论文标题
超越霍恩德斯基理论的超浮肿和额外的标量场
Superluminality in beyond Horndeski theory with extra scalar field
论文作者
论文摘要
我们研究了Horndeski理论的超浮肿问题，并具有额外的标量场，该标量磁场与重力耦合，在拉格朗日语中没有第二个衍生物。我们提出了在宇宙学背景，稳定性条件和声速表达式中扰动的二次作用。我们发现，在常规的额外标量的情况下，其扁平空间传播速度是光的，相互作用理论的模式之一必定是当这个标量滚动时，甚至任意缓慢时的模式。该结果符合超越Horndeski类（Lagrangian中有6个任意功能）和任何稳定的滚动背景的任何理论。更一般而言，缺乏超蓝性性的要求对理论的结构施加了非平凡的约束。
We study the superluminality issue in beyond Horndeski theory with additional scalar field, which is minimally coupled to gravity and has no second derivatives in the Lagrangian. We present the quadratic action for perturbations in cosmological backgrounds, stability conditions and expressions for sound speeds. We find that in the case of conventional additional scalar whose flat-space propagation speed is that of light, one of the modes in interacting theory is necessarily superluminal when this scalar rolls, even arbitrarily slowly. This result holds in any theory of the beyond Horndeski class (with 6 arbitrary functions in the Lagrangian) and for any stable rolling background. More generally, the requirement of the absence of superluminality imposes non-trivial constraints on the structure of the theory.
