On causality and its violation in f (R, Lm, T) gravity

In this paper, f (R, Lm, T) gravity is considered. It is a generalization of the theories f (R, T) and f (R, Lm). This modified theory of gravity exhibits strong geometry-matter coupling. The problem of causality and its violation is verified in this model. Such analysis is carried out using G & ouml;deltype solutions considering different types of matter. It is shown that this model allows both causal and non-causal solutions. These solutions depend directly on the content of matter present in the universe. For the non-causal solution, a critical radius is calculated, beyond which causality is violated. Taking different matter contents, an infinite critical radius emerges that leads to a causal solution. To obtain a causal solution, a natural relationship arises between the parameters of the theory.