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| Natura: | Preprint |
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2024
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| Accesso online: | https://arxiv.org/abs/2403.03799 |
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| _version_ | 1866912094646960128 |
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| author | Krywonos, Jordan Paradiso, Simone Krolewski, Alex Joudaki, Shahab Percival, Will |
| author_facet | Krywonos, Jordan Paradiso, Simone Krolewski, Alex Joudaki, Shahab Percival, Will |
| contents | When fitting cosmological models to data, a Bayesian framework is commonly used, requiring assumptions on the form of the likelihood and model prior. In light of current tensions between different data, it is interesting to investigate the robustness of cosmological measurements to statistical assumptions about the likelihood distribution from which the data was drawn. We consider the impact of changes to the likelihood caused by uncertainties due to the finite number of mock catalogs used to estimate the covariance matrix, leading to the replacement of the standard Gaussian likelihood with a multivariate $t$-distribution. These changes to the likelihood have a negligible impact on recent cosmic microwave background (CMB) lensing and baryon acoustic oscillation (BAO) measurements. We then extend our analysis to perform a sensitivity test on the Gaussian likelihoods typically adopted, considering how increasing the size of the tails of the likelihood (again using a $t$-distribution) affects cosmological inferences. For an open $Λ$CDM model constrained by BAO alone, we find that increasing the weight in the tails shifts and broadens the resulting posterior on the parameters, with a $\sim$0.2-0.4$σ$ effect on $Ω_Λ$ and $Ω_{\rm k}$. In contrast, the CMB temperature and polarization constraints in $Λ$CDM showed less than 0.03$σ$ changes in the parameters, except for $\{τ$, ln($10^{10}A_{\rm s})$, $σ_8$, $S_8$, $σ_8Ω_{\rm m}^{0.25}$, $z_{\rm re}$, $10^9A_{\rm s}e^{-2τ}\}$ which shifted by around 0.1-0.2$σ$. If we use solely $\ell < 30$ data, the amplitude $A_{\rm s} e^{-2τ}$ varies in the posterior mean by 0.7$σ$ and the error bars increase by 6%. We conclude, at least for current-generation CMB and BAO measurements, that uncertainties in the shape and tails of the likelihood do not contribute to current tensions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2403_03799 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Cosmological measurements from the CMB and BAO are insensitive to the tail probability in the assumed likelihood Krywonos, Jordan Paradiso, Simone Krolewski, Alex Joudaki, Shahab Percival, Will Cosmology and Nongalactic Astrophysics When fitting cosmological models to data, a Bayesian framework is commonly used, requiring assumptions on the form of the likelihood and model prior. In light of current tensions between different data, it is interesting to investigate the robustness of cosmological measurements to statistical assumptions about the likelihood distribution from which the data was drawn. We consider the impact of changes to the likelihood caused by uncertainties due to the finite number of mock catalogs used to estimate the covariance matrix, leading to the replacement of the standard Gaussian likelihood with a multivariate $t$-distribution. These changes to the likelihood have a negligible impact on recent cosmic microwave background (CMB) lensing and baryon acoustic oscillation (BAO) measurements. We then extend our analysis to perform a sensitivity test on the Gaussian likelihoods typically adopted, considering how increasing the size of the tails of the likelihood (again using a $t$-distribution) affects cosmological inferences. For an open $Λ$CDM model constrained by BAO alone, we find that increasing the weight in the tails shifts and broadens the resulting posterior on the parameters, with a $\sim$0.2-0.4$σ$ effect on $Ω_Λ$ and $Ω_{\rm k}$. In contrast, the CMB temperature and polarization constraints in $Λ$CDM showed less than 0.03$σ$ changes in the parameters, except for $\{τ$, ln($10^{10}A_{\rm s})$, $σ_8$, $S_8$, $σ_8Ω_{\rm m}^{0.25}$, $z_{\rm re}$, $10^9A_{\rm s}e^{-2τ}\}$ which shifted by around 0.1-0.2$σ$. If we use solely $\ell < 30$ data, the amplitude $A_{\rm s} e^{-2τ}$ varies in the posterior mean by 0.7$σ$ and the error bars increase by 6%. We conclude, at least for current-generation CMB and BAO measurements, that uncertainties in the shape and tails of the likelihood do not contribute to current tensions. |
| title | Cosmological measurements from the CMB and BAO are insensitive to the tail probability in the assumed likelihood |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2403.03799 |