Superhorizon isocurvature fluctuations relax tensions

Journal Article · 24 November 2024 · Physical Review. D.

DOI: https://doi.org/10.1103/physrevd.110.103545 · OSTI ID:2529407

Fumagalli, Alessandra ^[1]; Piškur, Yodovina ^[2]; Slosar, Anže ^[3]

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1. Univ. of Trieste (Italy); Istituto Nazionale di Astrofisica (INAF) (Italy). Osservatorio Astronomico di Trieste; Institute for Fundamental Physics of the Universe (IFPU) (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Trieste (Italy)
2. SISGA (Italy)
3. Brookhaven National Laboratory (BNL), Upton, NY (United States)

Here, we present a new class of models that have potential to alleviate tensions present in the cosmological data today. We postulate about variation in the sound horizon scale on superhorizon scales, i.e., on scales that are larger than that of the present observable low-redshift Universe (≳ 1Gpc) while at the same time smaller than the largest scales probed by the cosmic microwave background (CMB) (≲ 10Gpc). In this scenario, CMB peaks are naturally smoothed as preferred by the Planck data, while at the same time the low-redshift baryon acoustic oscillation calibration is partially decoupled from the CMB. Taking superhorizon variations in baryon fraction as an example and using approximate modeling, we find improvement in the best fit Planck power spectrum model Δχ² ~ 6 for 1 extra degree of freedom with the relevant extension parameter 10³σ_b = 2.10 ± 0.60, implying about 10% variations in baryon fraction across the Universe. At the same time, S₈ drops by about 1 sigma, easing tension with weak lensing surveys. We find that the combination of Planck 2018 data, eBOSS BAO data, and Riess et al. distance ladder Hubble parameter determination produce a satisfactory fit in our model if we allow for a phantom dark energy equation of state.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: SC0012704
• OSTI ID: 2529407
• Report Number(s): BNL--227647-2025-JAAM
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 10 Vol. 110; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English