Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Flavor Physics and Fine-Tuning in Theory Space

R. Sekhar Chivukula, Nick Evans, Elizabeth H. Simmons

TL;DR

The paper analyzes theory-space and related composite-Higgs models, showing that although such frameworks can suppress Higgs mass corrections with high-scale strong dynamics, flavor dynamics impose a strong lower bound on the compositeness scale $\Lambda$ (roughly $75$ TeV or higher, depending on parameters). By comparing flavor-induced FCNC bounds with naturalness limits from gauge and top-quark loop corrections, the authors find a tension: maintaining a light Higgs without fine-tuning while satisfying FCNC and CP constraints generally requires tuning at the percent level (or worse for CP) unless additional flavor symmetries or dynamics are invoked. Isospin-violation constraints provide a weaker but non-negligible bound, further pushing viable models toward multi-TeV scales. Overall, the low-energy theory-space Higgs sector alone does not solve flavor or CP problems, motivating additional symmetry structures or alternative dynamics in the underlying theory.

Abstract

Recently a new class of composite Higgs models have been developed which give rise to naturally light Higgs bosons without supersymmetry. Based on the chiral symmetries of ``theory space,'' involving replicated gauge groups and appropriate gauge symmetry breaking patterns, these models allow the scale of the underlying strong dynamics giving rise to the composite particles to be as large as of order 10 TeV, without any fine tuning to prevent large corrections to Higgs boson mass(es) of order 100 GeV. In this note we show that the size of flavor violating interactions arising generically from underlying flavor dynamics constrain the scale of the Higgs boson compositeness to be greater than of order 75 TeV, implying that significant fine-tuning is required. Without fine-tuning, the low-energy structure of the composite Higgs model alone is not sufficient to eliminate potential problems with flavor-changing neutral currents or excessive CP violation; solving those problems requires additional information or assumptions about the symmetries of the underlying flavor or strong dynamics. We also consider the weaker, but more model-independent, bounds which arise from limits on weak isospin violation.

Flavor Physics and Fine-Tuning in Theory Space

TL;DR

The paper analyzes theory-space and related composite-Higgs models, showing that although such frameworks can suppress Higgs mass corrections with high-scale strong dynamics, flavor dynamics impose a strong lower bound on the compositeness scale (roughly TeV or higher, depending on parameters). By comparing flavor-induced FCNC bounds with naturalness limits from gauge and top-quark loop corrections, the authors find a tension: maintaining a light Higgs without fine-tuning while satisfying FCNC and CP constraints generally requires tuning at the percent level (or worse for CP) unless additional flavor symmetries or dynamics are invoked. Isospin-violation constraints provide a weaker but non-negligible bound, further pushing viable models toward multi-TeV scales. Overall, the low-energy theory-space Higgs sector alone does not solve flavor or CP problems, motivating additional symmetry structures or alternative dynamics in the underlying theory.

Abstract

Recently a new class of composite Higgs models have been developed which give rise to naturally light Higgs bosons without supersymmetry. Based on the chiral symmetries of ``theory space,'' involving replicated gauge groups and appropriate gauge symmetry breaking patterns, these models allow the scale of the underlying strong dynamics giving rise to the composite particles to be as large as of order 10 TeV, without any fine tuning to prevent large corrections to Higgs boson mass(es) of order 100 GeV. In this note we show that the size of flavor violating interactions arising generically from underlying flavor dynamics constrain the scale of the Higgs boson compositeness to be greater than of order 75 TeV, implying that significant fine-tuning is required. Without fine-tuning, the low-energy structure of the composite Higgs model alone is not sufficient to eliminate potential problems with flavor-changing neutral currents or excessive CP violation; solving those problems requires additional information or assumptions about the symmetries of the underlying flavor or strong dynamics. We also consider the weaker, but more model-independent, bounds which arise from limits on weak isospin violation.

Paper Structure

This paper contains 6 sections, 30 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Flavor and Composite Higgs Bosons
  3. Composite Higgs Bosons from Theory Space
  4. Flavor and Fine-Tuning in Theory Space
  5. Isospin Violation
  6. Discussion

Figures (1)

  • Figure 1: A composite Higgs model based on an $N \times N$ toroidal lattice "theory space." $SU(3)$ gauge groups live at every site except $(1,1)$, while the links represent non-linear sigma fields transforming as $(3,\bar{3})$'s under the adjacent gauge symmetries. Only an $SU(2) \times U(1)$ subgroup of an $SU(3)$ global symmetry group is gauged at site $(1,1)$. As described in the text, $N^2-1$ sets of Goldstone bosons are eaten, $N^2-1$ get mass from "plaquette operators" which explicitly break the chiral symmetries, and two sets remain in the very low-energy theory. This illustration comes from Lane:2002pe.