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Equivalence principle violation in metric-affine gravity and finite-temperature effects

Emmanuele Battista1,*, Roberto Campagnola1,†, Salvatore Capozziello2,3,4,‡, and Giuseppe Fiorillo5,§

  • *Contact author: ebattista@lnf.infn.it
  • †Contact author: roberto.campagnola@lnf.infn.it
  • ‡Contact author: capozziello@na.infn.it
  • §Contact author: giufiorillo@unisa.it
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Phys. Rev. D 114, 024009 – Published 6 July, 2026

DOI: https://doi.org/10.1103/7qp5-9kzk

Abstract

Possible violations of the equivalence principle are investigated within the framework of metric-affine gravity, and their connections to finite-temperature effects are highlighted. Thermal corrections to particle dynamics, originally derived in a quantum-field-theory setting, can be evaluated in a purely Riemannian framework and lead to a shift in the gravitational-to-inertial mass ratio. We show that the ensuing departure from universality of free fall can be also formulated in metric-affine gravity, where the presence of the nonmetricity tensor modifies the Newtonian law in a way that closely parallels the finite-temperature scenario. Furthermore, we introduce a generalized Fermi-Walker derivative adapted to non-Riemannian contexts, which naturally reveals that no orthonormal tetrad can be propagated along an observer worldline. Although metric-affine gravity admits a pointwise realization of the Einstein equivalence principle in its gauge-theoretic, elementary-matter form, the new operator offers a direct geometric signature that this principle, in its modern formulation, is not retained, in general. Potential tests of the analyzed effects are also discussed.

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Phys. Rev. D 114, 024009– Published 6 July, 2026
  • Received 7 January 2026
  • Accepted 1 June 2026
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