There are various seminars running during the semester:
The Sheffield Geometry and Physics Seminar, on Mondays at 2.00pm, starting in February
Pure maths Colloquium, on Wednesdays at 2.00pm (online)
Learning seminar on Algebraic Stacks, on Fridays at 3.00pm
The topology and the cosmology-relativity-gravitation seminars may also be of interest, as well as the complete lists of seminars hosted at the School of Mathematics and Statistics this week and this semester.