2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/50928A new mechanism for T and CPT violation is reviewed, which relies on chiral fermions, gauge interactions and nontrivial spacetime topology. Also discussed are the possible effects on the propagation of electromagnetic waves in vacuo, in particular for the cosmic microwave background radiation.Invited talk at the 7-th International Wigner Symposium, College Park MD, August 2001. v5: L/R identification above Eq. (28) correctedHigh Energy Physics - TheoryAstrophysicsHigh Energy Physics - Phenomenologytext