arXiv subjects

Satoshi Akagi

Publications and source records attributed to Satoshi Akagi.

6 recordsLinked to original sources

arXiv2018

Covariant constraints of massive gravity in metric formulation

We propose a simple method for deriving the constraints of the de Rham-Gabadadze-Tolley model in the metric and the Lagrangian formulation, as possible as keeping the Lorentz covariance. In our formulation, it is not necessary to use the Hamilton analysis, the vielbein formulation, nor the Stuckelberg trick for showing the Boulwer-Deser ghost-freeness. It realizes the Lorentz covariant expressions of the constraints in a certain parameter region.

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arXiv2018

Bottom-up approach to massive spin-two theory in arbitrary curved spacetime

The linear theory of massive spin-two field in arbitrary curved background is investigated. In flat spacetime, the Fierz-Pauli model is well-known as the unique linear theory describing the massive spin-two field. On the other hand, in order to construct the massive spin-two theory in fixed curved background with arbitrary metric, infinite series of nonminimal coupling terms are necessary. In [Nucl. Phys. B 584 (2000) 615], Buchbinder et al. have derived the condition for the ghost-freeness and they have solved the condition in small curvature approximation. In the leading order approximation, three free parameters of the leading order nonminimal coupling terms are allowed. However, existence of the completion corresponding to all the three parameters is not guaranteed. On the other hand, recently, a class of the completion is obtained by linearizing the dRGT model. However, the leading order nonminimal coupling terms of the linearized dRGT model depend only on one free parameter. Therefore, possibility of a class larger than the linearized dRGT model has not been excluded. In this paper, we develop the method for solving the conditions for ghost freeness in higher order and investigate whether lower order nonminimal coupling terms can be constrained by higher order conditions or not. As a result, we obtain an additional constraint on the leading order nonminimal coupling terms from the fourth order condition. Although the leading order nonminimal coupling terms of the linearized dRGT model is still a subclass of our resulting nonminimal coupling terms in the leading order, a trivial extension of the linearized dRGT model is perfectly equivalent to our resulting action.

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arXiv2018

Towards construction of ghost-free higher derivative gravity from bigravity

In this paper, the ghost-freeness of the higher derivative theory proposed by Hassan et al. in [Universe 1 (2015) 2, 92] is investigated. Hassan et al. believed the ghost-freeness of the higher derivative theory based on the analysis in the linear approximation. However, in order to obtain the complete correspondence, we have to analyze the model without any approximations. In this paper, we analyze two scalar model proposed in [Universe 1 (2015) 2, 92] with arbitrary nonderivative interaction terms. In any order with respect to perturbative parameter, we prove that we can eliminate the ghost for the model with any nonderivative interaction terms.

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arXiv2015

Stability analysis for new theories of massive spin-two particle and black hole entropy of new bigravity

In Phys.\ Rev.\ D 90 043006 (2014), we proposed a new ghost-free massive spin-two model in flat spacetime. Furthermore, as some extension, we couple the new model with a non-dynamical curved background in Phys.\ Rev.\ D 90 123013 (2014) and constructed new interaction terms without appearance of an extra mode. The characteristic property of the new model is the existence of nonlinear potential terms which give the nontrivial vacua. The presence of the nontrivial vacua, however, does not mean that the particle can be defined around all vacua. Therefore, in this paper, we discuss the condition for the new model to have stable vacua in flat spacetime and curved spacetime. Then, we couple this spin-two theory with a dynamical background and obtain the solutions. Moreover, we investigate the effect of this new spin-two model to the Einstein gravity by calculating the black hole entropy since the gravity coupled massive spin-two theory admits a black hole solution in addition to (anti-) de Sitter space solution.

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arXiv2014

New massive spin two model on curved space-time

We have proposed a new ghost-free model with interactions of massive spin two particles in Phys.\ Rev.\ D {\bf 90} (2014) 043006 [arXiv:1402.5737 [hep-th]]. Although the model is ghost-free on the Minkowski space-time, it is not obvious whether or not this desirable property is preserved on curved space-time. In fact, Buchbinder et al. already pointed out that the Fierz-Pauli theory is not ghost-free on curved space-time without non-minimal coupling terms. In this paper, we construct a new theory of massive spin two particles with non-minimal coupling on curved space-time and show that the model can be ghost-free. Furthermore, we propose new non-minimal coupling terms.

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arXiv2014

Renormalizable toy model of massive spin two field and new bigravity

In this paper, we propose a toy model of the renormalizable theory describing massive spin two field. Although the model is renormalizable, we show that the model contains ghost. The coupling of the theory with gravity can be regarded as a new kind of bimetric gravity or bigravity. We show that the massive spin two field plays the role of the cosmological constant.

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