Nambu-Goldstone boson phenomenology in Domain-Wall Standard Model

TL;DR

This paper explores a five-dimensional domain-wall model where a Nambu-Goldstone boson emerges, analyzing its interactions, astrophysical and collider constraints, and prospects for detection at future colliders.

Contribution

It introduces the phenomenology of NG bosons in the DWSM, deriving experimental bounds and proposing detection strategies for KK-mode fermions.

Findings

Lower bound of 1 TeV on KK-mode quark and lepton masses

Reinterpretation of LHC bounds on supersymmetric particles

Potential for future collider detection of KK fermions

Abstract

We investigate the Domain-Wall Standard Model (DWSM), a five-dimensional framework in which all Standard Model (SM) particles are localized on a domain wall embedded in a non-compact extra spatial dimension. A distinctive feature of this setup is the emergence of a Nambu-Goldstone (NG) boson, arising from the spontaneous breaking of translational invariance in the extra dimension due to the localization of SM chiral fermions. This NG boson couples via Yukawa interactions to SM fermions and their Kaluza-Klein (KK) excitations. We study the phenomenology of this NG boson and derive constraints from astrophysical processes (supernova cooling), Big Bang Nucleosynthesis (BBN), and collider searches for KK-mode fermions at the Large Hadron Collider (LHC). The strongest limits arise from LHC data: we reinterpret existing mass bounds on squarks and sleptons in simplified supersymmetric models (assuming a massless lightest neutralino), as well as limits on exotic hadrons containing long-lived squarks or long-lived charged sleptons in the regime of extremely small Yukawa couplings. From this analysis, we obtain a conservative lower bound of 1 TeV on the masses of KK-mode quarks and charged leptons. Finally, we discuss the prospects for producing KK-mode fermions at future high-energy lepton colliders and outline strategies to distinguish their signatures from those of sfermions.