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Abstract

We explore a parity-violating extension to the Einstein-Maxwell theory within the framework of effective field theory (EFT). The model is characterized by a dimension-eight operator, suppressed by the fourth power of a new physics energy scale $\Lambda$, which couples the electromagnetic field strength tensor $F_{\mu\nu}$ to its dual. This operator, proportional to $(F_{\alpha\beta}F^{\alpha\beta})(F_{\gamma\delta}\tilde{F}^{\gamma\delta})$, introduces a non-linear modification to both gravitational and electromagnetic dynamics. We derive the complete set of self-consistent field equations from the modified action. The gravitational field equations reveal that the electromagnetic stress-energy tensor's contribution to spacetime curvature is modulated by a factor $\Omega$ that depends linearly on $\vec{E}\cdot\vec{B}$. A sufficiently large and positive $\vec{E}\cdot\vec{B}$ could, in principle, render this factor negative, leading to a violation of the weak energy condition (WEC). However, the primary focus of this work is to assess the physical viability of such a scenario. We analyze the model's key phenomenological prediction: vacuum birefringence. By comparing our predictions with stringent constraints from high-precision terrestrial experiments like PVLAS and astrophysical observations of magnetars, we establish a robust lower bound on the new physics scale, $\Lambda \gtrsim 100$ TeV. This bound implies that the threshold for WEC violation is orders of magnitude beyond the field strengths observed anywhere in the universe, effectively suppressing this phenomenon. We conclude by discussing the theoretical self-consistency of the model and presenting an exact solution at the WEC violation threshold.