J-PAS and PFS surveys in the era of dark energy and neutrino mass measurements

Fisher-matrix forecasts are presented for the cosmological surveys of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) and the Subaru Prime Focus Spectrograph (PFS). The wide, low-redshift coverage of J-PAS and the high-density, high-redshift mapping of PFS are strongly complementary: combining the two reduces marginalized uncertainties on all primary parameters compared with either survey individually. Adding the joint J-PAS+PFS data to next-generation CMB measurements from the Simons Observatory (SO) and \textsc{LiteBird} yields an expected precision of $σ(\sum m_ν)=0.017,$eV in the $Λ$CDM$+\sum m_ν+N_{\rm eff}$ framework, sufficient to disfavour the inverted neutrino hierarchy at $2.34,σ$ if the true mass sum equals the normal-ordering minimum. Motivated by recent DESI results, we also forecast within a $w_0w_a$CDM$+\sum m_ν+N_{\rm eff}$ cosmology, adopting the DESI,DR2 best-fit values ($w_0=-0.758$, $w_a=-0.82$) as fiducial. The combination CMB+J-PAS+PFS then delivers $σ(w_0)=0.044$ and $σ(w_a)=0.18$, corresponding to a $5.1,σ$ preference for a time-varying dark-energy equation of state. These findings show that J-PAS and PFS, especially when coupled with Stage-IV CMB observations, will provide competitive tests of neutrino physics and the dynamics of cosmic acceleration.

💡 Research Summary

This paper presents Fisher‑matrix forecasts for the upcoming J‑PAS (Javalambre Physics of the Accelerating Universe Astrophysical Survey) and PFS (Prime Focus Spectrograph) surveys, emphasizing their complementary redshift coverage and the resulting synergy when combined with next‑generation CMB observations from the Simons Observatory (SO) and LiteBIRD. J‑PAS will map ~8,500 deg² at low redshift (z ≲ 1) using 54 narrow‑band filters, achieving photometric redshift precision σ_z≈0.003(1+z) and delivering billions of LRG, ELG, and QSO targets. PFS will obtain high‑resolution spectra for ~4 million emission‑line galaxies over 1,464 deg², reaching σ_z≈0.0007(1+z) and extending the tracer sample to z ≈ 2.4. Because the sky footprints barely overlap, the two surveys can be treated as statistically independent, allowing a straightforward addition of their Fisher matrices.

The authors model massive neutrino effects on the expansion rate and linear growth, using the standard free‑streaming suppression of the cold‑plus‑baryon power spectrum. They adopt a linear bias prescription b(z)=b₀/D_cb(z) with tracer‑specific b₀ values, and restrict the analysis to quasi‑linear scales (k_max≈0.2 h Mpc⁻¹) where non‑linear bias and scale‑dependent effects are negligible. Redshift‑space distortions, Finger‑of‑God damping, and photometric redshift errors are incorporated via Gaussian kernels in the anisotropic galaxy power spectrum P_g(k,μ,z).

CMB priors from SO and LiteBIRD are included, providing tight constraints on τ, A_s, n_s, Ω_b h², Ω_c h², and especially on Σm_ν and N_eff. When the joint J‑PAS+PFS data are combined with these CMB measurements in a ΛCDM + Σm_ν + N_eff framework, the forecasted 1σ uncertainty on the sum of neutrino masses is σ(Σm_ν)=0.017 eV. This precision is sufficient to disfavor the inverted mass hierarchy at 2.34σ if the true sum equals the normal‑ordering minimum (~0.06 eV).

Motivated by recent DESI DR2 results, the authors also explore a w₀wₐCDM + Σm_ν + N_eff model, adopting the DESI best‑fit values w₀=−0.758 and wₐ=−0.82 as the fiducial cosmology. In this extended parameter space, the combined CMB+J‑PAS+PFS data yield σ(w₀)=0.044 and σ(wₐ)=0.18, corresponding to a 5.1σ preference for a time‑varying dark‑energy equation of state over a cosmological constant.

Comparisons with a five‑year DESI forecast show that J‑PAS and PFS together achieve comparable or superior constraints, particularly because the low‑z wide‑area J‑PAS data break degeneracies that affect the high‑z PFS measurements, and vice versa. The multi‑tracer approach further reduces sample variance, enhancing sensitivity to both neutrino mass and dark‑energy dynamics.

The paper concludes that the joint J‑PAS and PFS surveys, when coupled with Stage‑IV CMB experiments, will provide competitive and complementary tests of fundamental physics: they can measure the neutrino mass sum to a few × 10⁻³ eV, potentially resolve the mass hierarchy, and detect deviations from w=−1 at the few‑percent level. The authors note that their forecasts rely on linear theory, simple bias models, and idealized redshift errors; future work will need to address non‑linear modeling, systematic uncertainties in photometric redshifts, and realistic survey systematics to fully realize these prospects.