Cosmology of the Galileon from Massive Gravity (1106.3312v3)

Abstract: We covariantize the decoupling limit of massive gravity proposed in arXiv:1011.1232 and study the cosmology of this theory as a proxy, which embodies key features of the fully non-linear covariant theory. We first confirm that it exhibits a self-accelerating solution, similar to what has been found in arXiv:1010.1780, where the Hubble parameter corresponds to the graviton mass. For a certain range of parameters fluctuations relative to the self-accelerating background are stable and form an attractor solution. We also show that a degravitating solution can not be constructed in this covariantized proxy theory in a meaningful way. As for cosmic structure formation, we find that the helicity-0 mode of the graviton causes an enhancement relative to LCDM. For consistency we also compare proxy theories obtained starting from different frames in the decoupling limit and discuss the possibility of obtaining a non-representative proxy theory by choosing the wrong starting frame.

• The paper demonstrates that self-accelerating cosmological solutions emerge from massive gravity, with the Hubble parameter linked to the graviton mass.
• It analyzes the stability and attractor properties of fluctuations around the self-accelerating background, comparing the findings with the ΛCDM cosmology.
• The study examines theoretical constraints on ghost instabilities and outlines potential experimental directions for probing cosmic structure formation.

Cosmology of the Galileon from Massive Gravity

The paper "Cosmology of the Galileon from Massive Gravity" by Claudia de Rham and Lavinia Heisenberg delineates an exploration of the cosmological implications presented by a covariantized version of the decoupling limit in massive gravity theories. The investigation serves as a proxy to illuminate key features underpinning the fully non-linear covariant theory of massive gravity. This article capitalizes on the foundational premises of the self-accelerating universe as induced by massive gravity, critically examining the stability and attractor properties inherent within the theoretical model while contrasting its findings against the standard $\Lambda$CDM cosmological model.

Self-Acceleration and Galileon Interactions

The authors initially confirm the existence of a self-accelerating cosmological solution. Here, the Hubble parameter is equated to the mass of the graviton, drawing parallels to discoveries identified in prior studies. Within specific parameter domains, fluctuations surrounding this self-accelerating background demonstrate stability, potentially forming an attractor solution. This framework challenges conventional perspectives by positing an enhanced cosmic structure formation relative to $\Lambda$CDM, driven by the helicity-0 mode of the graviton.

Stability and Degravitation

A consequential investigation undertaken by de Rham and Heisenberg examines potential ghost-like instabilities within the massive gravity constructs. The paper posits constraints ensuring stability while systematically dissecting whether a degravitating solution can be meaningfully nurtured in their covariantized proxy theory. Although self-accelerating solutions hold promise within massive gravity frameworks, they do not holistically address the cosmological constant problem, a mismatch between theoretical expectations and empirical observations in vacuum energy density.

Theoretical and Practical Implications

The implications of this paper are multifaceted, contributing both theoretically and practically to the field of cosmology. From a theoretical vantage point, the results advance the discourse surrounding modified gravity theories, offering novel avenues by which cosmic accelerated expansion can be interpreted. On a practical level, the insights generated may inspire experimental studies designed to probe the veracity of massive gravity models in cosmic structure formation and gravitational clustering, contrasting these phenomena against established expectations of the $\Lambda$CDM model.

Future Directions

Looking ahead, future research is poised to explore the observational ramifications of Galileon cosmologies as posited within this paper. The exploration of gravitational behavior on larger scales, interactive dynamics within cosmological bodies, and the nuanced contributions of helicity modes to cosmic structure formation are of particular interest. Given the foundational nature of this investigation, the continued paper of these facets promises to enrich our understanding of the universe, potentially reshaping cosmological models in alignment with emerging empirical evidence.

In summary, "Cosmology of the Galileon from Massive Gravity" is significant in laying the groundwork for advanced discussions surrounding Galileon cosmologies and massive gravity theories. The identification of stable self-accelerating solutions and their implications in cosmic structure formation mark pivotal steps toward broadening cosmological frameworks, highlighting the need for revisiting classical interpretations within modern astronomy.