Near-Horizon Scrambling Membranes: A Minimal Phenomenological Waveform Model for Dissipative Horizonless Compact Objects

Abstract

We present a four-parameter phenomenological waveform model for compact objects possessing a dissipative near-horizon membrane in place of a classical event horizon. The Near-Horizon Scrambling Membrane (NHSM) model deforms standard binary black hole (BBH) waveform templates through three distinct observational channels: conservative tidal dephasing in the inspiral, dissipative heating through merger, and modified late-time ringdown structure via a weak-cavity transfer function. The model is parameterized by a compactness offset ϵ, a conservative response amplitude Λ⋆ , a membrane absorptivity A, and a scrambling exponent δ, and is designed to occupy the almost-black-hole corner of parameter space where the exterior spacetime remains observationally Kerr-like. We propose three constitutive laws connecting effective membrane parameters to waveform observables, present recommended priors and consistency constraints motivated by ergoregion stability requirements and existing gravitational-wave bounds, and demonstrate the model’s behavior through synthetic injections. In the conservative limit, the primary deviation channel is dissipative heating rather than echoes or tidal deformability, consistent with the current observational landscape; in an illustrative Fisher forecast for GW150914-like systems, the heating channel constrains membrane deviations roughly 70 times more tightly than the conservative tidal channel. The NHSM parameterization provides a compact, testable deformation family for probing the “no entry versus no return” distinction at the horizon scale with current and next-generation gravitational-wave detectors.

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