LIGO Document P2600217-v10
- We report results from a search for an isotropic stochastic gravitational-wave background using data from the first observing run through April 1, 2025 during the fourth observing run of the LIGO--Virgo--KAGRA Collaboration. New frequency-domain cuts are implemented to address a class of non-stationary spectral noise features that were not effectively identified and mitigated by existing data-quality checks in past analyses. Consequently, previously analyzed data from the fourth observing run are re-processed with the updated cuts. We find no evidence for a stochastic background signal and place upper limits on the gravitational-wave energy density. In particular, for a background following a power law with spectral index 2/3 as predicted by inspiralling compact binaries, we find \( \Omega_\mathrm{GW}(25~\mathrm{Hz}) \leq 2.0 \times 10^{-9} \), and scale invariant backgrounds are constrained to \( \Omega_\mathrm{GW}(25~\mathrm{Hz}) \leq 2.8 \times 10^{-9} \), both at the 95% credible level for a log-uniform prior on \( \Omega_\mathrm{GW} \). Relative to the previous constraints recomputed with the new frequency-domain cuts, these limits improve by a factor of 1.4. We also update bounds on alternative gravity scenarios predicting non-standard polarization modes, and we verify that correlated magnetic noise sources remain below the sensitivity of this search. Combining these observational constraints with population models of compact binary coalescences informed by the latest gravitational-wave transient catalog, GWTC-5.0, we predict the amplitude of the compact binary background to be \( \Omega_\mathrm{CBC}(25~\mathrm{Hz}) = 6.3^{+5.0}_{-2.2} \times 10^{-10} \) at 90% confidence.
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