Inflationary Cosmology

What is Inflation?

The Inflation theory, developed by Alan Guth, Andrei Linde, Paul Steinhardt, and Andy Albrecht proposes a period of extremely rapid (exponential) expansion of the universe leading to the Big Bang expansion, during which time the energy density of the universe was dominated by a cosmological constant term that later decayed to produce the matter and radiation that fill the universe today.

A representation of inflation on the timeline of the universe.

Inflation explains seeds the inhomogeneities by quantum fluctuation, which grows by gravitational instabilities and eventually form all structures we know today – galaxies and stars.

The Inflation theory links important ideas in modern physics, such as symmetry breaking and phase transitions, to cosmology. Inflation is a very good idea which explains away the shortcomings of the standard big bang model. Simple and elegant though it is, a concrete model within a fundamental framework has proved elusive till now.

Prediction of inflation theory

The inflationary cosmology has got immense support from experimental data and makes important predictions:

That the density of the universe is close to the critical density, and thus the geometry of the universe is flat.
That the fluctuations in the primordial density in the early universe had the same amplitude on all physical scales.
That there should be, on average, equal numbers of hot and cold spots in the fluctuations of the cosmic microwave background temperature.

B mode

Especially, measurement of B-modes of the CMB polarization will provides direct evidence for gravitational waves and hence inflation.

Scattering coupled with tensor modes causes B-modes as shown on the left.
Though B-modes are the most direct test of inflation, their signal is expected to be extremely small (<0.1mK), which will be a very challenging observation.

The Works at KIAS

Much still needs to be understood about the mechanism of generation and evolution of primordial density perturbations which are imprinted in the CMB and which are expected to have seeded the large scale structures that we see today. String theory provides some promising candidates for the inflaton since there are a plethora of scalar fields that are present in the string spectrum. The action that describes these fields are generically of the Dirac-Born-Infeld form. We are interested in understanding the nature of perturbations generated by such fields in situations where there are more than one phase of inflation and how the signature of such models may show up in the CMB spectrum.

Further Reading:

Alan H. Guth & Paul J.Steinhardt, "The Inflationary Universe", Scientific American, May 1984.
Andrei Linde, "The Self-Reproducing Inflationary Universe", Scientific American, November 1994.
Gary Watson, "An Exposition on Inflationary Cosmology", WWWarticle, 2000.
Alan H. Guth, "The Inflationary Universe : The Quest for a New Theory of Cosmic Origins", 1998.