arXiv subjects

Kyosuke Tomonari

Publications and source records attributed to Kyosuke Tomonari.

10 recordsLinked to original sources

arXiv2026

Gauge-invariant cosmological perturbations in Type 3 New General Relativity and background-hierarchy bounds

In this paper, we investigate background-hierarchy bounds in Type~3 of New General Relativity (NGR). These bounds arise when the contribution associated with the evolution of the background spacetime exceeds that of the kinetic term in the perturbed Lagrangian. Type~3 of NGR has two free parameters and is described in a pure-tetrad formulation while preserving diffeomorphism invariance and spatial rotations. We first review Type~3 and identify preferable gauge choices for metric-affine gauge theories of gravity with Weitzenb\"ock connection, including NGR, from the viewpoint of symmetry in both Dirac--Bergmann analysis and linear perturbation theory. We then revisit the perturbative analysis of Type~3 and show that the propagating modes are correctly identified even when the perturbed Lagrangian is not written solely in terms of gauge-invariant variables. Finally, we derive the background-hierarchy bounds for the scalar, transverse-vector, and tensor modes around a flat FLRW background, and identify the region of parameter space in which the linear perturbation theory of Type~3 remains viable for cosmological applications.

gr-qc↗

arXiv2025

Cosmological Perturbation in New General Relativity: Propagating mode from the violation of local Lorentz invariance

We investigate the propagating modes of New General Relativity (NGR) in second-order linear perturbations in the Lagrangian density (first-order in field equations). The Dirac-Bergmann analysis has revealed a violation of local Lorentz invariance in NGR. We review the recent status of NGR, considering the results of its Dirac-Bergmann analysis. We then reconsider the vierbein perturbation framework and identify the origin of each perturbation field in the vierbein field components. This identification is mandatory for adequately fixing gauges while guaranteeing consistency with the invariance ensured by the Dirac-Bergmann analysis. We find that the spatially flat gauge is adequate for analyzing a theory with the violation of local Lorentz invariance. Based on the established vierbein perturbative framework, introducing a real scalar field as matter, we perform a second-order perturbative analysis of NGR with respect to tensor, scalar, pseudo-scalar, and vector and pseudo-vector modes. We reveal the possible propagating modes of each type of NGR. In particular, we find that Type 3 has stable five propagating modes, \textit{i.e.}, tensor, scalar, and vector modes, compared to five non-linear degrees of freedom, which results in its Dirac-Bergmann analysis; the linear perturbation theory of Type 3 is preferable for applications to cosmology. Finally, we discuss our results in comparison to previous related work and conclude this study.

gr-qc↗

arXiv2025

Revisiting Coincident GR in Internal STEGR Formulation

We revisit Coincident General Relativity (CGR) in the gauge approach to gravity based on Symmetric Teleparallel Equivalent to General Relativity (STEGR) in the \textit{internal-space formulation}, which one of the authors recently proposed in Ref.~[J. Math. Phys. 66 (2025) 5, 052505]. First, we review the standard formulation of STEGR theories in the Palatini approach to gravity, in which formulation we impose the teleparallel and torsion-free conditions by using Lagrange multipliers. Second, we introduce the STEGR theories in the gauge approach to gravity, which is formulated in the internal space, and derive its field equations. We briefly discuss whether the Ostrogradski ghost instability exists and find that the theory may require a degenerate condition to be imposed. Finally, assuming the coincident gauge, we derive CGR in both terms of the action integral and the field equation. Discussing the possible kinematics of the STEGR theory, we formulate a motion of a test scalar particle in the spacetime with non-metricity.

gr-qc↗

arXiv2025

Degrees of Freedom of New General Relativity I: Type 2, Type 3, Type 5, and Type 8

We investigate the degrees of freedom of new general relativity. This theory is a three-parameter theory and is classified into nine irreducible types according to the rotation symmetry of $SO(3)$ on each leaf of ADM-foliation. In this work, we focus on unveiling the degrees of freedom of the physically interesting types of NGR: Type 2, Type 3, Type 5, and Type 8, which contain the gravitational propagating degrees of freedom. First, we revisit the theory based on the gauge approach to gravity and reformulate the Lagrangian of the theory. Second, we review the irreducible decomposition of the theory while focusing on the Hamiltonian and the primary constraints in each type. Third, we perform the Dirac-Bergmann analysis to unveil the degrees of freedom of the theory in the case of Type 2, Type 3, Type 5, and Type 8. We find a novel new behavior of constraints in Type 8, which is classified as second-class but not to determine any Lagrange multipliers and to provide the gauge invariance of the theory under the satisfaction of a specific condition of the multipliers. The degrees of freedom of Type 2, Type 3, and Type 5 are unveiled as six, five, and seven, respectively. The degrees of freedom of Type 8 is either four under a specific condition to the Lagrange multipliers or six in the generic case. Finally, we conclude this work with five future perspectives.

gr-qc↗

arXiv2025

STEGR in Internal-Space Formulation: Formalisms, Primary Constraints, and Possible Internal Symmetries

We establish the theories of Symmetric Teleparallel Equivalent to General Relativity (STEGR) in the internal-space and investigate possible internal-space symmetries among primary constraint densities in the theories. First of all, we revisit STEGR in terms of the gauge approach to gravity and formulate it in the internal-space set-up. We find three possible formalisms according to the vanishing-torsion property. Then, we investigate possible internal-space symmetries in each formalism. We find that in our formulation there are two possible symmetries. One satisfies the translation symmetry but broken in the local symmetry provided by the general linear group which contains the local Lorentz symmetry. The other satisfies the latter symmetry but is absent in the former symmetry. Finally, we conclude this work and show future perspectives.

gr-qc↗

arXiv2024

Degrees of Freedom of New General Relativity:\\ Type 4, Type 7, and Type 9

We investigate degrees of freedom in New General Relativity. This theory is the three-parameter extension of Teleparallel Equivalent to GR and classified into nine irreducible types according to the rotation symmetry $SO(3)$ on each leaf of ADM-foliation. In the previous work~[{\it Phys. Rev. D 112 (2025) 8, 084052}], we investigated the degrees of freedom in NGR types that are of interest in describing gravity: Type 2, Type 3, Type 5, and Type 8. In this work, we focus on unveiling those numbers in all other types to complete the analysis of NGR. After providing the Hamiltonian formulation of NGR and considering in detail the regularity of NGR, we perform the analysis of Type 4, Type 7, and Type 9. We reveal that the degrees of freedom of Type 4, Type 7, and Type 9 are five, zero (purely topological system in bulk spacetime), and three, respectively. Type 4 and Type 9 have second-class constraint densities only, whereas Type 7 has first-class constraint densities only. In every type, no bifurcation occurs. In particular, Type 4 and Type 7 are irregular and provide specific examples of handling irregular systems. Since no general method is known for treating an irregular system, this work contributes to furthering the understanding of irregular systems.

gr-qc↗

arXiv2024

A unified-description of curvature, torsion, and non-metricity of the metric-affine geometry with the Möbius representation

We establish the mathematical fundamentals for a unified description of curvature, torsion, and non-metricity 2-forms in the way extending the so-called Möbius representation of the affine group, which is the method to convert the semi-direct product into the ordinary matrix product, to revive the fertility of gauge theories of gravity. First of all, we illustrate the basic concepts for constructing the metric-affine geometry. Then the curvature and torsion 2-forms are described in a unified manner by using the Cartan connection of the Möbius representation of the affine group. In this unified-description, the curvature and torsion are derived by Cartan's structure equation with respect to a common connection 1-form. After that, extending the Möbius representation, the dilation and shear 2-forms, or equivalently, the non-metricity 2-form, are introduced in the same unified manner. Based on the unified-description established in this paper, introducing a new group parametrization and applying the Inönü-Wigner group contraction to the full theory, the relationships among symmetries, geometric quantities, and geometries are investigated with respect to the three gauge groups: the metric-affine group and its extension, and an extension of the (anti)-de Sitter group in which the non-metricity exists. Finally, possible applications to theories of gravity are briefly discussed.

gr-qc↗

arXiv2024

Dirac-Bergmann analysis and Degrees of Freedom of Coincident $f(Q)$-gravity

We investigate the propagating degrees of freedom of $f(Q)$-gravity in a $4$-dimensional space-time under the imposition of the coincident gauge by performing the Dirac-Bergmann analysis. In this work, we start with a top-down reconstruction of the metric-affine gauge theory of gravity based only on the concept of a vector bundle. Then, the so-called geometrical trinity of gravity is introduced and the role of the coincident GR is clarified. After that, we reveal relationships between the boundary terms in the variational principle and the symplectic structure of the theory in order to confirm the validity of the analysis for our studied theories. Then, as examples, we revisit the analysis of GR and its $f(\lc{R})$-extensions. Finally, after reviewing the Dirac-Bergmann analysis of the coincident GR and that of $f(T)$-gravity, we perform the analysis of coincident $f(Q)$-gravity. Under the imposition of appropriate spatial boundary conditions, we find that, as a generic case, the theory has five primary, three secondary, and two tertiary constraint densities and all these constraint densities are classified into second-class constraint density; the number six is the propagating degrees of freedom of the theory and there are no longer any remaining gauge degrees of freedom. We also discuss the condition of providing seven pDoF as a generic case. The violation of diffeomorphism invariance of coincident $f(Q)$-gravity make it possible to emerge such several sectors.

gr-qc↗

arXiv2023

On the well-posed variational principle in degenerate point particle systems using embeddings of the symplectic manifold

A methodology on making the variational principle well-posed in degenerate systems is constructed. In the systems including higher-order time derivative terms being compatible with Newtonian dynamics, we show that a set of position variables of a coordinate system of a given system has to be fixed on the boundaries and that such systems are always Ostrogradski stable and causal. For these systems, Frobenius integrability conditions are derived in explicit form. Relationships between integral constants indicated from the conditions and boundary conditions in a given coordinate system are also investigated by introducing three fundamental correspondences between Lagrange and Hamilton formulation. Based on these ingredients, we formulate problems that have to be resolved to realize the well-posedness in the degenerate systems. To resolve the problems, we compose a set of embbedings that extract a subspace holding the symplectic structure of the entire phase space in which the variational principle should be well-posed. Using these embeddings, we establish a methodology to set appropriate boundary conditions that the well-posed variational principle demands. Finally, we apply the methodology to examples and summarize this work as three-step procedure such that one can use just by following it.

math-ph↗

arXiv2023

Boundary Conditions for Constraint Systems in Variational Principle

We show the well-posed variational principle in constraint systems. In a naive procedure of the variational principle with constraints, the proper number of boundary conditions does not match with that of physical degrees of freedom dynamical variables, which implies that, even in theories with up to first order derivatives, the minimal (or extremal) of the action with the boundary terms is not a solution of equation of motion in the Dirac procedure of constrained systems. We propose specific and concrete steps to solve this problem. These steps utilize the Hamilton formalism, which allows us to separate the physical degrees of freedom from the constraints. It reveals the physical degrees of freedom which is necessary to be fixed on boundaries, and also enables us to specify the variables to be fixed and the surface terms.

hep-th↗