The BAO-CMB Tension and Implications for Inflation
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arXiv
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| Format: | Preprint |
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2025
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| author | Ferreira, Elisa G. M. McDonough, Evan Balkenhol, Lennart Kallosh, Renata Knox, Lloyd Linde, Andrei |
| author_facet | Ferreira, Elisa G. M. McDonough, Evan Balkenhol, Lennart Kallosh, Renata Knox, Lloyd Linde, Andrei |
| contents | The scalar spectral index $n_s$ is a powerful test of inflationary models. The tightest constraint on $n_s$ to date derives from the combination of cosmic microwave background (CMB) data with baryon acoustic oscillation (BAO) data. The resulting $n_s$ constraint is shifted significantly upward relative to the constraint from CMB alone, with the consequence that previously preferred inflationary models are seemingly disfavored by $\gtrsim 2 σ$. Here we show that this shift in $n_s$ is the combined effect of a degeneracy between $n_s$ and BAO parameters exhibited by CMB data and the tension between CMB datasets and DESI BAO data under the assumption of the standard cosmological model. Given the crucial role of $n_s$ in discriminating between inflationary models, we urge caution in interpreting CMB+BAO constraints on $n_s$ until the BAO-CMB tension is resolved. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_12459 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The BAO-CMB Tension and Implications for Inflation Ferreira, Elisa G. M. McDonough, Evan Balkenhol, Lennart Kallosh, Renata Knox, Lloyd Linde, Andrei Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory The scalar spectral index $n_s$ is a powerful test of inflationary models. The tightest constraint on $n_s$ to date derives from the combination of cosmic microwave background (CMB) data with baryon acoustic oscillation (BAO) data. The resulting $n_s$ constraint is shifted significantly upward relative to the constraint from CMB alone, with the consequence that previously preferred inflationary models are seemingly disfavored by $\gtrsim 2 σ$. Here we show that this shift in $n_s$ is the combined effect of a degeneracy between $n_s$ and BAO parameters exhibited by CMB data and the tension between CMB datasets and DESI BAO data under the assumption of the standard cosmological model. Given the crucial role of $n_s$ in discriminating between inflationary models, we urge caution in interpreting CMB+BAO constraints on $n_s$ until the BAO-CMB tension is resolved. |
| title | The BAO-CMB Tension and Implications for Inflation |
| topic | Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2507.12459 |