Sebastian Schlegel Mejia

I am a PhD student at the University of Edinburgh. My advisor is Ben Davison.


Research interests

My general interests lie in moduli spaces and enumerative geometry. More specifically, I have been interested in categorified Donaldson–Thomas theory, cohomology and derived categories of moduli spaces, and cohomological/categorical Hall algebras.


Listed in reverse chronological order. The links are to the arXiv pages.

  1. BPS algebras and generalised Kac–Moody algebras from 2-Calabi–Yau categories, joint with Ben Davison and Lucien Hennecart, March 2023
  2. BPS Lie algebras for totally negative 2-Calabi–Yau categories and nonabelian Hodge theory for stacks, joint with Ben Davison and Lucien Hennecart, December 2022 (submitted)
  3. BPS cohomology for rank 2 degree 0 Higgs bundles (and more), January 2022 (submitted)



April 2023, Skye, "Skye 2023: Workshop on Hall algebras and vertex algebras in enumerative geometry"
March 2023, Edinburgh, Workshop "The geometry of double affine Hecke algebras and Coulomb branches"
March 2023, Liverpool, Talk at AG Seminar
January 2023, Oxford, "Quivers, Clusters, Moduli and Stability"
December 2022, Glasgow, "Workshop on Singularities and Mirror Symmetry"
October 2022, Aussois, Workshop "Donaldson–Thomas invariants in Aussois"
September 2022, London, "5th BrAG meeting"
August 2022, Cetraro, School on "Hyperkähler manifolds and related geometries"
June-July 2022, Lisbon, "School on Mirror Symmetry and Moduli Spaces"
June 2022, Levico Terme, Conference "New Perspectives on Hyperkähler Manifolds"
June 2022, Levico Terme, School on "Moduli spaces and stability conditions"
May 2022, Paris, Conference "GAeL XXIX"
November 2021, Lausanne, Talk at Groups, Arithmetic & Algebraic Geometry Seminar at EPFL
October 2021, Oberwolfach, Oberwolfach Seminar: "New Techniques in Resolutions of Singularities"
July 2021, Paris, IHÉS Summer school: "Enumerative Geometry, Physics and Representation Theory"
February 2020, Bonn, Hausdorff School: “Perverse Sheaves in Enumerative Geometry”

Past Organization

Together with Ben Davison and Lucien Hennecart, I organised the EGRET seminar from October 2021 to December 2022.

Together with Ben Brown, I organised Hodge Club for the academic year 2020-2021.