Scalar Dark Matter and Standard Model with Four Generations

TL;DR

This paper investigates a scalar dark matter model within the Standard Model extended to four generations, analyzing experimental constraints and potential signals in Higgs and flavor-changing decays at colliders.

Contribution

It introduces the SM4+D model with a scalar dark matter candidate and explores its experimental implications and constraints from direct detection and collider processes.

Findings

A significant parameter space remains compatible with experiments.

Darkon-Higgs interactions can enhance Higgs invisible decay modes.

Potential observable flavor-changing decays involving darkon at colliders.

Abstract

We consider a scalar dark matter model, the SM4+D, consisting of the standard model with four generations (SM4) and a real gauge-singlet scalar called darkon, D, as the weakly interacting massive particle (WIMP) dark-matter (DM) candidate. We explore constraints on the darkon sector of the SM4+D from WIMP DM direct-search experiments, including CDMS II and CoGeNT, and from the decay of a B meson into a kaon plus missing energy. We find that a sizable portion of the darkon parameter space is still compatible with the experimental data. Since the darkon-Higgs interaction may give rise to considerable enhancement of the Higgs invisible decay mode, the existence of the darkon could lead to the weakening or evasion of some of the restrictions on the Higgs mass in the presence of fourth-generation quarks. In addition, it can affect the flavor-changing decays of these new heavy quarks into a lighter quark and the Higgs boson, as the Higgs may subsequently decay invisibly. Therefore we also study these flavor-changing neutral transitions involving the darkon, as well as the corresponding top-quark decay t -> cDD, some of which may be observable at the Tevatron or LHC and thus provide additional tests for the SM4+D.