research

My research has focussed on the epoch of recombination, ~ 400,000 years after the Big Bang. Specifically to this period, I have been primarily interested in the various ways that electrons and photons interact as the Universe goes from opaque to transparent. This happens when the background interaction rate, quantified by Thomson scattering, drops below the net background Hubble flow, a driving expansion of the Universe. As this happens, the photons are decoupled from the hot bath of electrons (often referred to as the ‘primeval plasma’) and they free-stream in every direction across the Universe generating the cosmic microwave background (CMB). You can access my Ph.D thesis which focussed on non-standard variations to the recombination history and the impact of these changes on the CMB anisotropies here. A summary of my research interests are as follows:

• Physics of recombination: how free electrons, protons and helium nuclei became atoms
• Modelling recombination and the CMB with non-standard physics: variations of fundamental constants, dark energy, primordial magnetic fields
• Statistical methods for cosmology: constructing likelihoods, using Monte Carlo simulations, principal component analysis and Fisher matrices for deeper parameter estimation
  • For the future I want to look at ML techniques applied to higher order physics problems with heavy CPU usage. This has a number of applications but primarily, looking at separating known inherent, tedious calculations from the wider aspects of the problem (case dependent vs. case independent computations)
• Spectral distortions of the CMB: upcoming missions will look to focus on studying the tiny fluctuations that appear in the intensity of light from the background radiation as for different frequencies. These point to non-thermal processes associated with well-known physics and also deeply untested physical phenomena that ^{_{for most cases}} cannot be explored by other probes.

The process by which this veil of anisotropies from the Big Bang dissects or decouples itself from the background baryons (here protonic nuclei and electrons) is specifically recombination. The full atomic physics and in-depth dynamic radiative transfer problem underpinning these interactions is very complicated and has required 50+ publications from 2002-2016 with the original theoretical work being carried out in the 1960s and 1970s.

Specifically, the ways that the background radiation changes due to non-standard physics has fascinated me for years. The process of recombination is a relationship between protons and electrons; so any modification to the fundamental relation between these particles can drastically modify how the light and electrons interact together. Parametric changes such as the variation of fundamental constants or higher amounts of primordial helium have a direct impact on the decoupling of photons. These can either manifest in the CMB anisotropies or wiggles on the energy spectrum that point to non-thermal equilibrium known as spectral distortions.

All the research mentioned here, in my curriculum vitae and ensuing publications was carried out at the Jodrell Bank Centre for Astrophysics in Manchester. Credit for supervision, primary lead on research ideas and guidance for the course of my PhD and general researcher life has to go to Prof. Jens Chluba - without whom, this work would never have happened.