Violation of causality in f(R) gravity

Causality Constraints on Massive Gravity

The de Rham-Gabadadze-Tolley massive gravity admits pp-wave backgrounds on which linear fluctuations are shown to undergo time advances for all values of the parameters. The perturbations may propagate in closed time-like curves unless the parameter space is constrained to a line. These classical phenomena take place well within the theory's validity regime.

Violation of causality in $f(T)$ gravity

[Abridged] In its standard formulation, the $f(T)$ field equations are not invariant under local Lorentz transformations, and thus the theory does not inherit the causal structure of special relativity. A locally Lorentz covariant $f(T)$ gravity theory has been devised recently, and this local causality problem has been overcome. The nonlocal question, however, is left open. If gravitation is to be described by this covariant $f(T)$ gravity theory there are a number of issues that ought to be examined in its context, including the question as to whether its field equations allow homogeneous Gö…

标量-高斯-博内（Scalar-Gauss-Bonnet）引力：红外因果性与引力波观测的可探测性

Scalar-Gauss-Bonnet gravity: Infrared causality and detectability of GW observations

该研究分析标量-高斯-博内引力中黑洞背景下波散射的时间延迟，通过红外因果性约束理论截断尺度下限，探讨其在双黑洞并合引力波中的可探测性，发现新增标量自由度可为规划观测提供可探测窗口。

弱引力、破坏因果性的论证能否约束修正引力？

Can weak-gravity, causality-violation arguments constrain modified gravity?

本文研究了平坦时空振幅因果性论证在约束修正引力中的局限性，发现此类约束仅在弱引力区域有效且远不如天体物理观测严格，基于振幅的因果性约束通常不如其他实验界限严苛。

从动力学三角剖分到描述我们宇宙的量子引力的因果之路

The causality road from dynamical triangulations to quantum gravity that describes our Universe

本文在因果性引导下，从动力学三角剖分出发，提出基于W-和Jordan代数的量子引力理论，解释宇宙起源、暴胀、拓扑几何形成及大爆炸能量，并导出修正弗里德曼方程以解释加速膨胀，无需宇宙学常数。

Gödel-type universes in f(R) gravity

The $f(R)$ gravity theories provide an alternative way to explain the current cosmic acceleration without a dark energy matter component. If gravity is governed by a $f(R)$ theory a number of issues should be reexamined in this framework, including the violation of causality problem on nonlocal scale. We examine the question as to whether the $f(R)$ gravity theories permit space-times in which the causality is violated. We show that the field equations of these $f(R)$ gravity theories do not exclude solutions with breakdown of causality for a physically well-motivated perfect-fluid matter cont…