标题： 弦乐似 Quintessence 模型中慢滚参数的渐近界 显示英文标题

标题： Asymptotic bound on slow-roll parameter in stringy quintessence model

摘要： 我们研究了弦论 quintessence 模型中体积模量和标量场（dilaton）的晚期行为，重点关注它们对哈勃慢滚参数$\epsilon$的贡献，该参数直接衡量时空几何偏离 de Sitter 空间的程度。 当只允许其中一个模量运动时，$\epsilon$在晚期收敛到一个稳定的不动点。 这个不动点值大于$1$，因此慢滚无法实现。 此外，如果 quintessence 势的衰减率大于某个临界值，势的正性要求稳定的不动点值由$3$给出，与模量动力学的细节无关。 否则，不动点值与势的慢滚参数一致。 当体积模量和标量场同时沿势下降时，我们可以找到两个模量对$\epsilon$的贡献在不动点处满足的关系。 在这种情况下，不动点值一般不是单场情况下的固定点值的简单叠加，并且不能超过$3$。 显示英文摘要

摘要： We study the late time behavior of the scalar part of the volume modulus and the dilaton in stringy quintessence model, focusing on their contributions to the Hubble slow-roll parameter $\epsilon$ which directly measures the deviation of the spacetime geometry from de Sitter space. When only one of the moduli is allowed to move, $\epsilon$ converges to the stable fixed point at late time. The fixed point value is larger than $1$, thus the slow-roll cannot be realized. Moreover, if the decay rate of the quintessence potential is larger than some critical value, the positivity of the potential imposes that the stable fixed point value is just given by $3$, independent of the details of the moduli dynamics. Otherwise, the fixed point value coincides with the potential slow-roll parameter. When both the volume modulus and the dilaton roll down the potential simultaneously, we can find the relation between the contributions of two moduli to $\epsilon$ satisfied at the fixed point. In this case, the fixed point value is not in general the simple sum of fixed point values in the single field case and cannot be larger than $3$.