As of 2021 I am no longer taking PhD students. Please address enquiries about PhD admissions in number theory to someone else.
I am a signatory of the petition The Cost of Knowledge, and am no longer willing to undertake refereeing (or any other work) for Elsevier publications.
I tend not to be in Cambridge for much of the summer months, and in particular I do not take on students for summer internships. Please do not write asking if I can.

a.j.scholl@dpmms.cam.ac.uk