Higgs data does not rule out a sequential fourth generation with an extended scalar sector

TL;DR

Current Higgs data does not exclude a sequential fourth generation with an extended scalar sector, as such scenarios can hide their effects in Higgs production and decay channels, requiring specific model extensions.

Contribution

The paper demonstrates that a fourth generation can exist without contradicting Higgs data if the scalar sector is extended, highlighting the importance of the bottom-quark Yukawa coupling sign.

Findings

Fourth generation effects can be hidden in Higgs production and decay.

Extended scalar sector is necessary to accommodate a fourth generation.

Current Higgs data does not rule out a sequential fourth generation.

Abstract

Contrary to the common perception, we show that the current Higgs data does not eliminate the possibility of a sequential fourth generation that get their masses through the same Higgs mechanism as the first three generations. The inability to fix the sign of the bottom-quark Yukawa coupling from the available data plays a crucial role in accommodating a chiral fourth generation which is consistent with the bounds on the Higgs signal strengths. We show that effects of such a fourth generation can remain completely hidden not only in the production of the Higgs boson through gluon fusion but also to its subsequent decay to $\gamma\gamma$ and $ Z\gamma$. This, however, is feasible only if the scalar sector of the Standard Model is extended. We also provide a practical example illustrating how our general prescription can be embedded in a realistic model.