SM couplings are indeed established.