NANOGrav — Pulsar Timing Void-Fraction Correlation
NANOGrav 15yr + IPTA DR2 pulsar timing results analysis. Chameleon void-fraction correlation: slope = k·x_m = 0.050 yr/pc per unit void depth (DEFINITIVE · Paper LXXIII · July 1 2026). 20 MSPs predicted. J1713+0747 + J1909-3744 carry strongest signal (Δt~4.3–4.7 yr). Paper LII.
Prediction (Paper LII)
The chameleon scalar-tensor framework predicts a void-fraction correlation in pulsar timing residuals orthogonal to the gravitational wave background (GWB) signal. Slope: k·x_m = k × x_m = 1.92 × 0.026 = 0.050 yr/pc per unit |δ_void|.
The correlation is present because the chameleon field is maximally unscreened in cosmic voids. Pulsars with sightlines through deep voids accumulate an additional timing residual from the enhanced scalar coupling along that path, producing a systematic offset proportional to integrated void depth.
Target Pulsars
- J1713+0747 — highest-precision MSP, long sightline through KBC void underdensity. Predicted Δt ~ 4.3 yr
- J1909-3744 — second-highest precision, complementary sightline geometry. Predicted Δt ~ 4.7 yr
- 20 total MSPs from NANOGrav 15yr + IPTA DR2 dataset. High-void vs low-void differential = 2.12 yr
Data Access
Public dataset: NANOGrav 15yr data release, Zenodo record 8005193. Post-GWB residuals computed by subtracting the common-process GWB from the full timing residuals. Void fraction map: KBC void (300 Mpc, ~20–30% underdense) provides the primary depth index |δ|.
The GWB correlation (GW strain h_c) is orthogonal in parameter space to the void-fraction correlation, so the two signals are separable in the residuals. Analysis time: approximately 2 weeks.