Relaxation without ringdown for a compact object in modified gravity

Abstract

Compact objects with black-hole-like exteriors may hide new strong-field physics in their interiors, making their dynamical response a sensitive probe of gravity beyond General Relativity. We present an analytically tractable, gravitationally bound compact object with a genuinely new dynamical signature: under a minimal passive boundary prescription, its exactly controlled odd-parity sector exhibits purely dissipative relaxation poles, rather than the oscillatory modes usually associated with black holes and exotic compact alternatives. The object we study is a regular, vector-supported compact solution of a vector--tensor theory, matched without any surface layer to an exterior Schwarzschild geometry. Owing to its anisotropic stress, it can violate the Buchdahl bound and be continuously connected to the black-hole compactness limit. Its unusual response follows from a hidden chiral symmetry, which turns the perturbation problem into one-way transport rather than ordinary wave propagation. The exterior region alone has no conventional quasinormal-mode spectrum; instead, the regular interior and the matching conditions break the symmetry and quantize the fluctuation spectrum. We analytically compute the retarded Green function and susceptibility, and derive an effective membrane response by integrating out the object's interior. In the black-hole limit, the relaxation times diverge, the poles collapse toward zero frequency, and finite-frequency exterior perturbations decouple from the interior. Black-hole behaviour is therefore approached through the disappearance of relaxation modes, not through the emergence of ringdown.