A Prediction for DESI Full-Shape: Increasing Tomographic Ωm(z) Trend
Abstract
To confirm ΛCDM deviations are due to missing physics (not systematics), one should demonstrate that the model fitting parameters exhibit qualitatively similar redshift drift across independent observables. This is the only way one guarantees new physics. Here, we show that a recent Dark Energy Spectroscopic Instrument (DESI) DR2 Full-Shape (FS) modelling Lyman-α constraint at zeff = 2.33 combined with earlier DR1 FS modelling constraints with 0.295 ≤ zeff ≤ 1.491 leads to a straight line Ωm(z) = m z + c with slope m = 0.022 ± 0.012, $1.8 σ$ removed from constant Ωm. Akaike Information Criterion and Bayesian evidence confirm that constant Ωm and increasing Ωm(z) are statistically indistinguishable. Through the Om(z) diagnostic, we review how increasing and decreasing Ωm(z) trends map to phantom and quintessence dark energy (DE) regimes, respectively. While FS modelling constraints map to phantom DE, the decreasing and increasing Ωm(z) trends in DESI BAO and DESI with external data make a phantom crossing inevitable. Since dynamical DE is but one interpretation for Ωm(z) trends, it is imperative that different datasets converge on their Ωm(z) trends before one jumps to physical conclusions. We forecast how DESI FS modelling Ωm constraints will improve up to the final data release and explore the implications for model selection.
Related
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- The DESI Y1 RR Lyrae Catalog. II. The Metallicity Dependency of Pulsational Properties, the Shape of the RR Lyrae Instability Strip, and Metal Rich RR Lyrae
BibTeX
@misc{colgain2026prediction,
title = {{A Prediction for DESI Full-Shape: Increasing Tomographic $Ω_m(z)$ Trend}},
author = {Eoin Ó Colgáin and M. M. Sheikh-Jabbari},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.19883},
eprint = {2608.19883},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.19883},
}
RIS
TY - UNPB
TI - A Prediction for DESI Full-Shape: Increasing Tomographic Ω_m(z) Trend
AU - Eoin Ó Colgáin
AU - M. M. Sheikh-Jabbari
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2608.19883
UR - https://arxiv.org/abs/2608.19883
AB - To confirm ΛCDM deviations are due to missing physics (not systematics), one should demonstrate that the model fitting parameters exhibit qualitatively similar redshift drift across independent observables. This is the only way one guarantees new physics. Here, we show that a recent Dark Energy Spectroscopic Instrument (DESI) DR2 Full-Shape (FS) modelling Lyman-α constraint at z_eff = 2.33 combined with earlier DR1 FS modelling constraints with 0.295 ≤ z_eff ≤ 1.491 leads to a straight line Ω_m(z) = m z + c with slope m = 0.022 ± 0.012, $1.8 σ$ removed from constant Ω_m. Akaike Information Criterion and Bayesian evidence confirm that constant Ω_m and increasing Ω_m(z) are statistically indistinguishable. Through the Om(z) diagnostic, we review how increasing and decreasing Ω_m(z) trends map to phantom and quintessence dark energy (DE) regimes, respectively. While FS modelling constraints map to phantom DE, the decreasing and increasing Ω_m(z) trends in DESI BAO and DESI with external data make a phantom crossing inevitable. Since dynamical DE is but one interpretation for Ω_m(z) trends, it is imperative that different datasets converge on their Ω_m(z) trends before one jumps to physical conclusions. We forecast how DESI FS modelling Ω_m constraints will improve up to the final data release and explore the implications for model selection.
ER -