Cosmology in Extended Parameter Space with DESI Data Release 2 Baryon Acoustic Oscillations: A 2 σ + Detection of Nonzero Neutrino Masses with an Update on Dynamical Dark Energy and Lensing Anomaly

Abstract We obtain constraints in a 12 parameter cosmological model using the recent Dark Energy Spectroscopic Instrument Data Release (DR) 2 Baryon Acoustic Oscillations (BAO) data, combined with cosmic microwave background (CMB) power spectra (Planck Public Release, PR, 4) and lensing (Planck PR4 + Atacama Cosmology Telescope DR 6) data, uncalibrated Type Ia supernovae (SNe) data from Pantheon+ and Dark Energy Survey (DES) Year 5 (DESY5) samples, and Weak Lensing (WL; DES Year 1) data. The cosmological model consists of six Λ cold dark matter parameters and additionally, the dynamical dark energy parameters ( w 0 , w a ), the sum of neutrino masses (∑ m ν ), the effective number of non-photon radiation species ( N eff ), the scaling of the lensing amplitude ( A lens ), and the running of the scalar spectral index ( α s ). Our major findings are the following: (i) With CMB+BAO+DESY5+WL, we obtain the first 2 σ + detection of a non-zero ∑ m ν = 0.1 9 − 0.18 + 0.15 eV (95%). Replacing DESY5 with Pantheon+ still yields a ∼1.9 σ detection. (ii) The cosmological constant lies at the edge of the 95% contour with CMB+BAO+Pantheon+ but is excluded at 2 σ + with DESY5, leaving evidence for dynamical dark energy data-set dependent and inconclusive. (iii) With CMB+BAO+SNe+WL, A lens = 1 is excluded at >2 σ , while it remains consistent with unity without WL data—suggesting that the existence of lensing anomaly with Planck PR4 likelihoods may depend on non-CMB data sets. (iv) The Hubble tension persists at 3.6 σ –4.2 σ with CMB+BAO+SNe; WL data have minimal impact.