Constraints on $f(R_{ijkl}R^{ijkl})$ gravity: An evidence against the covariant resolution of the Pioneer anomaly

TL;DR

This paper investigates modifications to general relativity involving curvature invariants, finding that such corrections cannot covariantly resolve the Pioneer anomaly due to strong observational constraints from Earth-based measurements.

Contribution

It demonstrates that specific curvature-based corrections to gravity cannot explain the Pioneer anomaly without conflicting with existing high-precision measurements.

Findings

The correction term with a 1/3 power of Riemann tensor invariants predicts a constant anomalous acceleration.

High-precision Earth measurements impose strict bounds on these corrections.

The bounds refute the covariant resolution of the Pioneer anomaly.

Abstract

We consider corrections in the form of $\Delta L(R_{ijkl}R^{ijkl})$ to the Einstein-Hilbert Lagrangian. Then we compute the corrections to the Schwarszchild geometry due to the inclusion of this general term to the Lagrangian. We show that $\Delta L_3=\alpha_{{1/3}}(R_{ijkl}R^{ijkl})^{{1/3}}$ gives rise to a constant anomalous acceleration for objects orbiting the Sun onward the Sun. This leads to the conclusion that $\alpha_{{1/3}}=(13.91\pm 2.11) \times 10^{-26}(\frac{1}{\text{meters}})^{{2/3}}$ would have covariantly resolved the Pioneer anomaly if this value of $\alpha_{{1/3}}$ had not contradicted other observations. We notice that the experimental bounds on $\Delta L_3$ grows stronger in case we examine the deformation of the space-time geometry around objects lighter than the Sun. We therefore use the high precision measurements around the Earth (LAGEOS and LLR) and obtain a very strong constraint on the corrections in the form of $\Delta L(R_{ijkl}R^{ijkl})$ and in particular $\Delta L=\alpha_n(R_{ijkl}R^{ijkl})^n$. This bound requires $\alpha_{{1/3}}\leq6.12\times 10^{-29}(\frac{1}{\text{meters}})^{{2/3}}$. Therefore it refutes the covariant resolution of the Pioneer anomaly.