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Generating the fermion mass hierarchy at the TeV scale

Nima Arkani-Hamed, Carolina Figueiredo, Lawrence J. Hall, Claudio Andrea Manzari

Abstract

We propose a class of theories to generate quark and lepton mass matrices where the scale of new physics is at the TeV scale, without inducing the large flavor and CP violating processes that are often thought to relegate the origin of flavor to energies above $\sim 100$ TeV. The models have new vector-like leptons and quarks, with mass mixings to each other and Yukawa couplings to light Standard Model fields encoded in "chains" reminiscent of dimensional deconstruction. Locality in the chains both generates the hierarchical Standard Model Yukawa matrices, and ensures that CP and flavor violating effects are small, even with the vector-like particles at the TeV scale. A simple extension also generates neutrino masses, whose tiny size is parametrically related to the square of the electron Yukawa coupling. We outline the essential features of these models, explain how fermion mass hierarchies and mixing angles emerge, and explore their phenomenological implications. This framework can be tested both in the final run of the LHC as well as at possible future colliders operating at the 10 TeV scale, and we identify some of the distinctive experimental signatures associated with the production and decay of the new vector-like fermions.

Generating the fermion mass hierarchy at the TeV scale

Abstract

We propose a class of theories to generate quark and lepton mass matrices where the scale of new physics is at the TeV scale, without inducing the large flavor and CP violating processes that are often thought to relegate the origin of flavor to energies above TeV. The models have new vector-like leptons and quarks, with mass mixings to each other and Yukawa couplings to light Standard Model fields encoded in "chains" reminiscent of dimensional deconstruction. Locality in the chains both generates the hierarchical Standard Model Yukawa matrices, and ensures that CP and flavor violating effects are small, even with the vector-like particles at the TeV scale. A simple extension also generates neutrino masses, whose tiny size is parametrically related to the square of the electron Yukawa coupling. We outline the essential features of these models, explain how fermion mass hierarchies and mixing angles emerge, and explore their phenomenological implications. This framework can be tested both in the final run of the LHC as well as at possible future colliders operating at the 10 TeV scale, and we identify some of the distinctive experimental signatures associated with the production and decay of the new vector-like fermions.
Paper Structure (14 sections, 50 equations, 2 figures, 1 table)

This paper contains 14 sections, 50 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Chain Models
  3. Constraints
  4. Collider Signals
  5. Outlook
  6. Deriving low-energy constraints
  7. Constraints from flavor
  8. Lepton Sector: $\ell_i \to \ell_f \gamma$ ---
  9. Lepton Sector: $l \to 3l$ ---
  10. Lepton Sector: $e_i \to e_j$ conversion ---
  11. Lepton Sector: Tests of Lepton Flavor Universality ---
  12. Quark Sector: Meson mixing---
  13. Neutrino Masses
  14. Spontaneous Breaking of the Flavor Symmetry at the TeV scale

Figures (2)

  • Figure 1: (Left) Mass and Yukawa matrices for VL and light fermions. (Right) Graphical representation of interactions via chains. The links of the chains are of three types: dashed lines represent Yukawa couplings, $\lambda_i l_i E^c_{i,1} h$, the double solid lines represent vector-like masses, $M_{I} E_{I}^c E_{I}$, and the wiggly lines denote soft breaking off-diagonal mass mixing, $\mu^E_{IJ} E_{I} E^c_{J}$. In green, we represent a link between chains that generates a non-zero off-diagonal entry in the mass matrix.
  • Figure S1: Chains for neutrinos. In addition to the chains presented in the main text (fig. \ref{['fig:LeptonChains']}), we have $3$ new chains of SM singlet states, $N_{i,q}$. At the end of these new chains, we have singlets that are also neutral under the flavor symmetry, $\nu^c_{i}$, which mix via a Majorana mass term $M_{ij} \nu^c_{i}\nu^c_{j}$, represented in green.