The non-gauge nature of the newly discovered forces

Gian Francesco Giudice is the head of CERN Theoretical Physics Department.

He has written an important essay titled “On Future High-Energy Colliders“. This is not about the technical details of future colliders. He discusses the current state and the future of particle physics (also known as high-energy physics). What makes this essay different is that it mentions “newly discovered forces“.

“One of the most striking results of the LHC exploration was the discovery of a completely new type of force. Before the discovery of the Higgs boson, we knew of four fundamental forces governing natural phenomena (strong, weak, electromagnetic forces and gravity). All of them were successfully deduced from a single conceptual principle — called ‘gauge symmetry.’ In the meantime, the LHC has discovered the existence of new forces in nature. These forces control how the Higgs boson interacts with quarks and leptons and, so far, the LHC has identified their effect on top and bottom quarks and on tau leptons (the so-called ‘third generation’). According to the Standard Model, these new forces are as fundamental as those previously known, but of a different nature — not ‘gauge-like.’ While the Standard Model properly describes these forces, it is silent on the origin of the many free parameters associated with them or on any deeper explanation of their complex structure.”

The mention of “newly discovered forces” was a big surprise for me. It shouldn’t have been because this was nicely explained in a Symmetry Magazine article in 2015.

“There are three inherent qualifications required for a field to generate a force: The field must be able to switch on and off. It must have a preferred direction. And it must be able to attract or repel. Normally the Higgs field fails the first two requirements—it’s always on, with no preferred direction. But in the presence of a Higgs boson, the field is distorted, theoretically allowing it to generate a force.”

The Symmetry Magazine quotes Matt Strassler:

“We think that two particles can pull on each other using the Higgs field. The same equations we used to predict that the Higgs particle should exist, and how it should decay to other particles, also predict this force will exist.”

Back to G. F. Giudice’s essay: 

Structural problems of the particle theory

  • nature of the Higgs boson
  • Higgs naturalness
  • origin of symmetry breaking dynamics
  • stability of the Higgs potential
  • existence of three generations of matter
  • pattern of quark and lepton masses and mixings
  • dynamics generating neutrino masses

Problems embedding the particle theory into a broader framework

  • unification of forces
  • quantum gravity
  • cosmological constant

Problems in attempts to give particle-physics explanations of cosmological properties

  • nature and origin of dark matter
  • dark energy
  • cosmic baryon asymmetry
  • cosmic inflation

Most likely place to find surprises at the LHC

  • Higgs naturalness
  • dark matter

The Higgs program

  1. The first goal is to measure the Higgs coupling constants (which determine the interaction strengths of all forces involving Higgs bosons) with precision.”
  2. “The new Higgs forces have been measured so far only for the third generation of matter (top, bottom, tau). The next challenge is to test the Higgs forces for second-generation particles, especially the charm quark and the muon.”
  3. “Another important test is the measurement of the so-called ‘invisible Higgs decay’, which corresponds to the disintegration of the Higgs boson into particles that cannot be directly revealed by particle detectors at high-energy colliders, such as neutrinos. ‘Invisible Higgs decays’ are especially interesting because they explore possible new types of elusive particles, maybe related to the nature of dark matter. “
  4. “Another target of the Higgs program is the measurement of the Higgs self-interaction,  which is a direct test of the new kind of force that is thought to be responsible for generating the non-trivial structure of the Higgs vacuum. Such a measurement will also provide us with the elements to reconstruct theoretically the details of the phase transition that is believed to have occurred in the universe only 10−11 seconds after the Big Bang.”
  5. “Finally, another goal is to measure a variety of rare Higgs decays, which are rich with important information. For instance, the Higgs decay into Z and a photon is an efficient probe of new physics effects occurring at very short distances; Higgs decays into two different leptons (𝜏𝜇, 𝜏e or 𝜇e) or into CP-violating final states can probe the nature of symmetries in the particle world.”
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