SPECIAL MCTP COLLOQUIUM<br>Groundbreaking Discovery of Gravitational Waves from Inflation in BICEP2 Cosmic Microwave Detector

Cosmology has just had a major discovery: gravity waves from the early Universe. The Cosmic Microwave Background polarization experiment BICEP2 has announced detection of B-modes, which can be explained as the gravitational wave signature of inflation. We will discuss how these were found and their significance for cosmology. This discovery, if confirmed in future data sets, is a “smoking gun” for inflation. Further, when combined with data from the Planck satellite, thousands of inflation models have now been ruled out. Remaining simple models are few, and include natural inflation and quadratic potentials. Natural inflation uses “axions” as the inflaton, where the term “axion” is used loosely for a field with a flat potential as a result of a shift symmetry. That inflation could be so dramatically confirmed so quickly as a theory of the earliest Universe comes as a great surprise.