Researchers have explored the warm inflation model within the framework of scalar-tensor theories of gravity, specifically in the 'defining frame'. This approach allows for the specification of the fundamental theory and its parameters. By translating the resulting dynamics to the Einstein frame, it is observed that modified-gravity effects suppress the dissipation ratio. This finding suggests that, although the effective dynamics of warm inflation can be consistently analyzed in both frames, the dissipative regimes do not necessarily coincide between them, introducing additional complexity in understanding the early universe.

A key result of this study is that quantum perturbations can dominate the scalar power spectrum, even in a high-temperature, strong-dissipation regime within the defining frame. This contrasts with some previous expectations and underscores the importance of considering modified gravity effects. The ability of quantum fluctuations to prevail over thermal ones under these conditions has significant implications for the generation of the seeds of cosmic structures we observe today.

The authors calculated the scalar spectral index and the tensor-to-scalar ratio for a non-minimal coupling function of the form $F(\Phi) = 1+\xi(\Phi/m_{\rm P})^2$, using a quartic potential. They considered both constant and quadratically field-dependent dissipation coefficients. From these calculations, they identified benchmark points that are compatible with current constraints imposed by cosmic microwave background (CMB) observations. These results provide new avenues for testing inflation and modified gravity models with cosmological data.