TY  - JOUR
AU  - Alfonso, V. I.
AU  - Bejarano, C.
AU  - Beltran Jimenez, J.
AU  - Olmo, G. J.
AU  - Orazi, E.
PY  - 2017
DA  - 2017//
TI  - The trivial role of torsion in projective invariant theories of gravity with non-minimally coupled matter fields
T2  - Class. Quantum Gravity
JO  - Classical and Quantum Gravity
SP  - 235003 - 20pp
VL  - 34
IS  - 23
PB  - Iop Publishing Ltd
KW  - modified gravity
KW  - metric-affine theories
KW  - torsion
KW  - non-minimal couplings
AB  - 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.
SN  - 0264-9381
UR  - http://arxiv.org/abs/1705.03806
UR  - https://doi.org/10.1088/1361-6382/aa9151
DO  - 10.1088/1361-6382/aa9151
LA  - English
N1  - WOS:000414726500001
ID  - Alfonso_etal2017
ER  -