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Observable contributions of new exotic quarks to quark mixing

F. del Aguila, M. Perez-Victoria, J. Santiago

TL;DR

This work develops a unified effective field theory framework for SM extensions with vector-like quarks to study observable quark-mixing effects. By integrating out the heavy vector-like states at tree level, it derives a set of seven dimension-6 operators that modify quark-gauge and quark-Higgs couplings, and expresses these corrections through X^{uL}_{ij}, X^{uR}_{ij}, X^{dL}_{ij}, X^{dR}_{ij}, W^L_{ij}, W^R_{ij}, Y^{u,d}_{ij}. The authors show that these corrections induce tree-level FCNCs in the neutral sector, non-unitary left-handed charged currents, and Higgs-mediated effects, with semidefinite coefficient matrices yielding predictive inequalities to discriminate among exotic-quark multiplets. They provide explicit relations and bounds that depend on the type of vector-like quark added, enabling model discrimination from precision measurements of Z, W, and H couplings, particularly in the top-quark sector where deviations of order ~1% are feasible. The framework isolates TeV-scale new physics and guides experimental tests to identify or constrain vector-like quark extensions.

Abstract

Models with new vector-like quarks can produce observable quark mixing effects which are forbidden in the Standard Model. We classify all such models and write down the effective Lagrangian that results from integrating out the new quarks. We study the relations between neutral and charged currents and discuss how to distinguish among the different possibilities.

Observable contributions of new exotic quarks to quark mixing

TL;DR

This work develops a unified effective field theory framework for SM extensions with vector-like quarks to study observable quark-mixing effects. By integrating out the heavy vector-like states at tree level, it derives a set of seven dimension-6 operators that modify quark-gauge and quark-Higgs couplings, and expresses these corrections through X^{uL}_{ij}, X^{uR}_{ij}, X^{dL}_{ij}, X^{dR}_{ij}, W^L_{ij}, W^R_{ij}, Y^{u,d}_{ij}. The authors show that these corrections induce tree-level FCNCs in the neutral sector, non-unitary left-handed charged currents, and Higgs-mediated effects, with semidefinite coefficient matrices yielding predictive inequalities to discriminate among exotic-quark multiplets. They provide explicit relations and bounds that depend on the type of vector-like quark added, enabling model discrimination from precision measurements of Z, W, and H couplings, particularly in the top-quark sector where deviations of order ~1% are feasible. The framework isolates TeV-scale new physics and guides experimental tests to identify or constrain vector-like quark extensions.

Abstract

Models with new vector-like quarks can produce observable quark mixing effects which are forbidden in the Standard Model. We classify all such models and write down the effective Lagrangian that results from integrating out the new quarks. We study the relations between neutral and charged currents and discuss how to distinguish among the different possibilities.

Paper Structure

This paper contains 4 sections, 19 equations, 1 figure, 6 tables.

Table of Contents

  1. Introduction
  2. Effective Lagrangian for extensions with exotic quarks
  3. Corrections to quark couplings
  4. Relations and Bounds

Figures (1)

  • Figure 1: Diagrams contributing to dimension 6 operators in the effective Lagrangian. Light (heavy) quarks are depicted by a single (double) line.