University of Minnesota
School of Physics & Astronomy


Talking about the Primordial Universe

Neil Barnaby
Neil Barnaby
Alex Schumann

Neil Barnaby is a theoretical cosmologist whose research deals with the physics of primordial Universe. Barnaby says he was drawn to Cosmology because “it was a way to do some of the same mathematical calculations and still be in touch with real-world observations.”

One of the biggest pieces of observational data which physicists have to work with is the Cosmic Microwave Background (CMB), the radioactive afterglow of the Big Bang. This radiation is extremely homogeneous; almost the same temperature at any point in any direction in the Universe, but there are tiny fluctuations (10 5) in temperature. These fluctuations originate from quantum mechanical processes in the early Universe. "By studying these fluctuations we can understand not just how they were imprinted, but also what kind of physics was responsible for imprinting them," Barnaby says.

Barnaby and his collaborator, Professor Marco Peloso of the School of Physics and Astronomy are working on the question of fluctuations imprinted during the inflation period of the early Universe, a period that lasted all of 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds. The theory goes that the Universe underwent a dramatic increase in volume. During this time the energy budget of the Universe was dominated not by the usual kind of matter, but a slightly exotic kind called a scalar field which was in a condensate state. Barnaby compares this field to an ocean, where the ripples and waves on the surface are quantum mechanical processes. Eventually this field decays into radiation. "The decay implies that the inflaton, the particle associated with this field, must interact with regular matter, and those interactions are what we've been studying with regards to the observable fluctuations," Barnaby says.

This model answers the question “where did all the radiation and matter in the Universe come from, by positing that it came from the decay of this field. The Inflaton, is similar to the Higgs Boson. Barnaby says the Higgs will probably be the first scalar field seen, and that the early Universe is dominated by a similar scalar field. He compares the difference between an Inflaton and a Higgs Boson as the difference between a quark and electron.

"We are learning the particle physics properties of this particle. The question is how it interacts with other particles in nature, how it interacts with photons, parity." In the last couple of years Barnaby and Peloso have been finding a lot of interesting signatures, and have found that they can learn a lot more about this Inflaton particle than previously believed. "Everyone expected it had to couple to something because it had to decay, but it hadn’t been thought through what the implications of these coupling were, and it lead to a whole slew, of observational signatures." Using data from satellite observatories, WMAP and PLANK, which measured the temperature fluctuations and provided the theorists with key correlation functions, Barnaby and Peloso were able to make some novel discoveries. "The usual assumption is that these fluctuations are very close to Gaussian distribution. (Distributed like a bell curve around the average). It turns out that there’s a measurable departure from Gaussian distribution. This has been a big thrust in my research in the last couple of years."