Kitt Peak, February 2025, during a DESI support observer shift.
Denys Wilkinson Building
Keble Road, Oxford OX1 3RH
alexcharlesreeves@gmail.com
I am a cosmologist at the University of Oxford, where I hold an SNSF Postdoc.Mobility fellowship.
My research is about getting reliable cosmological results out of large surveys. Galaxy surveys and the cosmic microwave background are sensitive to many of the same parameters, and analysing them together gives much tighter constraints than either one alone. Doing this properly means modelling every probe consistently, including the correlations between them. During my PhD I built a pipeline that does this for weak lensing, galaxy clustering, BAO, the ISW effect and CMB lensing, and applied it to real data, most recently the DESI Legacy Imaging Surveys.
A lot of my time goes into checking whether a result can be trusted. Covariance matrices estimated from a limited number of simulations, emulator errors in the parts of parameter space that matter most, and volume projection effects in high-dimensional posteriors can all shift a constraint by a noticeable amount.
I also work on modelling galaxy clustering with the effective field theory of large-scale structure. With Pierre Zhang and Henry Zheng I wrote PyBird-JAX, a faster and differentiable version of PyBird that makes full-shape analyses much quicker to run.
I am a member of DESI and LSST-DESC. I did my PhD with Alexandre Refregier at ETH Zürich, and my undergraduate degree and Part III at Downing College, Cambridge.
If you are at school and thinking about studying physics, I keep a list of books and resources. I am also happy to answer questions about Oxbridge interviews by email.