Constraints with CMB lensing on dark matter decays to massive decay products
Abstract
Motivated by the recent measurements by the Dark Energy Spectroscopic Instrument (DESI) which suggest a late-time matter density approximately 5\% lower than that inferred from Planck we investigate models in which dark matter decays to two less massive, and thus warm, states. The decaying dark matter (DDM) models are parameterized by the fraction f of dark matter that decays, the decay rate Γ, and the fraction ε of the mass retained by the decay products. To efficiently explore the warm decay product regime, we employ \texttt{CLASSIER-DDM}, a modified version of the public Boltzmann solver \texttt{CLASS} that solves the perturbation equations with DDM via an integral-equation method. We consider DESI DR2 baryon acoustic oscillations and Planck 2018 CMB data including lensing, and find that DDM models are not favored over the ΛCDM model. This result arises because CMB lensing tightly constrains the velocity kicks imparted to decay products. For example, for f≃0.5, we find 1σ constraints to the decay-product kick velocities an order of 10−2 to 10−3 times the speed of light for decay redshifts from shortly after recombination until today. Nonetheless, the allowed parameter space includes models with sufficient power suppression at small-scales to potentially address dwarf galaxy anomalies. Our results also suggest that explanations for DESI that involve dark-matter decays to one massive and one massless particle will be constrained by CMB lensing.
Versions
Related
- Stacked strong and weak lensing united: Improved measurement of the stellar and dark matter distributions in massive early-type galaxies at z∼ 0.5
- Strong-lensing perturber signatures in self-interacting dark matter simulations
- Dark Energy Survey year 6 results: Cosmological constraints from galaxy clustering and weak lensing
- Sound-Horizon-Agnostic Forecast for Constraints on H0 and Σmν from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing
- Probing massive star formation with intrinsic multiplicity constraints from TESS eclipsing binaries
BibTeX
@misc{bencke2026constraints,
title = {{Constraints with CMB lensing on dark matter decays to massive decay products}},
author = {Anna Bencke and Nanoom Lee and Marc Kamionkowski},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.14849},
eprint = {2606.14849},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.14849},
}
RIS
TY - UNPB
TI - Constraints with CMB lensing on dark matter decays to massive decay products
AU - Anna Bencke
AU - Nanoom Lee
AU - Marc Kamionkowski
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2606.14849
UR - https://arxiv.org/abs/2606.14849
AB - Motivated by the recent measurements by the Dark Energy Spectroscopic Instrument (DESI) which suggest a late-time matter density approximately 5\% lower than that inferred from Planck we investigate models in which dark matter decays to two less massive, and thus warm, states. The decaying dark matter (DDM) models are parameterized by the fraction f of dark matter that decays, the decay rate Γ, and the fraction ε of the mass retained by the decay products. To efficiently explore the warm decay product regime, we employ \texttt{CLASSIER-DDM}, a modified version of the public Boltzmann solver \texttt{CLASS} that solves the perturbation equations with DDM via an integral-equation method. We consider DESI DR2 baryon acoustic oscillations and Planck 2018 CMB data including lensing, and find that DDM models are not favored over the ΛCDM model. This result arises because CMB lensing tightly constrains the velocity kicks imparted to decay products. For example, for f≃0.5, we find 1σ constraints to the decay-product kick velocities an order of 10^−2 to 10^−3 times the speed of light for decay redshifts from shortly after recombination until today. Nonetheless, the allowed parameter space includes models with sufficient power suppression at small-scales to potentially address dwarf galaxy anomalies. Our results also suggest that explanations for DESI that involve dark-matter decays to one massive and one massless particle will be constrained by CMB lensing.
ER -