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On Consistent Theories of Massive Spin-2 Fields Coupled to Gravity
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
2013 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 5, 086- p.Article in journal (Refereed) Published
Abstract [en]

We consider the issues that arise out of interpreting the ghost-free bimetric theory as a theory of a spin-2 field coupled to gravity. This requires identifying a gravitational metric and parameterizing deviations of the resulting theory from general relativity. To this end, we first consider the most general bimetric backgrounds for which a massless and a massive spin-2 fluctuation with Fierz-Pauli mass exist. These backgrounds coincide with solutions in general relativity. Based on this, we obtain nonlinear extensions of the massive and massless spin-2 fields. The background value of the nonlinear massive field parameterizes generic deviations of the bimetric theory from GR. It is also shown that the nonlinear massless field does not have standard ghost-free matter couplings, and hence cannot represent the gravitational metric. However, an appropriate gravitational metric can still be identified in the weak gravity limit. Hence in the presence of other neutral spin-2 fields, the weak gravity limit is crucial for compatibility with general relativity. We also write down the action in terms of the nonlinear massive spin-2 field and obtain its ghost-free couplings to matter. The discussion is then generalized to multimetric theories.

Place, publisher, year, edition, pages
2013. no 5, 086- p.
Keyword [en]
Classical Theories of Gravity, Cosmology of Theories beyond the SM
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-83250DOI: 10.1007/JHEP05(2013)086ISI: 000321375600003OAI: oai:DiVA.org:su-83250DiVA: diva2:574786
Available from: 2012-12-06 Created: 2012-12-06 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Unravelling Consistent Spin-2 Interactions
Open this publication in new window or tab >>Unravelling Consistent Spin-2 Interactions
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recently, a unique formulation of a classically consistent theory of massive spin-2 fields has emerged. In this thesis I address a few of the primary questions that arise once such a theory is available.

I will discuss cosmological solutions in a bimetric setup and show that, as far as the background evolution is concerned, a theory of interacting spin-2 fields remain a viable option to the mainstream ΛCDM concordance model. In general, the bimetric solutions are quite different from general relativistic solutions and hence in many situations will not be supported by observations. I highlight a particularly useful class of bimetric solutions which mimic general relativity exactly at the background level. This class of solutions is very special since it both uniquely provide the maximally symmetric vacuum solutions in the absence of matter sources as well as uniquely provide a massive Fierz-Pauli wave equation for perturbations of these backgrounds. This allow us a clear interpretation of the spectrum of perturbations in terms of mass eigenstates. I provide a nonlinear extension of these mass eigenstates into nonlinear fields which are not true mass eigenstates but still provide useful input into the theoretical understanding of the theory. These nonlinear extensions are particularly interesting both with respect to parameterizing generic deviations of the bimetric solutions to general relativistic solutions, as well as providing further insight into some unresolved questions related to ``massive gravity" in maximally symmetric backgrounds, such as the illusive nature of the Higuchi bound and its accompanying linear on-shell gauge invariance.

The special structure of the consistent interacting theory provides the basic tool to start to unravel some of the mysteries connected with spin-2 fields, with hope to reinvestigate many fundamental open questions explicitly related to the gravitational sector of field theory.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2012. 135 p.
Keyword
Modified Gravity, Massive Spin-2, Spin-2 Interactions
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-83258 (URN)978-91-7447-618-7 (ISBN)
Public defence
2013-01-28, FA32, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted. Paper 6: Submitted.

 

Available from: 2013-01-07 Created: 2012-12-06 Last updated: 2012-12-14Bibliographically approved
2. Classically Consistent Theories of Interacting Spin-2 Fields
Open this publication in new window or tab >>Classically Consistent Theories of Interacting Spin-2 Fields
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This doctoral thesis comprises a study of recently developed nonlinear theories for massive spin-2 fields that go by the names of Massive Gravity and Bimetric Theory. As we demonstrate in a Hamiltonian analysis, the construction of these theories avoids the notorious Boulware-Deser ghost instability that generically plagues nonlinear spin-2 interactions and renders their description inconsistent. We explore the mass spectrum of ghost-free Bimetric Theory and reformulate its action in terms of nonlinear mass eigenstates. A generalized version of the theory with multiple vielbein interactions is reviewed and then reexpressed in terms of metrics. Homogeneous and isotropic solutions to the equations of motion in Bimetric Theory are derived and discussed in the context of cosmology. We furthermore single out particular values for the parameters in the bimetric interaction potential for which the theory could potentially contain an additional gauge redundancy. This establishes a unique candidate for a nonlinear theory of a partially massless spin-2 field. Finally, we reveal a close connection of Bimetric Theory to a certain class of higher-curvature theories for gravity and offer a solution to their ghost problems. In particular we find that, in four space-time dimensions, the bimetric candidate for nonlinear partial masslessness is closely related to Conformal Gravity.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2013. 134 p.
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-96167 (URN)978-91-7447-791-7 (ISBN)
Public defence
2013-12-12, sal FA32, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 6: Submitted. Paper 8: Manuscript.

Available from: 2013-11-20 Created: 2013-11-12 Last updated: 2013-11-12Bibliographically approved

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Publisher's full texthttp://arxiv.org/abs/1208.1515

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