Kinetic-theory derivation and Bayesian analysis of the finite-temperature shifted CMB power spectrum
Abstract
Finite-temperature quantum-gravitational corrections to the cosmological constant introduce two additional density parameters, ΩΛ2 and ΩΛ3, the associated terms of which scale as a−4 and a−2, respectively. In previous work (Papers I and II), these parameters were studied using machine-learning methods that identified a best-fit point. Here we complete the picture with two complementary analyses. First, we perform a Bayesian MCMC analysis using a modified version of \textsc{class} against the Planck 2018 likelihoods. This tells us what the data can constrain once all parameter uncertainties have been marginalized over. Both parameters are consistent with zero, with ΩΛ3 constrained only from one side. Second, we build a CMB pipeline from scratch, following Weinberg's kinetic-theory formulation and validating it against \textsc{class}. This allows us to study the underlying physics. The response analysis carried out with it shows that ΩΛ3 is almost entirely absorbed by a shift in h over the well-measured acoustic multipoles. The part of the signal that cannot be absorbed resides at low ℓ, where cosmic variance dominates. Meanwhile, the ΩΛ2 signature is nearly degenerate with the overall amplitude of the spectrum. The effects of both parameters on the CMB power spectrum are small, since they represent higher-order thermal corrections to the cosmological constant. The resulting constraints are correspondingly weak: the induced shifts are largely absorbed by degeneracies with h and with the overall normalization of the spectrum. This is the reason why neither parameter is detected.
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BibTeX
@misc{park2026kinetictheory,
title = {{Kinetic-theory derivation and Bayesian analysis of the finite-temperature shifted CMB power spectrum}},
author = {I. Y. Park},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.05435},
eprint = {2610.05435},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.05435},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Kinetic-theory derivation and Bayesian analysis of the finite-temperature shifted CMB power spectrum
AU - I. Y. Park
PY - 2026
DA - 2026/10/04
PB - arXiv
DO - 10.48550/arxiv.2610.05435
UR - https://arxiv.org/abs/2610.05435
AB - Finite-temperature quantum-gravitational corrections to the cosmological constant introduce two additional density parameters, Ω_Λ_2 and Ω_Λ_3, the associated terms of which scale as a^−4 and a^−2, respectively. In previous work (Papers I and II), these parameters were studied using machine-learning methods that identified a best-fit point. Here we complete the picture with two complementary analyses. First, we perform a Bayesian MCMC analysis using a modified version of \textsc{class} against the Planck 2018 likelihoods. This tells us what the data can constrain once all parameter uncertainties have been marginalized over. Both parameters are consistent with zero, with Ω_Λ_3 constrained only from one side. Second, we build a CMB pipeline from scratch, following Weinberg's kinetic-theory formulation and validating it against \textsc{class}. This allows us to study the underlying physics. The response analysis carried out with it shows that Ω_Λ_3 is almost entirely absorbed by a shift in h over the well-measured acoustic multipoles. The part of the signal that cannot be absorbed resides at low ℓ, where cosmic variance dominates. Meanwhile, the Ω_Λ_2 signature is nearly degenerate with the overall amplitude of the spectrum. The effects of both parameters on the CMB power spectrum are small, since they represent higher-order thermal corrections to the cosmological constant. The resulting constraints are correspondingly weak: the induced shifts are largely absorbed by degeneracies with h and with the overall normalization of the spectrum. This is the reason why neither parameter is detected.
ER -