arXiv subjects

Wangzheng Zhang

Publications and source records attributed to Wangzheng Zhang.

9 recordsLinked to original sources

arXiv2026

Radial velocity statistics of cosmic voids as a probe of interacting dark energy

Due to their vast sizes and extremely low densities, the dynamics of cosmic voids are largely decoupled from complex, small-scale baryonic physics and are highly sensitive to the background expansion of the Universe. This makes them clean and sensitive probes of dark energy's properties. Using N-body simulations, we show that the void radial velocity and velocity dispersion profiles are sensitive to the Type 3 interacting dark energy model parameters, the momentum coupling $β$ ($<0$) and the scalar field parameter $λ$. Within the $1σ$ range of the best-fit values of $β$ and $λ$ constrained by Planck CMB, DESI BAO, and DES-Y5 supernova data, we find up to $\sim 30\%$ deviations in the void radial-velocity and velocity-dispersion profile spans relative to the uncoupled scenario, which can be well-approximated by a 4-parameter quadratic regression model. This demonstrates that the void radial velocity statistics provide an independent and observationally accessible probe of the dark-sector interaction in the Type 3 model.

astro-ph.CO↗

arXiv2026

Measuring neutrino mass and asymmetry through galaxy pairwise peculiar velocity

Cosmic neutrinos are among the most abundant fermions in the Universe, yet the values of their masses and chemical potentials remain uncertain. In this Letter, we present the first constraints on the total neutrino mass $M_ν$ and the neutrino asymmetry parameter $η^2$ derived from the mean galaxy pairwise peculiar velocity in the quasi-linear and nonlinear regimes. We develop a simulation-based analysis pipeline that connects neutrino properties to predictions of galaxy pairwise velocity, and apply it to galaxy data from the Cosmicflows-4 grouped catalog. Our analysis is performed within two independent cosmological frameworks, based on cosmological parameters derived from Cosmic microwave background (CMB) and local distance ladder measurements, respectively. By performing fits to the galaxy pairwise velocity, we obtain consistent constraints from both frameworks. Quoting posterior means with 68% CL, we find $M_ν= 0.24^{+0.34}_{-0.18}\ \mathrm{eV}$ and $η^2 = 2.14^{+0.30}_{-0.32}$ in the CMB framework, and $M_ν= 0.37^{+0.34}_{-0.26}\ \mathrm{eV}$ and $η^2 = 2.4^{+2.1}_{-1.6}$ in the local framework. In particular, we find a 7$σ$ measurement of a non-zero neutrino asymmetry in the CMB framework. These neutrino parameters are consistent with those, in our previous work, obtained from the Planck CMB temperature power spectrum. These results demonstrate that galaxy pairwise velocities provide an independent and sensitive probe of neutrino properties, opening a new avenue for testing neutrino physics with large-scale structure observations.

astro-ph.CO↗

arXiv2026

PySCo-EFT and ECOSMOG-EFT: a tandem of N-body simulation codes for the Effective Field Theory of Dark Energy

Modified gravity theories constitute viable alternatives to the standard cosmological model for explaining the observed late-time accelerated expansion of the Universe. The Effective Field Theory of Dark Energy (EFTofDE) is an efficient framework to describe a wide range of such theories with a limited number of parameters. To robustly constrain them by comparison with clustering and weak lensing data from upcoming large-scale structure surveys, high-resolution cosmological N-body simulations are required to obtain accurate predictions for the matter distribution on non-linear scales. We introduce two new N-body simulation codes for EFTofDE cosmologies: PySCo-EFT, a Python-based particle mesh code, and ECOSMOG-EFT, a RAMSES-based code with adaptive mesh refinement. We consider Horndeski models with a luminal gravitational wave speed. We use iterative solvers and multigrid schemes to solve for the additional scalar field equation in both codes, incorporating the non-linear Vainshtein screening mechanism. We present validation and convergence tests of the codes. We obtain a sub-0.5 percent agreement with linear theory on large scales and a similar agreement between the two codes on non-linear scales. The dominant numerical effects on the matter-power-spectrum boost are mass resolution, finite-volume effects, refinement threshold, and starting redshift, but they are limited to below 2% at the largest wavenumbers (k=10 h/Mpc) for the range of tested values. We investigate the impact of the EFTofDE parameters on the matter-power-spectrum ratios between EFTofDE and $Λ$CDM cases. Depending on the EFTofDE parameters, the screening plays a negligible or dominant role compared to the linearised field equations. Our codes provide tools for generating fast and accurate predictions of the impact of the EFTofDE on the clustering of matter, incorporating non-linear screening.

astro-ph.CO↗

arXiv2026

Probing the Type 3 interacting dark-energy model using matter pairwise velocity

Dark sector interactions can be explored via the so-called Type 3 model where dark matter and dark energy exchange momentum only, so as to minimize deviations from the $Λ$CDM background expansion history. Using N-body simulations, we analyze the imprint of Type 3 model parameters, the momentum exchange coupling constant $β$ and the slope of scalar field potential $λ$, on large-scale structure observables, particularly the matter pairwise velocity statistics. We find that the effects of $β$ ($<0$) and $λ$ on the mean matter peculiar pairwise velocity and velocity dispersion are degenerate. Our results highlight the potential of velocity statistics as a probe of dark sector interactions and underscore the importance of disentangling $β$ and $λ$ in cosmological analyses.

astro-ph.CO↗

arXiv2026

Halo abundance and clustering in cosmologies with massive and asymmetric neutrinos

Neutrinos are the most abundant fermions in the Universe and influence the formation of large-scale structure through both their non-zero masses and a possible chemical potential which can be described by a single asymmetry parameter. While most previous studies have focused on the impact of the neutrino mass, the role of neutrino asymmetry remains comparatively unexplored. In this work, we investigate how massive neutrinos ($M_ν=0-0.24\,\mathrm{eV}$) with a non-zero asymmetry parameter ($η^{2}=0-0.8$) modify the halo mass function (HMF) and halo bias using cosmological N-body simulations with cosmological parameters consistently refitted to CMB observations. We find that at all redshifts, neutrino mass suppresses the abundance of massive halos, whereas neutrino asymmetry enhances the HMF over a broad mass range. At z=0, the abundance of the most massive halos is reduced by up to ~30% in the largest-mass case ($M_ν=0.24\,\mathrm{eV}$), while neutrino asymmetry ($η^{2}=0.8$) produces a maximum ~5% enhancement. These effects become increasingly pronounced at higher redshifts: by z=4 and z=9, the enhancement induced by neutrino asymmetry reaches ~25% and ~75%, respectively, while the corresponding suppression due to neutrino mass deepens to below ~40% and ~70% of the massless case. For halo bias, we find that halos with masses above $10^{13.4}\,\mathrm{M_\odot}$ exhibit an enhanced large-scale bias due to neutrino mass, reaching up to ~5% at z=0, while neutrino asymmetry reduces the bias by a few percent on linear scales. These trends strengthen with redshift, with the enhancement and suppression growing to ~15% and ~10% at z=2, respectively. Linear bias models provide an adequate, though not exact, description of halo bias in massive-neutrino cosmologies. Our results demonstrate that halo abundance and clustering offer sensitive probes of both neutrino mass and asymmetry.

astro-ph.CO↗

arXiv2025

Measuring neutrino mass and asymmetry with matter pairwise velocities

Neutrinos are believed to be the most abundant fermions in the Universe, but their masses are unknown, except for being non-zero but much smaller than other fermions. Cosmological relic neutrinos could also have non-zero chemical potentials (or asymmetries). Using neutrino-involved N-body simulations, we investigate the neutrino effects on the matter pairwise velocity, which itself is an interesting probe of cosmology. We find that for light-halo ($[10^{11},10^{13}]\ M_\odot$) mean pairwise velocity, in the transition range ($[4,15]\ \mathrm{Mpc}$), the effects of neutrino masses overwhelm the effects of neutrino asymmetries, while in the two-halo-group range ($[25,50]\ \mathrm{Mpc}$), for both light and heavy haloes ($[10^{13},10^{15}]\ M_\odot$), the effects of neutrino asymmetries dominate, making it possible to disentangle the two effects. We provide fitting formulae to quantify the effects of neutrino mass and asymmetry on halo-halo pairwise velocities.

astro-ph.CO↗

arXiv2025

Refitting cosmological data with neutrino mass and degeneracy

A simple and natural extension of the standard Lambda cold dark matter ($Λ$CDM) model is to allow relic neutrinos to have finite chemical potentials. We confront this $Λ$CDM$ξ$ model, a $Λ$CDM with neutrino mass $M_ν$ and degeneracy $ξ_3$ as additional parameters, with various cosmological data sets. We find that the $H_0$ and $S_8$ tensions become significant only in the presence of the cosmic microwave background (CMB) polarization data. Specifically, the global and local measurements agree to within 0.8$σ$ and 1.6$σ$ for the $H_0$ and $S_8$ tensions, respectively, when the CMB polarization data are not included. Therefore, the $H_0$ and $S_8$ tensions exist between CMB temperature and polarization data, both being global measurements. Fitting the $Λ$CDM$ξ$ model to the CMB temperature data, we find 3$σ$ evidence for nonzero neutrino mass ($M_ν=0.57^{+0.17}_{-0.13}\,\mathrm{eV}$) and degeneracy ($ξ_3=1.13^{+0.41}_{-0.19}$), and the O(1) neutrino degeneracy parameter is compatible with Big Bang nucleosynthesis data. The scalar index $n_s$ exceeds 1 slightly, which is compatible with some hybrid inflation models. Furthermore, the recent DESI baryon acoustic oscillation data prefer the $Λ$CDM$ξ$ model to the Planck $Λ$CDM model. Similar results are obtained when including additional supernova data, while the inclusion of the Atacama Cosmology Telescope $τ$ prior shifts the preferred $M_ν$ and $ξ_3$ values closer to zero and brings $n_s$ back to the values favored when the polarization data are included.

hep-ph↗

arXiv2025

Impact of light sterile neutrinos on cosmological large scale structure

Sterile neutrinos with masses on the $\mathrm{eV}$ scale are promising candidates to account for the origin of neutrino mass and the reactor neutrino anomalies. The mixing between sterile and active neutrinos in the early universe could result in a large abundance of relic sterile neutrinos, which depends on not only their physical mass $m_{\rm phy}$ but also their degree of thermalization, characterized by the extra effective number of relativistic degrees of freedom $ΔN_{\rm eff}$. Using neutrino-involved N-body simulations, we investigate the effects of sterile neutrinos on the matter power spectrum, halo pairwise velocity, and halo mass and velocity functions. We find that the presence of sterile neutrinos suppress the matter power spectrum and halo mass and velocity functions, but enhance the halo pairwise velocity. We also provide fitting formulae to quantify these effects.

astro-ph.CO↗

arXiv2024

Measuring the Hubble constant through the galaxy pairwise peculiar velocity

The Hubble constant $H_0$, the current expansion rate of the universe, is one of the most important parameters in cosmology. The cosmic expansion regulates the mutually approaching motion of a pair of celestial objects due to their gravity. Therefore, the mean pairwise peculiar velocity of celestial objects, which quantifies their relative motion, is sensitive to both $H_0$ and the dimensionless total matter density $Ω_m$. Based on this, using the Cosmicflows-4 data, we measured $H_0$ for the first time via the galaxy pairwise velocity in the nonlinear and quasi-linear range. Our results yield $H_0=75.5\pm1.4$ km s$^{-1}$ Mpc$^{-1}$ and $Ω_m=0.311^{+0.029}_{-0.028}$ . The uncertainties of $H_0$ and $Ω_m$ can be improved to around 0.6% and 2%, respectively, if the statistical errors become negligible in the future.

astro-ph.CO↗