%0 Journal Article %T The trivial role of torsion in projective invariant theories of gravity with non-minimally coupled matter fields %A Alfonso, V. I. %A Bejarano, C. %A Beltran Jimenez, J. %A Olmo, G. J. %A Orazi, E. %J Classical and Quantum Gravity %D 2017 %V 34 %N 23 %I Iop Publishing Ltd %@ 0264-9381 %G English %F Alfonso_etal2017 %O WOS:000414726500001 %O exported from refbase (https://references.ific.uv.es/refbase/show.php?record=3353), last updated on Mon, 20 Nov 2017 09:18:44 +0000 %X We study a large family of metric-affine theories with a projective symmetry, including non-minimally coupled matter fields which respect this invariance. The symmetry is straightforwardly realised by imposing that the connection only enters through the symmetric part of the Ricci tensor, even in the matter sector. We leave the connection completely free (including torsion), and obtain its general solution as the Levi-Civita connection of an auxiliary metric, showing that the torsion only appears as a projective mode. This result justifies the widely used condition of setting vanishing torsion in these theories as a simple gauge choice. We apply our results to some particular cases considered in the literature, including the so-called Eddington-inspired-Born-Infeld theories among others. We finally discuss the possibility of imposing a gauge fixing where the connection is metric compatible, and comment on the genuine character of the non-metricity in theories where the two metrics are not conformally related. %K modified gravity %K metric-affine theories %K torsion %K non-minimal couplings %R 10.1088/1361-6382/aa9151 %U http://arxiv.org/abs/1705.03806 %U https://doi.org/10.1088/1361-6382/aa9151 %P 235003 - 20pp