Distinguishing Coupled Dark Matter Dark Energy from Kinematic Phantom Crossing
Abstract
Recent measurements of cosmic expansion have renewed interest in dark-energy scenarios in which the effective equation of state exhibits phantom-like evolution and may cross w=−1. Such behavior, however, does not require a fundamental phantom field: in coupled dark-energy-dark-matter~(CDEDM) models, energy exchange between a canonical scalar field and cold dark matter, happens Lagrangian labels, can reproduce the same effective equation of state evolution as that of phenomenological w0waCDM model. We show that this microscopic interaction leaves distinctive, testable signatures in structure growth by forming a two-fluid system in which only cold dark matter feels the scalar-mediated fifth force (and an associated drag term), while baryons remain uncoupled. When combined with neutrino-free streaming, this setup generates a characteristic coupling, neutrino-mass degeneracy, whose leading scaling ∑ mν∝ fc2 α2 follows analytically from the two-fluid growth equations. Using DESI DR2 BAO, CMB distance information, ACT DR6 lensing, redshift-space distortions, and three supernova compilations, we find that this scaling is recovered for both exponential and inverse-power-law potentials. We further show that the dominant contribution to the growth response arises from the coupling-induced modification of the background evolution, with the fifth force enhancing growth and the drag partially counteracting it. Finally, the interaction induces a running dark-matter mass, changing it at recombination by 4.3%--5.5%, so CMB distance calculations must account for the evolving dark-matter density. These correlated growth and recombination effects provide a route to distinguish interaction-driven phantom crossing from purely kinematic dark-energy parametrizations.
Related
- Beyond w0−wa and Phantom Crossing: Testing Models of Coupled Dark Sector
- Quantifying and testing the evidence for a phantom crossing
- Addressing the DESI DR2 phantom-crossing anomaly and enhanced H 0 tension with reconstructed scalar-tensor gravity
- Viable Phantom Crossing in Softly Broken Shift Symmetric Gravity
- Constraints on Horndeski gravity with phantom crossing
BibTeX
@misc{ganguly2026distinguishing,
title = {{Distinguishing Coupled Dark Matter Dark Energy from Kinematic Phantom Crossing}},
author = {Samit Ganguly and Koushik Dutta and Goutam Manna},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.19602},
eprint = {2609.19602},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.19602},
note = {CC BY-SA 4.0},
}
RIS
TY - UNPB
TI - Distinguishing Coupled Dark Matter Dark Energy from Kinematic Phantom Crossing
AU - Samit Ganguly
AU - Koushik Dutta
AU - Goutam Manna
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.19602
UR - https://arxiv.org/abs/2609.19602
AB - Recent measurements of cosmic expansion have renewed interest in dark-energy scenarios in which the effective equation of state exhibits phantom-like evolution and may cross w=−1. Such behavior, however, does not require a fundamental phantom field: in coupled dark-energy-dark-matter~(CDEDM) models, energy exchange between a canonical scalar field and cold dark matter, happens Lagrangian labels, can reproduce the same effective equation of state evolution as that of phenomenological w_0w_aCDM model. We show that this microscopic interaction leaves distinctive, testable signatures in structure growth by forming a two-fluid system in which only cold dark matter feels the scalar-mediated fifth force (and an associated drag term), while baryons remain uncoupled. When combined with neutrino-free streaming, this setup generates a characteristic coupling, neutrino-mass degeneracy, whose leading scaling ∑ m_ν∝ f_c^2 α^2 follows analytically from the two-fluid growth equations. Using DESI DR2 BAO, CMB distance information, ACT DR6 lensing, redshift-space distortions, and three supernova compilations, we find that this scaling is recovered for both exponential and inverse-power-law potentials. We further show that the dominant contribution to the growth response arises from the coupling-induced modification of the background evolution, with the fifth force enhancing growth and the drag partially counteracting it. Finally, the interaction induces a running dark-matter mass, changing it at recombination by 4.3%--5.5%, so CMB distance calculations must account for the evolving dark-matter density. These correlated growth and recombination effects provide a route to distinguish interaction-driven phantom crossing from purely kinematic dark-energy parametrizations.
ER -