Probing Non-Cold Dark Matter with Modified Emergent Dark Energy
Abstract
In the standard ΛCDM cosmology, dark matter is assumed to be a pressureless cold fluid with wdm=0. However, the microscopic nature of dark matter remains unknown, and whether its equation-of-state parameter strictly vanishes deserves observational scrutiny. In this work, we introduce a free dark matter equation-of-state parameter wdm within the Modified Emergent Dark Energy (MEDE) framework, constructing the MEDE+wdm model. We systematically derive its background evolution and linear perturbation equations, and constrain the model parameters using Planck 2018 cosmic microwave background (CMB), DESI DR2 baryon acoustic oscillation (BAO), and three independent Type Ia supernova datasets: Pantheon+, Union3, and DES5YR. Using the CMB + BAO + DES5YR combination, we find a preference for a positive dark matter equation of state, wdm=0.00128±0.00044, together with a 3σ level preference for quintessence-like dark energy evolution, α=−0.66±0.22. When the local H0 prior is included, the constraint on wdm remains essentially unchanged, whereas α shifts toward the ΛCDM limit, yielding α=−0.18±0.18. Bayesian model comparison favors ΛCDM over MEDE+wdm, although the preference is reduced to the weak level after including the local H0 prior. Overall, current observations exhibit a 2.6σ--3σ preference for a nonzero wdm at the parameter-posterior level, but this indication does not yet constitute a robust detection of non-cold dark matter.
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BibTeX
@misc{wang2026probing,
title = {{Probing Non-Cold Dark Matter with Modified Emergent Dark Energy}},
author = {Jun-Chao Wang and Yan-Hong Yao},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.16068},
eprint = {2609.16068},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.16068},
}
RIS
TY - UNPB
TI - Probing Non-Cold Dark Matter with Modified Emergent Dark Energy
AU - Jun-Chao Wang
AU - Yan-Hong Yao
PY - 2026
DA - 2026/09/13
PB - arXiv
DO - 10.48550/arxiv.2609.16068
UR - https://arxiv.org/abs/2609.16068
AB - In the standard ΛCDM cosmology, dark matter is assumed to be a pressureless cold fluid with w_dm=0. However, the microscopic nature of dark matter remains unknown, and whether its equation-of-state parameter strictly vanishes deserves observational scrutiny. In this work, we introduce a free dark matter equation-of-state parameter w_dm within the Modified Emergent Dark Energy (MEDE) framework, constructing the MEDE+w_dm model. We systematically derive its background evolution and linear perturbation equations, and constrain the model parameters using Planck 2018 cosmic microwave background (CMB), DESI DR2 baryon acoustic oscillation (BAO), and three independent Type Ia supernova datasets: Pantheon+, Union3, and DES5YR. Using the CMB + BAO + DES5YR combination, we find a preference for a positive dark matter equation of state, w_dm=0.00128±0.00044, together with a 3σ level preference for quintessence-like dark energy evolution, α=−0.66±0.22. When the local H_0 prior is included, the constraint on w_dm remains essentially unchanged, whereas α shifts toward the ΛCDM limit, yielding α=−0.18±0.18. Bayesian model comparison favors ΛCDM over MEDE+w_dm, although the preference is reduced to the weak level after including the local H_0 prior. Overall, current observations exhibit a 2.6σ--3σ preference for a nonzero w_dm at the parameter-posterior level, but this indication does not yet constitute a robust detection of non-cold dark matter.
ER -