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arXiv · 2610.08546

Universal Relations Meet Causality: Bounding the Dynamical Love Number of Neutron Stars

Alex Kehagias·Antonio Riotto
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Abstract

The frequency-dependent tidal response of a neutron star is constrained by causality, reality and passivity, which turn a suitably rescaled response into a holomorphic self-map of the upper complex frequency half-plane after some suitable conditions. The Schwarz--Pick theorem then bounds the leading dynamical correction to the tidal deformability from above. In this work we confront this bound with the most recent calculations of the dynamical tidal response in the literature which have also shown that the static tidal deformability and its correction at second order in frequency are tightly correlated. We find that the bound is saturated to within a few per cent, a quantitative confirmation of f-mode dominance in the relativistic regime. The combination of the static deformability with an independent determination of the f-mode frequency thus may provide an equation-of-state-independent upper limit on the dynamical tide.

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Alex Kehagias, Antonio Riotto. 2026-10-06. Universal Relations Meet Causality: Bounding the Dynamical Love Number of Neutron Stars. https://arxiv.org/abs/2610.08546

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