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Perspectives and Questions: Toward an Expansive Agenda for Particle Physics

Chris Quigg

TL;DR

This essay argues that the post-Higgs era demands a broad, opportunistic research program across particle physics, spanning flavor, neutrino physics, QCD, unified theories, and cosmology. It champions an expansive, multi-scale approach that combines effective field theory with precision measurements and diverse experimental avenues, from future high-energy colliders to cosmic and laboratory probes of dark matter and feebly interacting particles. Central to the agenda is a deep investigation of the Higgs sector, including absolute branching fractions, the total width $\Gamma_H$, and the potential Higgs self-coupling, to map any deviations from Standard Model expectations around $M_H \approx 125.20\, \mathrm{GeV}$ and to explore hidden-sector portals. The paper also emphasizes the integration of cosmology with particle physics and the sustained development of accelerator technologies, proposing a portfolio of next-generation machines (e.g., $e^+e^-$ Higgs factories, a $100$-TeV hadron collider, muon colliders) to illuminate fundamental questions about unification, the origin of masses, and the structure of spacetime, while remaining attentive to unexpected discoveries at yet-unknown scales. It is a call for a diverse, long-horizon program that merges theory, experiment, and technology to push beyond the Standard Model and to understand the universe from the smallest to the largest scales.

Abstract

Global celebration greeted the 2012 discovery at CERN's Large Hadron Collider of a particle that matches the textbook description of the Higgs boson. That achievement validated a remarkable chain of theoretical reasoning that combined the prescriptive notion of electroweak gauge symmetry with a simple, but \emph{ad hoc}, embodiment of spontaneous symmetry breaking. It was made possible by generational triumphs of accelerator art and experimental technique, and by human resourcefulness and collaboration on a global scale, all sustained by the enlightened support of many governments and institutions. Some imagine that, once the keystone of the standard model of particle physics has been set, our subject is over. Others worry that we may be at an impasse because no comparable wonders have appeared, leaving us without well-defined clues to a more complete paradigm. I am neither so readily satisfied nor so {easily} discouraged: we have so much more to learn! This essay surveys many questions that, taken together, constitute an inspiring array of opportunities to enhance our understanding of the physical world.

Perspectives and Questions: Toward an Expansive Agenda for Particle Physics

TL;DR

This essay argues that the post-Higgs era demands a broad, opportunistic research program across particle physics, spanning flavor, neutrino physics, QCD, unified theories, and cosmology. It champions an expansive, multi-scale approach that combines effective field theory with precision measurements and diverse experimental avenues, from future high-energy colliders to cosmic and laboratory probes of dark matter and feebly interacting particles. Central to the agenda is a deep investigation of the Higgs sector, including absolute branching fractions, the total width , and the potential Higgs self-coupling, to map any deviations from Standard Model expectations around and to explore hidden-sector portals. The paper also emphasizes the integration of cosmology with particle physics and the sustained development of accelerator technologies, proposing a portfolio of next-generation machines (e.g., Higgs factories, a -TeV hadron collider, muon colliders) to illuminate fundamental questions about unification, the origin of masses, and the structure of spacetime, while remaining attentive to unexpected discoveries at yet-unknown scales. It is a call for a diverse, long-horizon program that merges theory, experiment, and technology to push beyond the Standard Model and to understand the universe from the smallest to the largest scales.

Abstract

Global celebration greeted the 2012 discovery at CERN's Large Hadron Collider of a particle that matches the textbook description of the Higgs boson. That achievement validated a remarkable chain of theoretical reasoning that combined the prescriptive notion of electroweak gauge symmetry with a simple, but \emph{ad hoc}, embodiment of spontaneous symmetry breaking. It was made possible by generational triumphs of accelerator art and experimental technique, and by human resourcefulness and collaboration on a global scale, all sustained by the enlightened support of many governments and institutions. Some imagine that, once the keystone of the standard model of particle physics has been set, our subject is over. Others worry that we may be at an impasse because no comparable wonders have appeared, leaving us without well-defined clues to a more complete paradigm. I am neither so readily satisfied nor so {easily} discouraged: we have so much more to learn! This essay surveys many questions that, taken together, constitute an inspiring array of opportunities to enhance our understanding of the physical world.

Paper Structure

This paper contains 14 sections, 1 equation, 1 figure, 1 table.

Table of Contents

  1. Prologue
  2. Anticipations of a New World
  3. Questions Our Forebears Pondered
  4. Context
  5. How to Progress?
  6. Beyond the Higgs-Boson Discovery
  7. More Insights on the TeV Scale & Beyond?
  8. Flavor I: the Problem of Identity
  9. Flavor II: Neutrino Physics
  10. Don't Forget the Strong Interactions!
  11. Unified Theories
  12. Where Is the Next Important Scale?
  13. The Cosmic Connection
  14. Final Remarks

Figures (1)

  • Figure 1: A schematic representation of the quarks and leptons, the fundamental constituents of the standard model of particle physics. The color-triplet quarks are painted red, green, and blue; the left-handed weak-isospin doublets are indicated by the stacked pairs. Interactions are governed by $\mathrm{SU(3)_c} \otimes \mathrm{SU(2)_L} \otimes \mathrm{U(1)}_Y$ gauge symmetry, spontaneously broken to $\mathrm{SU(3)_c} \otimes \mathrm{U(1)}_{\mathrm{em}}$.