DOI: 10.1103/PhysRevD.105.063525
Abstract:

Recent weak lensing surveys have revealed that the direct measurement of the parameter combination S8≡σ8(Ωm/0.3)0.5S8​≡σ8​(Ωm​/0.3)0.5-- where σ8σ8​ is a measure of the amplitude of matter fluctuations on 8 h−1h−1Mpc scales -- is ∼3σ∼3σ discrepant with the value reconstructed from cosmic microwave background (CMB) data assuming the ΛΛCDM model. In this article, we show that it is possible to resolve the tension if dark matter (DM) decays with a lifetime of Γ−1≃55 GyrsΓ−1≃55 Gyrs into one massless and one massive product, and transfers a fraction ε≃0.7 %ε≃0.7 % of its rest mass energy to the massless component. The velocity-kick received by the massive daughter leads to a suppression of gravitational clustering below its free-streaming length, thereby reducing the σ8σ8​ value as compared to that inferred from the standard ΛΛCDM model, in a similar fashion to massive neutrino and standard warm DM. Contrarily to the latter scenarios, the time-dependence of the power suppression and the free-streaming scale allows the 2-body decaying DM scenario to accommodate CMB, baryon acoustic oscillation, growth factor and un-calibrated supernova Ia data. We briefly discuss implications for DM model building, galactic small-scale structure problems and the recent Xenon-1T excess. Future experiments measuring the growth factor to high accuracy at 0≲z≲10≲z≲1 can further test this scenario.

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DOI: 10.1103/PhysRevD.106.023516
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Ref Arxiv: 2208.12992
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Abstract:

The Hubble tension can be addressed by modifying the sound horizon ($r_s$) before recombination, triggering interest in $r_s$-free early-universe estimates of the Hubble constant, $H_0$. Constraints on $H_0$ from an $r_s$-free analysis of the full shape BOSS galaxy power spectra within LCDM were recently reported and used to comment on the viability of physics beyond LCDM. Here we demonstrate that $r_s$-free analyses with current data depend on the model and the priors placed on the cosmological parameters, such that LCDM analyses cannot be used as evidence for or against new physics. We find that beyond-LCDM models which introduce additional energy density with significant pressure support, such as early dark energy (EDE) or additional neutrino energy density ($\Delta N_{\rm eff}$), lead to larger values of $H_0$. On the other hand, models which only affect the time of recombination, such as a varying electron mass ($\Delta m_e$), produce $H_0$ constraints similar to LCDM. Using BOSS data, constraints from light element abundances, cosmic microwave background (CMB) lensing, a CMB-based prior on the scalar amplitude ($A_s$), spectral index ($n_s$), and $\Omega_m$ from the Pantheon+ supernovae data set, we find that in LCDM, $H_0=64.9\pm 2.2$ km/s/Mpc; EDE, $H_0=68.7^{+3}_{-3.9}$; $\Delta N_{\rm eff}$, $H_0=68.1^{+2.7}_{-3.8}$; $\Delta m_e$, $H_0=64.7^{+1.9}_{-2.3}$. Using a prior on $\Omega_m$ from uncalibrated BAO and CMB measurements of the projected sound horizon, these values become in LCDM, $H_0=68.8^{+1.8}_{-2.1}$; EDE, $H_0=73.7^{+3.2}_{-3.9}$; $\Delta N_{\rm eff}$, $H_0=72.6^{+2.8}_{-3.7}$; $\Delta m_e$, $H_0=68.8\pm 1.9$. With current data, none of the models are in significant tension with SH0ES, and consistency tests based on comparing $H_0$ posteriors with and without $r_s$ marginalization are inconclusive with respect to the viability of beyond LCDM models.

Comments: 18 pages, 15 figures, comments welcome

Abstract:

We investigate constraints on early dark energy (EDE) using ACT, SPT-3G 2018, {\it Planck} polarization, and restricted {\it Planck} temperature data (at $\ell<650$), finding a $3.3\sigma$ preference ($\Delta\chi^2=-16.2$ for three additional degrees of freedom) for EDE over $\Lambda$CDM. The EDE contributes a maximum fractional energy density of $f_{\rm EDE}(z_c) = 0.163^{+0.047}_{-0.04}$ at a redshift $z_c = 3357\pm 200$ and leads to a CMB inferred value of the Hubble constant $H_0 = 74.2^{+1.9}_{-2.1}$ km/s/Mpc. We find that {\it Planck} and ACT data provide the majority of the improvement in $\chi^2$, and that the inclusion of SPT-3G pulls the posterior of $f_{\rm EDE}(z_c)$ away from $\Lambda$CDM. This is the first time that a moderate preference for EDE has been reported for these three combined CMB data sets. We find that including measurements of supernovae luminosity distances and the baryon acoustic oscillation standard ruler only minimally affects the preference ($3.0\sigma$), while measurements that probe the clustering of matter at late times -- the lensing potential power spectrum from {\it Planck} and $f \sigma_8$ from BOSS -- decrease the significance of the preference to 2.6$\sigma$. Conversely, adding a prior on the $H_0$ value as reported by the \SHOES{} collaboration increases the preference to the $4-5\sigma$ level. In the absence of this prior, the inclusion of \textit{Planck} TT data at $\ell>1300$ reduces the preference from $3.0\sigma$ to $2.3\sigma$ and the constraint on $f_{\rm EDE}(z_c)$ becomes compatible with \LCDM{} at $1\sigma$. We explore whether systematic errors in the \textit{Planck} polarization data may affect our conclusions and find that changing the TE polarization efficiencies significantly reduces the \textit{Planck} preference for EDE. More work will be necessary to establish whether these hints for EDE within CMB data alone are the sole results of systematic errors or an opening to new physics.