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Contribution from Nonlinear Quasi-normal Modes in GW250114

Yuxin Yang, Changfu Shi, Yi-Ming Hu

Abstract

We report evidence for nonlinear gravitational effects in the ringdown signal of gravitational wave event GW250114. Using Bayesian inference, we find that the inclusion of a nonlinear quasi-normal mode (220Q), a second-order harmonic predicted by general relativity, is statistically favored over the standard linear model (440 mode) when analyzing the post-merger oscillations. Specifically, models incorporating the 220Q mode yield higher Bayes factors than those including only the linear 440 mode, and produce remnant black hole parameters (mass and spin) more consistent with full numerical relativity simulations. This suggests that nonlinear mode coupling contributes significantly to the ringdown phase, opening a new avenue to probe strong-field gravity beyond linear approximations.

Contribution from Nonlinear Quasi-normal Modes in GW250114

Abstract

We report evidence for nonlinear gravitational effects in the ringdown signal of gravitational wave event GW250114. Using Bayesian inference, we find that the inclusion of a nonlinear quasi-normal mode (220Q), a second-order harmonic predicted by general relativity, is statistically favored over the standard linear model (440 mode) when analyzing the post-merger oscillations. Specifically, models incorporating the 220Q mode yield higher Bayes factors than those including only the linear 440 mode, and produce remnant black hole parameters (mass and spin) more consistent with full numerical relativity simulations. This suggests that nonlinear mode coupling contributes significantly to the ringdown phase, opening a new avenue to probe strong-field gravity beyond linear approximations.
Paper Structure (1 section, 2 equations, 3 figures, 1 table)

This paper contains 1 section, 2 equations, 3 figures, 1 table.

Table of Contents

  1. Supplemental material

Figures (3)

  • Figure 1: The upper panel shows the Bayes factors $\log_{10}B$ between the listed models against the $220$-only model, estimated at different start times. The lower panel presents the Bayes factor difference between the $220+221+220Q$ and $220+221+440$ models. $2\sigma$ error bars are given to indicate the estimation uncertainties.
  • Figure 2: $90\%$ credible regions under different models for BH mass and spin, using the data starting from $\Delta t = 4 t_{M_z}$.
  • Figure 3: Bayes factors between the models that include $220Q$ mode/$440$ mode and those without, shown in green/red. Calculation obtained through the Savage-Dickey ratio method, with the error bars indicating $2\sigma$ credible intervals.