Extended mimetic gravity: Hamiltonian analysis and gradient instabilities
Extended mimetic gravity: Hamiltonian analysis and gradient instabilities
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DOI：
10.1088/1475-7516/2017/11/038
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发表时间：
2017-08
影响因子：
6.4
通讯作者：
Kazufumi Takahashi;Tsutomu Kobayashi
中科院分区：
文献类型：
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作者：
Kazufumi Takahashi;Tsutomu Kobayashi
我们提出了一类新的退化高阶标量张量理论作为模拟重力的扩展。通过对非简并的“种子”标量张量理论进行不可逆的共形变换，我们可以生成最多三个物理自由度的一大类理论。我们确定了一个通用的种子理论，这是可能的。本文还研究了这些扩展模拟理论中的宇宙学摄动。结果表明，张量摄动或标量摄动都存在梯度不稳定性，除非标量摄动可能是强耦合的，否则会出现鬼影不稳定性。
We propose a novel class of degenerate higher-order scalar-tensor theories as an extension of mimetic gravity. By performing a noninvertible conformal transformation on “seed” scalar-tensor theories which may be nondegenerate, we can generate a large class of theories with at most three physical degrees of freedom. We identify a general seed theory for which this is possible. Cosmological perturbations in these extended mimetic theories are also studied. It is shown that either of tensor or scalar perturbations is plagued with gradient instabilities, except for a special case where the scalar perturbations are presumably strongly coupled, or otherwise there appear ghost instabilities.