arXiv subjects

Run-Qing Zhao

Publications and source records attributed to Run-Qing Zhao.

4 recordsLinked to original sources

arXiv2026

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

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.

gr-qc↗

arXiv2026

Dynamics and observational signatures of warm Dirac-Born-Infeld inflation with nonminimal derivative coupling

This paper investigates a warm Dirac-Born-Infeld (DBI) inflationary model with nonminimal derivative coupling (NMDC) to gravity, where the inflaton kinetic term interacts with the Einstein tensor, thereby improving the effective gravitational friction. This model seamlessly integrates the noncanonical DBI kinetic structure, the NMDC-induced gravitational friction, and thermal dissipation. We formulate the background evolution equations along with the corresponding slow-roll stability conditions, leading to analytic results for the scalar spectral index $n_s$ and the tensor-to-scalar ratio $R$. By applying these results to power-law potentials with $n=2$ and $n=4$, the model parameter space is constrained using the \emph{Planck} 2018 data. The findings indicate that the interaction between NMDC-induced gravitational friction and thermal dissipation effectively modulates $n_s$ and significantly expands the viable parameter space. In the $(n_s,R)$ plane, the predictions for $N=50$ fall within the 95\% confidence-level region, while those for $N=60$ extend into the 68\% confidence-level region and approach the observationally preferred central values. For the representative parameter choices examined, the tensor-to-scalar ratio is notably suppressed, generally within the range $10^{-8}\lesssim R\lesssim10^{-5}$. Moreover, the combined damping mechanism relaxes the slow-roll condition related to $\eta$ and limits the inflaton field excursion, thus addressing the $\eta$ problem without incurring super-Planckian field variations. These results indicate that warm DBI inflation with NMDC offers a theoretically coherent and observationally viable inflationary model, showcasing the complementary effects of thermal dissipation and enhanced gravitational friction in the context of modified gravity.

gr-qc↗

arXiv2025

Primordial non-Gaussianity in noncanonical warm inflation with nonminimal derivative coupling

This paper presents and investigates non-Gaussian perturbations for the warm k-inflation model that is driven by pure kinetic energy. The two complementary components of the overall non-Gaussianity are the three-point and four-point correlations. The intrinsic non-Gaussian component, denoted as the nonlinear parameter f_{NL}^{int}, is rooted in the three-point correlation for the inflaton field. Meanwhile, the \delta N part non-Gaussianity, denoted as f_{NL}^{\delta N}, is the contribution attributed to the four-point correlation function of the inflaton field. In this paper, the above two components in warm k-inflation are individually computed and analyzed. Then, comparisons and discussions between them are conducted, and the non-Gaussian theoretical results are compared with experimental observations to determine the range of model parameters within the allowable range of observation.

gr-qc↗

arXiv2024

Noncanonical warm inflation with nonminimal derivative coupling

This study extended noncanonical warm inflation to the nonminimal derivative coupling scenario. The fundamental equations, including the evolution equations and the slow roll equations of this new framework, were derived. The enlarged damping term, which encompasses both gravitationally enhanced friction and thermal damping, resulted in a well overdamped inflationary process, ensuring that the slow roll approximations can be satisfactorily satisfied. A linear stability analysis corroborated the viability of this approach, yielding significantly relaxed slow roll conditions within the context of noncanonical warm inflation with nonminimal derivative coupling. Subsequently, the density fluctuations in this new framework were analyzed, leading to approximately analytic results for the power spectrum, spectral index, and related quantities. Both the energy scale at horizon crossing and the tensor-to-scalar ratio decreased considerably because of the effects of thermal damping and nonminimal derivative coupling. The upper bound for field excursion remained safely sub-Planckian in this inflationary scenario. Thus we reached a successful and meaningful model to broad the scope of warm inflation.

gr-qc↗