Super-Eddington accreting massive black holes explore high-zz cosmology: Monte-Carlo simulations

In this paper, we simulate Super-Eddington accreting massive black holes (SEAMBHs) as the candles to probe cosmology for the first time. SEAMBHs have been demonstrated to be able to provide a new tool for estimating cosmological distance. Thus, we create a series of mock data sets of SEAMBHs, especially in the high redshift region, to check their abilities to probe the cosmology. To fulfill the potential of the SEAMBHs on the cosmology, we apply the simulated data to three projects. The first is the exploration of their abilities to constrain the cosmological parameters, in which we combine different data sets of current observations such as the cosmic microwave background from {\it Planck} and type Ia supernovae from Joint Light-curve Analysis (JLA). We find that the high redshift SEAMBHs can help to break the degeneracies of the background cosmological parameters constrained by {\it Planck} and JLA, thus giving much tighter constraints of the cosmological parameters. The second uses the high redshift SEAMBHs as the complements of the low redshift JLA to constrain the early expansion rate and the dark energy density evolution in the cold dark matter frame. Our results show that these high redshift SEAMBHs are very powerful on constraining the early Hubble rate and the evolution of the dark energy density; thus they can give us more information about the expansion history of our Universe, which is also crucial for testing the $\Lambda$CDM model in the high redshift region. Finally, we check the SEAMBH candles' abilities to reconstruct the equation of state of dark energy at high redshift. In summary, our results show that the SEAMBHs, as the rare candles in the high redshift region, can provide us a new and independent observation to probe cosmology in the future.Comment: 11 pages, 7 figures. The version published in PR

Reheating phase diagram for single-field slow-roll inflationary models

We investigate the influence on the inflationary predictions from the reheating processes characterized by the $e$-folding number $N_{\mathrm{reh}}$ and the effective equation-of-state parameter $w_{\mathrm{reh}}$ during the reheating phase. For the first time, reheating processes can be constrained in the $N_{\mathrm{reh}}\!-\!w_{\mathrm{reh}}$ plane from Planck 2015. We find that for Higgs inflation with a nonminimal coupling to gravity, the predictions are insensitive to the reheating phase for current CMB measurements. We also find that the spontaneously broken SUSY inflation and axion monodromy inflation with $\phi^{2/3}$ potential, which with instantaneous reheating lie outside or at the edge of the $95\%$ confidence region in the $n_s\!-\!r$ plane from Planck 2015 TT,TE,EE$+$lowP, can well fit the data with the help of reheating processes. Future CMB experiments would put strong constraints on reheating processes.Comment: v1,7 pages,6 figures; v2,references added,updated with Planck 2015 results; v3,major revision,9 pages,6 figures; v4,final version to match the published version,12 pages,6 figure

Null test of the cosmic curvature using H(z)H(z) and supernovae data

We introduce a model-independent approach to the null test of the cosmic curvature which is geometrically related to the Hubble parameter $H(z)$ and luminosity distance $d_L(z)$. Combining the independent observations of $H(z)$ and $d_L(z)$, we use the model-independent smoothing technique, Gaussian processes, to reconstruct them and determine the cosmic curvature $\Omega_K^{(0)}$ in the null test relation. The null test is totally geometrical and without assuming any cosmological model. We show that the cosmic curvature $\Omega_K^{(0)}=0$ is consistent with current observational data sets, falling within the $1\sigma$ limit. To demonstrate the effect on the precision of the null test, we produce a series of simulated data of the models with different $\Omega_K^{(0)}$. Future observations in better quality can provide a greater improvement to constrain or refute the flat universe with $\Omega_K^{(0)}=0$.Comment: To match the published versio

Reconstruction of the primordial power spectra with Planck and BICEP2

By using the cubic spline interpolation method, we reconstruct the shape of the primordial scalar and tensor power spectra from the recently released {\it Planck} temperature and BICEP2 polarization cosmic microwave background data. We find that the vanishing scalar index running (\dd n_s/\dd\ln k) model is strongly disfavored at more than $3\sigma$ confidence level on the $k=0.0002$ Mpc$^{-1}$ scale. Furthermore, the power-law parameterization gives a blue-tilt tensor spectrum, no matter using only the first 5 bandpowers $n_t = 1.20^{+0.56}_{-0.64} (95$ or the full 9 bandpowers $n_t = 1.24^{+0.51}_{-0.58} (95$ of BICEP2 data sets. Unlike the large tensor-to-scalar ratio value ($r\sim0.20$) under the scale-invariant tensor spectrum assumption, our interpolation approach gives $r_{0.002} < 0.060 (95{\rm CL})$ by using the first 5 bandpowers of BICEP2 data. After comparing the results with/without BICEP2 data, we find that {\it Planck} temperature with small tensor amplitude signals and BICEP2 polarization data with large tensor amplitude signals dominate the tensor spectrum reconstruction on the large and small scales, respectively. Hence, the resulting blue tensor tilt actually reflects the tension between {\it Planck} and BICEP2 data.Comment: complementary results without BICEP2 added, references add, typos corrected, 10 figures, 5 tables, 11 page

Friedmann cosmology on codimension 2 brane with time dependent tension

A solution of codimension 2 brane is found for which 4 dimensional Friedmann cosmology is recovered on the brane with time dependent tension, in the Einstein frame. The effective parameter $p/\rho$ of equation of state on the brane can be quintessence like, de Sitter like or phantom like, depending on integration constants of the solution.Comment: 6 pages, 4 figure

Dodging the cosmic curvature to probe the constancy of the speed of light

We develop a new model-independent method to probe the constancy of the speed of light $c$. In our method, the degeneracy between the cosmic curvature and the speed of light can be eliminated, which makes the test more natural and general. Combining the independent observations of Hubble parameter $H(z)$ and luminosity distance $d_L(z)$, we use the model-independent smoothing technique, Gaussian processes, to reconstruct them and then detect variation of the speed of light. We find no signal of deviation from the present value of the speed of light $c_0$. Moreover, to demonstrate the improvement in probing the constancy of the speed of light from future experiments, we produce a series of simulated data. The Dark Energy Survey will be able to detect $\Delta c /c_0 \sim 1\%$ at $\sim 1.5\sigma$ confidence level and $\Delta c /c_0 \sim 2\%$ at $\sim 3\sigma$ confidence level. If the errors are reduced to one-tenth of the expected DES ones, it can detect a $\Delta c /c_0 \sim 0.1\%$ variation at $\sim 2\sigma$ confidence level.Comment: 10 pages, several corrections and updates to match the published versio