Physics and Astronomy Colloquium

There is an on-going revolution in neutrino physics and astrophysics. Recent developments in observational cosmology and in laboratory experiments are providing insights into these mysterious particles. Neutrinos are neutral, spin-1/2 particles that interact only through the weak interaction and gravitation.

You have heard that individual neutrinos are ghostlike and can pass through light-years worth of lead. This is true. It then may come as a surprise to learn that neutrinos are responsible for much of the heavy lifting in astrophysical environments like the early universe and the gravitational collapse of stars and associated supernova explosions. However, like the hordes of staggering zombies in old horror movies, neutrinos can more than make up for their feeble individual interactions with huge numbers. They can transport entropy, energy, and lepton number through very dense matter that almost no other particles could get through. As a result, they can influence and even dominate macroscopic processes like the creation of the light elements in the Big Bang or the explosion of a supernova. Plus, neutrinos can act collectively in strange ways which, when coupled with these macroscopic processes, could give us insights into long standing questions about the properties of these particles.

In this talk we will discuss the basic properties of neutrinos, how this information was learned, recent insight into outstanding problems in neutrino physics, and some of the astrophysical issues mentioned above.