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Register a new userConstraints on the curvature of the Universe and dynamical dark energy from the Full-shape and BAO data
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Anton Chudaykin A. S.
Publication date
2020
fields
Physics
and research's language is
English
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We present limits on the parameters of the o$Lambda$CDM, $w_0$CDM, and $w_0 w_a$CDM models obtained from the joint analysis of the full-shape, baryon acoustic oscillations (BAO), big bang nucleosynthesis (BBN) and supernovae data. Our limits are fully independent of the data on the cosmic microwave background (CMB) anisotropies, but rival the CMB constraints in terms of parameter error bars. We find the spatial curvature consistent with a flat universe $Omega_k=-0.043_{-0.036}^{+0.036}$ ($68%$ C.L.); the dark-energy equation of state parameter $w_0$ is measured to be $w_0=-1.031_{-0.048}^{+0.052}$ ($68%$ C.L.), consistent with a cosmological constant. This conclusion also holds for the time-varying dark energy equation of state, for which we find $w_0=-0.98_{-0.11}^{+0.099}$ and $w_a=-0.33_{-0.48}^{+0.63}$ (both at $68%$ C.L.). The exclusion of the supernovae data from the analysis does not significantly weaken our bounds. This shows that using a single external BBN prior, the full-shape and BAO data can provide strong CMB-independent constraints on the non-minimal cosmological models.
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We study a phenomenological class of models where dark matter converts to dark radiation in the low redshift epoch. This class of models, dubbed DMDR, characterizes the evolution of comoving dark matter density with two extra parameters, and may be able to help alleviate the observed discrepancies between early- and late-time probes of the universe. We investigate how the conversion affects key cosmological observables such as the CMB temperature and matter power spectra. Combining 3x2pt data from Year 1 of the Dark Energy Survey, {it Planck}-2018 CMB temperature and polarization data, supernovae (SN) Type Ia data from Pantheon, and baryon acoustic oscillation (BAO) data from BOSS DR12, MGS and 6dFGS, we place new constraints on the amount of dark matter that has converted to dark radiation and the rate of this conversion. The fraction of the dark matter that has converted since the beginning of the universe in units of the current amount of dark matter, $zeta$, is constrained at 68% confidence level to be $<0.32$ for DES-Y1 3x2pt data, $<0.030$ for CMB+SN+BAO data, and $<0.037$ for the combined dataset. The probability that the DES and CMB+SN+BAO datasets are concordant increases from 4% for the $Lambda$CDM model to 8% (less tension) for DMDR. The tension in $S_8 = sigma_8 sqrt{Omega_{rm m}/0.3}$ between DES-Y1 3x2pt and CMB+SN+BAO is slightly reduced from $2.3sigma$ to $1.9sigma$. We find no reduction in the Hubble tension when the combined data is compared to distance-ladder measurements in the DMDR model. The maximum-posterior goodness-of-fit statistics of DMDR and $Lambda$CDM model are comparable, indicating no preference for the DMDR cosmology over $Lambda$CDM.
Baryon Acoustic Oscillation (BAO) surveys will be a leading method for addressing the dark energy challenge in the next decade. We explore in detail the effect of allowing for small amplitude admixtures of general isocurvature perturbations in addition to the dominant adiabatic mode. We find that non-adiabatic initial conditions leave the sound speed unchanged but instead excite different harmonics. These harmonics couple differently to Silk damping, altering the form and evolution of acoustic waves in the baryon-photon fluid prior to decoupling. This modifies not only the scale on which the sound waves imprint onto the baryon distribution, which is used as the standard ruler in BAO surveys, but also the shape, width and height of the BAO peak. We discuss these effects in detail and show how more general initial conditions impact our interpretation of cosmological data in dark energy studies. We find that the inclusion of these additional isocurvature modes leads to an increase in the Dark Energy Task Force Figure of merit by 140% and 60% for the BOSS and ADEPT experiments respectively when considered in conjunction with Planck data. We also show that the incorrect assumption of adiabaticity has the potential to bias our estimates of the dark energy parameters by $3sigma$ ($1sigma$) for a single correlated isocurvature mode, and up to $8sigma$ ($3sigma$) for three correlated isocurvature modes in the case of the BOSS (ADEPT) experiment. We find that the use of the large scale structure data in conjunction with CMB data improves our ability to measure the contributions of different modes to the initial conditions by as much as 100% for certain modes in the fully correlated case.
Constraining simultaneously the Dark Energy(DE) equation of state and the curvature of the Universe is difficult due to strong degeneracies. To circumvent this problem when analyzing data it is usual to assume flatness to constrain DE, or conversely, to assume that DE is a cosmological constant to constrain curvature. In this paper, we quantify the impact of such assumptions in view of future large surveys. We simulate future data for type Ia Supernovae (SNIa), Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO) for a large range of fiducial cosmologies allowing a small spatial curvature. We take into account a possible time evolution of DE through a parameterized equation of state : $w(a) = w_0 + (1-a) w_a$. We then fit the simulated data with a wrong assumption on the curvature or on the DE parameters. For a fiducial $Lambda$CDM cosmology, if flatness is incorrectly assumed in the fit and if the true curvature is within the ranges $0.01<Omega_k<0.03$ and $-0.07<Omega_k<-0.01$, one will conclude erroneously to the presence of an evolving DE, even with high statistics. On the other hand, models with curvature and dynamical DE can be confused with a flat $Lambda$CDM model when the fit ignores a possible DE evolution. We find that, in the future, with high statistics, such risks of confusion should be limited, but they are still possible, and biases on the cosmological parameters might be important. We conclude on recalling that, in the future, it will be mandatory to perform some complete multi-probes analyses, leaving the DE parameters as well as the curvature as free parameters.
We investigate the observational viability of a class of interacting dark energy (iDE) models in the light of the latest Cosmic Microwave Background (CMB), type Ia supernovae (SNe) and SH0ES Hubble parameter measurements. Our analysis explores the assumption of a non-zero spatial curvature, the correlation between the interaction parameter $alpha$ and the current expansion rate $H_0$, and updates the results reported in cite{micol}. Initially, assuming a spatially flat universe, the results show that the best-fit of our joint analysis clearly favours a positive interaction, i.e., an energy flux from dark matter to dark energy, with $alpha approx 0.2$, while the non-interacting case, $alpha = 0$, is ruled out by more than $3sigma$ confidence level. On the other hand, considering a non-zero spatial curvature, we find a slight preference for a negative value of the curvature parameter, which seems to relax the correlation between the parameters $alpha$ and $H_0$, as well as between $H_0$ and the normalization of the matter power spectrum on scales of 8$h^{-1}$ Mpc ($sigma_8$). Finally, we discuss the influence of considering the SH$0$ES prior on $H_0$ in the joint analyses, and find that such a choice does not change considerably the standard cosmology predictions but has a significant influence on the results of the iDE model.
We present new constraints on coupled dark energy from the recent measurements of the Cosmic Microwave Background Anisotropies from the Planck satellite mission. We found that a coupled dark energy model is fully compatible with the Planck measurements, deriving a weak bound on the dark matter-dark energy coupling parameter xi=-0.49^{+0.19}_{-0.31} at 68% c.l.. Moreover if Planck data are fitted to a coupled dark energy scenario, the constraint on the Hubble constant is relaxed to H_0=72.1^{+3.2}_{-2.3} km/s/Mpc, solving the tension with the Hubble Space Telescope value. We show that a combined Planck+HST analysis provides significant evidence for coupled dark energy finding a non-zero value for the coupling parameter xi, with -0.90< xi <-0.22 at 95% c.l.. We also consider the combined constraints from the Planck data plus the BAO measurements of the 6dF Galaxy Survey, the Sloan Digital Sky Survey and the Baron Oscillation Spectroscopic Survey.
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