Revisiting observational constraints on coupled exponential quintessence with energy and momentum transfers: degeneracy with massive neutrinos

Abstract

We investigate the impact of massive neutrinos on cosmological models in which dark energy, described by a quintessence scalar field $φ$ with an exponential potential, interacts with dark matter through both energy and momentum transfers. Previous analyses have shown that the inclusion of low-redshift data tends to favour the detection of a pure momentum transfer between the dark sectors, consistent with the fact that such a transfer generically suppresses the growth of cosmic structures. Since massive neutrinos also reduce matter clustering, a potential degeneracy between the interaction parameters and the neutrino mass may arise. After updating the observational constraints on the model parameters obtained in earlier studies, we investigate the effect of allowing the neutrino mass to vary. We find that the detection of momentum transfer degrades once massive neutrinos are included. This occurs because a new degeneracy emerges between the neutrino mass and the parameter governing the energy exchange between dark energy and dark matter. Our findings differ from previous results in the literature, where the detection of momentum transfer was reported to be robust against varying neutrino masses. This suggests that the robustness of such detections depends on the underlying model and should therefore be carefully reassessed for each specific interacting scenario.

Figures (8)

• Figure 1: Effects of coupled quintessence on the CMB angular power spectrum for temperature anisotropies. In the left panel, extreme cases with only momentum transfer ($Q=0$) and only energy transfer ($\beta=0$) are considered for fixed values of $\lambda=0.5$ and $m_\nu=0.06$ eV. In the right panel, we compare the impact of varying the neutrino mass $m_\nu$ in the $\nu$-QuintC ($\beta=1$, $Q=-0.1$, $\lambda=0.5$) and $\nu$-$\Lambda$CDM models. The relative ratios of $\bar{C}^{TT}_\ell$ are defined as $C^{TT}_\ell({\rm QuintC})/{C}^{TT}_\ell(\Lambda{\rm CDM})$ (left), ${C}^{TT}_\ell(\nu\text{-}\Lambda{\rm CDM})/{C}^{TT}_\ell(\Lambda{\rm CDM})$ (right-top), and ${C}^{TT}_\ell(\nu\text{-QuintC})/{C}^{TT}_\ell({\rm QuintC})$ (right-bottom).
• Figure 2: Effects on the matter power spectrum in the coupled quintessence model and in the combined model including massive neutrinos. In the left panel, the extreme cases with only momentum transfer ($Q=0$) and only energy transfer ($\beta=0$) are considered for fixed $\lambda=0.5$ and $m_\nu=0.06\,{\rm eV}$. In the right panel, we compare the impact of varying the neutrino mass $m_\nu$ in the $\nu$-QuintC ($\beta=1$, $Q=-0.1$, $\lambda=0.5$) and $\nu$-$\Lambda$CDM models. In both panels, the relative differences are shown in the lower subpanels, where $\bar{P}(k)\equiv P(k)/P(k)_{\rm fiducial}$.
• Figure 3: Constraints on the QuintC model, together with the $\Lambda$CDM model, derived from the combination of several datasets. In the two-dimensional planes, the inner and outer contours correspond to the $1\sigma$ and $2\sigma$ confidence regions, respectively.
• Figure 4: Constraints on the QuintC model obtained from the combination of several datasets, including BAO measurements from DESI-DR2 Adame_2025 and SNe Ia from DES-Y5 Abbott_2024.
• Figure 5: Constraints on the model parameters $\log_{10}\beta$ and $\lambda$ for the pure momentum-transfer case ($Q=0$), obtained by combining DESI-DR2 BAO measurements with the two SN datasets DES-Y5 and Pantheon+.