Null test for cosmic curvature using Gaussian process*

Abstract

The cosmic curvature ΩK,0, which determines the spatial geometry of the universe, is an important parameter in modern cosmology. Any deviation from ΩK,0=0 would have a profound impact on primordial inflation paradigm and fundamental physics. In this work, we adopt a cosmological model-independent method to test whether ΩK,0 deviates from zero. We use the Gaussian process to reconstruct the reduced Hubble parameter E(z) and the derivative of distance D′(z) from observational data, and then determine ΩK,0 with a null test relation. The cosmic chronometer (CC) Hubble data, baryon acoustic oscillation (BAO) Hubble data, and supernovae Pantheon sample are considered. Our result is consistent with a spatially flat universe within the domain of reconstruction 0<z<2.3, at the 1σ confidence level. In the redshift interval 0<z<1, the result favors a flat universe, while at z>1, it tends to favor a closed universe. In this sense, there is still a possibility for a closed universe. We also carry out the null test of the cosmic curvature at 0<z<4.5 using the simulated gravitational wave standard sirens, CC+BAO and redshift drift Hubble data. The result shows that in the future, with the synergy of multiple high-quality observations, we can tightly constrain the spatial geometry or exclude the flat universe.

Distinguishing ΛCDM from Evolving Dark Energy with Om Two-point Statistics: Implications from the Space-borne Gravitational-wave Detector

“…It should be noted that this approach assumes a priori the cosmological model, which makes such measurements modeldependent (Li et al 2016). In this paper, we utilize the newest 33 CC H(z) measurements with redshift up to ∼2, wherein 32 measurements have been extensively employed in previous studies (Borghi et al 2022;Wu et al 2023), while 1 measurement has been updated (Tomasetti et al 2023).…”

Constraints on Prospective Deviations from the Cold Dark Matter Model Using a Gaussian Process

“…Fortunately, the size of data used in the case of cosmological applications allows for a sensible reduction in the kernel numbers to be considered (as compared to other situations) and also allows us to perform some quick numerical experiments to find where the problem can hide. Readers are invited to check the following references, dealing with how GPs can be used in cosmology, and to learn the necessary mathematics behind this approach [45][46][47][48][49][50][51][52].…”

“…Moreover, it has been used in a scalar field potential reconstruction, allowing to constrain any given model revealing its connection to the swampland, among others [11]. In the literature, there are several important applications of this method to study cosmological and astrophysical problems (see [45][46][47][48][49][50][51][52], to mention a few).…”