https://doi.org/10.1140/epjc/s10052-019-7149-x
Regular Article - Theoretical Physics
Ghosts in metric-affine higher order curvature gravity
1
Departamento de Física Fundamental and IUFFyM, Universidad de Salamanca, 37008, Salamanca, Spain
2
Departament de Física Teòrica and IFIC, Centro Mixto Universitat de València - CSIC., Universitat de València, Burjassot, 46100, València, Spain
* e-mail: adria.delhom@uv.es
Received:
15
April
2019
Accepted:
16
July
2019
Published online:
7
August
2019
We disprove the widespread belief that higher order curvature theories of gravity in the metric-affine formalism are generally ghost-free. This is clarified by considering a sub-class of theories constructed only with the Ricci tensor and showing that the non-projectively invariant sector propagates ghost-like degrees of freedom. We also explain how these pathologies can be avoided either by imposing a projective symmetry or additional constraints in the gravity sector. Our results put forward that higher order curvature gravity theories generally remain pathological in the metric-affine (and hybrid) formalisms and highlight the key importance of the projective symmetry and/or additional constraints for their physical viability and, by extension, of general metric-affine theories.
© The Author(s), 2019
