Gravitational Waves as Thermodynamic Shear Excitations in Scalar-Tensor Gravity

2026/07/17 by David S. Pereira
#gr-qc

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Abstract

In Jordan-frame scalar--tensor gravity, a timelike scalar gradient defines an effective thermodynamic medium. We show that a transverse--traceless perturbation of a homogeneous shear-free background activates the local shear-work channel \mathcal W_ϕ=π_ab^(ϕ)σ^ab, with leading pure-TT contribution \mathcal P_{\rm TT}^[1,1] =\mathcal K\mathcal T χ_ij^{\rm TT}χ_{\rm TT}^ij/4. This stress power follows from local traction mechanics, enters the scalar-sector energy balance, and is gauge invariant at second order. The same scalar--tensor coupling controls non-GR tensor damping and appears with the opposite sign in a GR-normalized amplitude balance, although its interpretation as a separate tensor-energy source is normalization dependent. Scalar--tensor gravity thus provides a controlled example in which a propagating spin-2 mode acquires an intrinsically gravitational thermodynamic interpretation.

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