# Home

## Welcome!

I'm a theoretical physicist at the Kavli Institute for Cosmology, Cambridge (KICC), and the Cavendish Laboratory Astrophysics Group at the University of Cambridge. My research is focused on gravitational theory and quantum gravity, including alternatives to Einstein's general theory of relativity. Gravity is perhaps the most enigmatic of the four forces of Nature, and our best theory of gravity seems stubbornly classical. The other three forces (strong, weak and electromagnetic) are healthy quantum theories which comprise the standard model of particle physics. The effects of gravity are mostly apparent at large scales, such as are found in cosmology: motivating study of the history and structure of the Universe. The armillary sphere of Antonio Santucci represents a 16th century understanding of this structure, which has since evolved via minor revisions to the current Lambda-cold dark matter (LCDM) concordance model. Antonio's craftwork is as beautiful as LCDM, so I've included my other photos of the sphere in other pages.

I'm also currently the Rosamund Chambers Junior Research Fellow in Astrophysics at Girton College, Cambridge. I was based at Wolfson College for my Ph.D., and Queens' College for my undergraduate and master's in (physical) Natural Sciences. I grew up in Cornwall, which is the south-western tip of England. At the moment I'm dividing my time between Cambridge and the Lorentz Institute at Leiden University. I also work with researchers at CEICO in Prague.

The colourful image behind this text (courtesy of the ESA and Planck Collaboration) shows the polarised microwave sky, as dominated by the magnetised, dusty foreground of the milky way which lies along the equatorial plane. Behind it lies the fainter cosmic microwave background (CMB), a far more interesting signal from the early Universe and one of the very few ways we have to observationally test quantum gravity.

This site is still very much under construction so I apologise for all glitches! If you want to get in touch, feel free to drop me an email. Unfortunately, I don't use social media.

## Snap projects and reasons to reach out

Do you want to help organise an online modified gravity workshop in the summer of 2022? Do you know how to interpret the gauge status of Hamiltonian constraint multipliers which are themselves constrained only by PDEs? Do you know how to do QFT around a vector VEV background? Do you want to test a simple, novel and well-motivated $$w(z)$$ dark energy model against BAO and BBN constraints? These are some things I'm working on this season, send an email!

 Email wb263@cam.ac.uk wb263@mrao.cam.ac.uk ← should redirect ⤴ barker@lorentz.leidenuniv.nl ← should also redirect ⤴ Mobile +44—(0)7396—130513 Office +44—(0)1223—746437 ← not during pandemic GitHub wevbarker arXiv barker_w_1 ORCiD 0000-0002-1501-3221 Inspire HEP W.E.V.Barker.2 ← chronically incomplete NASA ADS barker, w. ← even worse than iNSPIRE Skype live:1e38761e619188ae Website wevbarker.com Address K34, Kavli Institute for Cosmology Madingley Road, Cambridge CB3 0HA, United Kingdom ← not during pandemic 233, Instituut-Lorentz voor Theoretische Fysica Niels Bohrweg 2, Leiden NL-2333 CA, The Netherlands ← not during pandemic

## Gravity on a lattice?

Here is a problem. Can we use thermal field theory techniques to find static gravitational fields in the nonlinear regime? Or, can we use lattice QCD codes to study GR? Below is a simple Monte-Carlo code for the Euclidean path integral of the scalar potential, in the presence of two static point masses. The code is broken, so the potential runs away to infinity... but could it ever work? If you're interested in this problem, or have experience in functional methods, or know that this has been tried before, please drop me an email!

## Interview puzzle

Here is a math interview question that was kept in reserve for the 2021 Girton admissions. Can you solve it? Bonus points if you know how it applies to theoretical physics :)

Here is a hint: how does the superficial divergence of a $$L=\partial_\mu\phi\partial^\mu\phi/2-\lambda\phi^n/n!$$ diagram go with loops, legs and vertices?