Let X be a smooth projective curve over the field of complex numbers, and fix a homogeneous representation ρ : GL(r)−→ GL(V). Then, one can associate to every vector bundle E of rank r over X a vector bundle Eρ with fibre V . We would like to study triples (E,L,φ) where E is a vector bundle of rank r over X , L is a line bundle over X , and φ : Eρ −→ L is a non-trivial homomorphism. This set-up...