This course was given at the CPT in Marseille in February and March 2018. Lecture 3 introduces basic mathematical tools: the group SU(2) and its unitary representations, the Hilbert space L2[SU(2)], and the Peter-Weyl theorem.
A latex transcript of the lectures is available here: https://arxiv.org/abs/2305.12215
(thanks to Pietropaolo Frisoni)