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Title: Perturbations in higher derivative gravity beyond maximally symmetric spacetimes

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Abstract:

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Higher derivative gravity is typically plagued by ghost-like states which spoil unitarity. In this talk, I will discuss a specific class of higher derivative gravity called Infinite Derivative Gravity (IDG), which is quadratic in curvature and characterized by form factors of infinite series of covariant derivatives. I will study (covariant) scalar-vector-tensor (SVT) perturbations at the quadratic level of its action, around conformally-flat non-maximally symmetric backgrounds. I will show how, generally, the SVT modes are coupled to each other at the level of the action and decouple in the known dS/AdS limits. Through simple examples of the full action, we will see how the form factors may be chosen to avoid the presence of any extra/ghost-like states in the spectrum.