论文标题
重新审视二次dhost理论
Quadratic DHOST theories revisited
论文作者
论文摘要
我们提出了一种新颖且非常简单的公式，该公式的高阶标量（DHOST）理论在某些标量场的第二个衍生物中是二次的，其lagrangian是二次的。使用度量的非正式转换，我们确定了一个特殊的“框架”（或度量），二次dhost理论的Lagrangian将其简化为通常的Einstein-Hilbert术语，以及一些取决于表征统一标量曲面超曲面的简单几何数量的术语。特别是，对于在物理上有趣的IA类中的二次dhost理论，拉格朗日人简单由爱因斯坦 - 希尔伯特（Einstein-Hilbert）术语组成，术语与统一标量场高空图的三维标量曲率成正比。在这种几何重新制定中，所有二次dOhost理论的分类变得特别透明，这也适用于仅在单一量表中退化的标量张量理论。
We present a novel and remarkably simple formulation of degenerate higher-order scalar-tensor (DHOST) theories whose Lagrangian is quadratic in second derivatives of some scalar field. Using disformal transformations of the metric, we identify a special "frame" (or metric) for which the Lagrangian of quadratic DHOST theories reduces to the usual Einstein-Hilbert term plus a few terms that depend on simple geometric quantities characterizing the uniform scalar field hypersurfaces. In particular, for quadratic DHOST theories in the physically interesting class Ia, the Lagrangian simply consists of the Einstein-Hilbert term plus a term proportional to the three-dimensional scalar curvature of the uniform scalar field hypersurfaces. The classification of all quadratic DHOST theories becomes particularly transparent in this geometric reformulation, which also applies to scalar-tensor theories that are degenerate only in the unitary gauge.
