Scalar-metric-affine theories: Can we get ghost-free theories from symmetry?

Aoki, Katsuki; Shimada, Keigo

doi:10.1103/physrevd.100.044037

Cited by 62 publications

(65 citation statements)

References 74 publications

(69 reference statements)

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“…In the literature, more attention has been given to theories with torsion, but recently there has been a great deal of interest for MAGs with non-metricity, see e.g. [3][4][5][6][7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

New class of ghost- and tachyon-free metric affine gravities

2020

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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 analyse, 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.1 By quadratic gravity we mean theories with action containing terms linear and quadratic in the Riemann tensor.2 As an example let us mention here Weyl geometry, where φ is constructed in terms of a vector field. This theory has been revisited recently in [27].3 By accidental symmetry we mean a gauge symmetry that is present in the linearized action but not in the full action 4 This is due to the use of the vierbein formalism. The general two-index tensor is the linearized vierbein and the three-index tensor is the linearized spin connection.

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Section: Introductionmentioning

confidence: 99%

New class of ghost- and tachyon-free metric affine gravities

2020

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“…In the context of the scalar-tensor theories, it was recently found that an additional local symmetry of the connection is associated with the ghost-free structure when the spacetime geometry is extended from Riemannian one [35,36]. Similar considerations are certainly worthwhile in the context of higher curvature theories.…”

Section: Discussionmentioning

confidence: 86%

Ghostfree quadratic curvature theories with massive spin-2 and spin-0 particles

Aoki

Mukohyama

2019

Phys. Rev. D

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We consider generic derivative corrections to the Einstein gravity and find new classes of theories without ghost around the Minkowski background by means of an extension of the spacetime geometry. We assume the Riemann-Cartan geometry, i.e. a geometry with a non-vanishing torsion, and consider all possible terms in the Lagrangian up to scaling dimension four. We first clarify the number, spins, and parities of all particle species around the Minkowski background and find that some of those particle species are ghosts for generic choices of parameters. For special choices of the parameters, on the other hand, those would-be ghosts become infinitely heavy and thus can be removed from the physical content of particle species. Imposing the conditions on the coupling constants to eliminate the ghosts, we find new quadratic curvature theories which are ghost-free around the Minkowski background for a range of parameters. A key feature of these theories is that there exist a non-ghost massive spin-2 particle and a non-ghost massive spin-0 particle in the graviton propagator, as well as the massless spin-2 graviton. In the limit of the infinite mass of the torsion, the Riemann-Cartan geometry reduces to the Riemannian geometry and thus the physical content of particle species coincides with that of the well-known quadratic curvature theory in the metric formalism, i.e. a massive spin-2 ghost, a massive spin-0 particle and the massless spin-2 graviton. Ghost-freedom therefore sets, besides other constraints, an upper bound on the mass of the torsion. In addition to the above mentioned particle species (a massive spin-2 particle, a massive spin-0 particle and the massless spin-2 graviton), the ghost-free theory contains either the set of a massive spin-1 and a massive spin-0 (Class I) or a couple of spin-1 (Class II). These additional particle species mediate gravity sourced by the spin of matter fields.

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“…[57] and has recently gained increasing attention [58, (see also Refs. [82][83][84][85][86]). When the Higgs field relaxes to its electroweak vacuum after inflation, the usual Einstein-Hilbert gravity of GR is retained regardless of the choice of formalism, i.e.…”

Section: Decomposing the Actionmentioning

confidence: 99%

Axion dark matter from Higgs inflation with an intermediate H_*

Tenkanen

Visinelli

2019

J. Cosmol. Astropart. Phys.

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In order to accommodate the QCD axion as the dark matter (DM) in a model in which the Peccei-Quinn (PQ) symmetry is broken before the end of inflation, a relatively low scale of inflation has to be invoked in order to avoid bounds from DM isocurvature fluctuations, H * O(10 9 ) GeV. We construct a simple model in which the Standard Model Higgs field is non-minimally coupled to Palatini gravity and acts as the inflaton, leading to a scale of inflation H * ∼ 10 8 GeV. When the energy scale at which the PQ symmetry breaks is much larger than the scale of inflation, we find that in this scenario the required axion mass for which the axion constitutes all DM is m 0 0.05 µeV for a quartic Higgs self-coupling λ φ = 0.1, which correspond to the PQ breaking scale v σ 10 14 GeV and tensor-to-scalar ratio r ∼ 10 −12 . Future experiments sensitive to the relevant QCD axion mass scale can therefore shed light on the physics of the Universe before the end of inflation.

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Scalar-metric-affine theories: Can we get ghost-free theories from symmetry?

Cited by 62 publications

References 74 publications

New class of ghost- and tachyon-free metric affine gravities

New class of ghost- and tachyon-free metric affine gravities

Ghostfree quadratic curvature theories with massive spin-2 and spin-0 particles

Axion dark matter from Higgs inflation with an intermediate H_*

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Scalar-metric-affine theories: Can we get ghost-free theories from symmetry?

Cited by 62 publications

References 74 publications

New class of ghost- and tachyon-free metric affine gravities

New class of ghost- and tachyon-free metric affine gravities

Ghostfree quadratic curvature theories with massive spin-2 and spin-0 particles

Axion dark matter from Higgs inflation with an intermediate H*

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Product

Resources

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Axion dark matter from Higgs inflation with an intermediate H_*