论文标题
标量调整理论中的Ostrogradsky模式，具有高阶导数耦合至关重要
Ostrogradsky mode in scalar-tensor theories with higher-order derivative couplings to matter
论文作者
论文摘要
指标转换是一种工具，可以找到超出一般相对性的重力理论。只要度量转换是常规的且可逆的，重力作用就可以保证不受危险的Ostrogradsky模式。通过标量场及其衍生物的指标转换，已经发现了各种堕落的高阶标量理论（DHOST），没有额外的自由度。在这项工作中，我们研究了物质耦合如何通过标量场的第二个衍生物通过度量转换来改变从Horndeski理论产生的理论的堕落性，从而将最小耦合的自由标量场作为物质场作为物质场。当转换是可逆的时，该理论等同于Horndeski理论，具有高阶导数耦合到物质标量场。在此Horndeski框架和统一仪表中工作，我们发现退化条件是可以解决的，并且物质度量必须具有一定的结构才能删除Ostrogragradsky模式。
A metric transformation is a tool to find a new theory of gravity beyond general relativity. The gravity action is guaranteed to be free from a dangerous Ostrogradsky mode as long as the metric transformation is regular and invertible. Various degenerate higher-order scalar-tensor theories (DHOST) without extra degrees of freedom have been found through the metric transformation with a scalar field and its derivatives. In this work, we examine how a matter coupling changes the degeneracy for a theory generated from the Horndeski theory through the metric transformation with the second derivative of a scalar field, taking a minimally-coupled free scalar field as the matter field. When the transformation is invertible, this theory is equivalent to the Horndeski theory with a higher-order derivative coupling to the matter scalar field. Working in this Horndeski frame and the unitary gauge, we find that the degeneracy conditions are solvable and the matter metric must have a certain structure to remove the Ostrogradsky mode.
