Search for sterile neutrinos in holographic dark energy cosmology: Reconciling Planck observation with the local measurement of the Hubble constant

We search for sterile neutrinos in the holographic dark energy cosmology by using the latest observational data. To perform the analysis, we employ the current cosmological observations, including the cosmic microwave background temperature power spectrum data from the Planck mission, the baryon acoustic oscillation measurements, the type Ia supernova data, the redshift space distortion measurements, the shear data of weak lensing observation, the Planck lensing measurement, and the latest direct measurement of $H_0$ as well. We show that, compared to the $\Lambda$CDM cosmology, the holographic dark energy cosmology with sterile neutrinos can relieve the tension between the Planck observation and the direct measurement of $H_0$ much better. Once we include the $H_0$ measurement in the global fit, we find that the hint of the existence of sterile neutrinos in the holographic dark energy cosmology can be given. Under the constraint of the all-data combination, we obtain $N_{\rm eff}= 3.76\pm0.26$ and $m_{\nu,\rm sterile}^{\rm eff}< 0.215\,\rm eV$, indicating that the detection of $\Delta N_{\rm eff}>0$ in the holographic dark energy cosmology is at the $2.75\sigma$ level and the massless or very light sterile neutrino is favored by the current observations.Comment: 10 pages, 4 figures; typos corrected, published in PR

Prospects for Constraining interacting dark energy cosmology with gravitational-wave bright sirens detected by future SKA-era pulsar timing arrays

Pulsar timing arrays (PTAs) have the potential to detect Nanohertz gravitational waves (GWs) that are usually generated by the individual inspiraling supermassive black hole binaries (SMBHBs) in the galactic centers. The GW signals as cosmological standard sirens can provide the absolute cosmic distances, thereby can be used to constrain the cosmological parameters. In this paper, we analyze the ability of future SKA-era PTAs to detect the existing SMBHBs candidates assuming the root mean square of timing noise $\sigma_t=20\ {\rm ns}$, and use the simulated PTA data to constrain the interacting dark energy (IDE) models with energy transfer rate $Q = \beta H\rho_c$. We find that, the future SKA-era PTAs will play an important role in constraining the IDE cosmology. Using only the mock PTA data consisting of 100 pulsars, we obtain $\sigma(H_0)=0.239\ {\rm km} \ {\rm s}^{-1} {\rm Mpc}^{-1}$ and $\sigma(\Omega_m)=0.0103$ in the I$\Lambda$CDM model, which are much better than the results from the Planck TT, TE, EE+lowE. However, the PTA data cannot provide a tight constraint on the coupling parameter $\beta$ compared with Planck, but the data combination of Planck+PTA can provide a rather tight constraint, i.e., $\sigma(\beta)=0.00232$, since the PTA data could break the parameter degeneracies inherent in CMB. In the I$w$CDM model, we obtain $\sigma(\beta)=0.00137$ and $\sigma(w)=0.0492$ from the Planck+PTA data combination. In addition, we also find that with the increase of the number of pulsars in PTA, the constraint results from the Planck+PTA will be further improved to some extent. We show that the observations of Nanohertz GWs with future SKA-era PTAs will provide a powerful tool for exploring the nature of dark energy and measuring the coupling between dark energy and dark matter