arXiv subjects

J. Flinckman

Publications and source records attributed to J. Flinckman.

3 recordsLinked to original sources

arXiv2026

Multi-gravity cosmology beyond pairwise interactions

We develop the cosmological framework for Hassan--Schmidt-May multi-gravity, a ghost-free extension of bimetric theory with genuinely non-pairwise interactions of multiple spin-2 fields. For metrics that are simultaneously homogeneous and isotropic, the background dynamics reduce to a modified Friedmann equation supplemented by a system of coupled quartic polynomial equations for the scale-factor ratios. The spin-2 interaction contributes to the Friedmann equation as an additional effective fluid. We identify a regular high-density branch that approaches the standard radiation- or matter-dominated Universe, while regular low-density branches approach proportional vacuum solutions, where the interaction acts as a cosmological constant and the leading correction to the effective spin-2 energy density provides an additional matter contribution. We also determine the relative null-cone structure: on the regular high-density branch, the additional null cones approach wider opening angles than the matter-coupled null cone, while all null cones coincide in the vacuum limit. At linear order, we solve the algebraic equations determining the non-metric vielbein perturbations, derive the first-order consistency equations and their scalar and vector projections, and obtain the complete system of coupled tensor perturbation equations. These results establish a framework for studying cosmological solutions and perturbations in ghost-free multi-gravity beyond bimetric theory and its pairwise-interacting extensions.

gr-qc↗

arXiv2025

Existence of ghost-eliminating constraints in multivielbein theory

We perform a Hamiltonian constraint analysis of the multivielbein theory proposed in [Phys. Rev. Lett. 122 (2019) 251101]. The analysis shows that the secondary constraints have the correct form to eliminate the problematic ghost fields that generally plague theories of interacting spin-2 fields. In particular, the would-be ghost fields are eliminated by the constraints associated with the lapse functions. The subsequent constraints must then determine the ghost momenta and the remaining non-dynamical variables. To establish this, we work with a restricted set of vielbeins with equal boost functions. This allows us to explicitly compute the additional constraints that eliminate the canonical momenta associated with the ghost fields and fix the remaining non-dynamical variables. Our analysis confirms that, subject to this restriction on the boosts, the theory with N interacting vielbeins propagates 2+5(N-1) modes. This corresponds to a nonlinear theory of one massless and N-1 massive spin-2 fields free of Boulware-Deser ghost instabilities.

hep-th↗

arXiv2024

Mass spectrum and linear perturbations of ghost-free multi-spin-2 theory

Motivated by the spin-2 nature of gravity, we consider a theory of N interacting spin-2 fields, formulated in terms of vielbeins which have been argued to be free of the Boulware-Deser ghost. This is the only known such theory with nontrivial multi-field interactions. We develop an all-order expansion of the vielbein in terms of the metric and Lorentz field perturbations, enabling an expansion of the action in arbitrary backgrounds to any order. The mass matrix is then analysed around proportional vielbein solutions corresponding to vacuum Einstein spacetimes. It is shown that the theory exhibits a non-tachyonic spectrum with one massless and N-1 massive spin-2 modes, regardless of the sign of the cosmological constant. While the massless mode is universal, the non-zero masses cannot generally be determined analytically, but we obtain the lower and upper bounds on each mass eigenvalue in terms of the parameters of the theory.

hep-th↗