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Nonpropagating ghost in covariant $f(Q)$ gravity
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abstract
$f(Q)$ gravity is an extension of the symmetric teleparallel equivalent to general relativity (STEGR). This work shows that based on the scalar-nonmetricity formulation, a scalar mode in $f(Q)$ gravity has a negative kinetic energy. This conclusion holds regardless of the coincident gauge frequently used in STEGR and $f(Q)$ gravity. To study the scalar mode, we further consider the covariant $f(Q)$ gravity as a special class in higher-order scalar tensor (HOST) theory and rewrite the four scalar fields, which play a role of the St\"{u}eckelberg fields associated with the diffeomorphism, by vector fields. Applying the standard Arnowitt-Deser-Misner (ADM) formulation to the new formulation of the $f(Q)$ gravity, we demonstrate that the ghost scalar mode can be eliminated by the second-class constraints, thus ensuring that $f(Q)$ gravity is a healthy theory.
Forward citations
Cited by 4 Pith papers
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Degrees of freedom of a quadratic scalar-nonmetricity theory
In quadratic scalar-nonmetricity gravity, Hamiltonian analysis shows 10, 8, and 8 degrees of freedom for cases II, V, and VI, while linear cosmological perturbation theory sees only 10, 6, and 5, indicating hidden str...
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Revisiting Coincident GR in Internal STEGR Formulation
The paper derives internal-STEGR field equations, recovers coincident GR as the coincident-gauge sector, and finds that massive test particles obey a norm-flow equation instead of geodesics.
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ACT-DR6 consistent inflation in generalised entropic cosmology and $f(Q)$ gravity
Reconstruction produces explicit f(Q) and generalised-entropic inflation models (and scalar-coupled versions) whose slow-roll parameters match ACT-DR6 + Planck-BAO constraints on n_s and r.
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Properties of compact objects in quadratic non-metricity gravity
Quadratic non-metricity gravity with a fitted coupling ξ can match PSR J0740+6620 while keeping the radial sound speed below c²/3, according to the paper's chosen metric ansatz.
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