Title: Screening fifth forces in k-essence and DBI models Show Chinese title

Title: 筛选k-本质和DBI模型中的第五力

Abstract: New fifth forces have not yet been detected in the laboratory or in the solar system, hence it is typically difficult to introduce new light scalar fields that would mediate such forces. In recent years it has been shown that a number of non-linear scalar field theories allow for a dynamical mechanism, such as the Vainshtein and chameleon ones, that suppresses the strength of the scalar fifth force in experimental environments. This is known as screening, however it is unclear how common screening is within non-linear scalar field theories. k-essence models are commonly studied examples of non-linear models, with DBI as the best motivated example, and so we ask whether these non-linearities are able to screen a scalar fifth force. We find that a Vainshtein-like screening mechanism exists for such models although with limited applicability. For instance, we cannot find a screening mechanism for DBI models. On the other hand, we construct a large class of k-essence models which lead to the acceleration of the Universe in the recent past for which the fifth force mediated by the scalar can be screened. Show Chinese abstract

Abstract: 新的第五种力尚未在实验室或太阳系中被检测到，因此通常很难引入新的轻标量场来介导这种力。 近年来，已经证明许多非线性标量场理论允许存在一种动态机制，例如Vainshtein机制和变色龙机制，这些机制在实验环境中抑制了标量第五种力的强度。 这被称为屏蔽，然而目前尚不清楚非线性标量场理论中屏蔽现象有多普遍。 k-essence模型是非线性模型的常见研究例子，其中DBI模型是最有动机的例子，所以我们问这些非线性是否能够屏蔽标量第五种力。 我们发现对于这类模型存在一个类似于Vainshtein的屏蔽机制，尽管其适用范围有限。 例如，我们无法找到DBI模型中的屏蔽机制。 另一方面，我们构造了一大类k-essence模型，这些模型导致宇宙在过去不久加速膨胀，并且由该标量介导的第五种力可以被屏蔽。