发表机构
Institute for Theoretical Physics and Cosmology, Zhejiang University of Technology; Department of Physics, Indian Institute of Technology, Kanpur（浙江工业大学理论物理与宇宙学研究所; 坎普尔印度理工学院物理系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
在爱因斯坦-标量-高斯-邦尼引力框架下，通过非最小耦合的标量场实现振荡暗能量，使有效状态方程多次穿越幻影分界线，同时保持稳定性并趋向德西特吸引子。
AI 中文摘要
来自暗能量光谱仪（DESI）的最新重子声学振荡测量，结合超新星观测，显示出对演化暗能量状态方程的轻微偏好，其中暗能量在较高红移时保持幻影（phantom）特性，而在约$z\backsimeq0.5$附近出现向精质（quintessence）区域的转变。除了状态方程的单调演化之外，振荡暗能量情景为动态暗能量提供了一种潜在的替代实现。我们在爱因斯坦-标量-高斯-邦尼引力框架内研究这种振荡情景，其中具有混合指数-二次势的标量场非最小耦合到高斯-邦尼（GB）不变量。我们选择了一个高斯GB耦合函数，其局域在势能最小值附近。在晚期宇宙时期，场因此围绕势能最小值振荡，并最终退出到稳定的德西特吸引子相。在最小耦合极限下，有效状态方程在低红移（$z\backsimeq0$）时在精质区域振荡，而不穿越幻影分界线。非最小耦合放大了振荡，并驱动有效状态方程多次穿越幻影分界线。尽管足够强的耦合可以诱导负的标量和张量声速，导致扰动模式不稳定。我们确定了参数空间中的一个区域，在该区域中模型经历多次幻影穿越，同时保持无鬼影和梯度不稳定性，并在未来接近稳定的德西特吸引子。
英文摘要
Recent baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument (DESI), combined with supernova observations, show a mild preference for an evolving dark-energy equation of state, in which dark energy remains phantom-like at higher redshift while a transition toward the quintessence regime emerges around $z\lesssim0.5$. Beyond the monotonic evolution of the equation of state, an oscillatory dark-energy scenario provides a potential alternative realization of dynamical dark energy. We study such an oscillatory scenario within the Einstein-scalar-Gauss-Bonnet gravity framework, where a scalar field with a hybrid exponential-quadratic potential couples nonminimally to the Gauss-Bonnet (GB) invariant. We choose a Gaussian GB coupling function localized around the minimum of the potential. During the late-time epoch, the field thereby oscillates around the potential minimum and eventually exits toward a stable de Sitter attractor phase. In the minimally coupled limit, the effective equation of state oscillates in the quintessence regime at low redshift, $z\sim0$, without crossing the phantom divide. The nonminimal coupling amplifies the oscillations and drives the effective equation of state across the phantom divide multiple times. Although a sufficiently strong coupling can induce negative scalar and tensor sound speeds, rendering the perturbation modes unstable. We identify a region of parameter space in which the model undergoes multiple phantom crossings while remaining free of ghost and gradient instabilities and approaching a stable de Sitter attractor in the future.
Comments18 pages, 6 figures. All comments and suggestions are welcome
