Rescuing palindromic universes with improved recombination modeling

Abstract

We explore the linearly quantized primordial power spectra associated with palindromic universes. Extending the results of Lasenby et al. [Phys. Rev. D 105, 083514 (2022)] and Bartlett et al. [Phys. Rev. D 105, 083515 (2022)], we improve the modeling of recombination and include higher orders in the photonic Boltzmann hierarchy. In so doing, we find that the predicted power spectra become largely consistent with observational data. The improved recombination modeling involves developing further techniques for dealing with the future conformal boundary, by integrating the associated perturbation equations both forwards and backwards in conformal time. The resulting wave vector quantization gives a lowest allowed wave number ${k}_{0}=9.93\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ and linear spacing $\mathrm{\ensuremath{\Delta}}k=1.63\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$, providing fits consistent with observational data equivalent in quality to the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model.