University of Minnesota
School of Physics & Astronomy

Spotlight

Going Beyond the Standard Model

Tony Gherghetta
Tony Gherghetta
Annie Bartels
                                                       

Tony Gherghetta is a theoretical particle physicist whose research focuses on extensions of the Standard Model of particle physics. The Standard Model describes the nature and interactions of the elementary building blocks of the Universe.

The last missing piece of the Standard Model was the recently discovered Higgs boson, an experimental triumph of the Large Hadron Collider at CERN. The Higgs boson confirms the mechanism for how elementary particles, such as electrons and quarks, get their mass. This is crucial for life as we know it because atoms would not exist if the electron were massless, and without quark masses the proton would decay. However the discovery of the Higgs boson raises more questions than it answers. Is the Higgs boson elementary or composite? Why is the Higgs boson so much lighter compared to the Planck scale and why is the electron a million times lighter than the top quark and neutrinos another million times lighter?

Furthermore, even with the Higgs boson, the Standard Model is not a complete description of Nature. It does not contain a viable dark matter candidate, fails to explain the baryon asymmetry of the Universe or why the magnitude of the electron and proton charge agree to one part in 1021, and does not include gravity. Clearly the Standard Model must be extended to include a deeper structure that will explain some of these fundamental shortcomings.

An elegant idea for extending the Standard Model is Supersymmetry, a nontrivial extension of spacetime symmetry. This provides a comprehensive framework to help address many fundamental questions, including why the Higgs boson is so light. It predicts superpartners for the elementary particles, which have yet to be seen at the Large Hadron Collider. Alternatively, the Higgs boson may be a composite particle (like the proton) containing constituents held together by some underlying new strong force. This force would produce heavier copies of the known elementary particles, including exotic electrically-charged states, and these should also be seen at the Large Hadron Collider.

Nonetheless, the conspicuously absent signs of new particles at the Large Hadron Collider has caused some consternation, with suggestions that the Universe may be fine-tuned in a landscape of many Universes known as the Multiverse. These ideas are, perhaps premature, but would be a radical departure from the thinking of the last 40 years.

Gherghetta says that we are just at the start of an extensive LHC experimental program and expectation is high that in 2015 when the LHC is turned back on at double the energy, it will discover signs of new physics whether supersymmetry or compositeness. "If we find just one new particle everyone will wonder what all the current fuss was about. Or they will discover nothing, which would lead to an even bigger revolution." Gherghetta for his part has kept an open mind, and believes these are exciting times. "We will soon have answers whether we like them or not."