Article: Shortcomings of New Parameterizations of Inflation
Authors: J. Martin, C. Ringeval and V. Vennin
The Cosmic Microwave Background radiation (CMB) is an amazingly simple and beautiful picture that is pivotal for observational cosmology. It is the oldest light in our Universe: it originates from when the Universe was only a sprightly 380,000 years old, much younger than its current 13.8 billion years. Cosmologists can measure this radiation to high precision and extract information about the early Universe. Specifically, they can learn about the epoch of inflation, which was a period of accelerated expansion in the first fractions of a second after the Big Bang.
There are hundreds of theoretical inflationary models that attempt to describe the physics of this epoch. All of them have slightly different predictions for the two important numbers, and . The number measures the relative strength of cosmological perturbations with different wavelengths: if it is exactly equal to one, all perturbations have the same power, if it is smaller than one, the longer wavelengths have more power and if it is bigger than one, the smaller wavelengths have more power. is, loosely speaking, the ratio of primordial gravitational waves to the other ...