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  • Current cosmological constraints mostly rely on information extracted from the background, which is degenerate with the neutrino mass�
  • Contrary to common belief, we found that neutrino mass information is primarily extracted from their wiggle suppression rather than from broadband suppression.

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  • This approach enables neutrino mass constraints based solely on the relative suppression of BAO wiggles—offering potentially weaker but more robust results against changes in background expansion.

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Hernan E. Noriega, Alejandro Aviles

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MOTIVATION

PROJECTION EFFECTS ON FULL SHAPE ANALYSIS

TAKEAWAY

Are current neutrino mass constraints reliable? insights from full shape

(Phys.Rev.D 111 (2025) 6, L061307)

Contact: henoriega@icf.unam.mx

BROADBAND vs WIGGLES: LOCALIZATION OF THE NEUTRINO SIGNAL

MODEL AND CODE

Redshift space power spectrum,

Beyond ΛCDM kernels: Massive neutrinos and certain MG models.

One of main PT codes of DESI

Includes: 1-loop terms, biasing, EFT counterterms, stochastic terms and IR-resummations

Decompose the two linear power spectra into broadband + wiggles and mix the pieces to obtain four models.

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BB00W00 and BB05W05 are control samples, while the rest are Frankensteins

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BB00W00: Broadband Mν=0.0 eV; Wiggles Mν=0.0 eV

BB00W05: Broadband Mν=0.0 eV; Wiggles Mν=0.5 eV

BB05W00: Broadband Mν=0.5 eV; Wiggles Mν=0.0 eV

BB05W05: Broadband Mν=0.5 eV; Wiggles Mν=0.5 eV

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Most of the neutrino information comes from the relative amplitude of the wiggles rather than the broadband suppression, contrary to what has been believed for decades!

Then, we evolve them non linearly and generate four synthetic data (window function, covariance x25 larger than eBOSS):

Cosmological findings from the combination of DESI and Planck data — and more recently, ACT and SPT — have placed very tight constraints on the total neutrino mass within the ΛCDM model, leading to tension with particle physics experiments.

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(97.9% deviation from NH limit)

Neutrino have two main effects

  1. They affect the background cosmology (geometry)
  2. They suppress structures on small scales

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The reason for the strong constraining power on neutrino mass is point 1), not point 2)

This behavior may indicate that we are observing projection effects that drive the estimated neutrino mass toward negative values.

The distributions do not recover the expected values.

Bayesian MCMC vs frequentist profile likelihood on noiseless synthetic eBOSS data

PL and MCMC give similar results when keeping other cosmological parameters to their true values, with small differences due to nuisance parameters

Degeneracy between cosmological parameters worsens the constraints on Mν (peaking at 0).

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Instituto de Ciencias Fisicas, UNAM, Mexico

Full-Shape captures the information from both background effects and the suppression of structure growth.

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