English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

A key assumption of the standard cosmological model is that the temperatureof the cosmic microwave background (CMB) radiation scales with cosmologicalredshift $z$ as $T_{\rm CMB}(z) \propto (1+z)$ at all times after recombinationat $z_\star \simeq 1090$. However, this assumption has only been preciselytested at $z \lesssim 3$. Here, we consider cosmological models withpost-recombination reheating (PRR), in which the CMB monopole temperatureabruptly increases due to energy injection after last scattering. Such ascenario can potentially resolve tensions between inferences of the currentcosmic expansion rate (the Hubble constant, $H_0$). We consider an explicitmodel in which a metastable sub-component of dark matter (DM) decays toStandard Model photons, whose spectral energy distribution is assumed to beclose to that of the CMB blackbody. A fit to Planck CMB anisotropy, COBE/FIRASCMB monopole, and SH0ES distance-ladder measurements yields $H_0 = 71.2 \pm1.1$ km/s/Mpc, matter fluctuation amplitude $S_8 = 0.774 \pm 0.018$, and CMBtemperature increase $\delta T_{\rm CMB} = 0.109^{+0.033}_{-0.044}$ K, which issourced by DM decay at $z \gtrsim 10$. However, matter density constraints frombaryon acoustic oscillation and supernovae data highly constrain this scenario,with a joint fit to all datasets yielding $H_0 = 68.69 \pm 0.35$ km/s/Mpc, $S_8= 0.8035 \pm 0.0081$, and $\delta T_{\rm CMB} < 0.0342$ K (95% CL upper limit).These bounds can be weakened if additional dark relativistic species arepresent in the early universe, yielding higher $H_0$. We conclude that currentdata disfavor models with significant PRR solely through its impact onbackground and linear-theory observables, completely independent of CMBspectral distortion constraints. However, a small amount of such energyinjection could play a role in restoring cosmological concordance.

Did the Universe Reheat After Recombination?