Title: Reviving Quintessence with an Exponential Potential Show Chinese title

Title: 具有指数势的 quintessence 的重生

Abstract: We examine a quintessence model with a modified exponential potential given by $V(\phi) = V_0(1+e^{-\lambda \phi})$. Unlike quintessence with a standard exponential potential, our model can yield an acceptable accelerated expansion at late times, while producing a distinct "early dark energy" signature at high redshift. We determine the evolution of the equation of state parameter, $w_\phi$, and the density parameter, $\Omega_\phi$, as a function of the scale factor. The strongest constraints on the model come from cosmic microwave background observations rather than supernova data. The former give the limit $\lambda > 13$. This model predicts a value of the effective neutrino number during Big Bang nucleosynthesis larger than the standard model value. It also provides a partial solution to the coincidence problem, in that the ratio of the quintessence energy density is always within a few orders of magnitude of the background radiation or matter density from the early universe up to the present, but it does not explain why the accelerated expansion is beginning near the present day, suggesting that these two different ways of characterizing the coincidence problem are not entirely equivalent. Show Chinese abstract

Abstract: 我们研究了一种具有修正指数势的五重态模型，该势由$V(\phi) = V_0(1+e^{-\lambda \phi})$给出。 与具有标准指数势的五重态不同，我们的模型可以在晚期产生可接受的加速膨胀，同时在高红移处产生一种独特的“早期暗能量”特征。 我们确定了状态方程参数$w_\phi$和密度参数$\Omega_\phi$随尺度因子的变化规律。 对该模型最强有力的限制来自宇宙微波背景观测，而不是超新星数据。 前者给出了限制$\lambda > 13$。 该模型预测了大爆炸核合成期间有效中微子数大于标准模型值。 它还部分解决了巧合问题，因为从早期宇宙到现在的背景辐射或物质密度范围内，五重态能量密度的比例始终在几个数量级内，但它并没有解释为什么加速膨胀开始于接近现在的时间点，这表明这两种描述巧合问题的方式并不完全等价。