Spectral Signatures of Active Fluctuations in Semiflexible Polymers

TL;DR

This paper investigates how active forces from an active bath influence the fluctuation spectrum of semiflexible polymers, revealing mode-specific reorganization and limitations of size-based measures.

Contribution

It introduces an effective noise model derived from active particle statistics, explaining spectral reorganization and comparing explicit and implicit bath models.

Findings

Active forces enhance low modes in the spectrum.

Persistence shifts spectral weight to longer wavelengths.

The theory explains mode reorganization but underestimates global size measures.

Abstract

We study how an active bath is transduced into the internal fluctuation spectrum of a semiflexible polymer. Starting from the statistics of active forces exerted by an explicit bath of active Brownian particles, we derive an effective description in terms of temporally persistent and spatially correlated noise, and test it against simulations of both explicit-bath and implicit-noise models. We find that activity reorganizes polymer fluctuations spectrally rather than uniformly: increasing the active force predominantly enhances the lowest modes, while increasing persistence shifts the spectral weight toward progressively longer wavelengths. The theory captures this mode-level reorganization well and explains the strong qualitative correspondence between explicit and implicit active baths over a broad parameter range. In contrast, global size measures such as the radius of gyration are systematically underestimated, which we trace to activity-induced bond stretching and contour-length renormalization absent from the present fixed-contour theory. Our results show that a semiflexible polymer acts as a multiscale probe of active matter, resolving the temporal and spatial structure of nonequilibrium forcing through its mode spectrum.