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Register a new userTension with the flat {Lambda}CDM model from a high redshift Hubble Diagram of supernovae, quasars and gamma-ray bursts
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In the current framework, the standard parametrization of our Universe is the so-called Lambda Cold Dark Matter ({Lambda}CDM) model. Recently, Risaliti & Lusso (2019) have shown a ~4{sigma} tension with the {Lambda}CDM model through a model-independent parametrization of a Hubble Diagram of supernovae Ia (SNe Ia) from the JLA survey and quasars. Model-independent approaches and independent samples over a wide redshift range are key to testing this tension and any possible systematics. Here we present an analysis of a combined Hubble Diagram of SNe Ia, quasars, and gamma-ray bursts (GRBs) to check the agreement of the quasar and GRB cosmological parameters at high redshifts (z>2) and to test the concordance flat {Lambda}CDM model with improved statistical accuracy. We build a Hubble diagram with SNe Ia from the Pantheon sample (Scolnic et al. 2018), quasars from the Risaliti & Lusso (2019) sample, and GRBs from the Demianski et al. (2017a) sample, where quasars are standardised through the observed non-linear relation between their ultraviolet and X-ray emission and GRBs through the correlation between the spectral peak energy and the isotropic-equivalent radiated energy (the so-called Amati relation). We fit the data with cosmographic models consisting of a fourth-order logarithmic polynomial and a fifth-order linear polynomial, and compare the results with the expectations from a flat {Lambda}CDM model. We confirm the tension between the best fit cosmographic parameters and the {Lambda}CDM model at ~4{sigma} with SNe Ia and quasars, at ~2{sigma} with SNe Ia and GRBs, and at >4{sigma} with the whole SNe Ia+quasars+GRB data set. The completely independent high-redshift Hubble diagrams of quasars and GRBs are fully consistent with each other, strongly suggesting that the deviation from the standard model is not due to unknown systematic effects but to new physics.
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Thanks to their enormous energy release, Gamma Rays Bursts (GRBs) have recently attracted a lot of interest to probe the Hubble diagram (HD) deep into the matter dominated era and hence complement Type Ia Supernovae (SNeIa). We consider here three different calibration methods based on the use of a fiducial LCDM model, on cosmographic parameters and on the local regression on SNeIa to calibrate the scaling relations proposed as an equivalent to the Phillips law to standardize GRBs finding any significant dependence. We then investigate the evolution of these parameters with the redshift to obtain any statistical improvement. Under this assumption, we then consider possible systematics effects on the HDs introduced by the calibration method, the averaging procedure and the homogeneity of the sample arguing against any significant bias.
Gamma ray bursts (GRBs) have recently attracted much attention as a possible way to extend the Hubble diagram to very high redshift. To this aim, the luminosity (or isotropic emitted energy) of a GRB at redshift z must be evaluated from a correlation with a distance independent quantity so that one can then solve for the luminosity distance D_L(z) and hence the distance modulus mu(z). Averaging over five different two parameters correlations and using a fiducial cosmological model to calibrate them, Schaefer (2007) has compiled a sample of 69 GRBs with measured mu(z) which has since then been widely used to constrain cosmological parameters. We update here that sample by many aspects. First, we add a recently found correlation for the X - ray afterglow and use a Bayesian inspired fitting method to calibrate the different GRBs correlations known insofar assuming a fiducial LCDM model in agreement with the recent WMAP5 data. Averaging over six correlations, we end with a new GRBs Hubble diagram comprising 83 objects. We also extensively explore the impact of varying the fiducial cosmological model considering how the estimated mu(z) change as a function of the $(Omega_M, w_0, w_a)$ parameters of the Chevallier - Polarski - Linder phenomenological dark energy equation of state. In order to avoid the need of assuming an {it a priori} cosmological model, we present a new calibration procedure based on a model independent local regression estimate of mu(z) using the Union SNeIa sample to calibrate the GRBs correlations. This finally gives us a GRBs Hubble diagram made out of 69 GRBs whose estimated distance modulus mu(z) is almost independent on the underlying cosmological model.
Tight constraints on cosmological parameters can be obtained with standard candles spanning a range of redshifts as large as possible. We propose to treat SN Ia and long Gamma-Ray Bursts (GRBs) as a single class of candles. Taking advantage of the recent release of the Supernova Legacy Survey and {it the recent finding of a tight correlation among the energetics and other prompt gamma-ray emission properties of GRBs}, we are able to standardize the luminosities/energetics of both classes of objects. In this way we can jointly use GRB and SNIa as cosmological probes to constrain Omega_m and Omega_L and the Dark Energy equation of state parameters through the same Bayesian method that we have, so far, applied to GRBs alone. Despite the large disparity in number (115 SNIa versus 19 GRBs) we show that the constraints on Omega_m and Omega_L are greatly improved by the inclusion of GRBs. More importantly, the result of the combined sample is in excellent agreement with the Lambda-CDM concordance cosmological model and does not require an evolving equation of state for the Dark Energy.
We carry out a multi-probe self-consistency test of the flat $Lambda$CDM model with the aim of exploring potential causes of the reported tensions between high- and low-redshift cosmological observations. We divide the model into two theory regimes determined by the smooth background (geometry) and the evolution of matter density fluctuations (growth), each governed by an independent set of Lambda Cold Dark Matter ($Lambda$CDM) cosmological parameters. This extended model is constrained by a combination of weak gravitational lensing measurements from the Kilo-Degree Survey, galaxy clustering signatures extracted from Sloan Digital Sky Survey campaigns and the Six-Degree Field Galaxy Survey, and the angular baryon acoustic scale and the primordial scalar fluctuation power spectrum measured in $textit{Planck}$ cosmic microwave background (CMB) data. We find strong consistency between the geometry and growth parameters, and with the posterior of standard $Lambda$CDM analysis. Tension in the amplitude of matter density fluctuations as measured by the parameter $S_8$ persists at around 3$sigma$, with a $1.5,%$ constraint of $S_8 = 0.776_{-0.008}^{+0.016}$ for the combined probes. We also observe a less significant preference (at least $2sigma$) for higher values of the Hubble constant, $H_0 = 70.5^{+0.7}_{-1.5},{rm km, s^{-1} Mpc^{-1}}$, as well as for lower values of the total matter density parameter $Omega_{rm{m}} = 0.289^{+0.007}_{-0.005}$ compared to the full $textit{Planck}$ analysis. Including the subset of the CMB information in the probe combination enhances these differences rather than alleviate them, which we link to the discrepancy between low and high multipoles in $textit{Planck}$ data.
The KBC void is a local underdensity with the observed relative density contrast $delta equiv 1 - rho/rho_{0} = 0.46 pm 0.06$ between 40 and 300 Mpc around the Local Group. If mass is conserved in the Universe, such a void could explain the $5.3sigma$ Hubble tension. However, the MXXL simulation shows that the KBC void causes $6.04sigma$ tension with standard cosmology ($Lambda$CDM). Combined with the Hubble tension, $Lambda$CDM is ruled out at $7.09sigma$ confidence. Consequently, the density and velocity distribution on Gpc scales suggest a long-range modification to gravity. In this context, we consider a cosmological MOND model supplemented with $11 , rm{eV}/c^{2}$ sterile neutrinos. We explain why this $ u$HDM model has a nearly standard expansion history, primordial abundances of light elements, and cosmic microwave background (CMB) anisotropies. In MOND, structure growth is self-regulated by external fields from surrounding structures. We constrain our model parameters with the KBC void density profile, the local Hubble and deceleration parameters derived jointly from supernovae at redshifts $0.023 - 0.15$, time delays in strong lensing systems, and the Local Group velocity relative to the CMB. Our best-fitting model simultaneously explains these observables at the $1.14%$ confidence level (${2.53 sigma}$ tension) if the void is embedded in a time-independent external field of ${0.055 , a_{_0}}$. Thus, we show for the first time that the KBC void can naturally resolve the Hubble tension in Milgromian dynamics. Given the many successful a priori MOND predictions on galaxy scales that are difficult to reconcile with $Lambda$CDM, Milgromian dynamics supplemented by $11 , rm{eV}/c^{2}$ sterile neutrinos may provide a more holistic explanation for astronomical observations across all scales.
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