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arXiv · 2607.12280

Dynamics of potential-free warm $\mathbf{k}$-inflation with nonminimal derivative coupling

Xiao-Min Zhang·Zi-Xin Bai·Run-Qing Zhao·Peng-Cheng Chu·Yun-Cai Feng·Zhi-Peng Peng·Xi-Bin Li
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Abstract

In contrast to potential-driven warm inflation models, this paper presents a new inflationary scenario driven purely by noncanonical kinetic terms. We derive the evolution equations and the associated slow-roll approximations specific to the kinetic case. The model incorporates a nonminimal derivative coupling that enhances gravitational friction; when combined with thermal damping, this leads to a significantly slower evolution of the pure kinetic inflaton. The resulting slow-roll approximations differ fundamentally from those of potential-driven inflation. The attractor behavior of this warm $k$-inflation with nonminimal derivative coupling is explored, confirming that slow-roll solutions can approach a strict exponential expansion attractor under relaxed slow-roll conditions. We further calculate the density fluctuation equations and obtain analytic expressions for the power spectrum, spectral index, and tensor-to-scalar ratio. Compared to standard inflation in general relativity, the energy scale at horizon crossing is lower, and the tensor-to-scalar ratio is significantly reduced due to the combined effects of thermal damping and nonminimal derivative coupling. The field excursion remains comfortably sub-Planckian. The model's predictions are in excellent agreement with the latest Planck 2018 data, offering a novel and successful extension of the warm inflation paradigm.

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Xiao-Min Zhang, Zi-Xin Bai, Run-Qing Zhao, Peng-Cheng Chu, Yun-Cai Feng, Zhi-Peng Peng, Xi-Bin Li. 2026-07-14. Dynamics of potential-free warm $\mathbf{k}$-inflation with nonminimal derivative coupling. https://doi.org/10.1140/epjc%2Fs10052-026-16025-z

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