Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEasily Interpretable Bulk Flows: Continuing Tension with the Standard Cosmological Model
78
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present an improved Minimal Variance (MV) method for using a radial peculiar velocity sample to estimate the average of the three-dimensional velocity field over a spherical volume, which leads to an easily interpretable bulk flow measurement. The only assumption required is that the velocity field is irrotational. The resulting bulk flow estimate is particularly insensitive to smaller scale flows. We also introduce a new constraint into the MV method that ensures that bulk flow estimates are independent of the value of the Hubble constant $H_o$; this is important given the tension between the locally measured $H_o$ and that obtained from the cosmic background radiation observations. We apply our method to the textit{CosmicFlows-3} catalogue and find that, while the bulk flows for shallower spheres are consistent with the standard cosmological model, there is some tension between the bulk flow in a spherical volume with radius $150$hmpc and its expectations; we find only a $sim 2%$ chance of obtaining a bulk flow as large or larger in the standard cosmological model with textit{Planck} parameters
rate research
Read More
The current Hubble constant tension is usually presented by comparing constraints on $H_0$ only. However, the post-recombination background cosmic evolution is determined by two parameters in the standard $Lambda$CDM model, the Hubble constant ($H_0$) and todays matter energy fraction ($Omega_{rm{m}}$). If we therefore compare all constraints individually in the $H_0$-$Omega_{rm{m}}$ plane, (1) various constraints can be treated as independently as possible, (2) single-sided constraints are easier to consider, (3) compatibility among different constraints can be viewed in a more robust way, (4) the model dependence of each constraint is clear, and (5) whether or not a nonstandard model is able to reconcile all constraints in tension can be seen more effectively. We perform a systematic comparison of different constraints in the $H_0$-$Omega_{rm{m}}$ space based on a flat $Lambda$CDM model, treating them as separately as possible. Constraints along different degeneracy directions consistently overlap in one region of the space, with the local measurement from Cepheid variable-calibrated supernovae being the most outlying, followed by the time-delay strong-lensing result. Considering the possibility that some nonstandard physics may reconcile the constraints, we provide a general discussion on nonstandard models with modifications at high, mid, or low redshifts, and the effect of local environmental factors. Due to the different responses of individual constraints to a modified model, it is not easy for nonstandard models to reconcile all constraints if none of them have unaccounted-for systematic effects.
We explore the possibility that matter bulk flows could generate the required vorticity in the electron-proton-photon plasma to source cosmic magnetic fields through the Harrison mechanism. We analyze the coupled set of perturbed Maxwell and Boltzmann equations for a plasma in which the matter and radiation components exhibit relative bulk motions at the background level. We find that, to first order in cosmological perturbations, bulk flows with velocities compatible with current Planck limits ($beta<8.5times 10^{-4}$ at $95%$ CL) could generate magnetic fields with an amplitude $10^{-21}$ G on 10 kpc comoving scales at the time of completed galaxy formation which could be sufficient to seed a galactic dynamo mechanism.
The abundance of clusters is a classical cosmological probe sensitive to both the geometrical aspects and the growth rate of structures. The abundance of clusters of galaxies measured by Planck has been found to be in tension with the prediction of the LCDM models normalized to Planck CMB fluctuations power spectra. The same tension appears with X-ray cluster local abundance. Massive neutrinos and modified gravity are two possible solutions to fix this tension. Alternatively, others options include a bias in the selection procedure or in the mass calibration of clusters. We present a study, based on our recent work, updating the present situation on this topic and discuss the likelihood of the various options.
Recent measurements of the D(p,$gamma)^3$He, nuclear reaction cross-section and of the neutron lifetime, along with the reevaluation of the cosmological baryon abundance from cosmic microwave background (CMB) analysis, call for an update of abundance predictions for light elements produced during the big-bang nucleosynthesis (BBN). While considered as a pillar of the hot big-bang model in its early days, BBN constraining power mostly rests on deuterium abundance. We point out a new $simeq1.8sigma$-tension on the baryonic density, or equivalently on the D/H abundance, between the value inferred on one hand from the analysis of the primordial abundances of light elements and, on the other hand, from the combination of CMB and baryonic oscillation data. This draws the attention on this sector of the theory and gives us the opportunity to reevaluate the status of BBN in the context of precision cosmology. Finally, this paper presents an upgrade of the BBN code PRIMAT.
We perform a general test of the $Lambda{rm CDM}$ and $w {rm CDM}$ cosmological models by comparing constraints on the geometry of the expansion history to those on the growth of structure. Specifically, we split the total matter energy density, $Omega_M$, and (for $w {rm CDM}$) dark energy equation of state, $w$, into two parameters each: one that captures the geometry, and another that captures the growth. We constrain our split models using current cosmological data, including type Ia supernovae, baryon acoustic oscillations, redshift space distortions, gravitational lensing, and cosmic microwave background (CMB) anisotropies. We focus on two tasks: (i) constraining deviations from the standard model, captured by the parameters $DeltaOmega_M equiv Omega_M^{rm grow}-Omega_M^{rm geom}$ and $Delta w equiv w^{rm grow}-w^{rm geom}$, and (ii) investigating whether the $S_8$ tension between the CMB and weak lensing can be translated into a tension between geometry and growth, i.e. $DeltaOmega_M eq 0$, $Delta w eq 0$. In both the split $Lambda{rm CDM}$ and $w {rm CDM}$ cases, our results from combining all data are consistent with $DeltaOmega_M = 0$ and $Delta w = 0$. If we omit BAO/RSD data and constrain the split $w {rm CDM}$ cosmology, we find the data prefers $Delta w<0$ at $3.6sigma$ significance and $DeltaOmega_M>0$ at $4.2sigma$ evidence. We also find that for both CMB and weak lensing, $DeltaOmega_M$ and $S_8$ are correlated, with CMB showing a slightly stronger correlation. The general broadening of the contours in our extended model does alleviate the $S_8$ tension, but the allowed nonzero values of $DeltaOmega_M$ do not encompass the $S_8$ values that would point toward a mismatch between geometry and growth as the origin of the tension.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
