My Research

The latest astronomical surveys are mapping the three-dimensional distribution of galaxies and clusters of galaxies on scales never before explored by science. The distribution of matter on such large scales (billions of light-years across) reflects the primordial density field in the very early universe, 14 billion years ago, a fraction of a second after the Big Bang.

Most current models for the origin of our Universe, propose that all the structure we see today resulted from essentially nothing: fluctuations in the vacuum state of quantum fields. Quantum fields possess fluctuations even in empty space and these can be swept up to large, astrophysical scales, by a period of rapid expansion, called "inflation" in the very early universe. Thus the large-scale structure of our Universe can be used to test physics at very high energy, including quantum field theory and general relativity.

Quantum fluctuations of free fields have a particularly simple, Gaussian distribution, leading to a simple primordial state with a symmetry between over-densities and under-densities. Particle interactions, including the essential non-linearity of Einstein's equations of general relativity, lead to slight asymmetries, or non-Gaussianities. Thus asymmetries, or non-Gaussianities, in the primordial density provide a potentially rich source of information about physical interactions in the very early universe.

My work has pioneered the study of primordial non-Gaussianity since I proposed the curvaton scenario for the origin of structure, working with David Lyth in 2001. I was also one of the first people to study non-Gaussianity generated in ekpyrotic and other pre big bang models which have been proposed as an alternative to inflation in the very early universe.

In 2009 I wrote a major review of cosmological perturbations with Karim Malik.

All my research papers are freely available on the arXiv, including those published in refereed journals.

Those are very technical. I gave a recent public talk on Inflation and the Origin of Cosmic Structure, which should be a bit more accessible.

You can see a list of all my recent talks on the ICG web pages here.

SONG time

Posted by David Wands on February 5 2013

We have announced in a paper on the arXiv today results from a new numerical code - SONG - which calculates the distribution of temperature fluctuations in the cosmic microwave background (CMB) radiation. Existing first-order codes calculate the power spectrum of fluctuations, but our second-order code goes to a whole new level of detail required to calculate the bispectrum (and skewness) of the temperature distribution, generated by non-linear scattering and gravity in the early universe. The SONG (Second-Order Non-Gaussianity) code has been 16 months in the making, lovingly hand-crafted by Christian Fidler and Guido Pettinari working in the ICG, at the University of Portsmouth, building on earlier work in Portsmouth by Cyril Pitrou. Teams in Paris and London and Cambridge have also released results in recent weeks and the challenge is now to understand some of the subtle differences between results obtained using different approaches. The goal is to produce robust predictions for the intrinsic CMB bispectrum which could be detected in forthcoming satellite experiments such as the ESA Planck satellite which plans to release its observational results in March 2013.

Daiwa Adrian Prize

Posted by David Wands on March 14 2011

Cosmologists from Portsmouth and Kyoto have been awarded the Daiwa Adrian Prize 2010 for collaborative research. We went along to the Royal Society in London in December to receive the award from Lady Adrian. The prize was awarded for our work on non-linear cosmological perturbations, providing theoretical predictions from our models of the very early universe for the statistical properties of the primordial density perturbations. Prof Misao Sasaki from the Yukawa Institute for Theoretical Physics at Kyoto University was there along with Marco Bruni and myself representing Portsmouth University.