Questions and answers with Chris Quigg
"I have devoted much energy to helping to define the future of particle physics—and the new accelerators that will take us there," says Fermilab theoretical physicist Chris Quigg on his professional website. Since graduating with his PhD in 1970 from the University of California, Berkeley, he has conducted research spanning many topics in particle physics, from heavy quarks to cosmic neutrinos.
Quigg is perhaps best known for his work on electroweak symmetry breaking and particle phenomenology. For example, in 1977 he and colleagues identified the theoretical upper limit for the mass of the Higgs boson. And his 1984 paper "Supercollider physics"—coauthored with Estia Eichten, Kenneth Lane, and Ian Hinchliffe and published in Reviews of Modern Physics—is credited with influencing the research now pursued at such facilities as CERN's Large Hadron Collider (LHC). In 2011 the American Physical Society awarded the authors of that paper the J. J. Sakurai Prize for Theoretical Particle Physics for helping to "chart a course of the exploration of TeV scale physics using multi-TeV hadron colliders."
Quigg is also author of the widely used graduate textbook Gauge Theories of the Strong, Weak, and Electromagnetic Interactions (Benjamin/Cummings, 1983). Three decades later Quigg has updated the book, which is reviewed in this month's issue of Physics Today. He says the second edition, published in 2013 by Princeton University Press, "is true to the spirit" of the original in "empowering the reader by showing how much can be computed and understood with relatively simple methods." Physics Today recently caught up with Quigg to seek his perspective on the progress particle physics has made since the publication of the first edition and on the future of the field.
PT:What motivated you to update the first edition of your book 30 years after the first?
Quigg: The first edition was a young physicist's optimistic account of a young subject—the application of gauge theories, in which interactions follow from symmetries, to the phenomena that rule the microworld. I believed then, as I do now, that the logic of the gauge principle should be part of the education of every physicist.
The timing of the first edition was propitious. Shortly after publication, experiments at CERN discovered the electroweak bosons W± and Z. Collaborations at the superconducting Tevatron at Fermilab found the top quark and made demanding tests of perturbative quantum chromodynamics (QCD). The Z factories—the Large Electron–Positron Collider and SLAC—validated the electroweak theory by making highly precise measurements of many observables featured in Gauge Theories. A wealth of evidence heralding QCD and the electroweak theory as two new laws of nature made it timely to look ahead. For the electroweak theory in particular, the focus moved from Z-boson studies to an exploration of the 1-TeV scale and the search for the agent of electroweak symmetry breaking, the theme of much of my own research.
The tests and applications of QCD are now much richer than what the first edition presented. Overall, there was so much progress in theory, experiment, and their interplay that a fresh look was called for. My perspective has matured and my judgment of what students and practitioners should know about has evolved. Particle physics and neighboring subjects also present a number of delightful new puzzles to contemplate, including the semi-surprise that neutrinos morph from one flavor to another.
The new edition is a bit heftier than the original, but it is true to the spirit of empowering the reader by showing how much can be computed and understood with relatively simple methods. And of course, my youthful optimism remains!
PT: How would you assess the progress that particle physics has made in that period? What are the field's accomplishments that you are most proud of, and what mysteries still remain that you thought would be solved by now?
Quigg: Consolidating our understanding of the standard model—QCD plus the electroweak theory—is a marvelous collective achievement that required coordinated efforts by accelerator builders, experimentalists, and theorists. I did not expect that the discovery of a light Higgs boson would come so quickly; the instruments and the people performed superbly. Building the case for neutrino oscillations took great inventiveness.
Beyond specifics, I have a high appreciation for the evolution of experimental technique and the flowering of global collaborations. I take great satisfaction in the deep engagement of theory with experiment and the increased exchanges with other areas of physics and astronomy. And I'm delighted by the unexpected, such as the spate of charmonium-like resonances [not simple charm–anticharm mesons], beginning with X(3872).
A big remaining mystery is, Where is the crack in the standard model that we think must be there? A question that preoccupies me is, What accounts for the unreasonable effectiveness of the standard model?
PT: What is your assessment of the current state of particle physics, including the quality and enthusiasm of current students? With the excitement over the Higgs and other advances, are you concerned that the field might be overhyped?
Quigg: It is an immensely exciting time. In common with many areas of physics and astronomy, particle physics has many challenging questions and the means to address them. Our students and postdocs are highly motivated, talented, and intensely curious. It's a test for our institutions, including funding agencies, to create rewarding career paths for the young people drawn to science by the excitement of our work.
When I was hiking in Europe in the weeks before the Higgs discovery was announced, it seemed that everyone I met wanted to know what was happening [at the LHC] in Geneva. Sharing our explorations with the public is good for science and good for society.
PT: What are the most exciting questions you see the particle-physics community answering in the short term, say within 10 years?
Quigg: I close the new edition of Gauge Theories with a list of 20 outstanding questions—many with multiple parts—and 1 great meta-question: How are we prisoners of conventional thinking?
Within 10 years we will certainly have a much more complete understanding of electroweak symmetry breaking and the character of the Higgs boson. The initial LHC results have shaken theorists out of a certain complacency; specifically, a lot of received wisdom about naturalness and supersymmetry is being reexamined. Searches for dark matter are reaching a decisive stage. Studies of processes that are highly suppressed in the standard model, such as lepton-flavor violation, flavor-changing neutral currents, and permanent electric dipole moments, will reach ever more interesting levels of sensitivity. A world with massive neutrinos poses questions about the nature of neutrino mixing, the existence of sterile neutrinos, and the character of the neutrino—is it a Dirac particle, a Majorana particle, or both? I suspect that we will find new phenomena in the strong interactions that teach us about the great richness of QCD.
PT: It appears that you have not written any books for a general audience, like many that have been written about the Higgs quest and discovery. Do you have plans to do so, and if so, what topics would you focus on and why?
Quigg: Thank you for asking! Bob Cahn and I are working to complete our book on particle physics, the standard model, and beyond. We relate what we know and how we came to know it by telling the tales of some fascinating people. We celebrate the great lengths to which scientists go to pursue their curiosity, often with consequences far afield. The organic nature of science, with its interplay of theory, experiment, and technology, is a leitmotif. How could we not explain what the Higgs boson is and why the discovery matters?
PT: What books are you currently reading?
Quigg: On the physics front, I am deep into A. Douglas Stone's admirable Einstein and the Quantum: The Quest of the Valiant Swabian (Princeton University Press, 2013; see the Physics Today review here). Age of Ambition (Farrar, Straus and Giroux, 2014), Evan Osnos's acute reportage on the New China, tops the current-affairs stack. On the literary side, I am finishing Yasmina Reza's Heureux les heureux (Flammarion, 2013) and beginning Updike (Harper, 2014) by Adam Begley. My current audiobook escape is The Cuckoo's Calling (Hachette Audio) by Robert Galbraith (better known as J. K. Rowling).