Graviton Mass Might Reduce Tension between Early and Late Time Cosmological Data

Area of Science:

• Cosmology
• Theoretical Physics
• Gravitational Physics

Background:

• The standard Lambda Cold Dark Matter (Λ-CDM) model predicts structure growth rates inconsistent with Redshift Space Distortion (RSD) measurements when cosmological parameters are fixed by Cosmic Microwave Background (CMB) data.
• This discrepancy suggests potential limitations in the standard cosmological model or the underlying physics of gravity.

Purpose of the Study:

• To investigate whether a massive graviton theory can resolve the tension between Λ-CDM predictions and observational data.
• To explore the phenomenology of the Minimal Theory of Massive Gravity (MTMG) and its implications for structure formation.
• To constrain the mass of the graviton using cosmological observations.

Main Methods:

• Utilized the Minimal Theory of Massive Gravity (MTMG), specifically a branch where the background evolution matches General Relativity (GR) but matter perturbation evolution is modified by graviton mass.
• Fitted the modified dynamics predicted by MTMG to existing Redshift Space Distortion (RSD) measurements.
• Employed cross-correlation analysis between the Integrated Sachs-Wolfe (ISW) effect and large-scale structure data.

Main Results:

• The MTMG model provides a significantly better fit to the RSD data compared to the Λ-CDM model, with the latter being less probable by 2 orders of magnitude.
• The analysis yields a value for the graviton mass squared of approximately μ² ≈ -(3×10⁻³³ eV)².
• This estimated graviton mass is consistent with the upper bound set by recent LIGO observations (|μ²| < (1.2×10⁻²² eV)²).

Conclusions:

• A nonzero graviton mass, as proposed by MTMG, offers a compelling resolution to the observed discrepancy in structure growth.
• The MTMG framework, particularly the chosen branch, successfully reconciles cosmological observations that challenge the standard Λ-CDM model.
• Cosmological observations, including RSD and ISW-LSS cross-correlations, can effectively constrain fundamental parameters like the graviton mass.