Thermal channels of scalar and tensor waves in Jordan-frame scalar--tensor gravity
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arXiv
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2026
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| author | Pereira, David S. Lobo, Francisco S. N Mimoso, José Pedro |
| author_facet | Pereira, David S. Lobo, Francisco S. N Mimoso, José Pedro |
| contents | We study first-order scalar and tensor perturbations of Jordan-frame scalar--tensor gravity about a spatially flat FLRW background using the Einstein-like effective-fluid decomposition of the scalar sector. In the scalar-gradient frame, we derive the perturbed effective density, pressure, heat flux, and anisotropic stress, and show that they admit an exact Eckart-type constitutive identification at linear order. We then show that these same quantities appear explicitly and exhaustively in the linearized field equations: the scalar Hamiltonian, momentum, trace, and traceless Einstein-like equations are governed, respectively, by the effective density, heat-flux, pressure, and anisotropic-stress channels, while the tensor propagation equation is governed by the transverse-traceless anisotropic-stress channel. In particular, the Jordan-frame modification of gravitational-wave damping is identified with the effective transverse-traceless anisotropic stress of the scalar sector. We also derive the perturbed evolution equation for the invariant product $κT$, clarify its gauge behavior, and show that flux matching on FLRW fixes only the background value $\overline{κT}$, not its perturbation. These results leave open the possibility that gravitational waves in scalar--tensor gravity admit a deeper thermodynamic characterization, perhaps even an intrinsic one, although the present analysis establishes this only at the level of an effective constitutive description. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_27386 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Thermal channels of scalar and tensor waves in Jordan-frame scalar--tensor gravity Pereira, David S. Lobo, Francisco S. N Mimoso, José Pedro General Relativity and Quantum Cosmology We study first-order scalar and tensor perturbations of Jordan-frame scalar--tensor gravity about a spatially flat FLRW background using the Einstein-like effective-fluid decomposition of the scalar sector. In the scalar-gradient frame, we derive the perturbed effective density, pressure, heat flux, and anisotropic stress, and show that they admit an exact Eckart-type constitutive identification at linear order. We then show that these same quantities appear explicitly and exhaustively in the linearized field equations: the scalar Hamiltonian, momentum, trace, and traceless Einstein-like equations are governed, respectively, by the effective density, heat-flux, pressure, and anisotropic-stress channels, while the tensor propagation equation is governed by the transverse-traceless anisotropic-stress channel. In particular, the Jordan-frame modification of gravitational-wave damping is identified with the effective transverse-traceless anisotropic stress of the scalar sector. We also derive the perturbed evolution equation for the invariant product $κT$, clarify its gauge behavior, and show that flux matching on FLRW fixes only the background value $\overline{κT}$, not its perturbation. These results leave open the possibility that gravitational waves in scalar--tensor gravity admit a deeper thermodynamic characterization, perhaps even an intrinsic one, although the present analysis establishes this only at the level of an effective constitutive description. |
| title | Thermal channels of scalar and tensor waves in Jordan-frame scalar--tensor gravity |
| topic | General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2603.27386 |