- Open Access
New horizons in effective field theory?
Phys. Rev. D 114, 024084 – Published 29 July, 2026
DOI: https://doi.org/10.1103/hkqk-932z
Abstract
We consider the most general parity symmetric effective scalar tensor theory in four dimensions containing terms up to fourth derivative order in the Lagrangian. It has been shown [H. S. Reall, [Phys. Rev. D 103, 084027 (2021)]] that this theory has three polarizations generically governed by different (nested) propagation cones, neither of which, in general, coincides with the light cone as defined by the metric. Consequently, the notion of a black hole horizon must be defined relative to the widest propagation cone and not with respect to the metric. We provide two theorems stating that, nevertheless, the horizon of a stationary black hole is null with respect to the metric and that, in fact, all three propagation cones touch on the horizon. The conditions in these theorems allow for rotating black holes. Our theorems thereby suggest that the notion of a Killing horizon, central in most discussions of black hole thermodynamics, retains its fundamental status and that certain thermodynamic paradoxes associated with multiple propagation cones are evaded.
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