The Early Universe

We are citizens of a cosmos that began in the hottest and densest state imaginable.   The early Universe is thus the realm of particle and nuclear physics.  We inhabit the aftermath of this cataclysm.

Big-Bang Nucleosynthesis

In the span of the first second to the first three minutes, the entire Universe was a vast nuclear fusion reactor.   In the primordial soup of particles and radiation, a blizzard of nuclear reactions assembled protons and neutrons into the lightest elements.  The most abundant elements in the universe today–ordinary hydrogen and helium–trace back to this epoch of big-bang nucleosynthesis, along with tiny amounts of lithium and rarer isotopes of hydrogen and helium.

Our group performs state-of-the-art calculations of the primordial abundances of the elements.  By combining these theoretical predictions with astronomical observations of light elements and of the cosmic microwave background radiation, we wield the earliest reliable probe of the cosmos.

Particle Dark Matter

Most of the matter in the cosmos is not only dark, but of a completely different nature than anything found in the laboratory to date.  There is good reason to suspect that dark matter takes the form of relic particles created in the early universe.  If so, dark matter demands new physics beyond the Standard Model of elementary particles that otherwise works spectacularly well in explaining laboratory data.

Our research studies the particle physics of dark matter, by investigating the consequences of dark matter interactions on cosmology and astrophysics.  We are particularly interested in the effects of dark matter decays and annihilations during primordial nucleosynthesis, and have used these to probe  Supersymmetry theories in regimes complementary to (and inaccessible to) collider experiments such as the LHC.

We also have studied the effect of dark matter annihilations producing gamma rays at the center of our Galaxy in the presence of our supermassive black hole (Sgr A*).