Primordial Inflation and BICEP2 results

March 17th 2014 has been a historical date for all of us cosmologists: the BICEP2 experiment results seem to provide evidence for  both gravitational waves and the inflationary expansion of the early Universe (even though the observed tensor-to-scalar ratio r = 0.20 at 1σ is in tension with the upper bound r<0.11 at 95% C.L. given by a combination of data from Planck, SPT, ACT and WMAP).

But what is cosmological inflation? As I write extensively in my PhD thesis, it was an accelerated (read: exponential) expansion of the Universe, which occurred right after the Big Bang explosion. It lasted from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds (even though r=0.2 now indicates that inflation began even earlier than that).

The theory of inflation was originally proposed in 1980 by Alan Guth and by Katsuhiko Sato, as a mechanism for solving some technical problems of the previous Big Bang theory (the so-called “standard Big Bang scenario”), which didn’t assume an accelerated expansion.

This first version of inflation was anyway predicting a too granular Universe, and still needed adjustments. This problem was solved in 1982 by Andrei Linde, and independently by Andreas Albrecht and Paul Steinhardt, in a revised version
that is now called new inflation. The basic idea is that inflation occurred by a scalar field (i.e. a particle) rolling down a potential energy hill. This particle is called the inflaton: it made the Universe expand fast and then, at the end of inflation, it disappeared decaying into the particle spectrum observed today, namely into the stars, galaxies, dark matter…and us 🙂

Most of my past and present work is devoted to this particle production mechanism indeed. I study how the particle spectrum was generated, according to different theories postulating a specific candidate to become this mysterious “inflaton”.
Professors Andrei Linde and Renata Kallosh get acknowledged of the discovery:

I won’t discuss the theory and the discovery any further, I just paste here links to internet sources which discuss these topics:


My PhD thesis


The BICEP2 paper:

Cosmology discussions:

As a last remark, I can say that one thing is certain: after the 2012 detection of the Higgs boson, the 2013 Planck satellite results and this latest discovery of gravitational waves and experimental proof of inflation, we are all definitely living exciting times!

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