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Nambu-Goldstone boson phenomenology in Domain-Wall Standard Model

Puja Das, Nobuchika Okada, Digesh Raut, Desmond Villalba

TL;DR

This work analyzes the Domain-Wall Standard Model in a non-compact extra dimension, where all SM fields are localized on a finite-width domain wall and a massless Nambu-Goldstone boson arises from broken translational invariance. It constructs the 4D effective theory, detailing the NG-boson couplings to SM fermions and their KK partners, and derives constraints from SN 1987A cooling, BBN, and LHC searches for KK-mode fermions. The strongest bounds come from LHC data, which imply a conservative lower limit of about 1 TeV on KK-mode quark and charged-lepton masses; astrophysical bounds further constrain the NG Yukawa couplings. The paper also discusses collider prospects, including distinguishing KK-mode fermions from sfermions at future high-energy lepton colliders via angular distributions and long-lived particle signatures.

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.

Nambu-Goldstone boson phenomenology in Domain-Wall Standard Model

TL;DR

This work analyzes the Domain-Wall Standard Model in a non-compact extra dimension, where all SM fields are localized on a finite-width domain wall and a massless Nambu-Goldstone boson arises from broken translational invariance. It constructs the 4D effective theory, detailing the NG-boson couplings to SM fermions and their KK partners, and derives constraints from SN 1987A cooling, BBN, and LHC searches for KK-mode fermions. The strongest bounds come from LHC data, which imply a conservative lower limit of about 1 TeV on KK-mode quark and charged-lepton masses; astrophysical bounds further constrain the NG Yukawa couplings. The paper also discusses collider prospects, including distinguishing KK-mode fermions from sfermions at future high-energy lepton colliders via angular distributions and long-lived particle signatures.

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.

Paper Structure

This paper contains 10 sections, 53 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Domain-Wall fermions and NG-mode coupling
  3. Kink solution along the extra spacial direction
  4. Domain-Wall Fermion
  5. Domain-Wall SM Fermions and NG-mode Couplings
  6. Phenomenological constraints on the NG-mode physics
  7. Constraint from supernova 1987A
  8. BBN bound
  9. LHC Bounds on KK-mode Fermion Mass
  10. Conclusion and discussion

Figures (2)

  • Figure 1: Summary of constraints from SN 1987A observations, BBN, and coupling perturbativity. The black solid line shows the upper limit from SN 1987A cooling (Raffelt criterion), excluding the region above it, while the black dashed line indicates the trapping condition limit, with the Raffelt criterion applicable only below this line. The blue line is the upper limit to satisfy the BBN bound, while the horizontal red line shows the perturbativity limit $y_\varphi \leq \sqrt{4\pi}$.
  • Figure 2: Normalized differential cross sections for pair productions of KK-mode electrons (black solid) and right-handed selectrons (black dashed), respectively. Here, we set the collider energy $\sqrt{s}=3$ TeV and $m_{E}=m_{{\tilde{e}}_R}=1$ TeV.