Early Universe Physics project

We are actively involved in developing models of the early universe, in particular the inflationary scenario, analyzing how this leads to the formation of large-scale structure, microwave background anisotropies and polarisation, and a background of gravitational waves.

Key elements of a PhD project might typically be:

  • study of various models of the early universe and the analysis of their observational consequences.
  • investigate signatures of these models in the microwave background
  • does the model lead to detectable cosmological gravitational waves, as might be seen by LISA
  • the formation and evaporation of primordial black holes.
Members particularly interested in this area of research: Tim Clifton, Karim Malik, and Reza Tavakol.

800px-WMAP 2010.png
Credit: NASA/WMAP Team

Cosmology of the Very Early Universe: Inflation and Superstrings

These are exciting times for early universe cosmology. The field is entering a new era where it is becoming possible to make detailed quantitative investigations into theoretical models of the universe's most distant past. This is of vital importance in view of the flood of data that will soon become available from forthcoming high redshift surveys, microwave background experiments and gravitational wave detectors. One of the most important early universe paradigms is inflation, which postulates a period of accelerated expansion at energy scales at or above those associated with the Grand Unified phase transition. It is now widely believed that the observed structures in the universe evolved via gravitational instability from tiny quantum fluctuations that were generated during this period. Inflation therefore provides a unique window onto physics at energies inaccessible to any other form of experiment.

Our research into the very early universe is focused around the theoretical and observational consequences of cosmological models based on superstring and 'M' theories. This is presently a very active area of research. Superstring theory represents the most promising candidate for a unified theory of the fundamental interactions, including gravity. During recent years, the discovery of duality symmetries in the theory has led to a dramatic paradigm shift. It is now widely believed that there exists a more fundamental theory of quantum gravity, known as 'M theory'. The low-energy limit of M theory is eleven-dimensional supergravity, thereby implying that it is more than another superstring theory.

Fundamental Questions

The unique features of M theory and superstring theory were important when the universe was less than 10^-35 seconds old. This is precisely the era when inflation is thought to have occurred. In view of this, we are addressing a series of fundamental questions in superstring cosmology:

  1. What are the different types of cosmological solutions that arise in these models?
  2. Is inflation possible in these theories?
  3. If inflation does arise, how generic is it and what is the physical mechanism that drives the rapid expansion?
  4. What are the observational consequences of such an inflationary expansion? In particular, do the quantum mechanical fluctuations that typically arise in inflation result in perturbations that are compatible with cosmological observations of the microwave background anisotropies?

String/M-theory requires the universe to be higher-dimensional for consistency. Recently, an exciting theoretical development has been the realization that the standard model interactions may be confined to a four-dimensional membrane or domain wall (corresponding to our observable universe), whereas gravitational interactions may also propagate through the extra dimensions (the bulk). This change in viewpoint is motivated in part by the discovery that the quantum dynamics of the D-branes can be described in terms of open strings whose ends are fixed on the brane. The cosmic expansion that we observe then arises due to the motion of our 'brane' through the higher dimensions. Our group has played a leading role in this rapidly developing field and there has been intense activity to derive cosmological models in this context.

Of particular interest in braneworld scenarios is the production of scalar and gravitational wave spectra during inflation. The brane-bulk corrections modify the scale-dependence and amplitudes of the perturbations, leading to potentially observable signatures. Indeed, the amplitude of tensor perturbations is larger than in the standard scenario and preliminary indications suggest that these perturbations may be detectable by the Planck satellite.

Topic attachments
I Attachment Action Size Date Who Comment
PNGpng 800px-WMAP_2010.png manage 561.8 K 2011-01-13 - 17:03 IanHuston  
Topic revision: r3 - 2013-04-08 - KarimMalik
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