Stability in quadratic torsion theories Teodor Borislavov Vasilev, Jose A. R. Cembranos, Jorge Gigante Valcarcel and Prado Martín-Moruno Eur. Phys. J. C, 77 11 (2017) 755 Published online: 10 November 2017 DOI: 10.1140/epjc/s10052-017-5331-6