New class of ghost- and tachyon-free metric affine gravities
Roberto Percacci,Ergin Sezgin +1 more
TLDR
In this paper, the spin-projection operators for a metric affine theory of gravity with terms up to second order in curvature were constructed, and they were used to analyze the most general six-parameter class of theories that are projective invariant.Abstract:
We construct the spin-projection operators for a theory containing a symmetric two-index tensor and a general three-index tensor. We then use them to analyze, at linearized level, the most general action for a metric affine theory of gravity with terms up to second order in curvature, which depends on 28 parameters. In the metric case, we recover known results. In the torsion-free case, we are able to determine the most general six-parameter class of theories that are projective invariant, contain only one massless spin 2 and no spin 3, and are free of ghosts and tachyons.read more
Citations
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Instabilities in metric-affine theories of gravity with higher order curvature terms
TL;DR: In this paper, the authors discuss the presence of ghostly instabilities for metric-affine theories constructed with higher order curvature terms and discuss different procedures to avoid the ghosts by adding additional constraints.
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Palatini quadratic gravity: spontaneous breaking of gauged scale symmetry and inflation
TL;DR: In this article, the authors studied quadratic gravity in the Palatini formalism where the connection and the metric are independent, and they showed that this theory has an elegant spontaneous breaking of gauged scale symmetry and mass generation in the absence of matter.
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Cosmological hyperfluids, torsion and non-metricity
TL;DR: In this paper, a model for cosmological hyperfluid fluids with intrinsic hypermomentum that induce spacetime torsion and non-metricity is presented.
Journal ArticleDOI
Instabilities in Metric-Affine Theories of Gravity
TL;DR: In this article, the authors discuss the presence of ghostly instabilities for metric-affine theories constructed with higher order curvature terms and discuss different procedures to avoid the ghosts by adding additional constraints.
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Gauging scale symmetry and inflation: Weyl versus Palatini gravity
TL;DR: In this article, a comparative study of Weyl and Palatini theories of quadratic gravity with scale symmetry is presented, where the necessary scalar field is not added ad-hoc to this purpose but is of geometric origin and part of the Weyl action.
References
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