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Interpreting Hubble tension with a cascade decaying dark matter sector

Quan Zhou, Zixuan Xu, Sibo Zheng

TL;DR

This work investigates a cascade decaying dark matter (CDDM) sector to address the Hubble tension by combining early-time relativistic DM production with late-time decay to neutrinos within a single $\Lambda$CDM extension. Using a minimal parameter set $\{\tau_M, M, m, \tau_m\}$, the authors derive the background and perturbation evolution, and perform MCMC fits to Planck 2018+BAO+Pantheon data with four model variants. They find that models incorporating both early and late-time effects (II and III) can reduce the tension to about $3.2σ$, with $M/m \approx 1.1\times10^4$, $\tau_M \approx 2.5\times10^3$ s, $\tau_m \approx 150$–$300$ Gyr, and $m \lesssim 5$ MeV, while remaining compatible with BBN, neutrino flux bounds, and matter-power/structure-formation constraints. The viable CDDM scenarios predict $S_8 \approx 0.84$ and $n_s \approx 0.95$, and a modestly enhanced matter power spectrum at intermediate scales, providing concrete observational targets for future tests and model realizations of the late- and early-time effects.

Abstract

Hubble tension can be alleviated by altering either early- or late-time $Λ$CDM. So far, extensive studies have shown that only early dark energy or ad hoc combinations of those two-fold effects can reduce the tension to $3σ$ level or lower. In this work, we improve the latter solution by considering a cascade decaying dark matter sector, where a parent particle produces relativistic dark matter in the early Universe and the dark matter subsequently decays to neutrinos in the late-time Universe. We parametrize this model with four model parameters, carry out a Markov Chain Monte Carlo fit to Planck 2018+BAO+Pantheon data sets, and compare it to Big Bang Nucleosynthesis limits, neutrino flux bounds, Planck data about matter power spectrum, and structure formation constraint. Within parameter regions reducing the Hubble tension to $3.2σ$ and compatible with the existing constraints, the main phenomenological features include a larger $S_{8}\sim 0.84$, smaller $n_{s}\sim 0.95$ and larger matter power spectrum relative to the $Λ$CDM, which are left for future tests.

Interpreting Hubble tension with a cascade decaying dark matter sector

TL;DR

This work investigates a cascade decaying dark matter (CDDM) sector to address the Hubble tension by combining early-time relativistic DM production with late-time decay to neutrinos within a single CDM extension. Using a minimal parameter set , the authors derive the background and perturbation evolution, and perform MCMC fits to Planck 2018+BAO+Pantheon data with four model variants. They find that models incorporating both early and late-time effects (II and III) can reduce the tension to about , with , s, – Gyr, and MeV, while remaining compatible with BBN, neutrino flux bounds, and matter-power/structure-formation constraints. The viable CDDM scenarios predict and , and a modestly enhanced matter power spectrum at intermediate scales, providing concrete observational targets for future tests and model realizations of the late- and early-time effects.

Abstract

Hubble tension can be alleviated by altering either early- or late-time CDM. So far, extensive studies have shown that only early dark energy or ad hoc combinations of those two-fold effects can reduce the tension to level or lower. In this work, we improve the latter solution by considering a cascade decaying dark matter sector, where a parent particle produces relativistic dark matter in the early Universe and the dark matter subsequently decays to neutrinos in the late-time Universe. We parametrize this model with four model parameters, carry out a Markov Chain Monte Carlo fit to Planck 2018+BAO+Pantheon data sets, and compare it to Big Bang Nucleosynthesis limits, neutrino flux bounds, Planck data about matter power spectrum, and structure formation constraint. Within parameter regions reducing the Hubble tension to and compatible with the existing constraints, the main phenomenological features include a larger , smaller and larger matter power spectrum relative to the CDM, which are left for future tests.

Paper Structure

This paper contains 13 sections, 21 equations, 5 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Cascade decaying dark matter sector: parametrization
  3. Production
  4. Decay
  5. MCMC analysis
  6. Data sets
  7. Numerical results
  8. Complementary tests
  9. BBN
  10. Neutrino flux
  11. Matter power spectrum
  12. Structure formation constraint
  13. Conclusion

Figures (5)

  • Figure 1: A short chain of MCMC fit of the CDDM models $I$-$IV$ in Table.\ref{['models']} to the Planck 2018+BAO+Pantheon data sets, as compared to the $\Lambda$CDM (in gray), where $H_0$ is in units of km s$^{-1}$Mpc$^{-1}$.
  • Figure 2: Same as in fig.\ref{['mcmc1']} but with the complete chain of the MCMC fit.
  • Figure 3: The parameter regions of CDDM models $I$-$IV$ compared to the BBN constraints Cyburt:2002uv and the relativistic criterion $M/m\geq 10$ adopted. Here, the contours of $\Delta N_{\rm{eff}}(t_{\rm{eq}})=\{0.05,0.1, 0.15\}$ at the time of radiation-matter equality are shown in dotted.
  • Figure 4: Neutrino flux constraints Arguelles:2022nbl on the CDDM models $I$-$IV$ in the mass range of $m\leq 1$ GeV including Borexino Borexino:2019wln, KamLAND KamLAND:2021gvi, and SK-$\bar{\nu}_{e}$W. Linyan, SK-Olivares Olivares-DelCampo:2017feq and SK atm Super-Kamiokande:2015qek.
  • Figure 5: Top: Data points Chabanier:2019eai collected from Planck 2018 CMB data and SDSS DR7 LRG, compared to the power spectrum $P_{m}(k)$ of best-fit Planck 2018 $\Lambda$CDM model (in solid black line) and of CDDM models $I$-$IV$ in Table.\ref{['models']}. Bottom: deviations of the CDDM models from the $\Lambda$CDM compared to the data.