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Massive gravity coupled to Galileons is ghost-free.

Melinda Andrews¹, Garrett Goon, Kurt Hinterbichler

¹Center for Particle Cosmology, Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. mgildner@sas.upenn.edu

Physical Review Letters

|August 27, 2013

Summary

We demonstrate a novel coupling of Galilean-invariant scalars (Galileons) to massive gravity, preserving Galilean symmetry. This construction avoids the Boulware-Deser ghost, retaining desirable features of both theories.

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Area of Science:

Theoretical Physics
High Energy Physics
Cosmology

Background:

Coupling scalar fields to gravity is crucial for understanding fundamental forces.
Generalized Galilean internal shift symmetries (Galileons) offer unique interaction properties.
Massive gravity theories aim to explain cosmic acceleration but often suffer from instabilities like the Boulware-Deser ghost.

Purpose of the Study:

To investigate the possibility of coupling Galileons to nonlinear massive gravity in four dimensions.
To ensure the constructed theory maintains Galilean symmetry.
To demonstrate the absence of the Boulware-Deser ghost in the proposed model.

Main Methods:

Developing a theoretical framework for coupling Dirac-Born-Infeld scalars with Galilean symmetries to massive gravity.
Analyzing the resulting interaction terms to confirm the preservation of Galilean symmetry.
Investigating the constraint structure of the theory to identify and eliminate potential ghosts.

Main Results:

Successfully coupled Galileons to nonlinear massive gravity in four dimensions while preserving Galilean symmetry.
The proposed interaction is not possible with massless general relativity.
The theory possesses the necessary primary constraint to eliminate the Boulware-Deser ghost.

Conclusions:

The developed theory successfully integrates Galileons with massive gravity, overcoming limitations of coupling to massless general relativity.
The absence of the Boulware-Deser ghost preserves the desirable characteristics of both Galileons and ghost-free massive gravity.
This construction offers a promising avenue for exploring modified gravity theories with stable scalar field interactions.