Eur. Phys. J. C (2026) 86: 594
https://doi.org/10.1140/epjc/s10052-026-15793-y

Regular Article - Theoretical Physics

Parameterized post-Newtonian analysis of quadratic gravity and solar system constraints

Department of Physics, Chongqing Key Laboratory for Strongly Coupled Physics, Chongqing University, 401331, Chongqing, People’s Republic of China

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Received: 26 March 2026
Accepted: 30 April 2026
Published online: 1 June 2026

Abstract

This work systematically investigates the post-Newtonian behavior of general quadratic gravity in the weak-field regime. By extending the Einstein–Hilbert action to include quadratic curvature terms as $\mathcal{L}\propto R-\lambda C^2+\mu R^2$, the theory introduces two massive modes: a scalar mode and a ghost tensor mode. Using the post-Newtonian expansion method, we derive the explicit expressions for the metric for a general source up to 1.5PN order. Furthermore, for a point-mass source, we extend the solution to 2PN order and evaluate the effective parameterized post-Newtonian parameters $\gamma (r)$ and $\beta (r)$. The results show that deviations from General Relativity are exponentially suppressed. The theory has the feature $\gamma (r)\equiv 1$ when $m_R=m_W$, and to ensure that gravity remains attractive, we have $m_W>m_R/4$. At short distance scales, the Newtonian potential no longer exhibits a 1/r behavior, but instead displays a polynomial dependence on r. The leading correction to $\beta (r)$ exhibiting a characteristic $\mathcal{O}(rln(r)e^{-mr})$ dependence. Based on the Solar System experiments, we derive preliminary constraints on the theory’s parameters: $m_R,m_W\gtrsim 23{\mathrm{AU}}^{-1}$, corresponding to $\lambda \lesssim 2.1\times {10}^{19}{\mathrm{m}}^2$ and $\mu \lesssim 7.1\times {10}^{18}{\mathrm{m}}^2$. This study provides a theoretical foundation for future tests of quadratic gravity using pulsar timing arrays, gravitational-wave observations, and laboratory-scale short-range gravity experiments.