A cosmic week at Fermilab

Fermilab Director
Nigel Lockyer

Scientists studying the cosmic microwave background (CMB) have made another large discovery. The announcement of evidence for gravitational waves from the universe’s inflationary epoch has a lot of people excited and was the talk of the week among particle physicists at Fermilab. It is truly impressive how much information has been extracted from the light that was generated 380,000 years after the big bang. For a particle physicist, the big question is, “What does it mean?”

By measuring the polarization of light from the CMB (a certain pattern of polarization called B-mode), we are learning about physics at energies of 1016 GeV. This value is a familiar one to particle physicists: It’s the scale at which theories predict the grand unification of the four forces of physics.

Now physicists are discussing whether last week’s discovery gives greater credibility to proton decay, a process predicted by some grand unified theories but never observed. The proposed LBNE experiment in South Dakota, which you have heard plenty about lately, will be able to search for proton decay in 35,000 tons of liquid argon, in addition to studying neutrino interactions.

The technique of measuring precisely the polarization from the CMB also leads to very tight constraints on the sum of the neutrino masses. This in itself is an important measurement and is strong motivation for making more precise measurements. Scientists also speculate that there may be additional types of neutrinos, called sterile neutrinos, which interact only through gravity or by mixing with other types of neutrinos. This is a topic being addressed by the soon-to-begin MicroBooNE neutrino program in the Booster beamline and two new proposals submitted to the laboratory’s Physics Advisory Committee last January.

The motivation for searching for sterile neutrinos increased last week when four scientists published their latest results. The connection between the formation of the universe’s structure and neutrino mass is a topic of significant interest in cosmology. Detailed calculations of the gravitational potentials in the early universe, and thus galaxy formation, are affected quite significantly depending on how greatly neutrinos contribute to the energy of the universe. This is due to the fact that neutrinos travel very quickly and do not deepen the “gravitational potential well” nearly as much as heavy, slow dark-matter particles.

While all this discussion was taking place, the Large Synoptic Survey Telescope collaboration was meeting at Fermilab to discuss their plans for the construction of a superb telescope. It would carry out a massive galaxy survey, up to 10 billion galaxies, or about 10 percent of all galaxies in the observable universe, to help determine the location and properties of dark matter and dark energy.

On another front, the Dark Energy Survey, conducted in Chile, identified a new mini-planet on the outer limits of our solar system as it was scanning the sky.

It really was an exciting, cosmic week.