Generalized Perturbations in Modified Gravity and Dark Energy

The book delves into the discrepancies between Einstein's General Relativity and cosmic observations, highlighting the need for dark matter and dark energy to reconcile these differences. It explores alternative theories of gravity, suggesting that modifications may be necessary on cosmological scales. The author presents a unifying framework to analyze the observational effects of various dark sector theories, focusing on formulating equations of state for dark sector perturbations. This theoretical approach aims to deepen the understanding of the universe's enigmatic components.