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Register a new userThe observational constraints on the flat $phi$CDM models
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Added by
Olga Avsajanishvili
Publication date
2017
fields
Physics
and research's language is
English
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Most dark energy models have the $Lambda$CDM as their limit, and if future observations constrain our universe to be close to $Lambda$CDM Bayesian arguments about the evidence and the fine-tuning will have to be employed to discriminate between the models. Assuming a baseline $Lambda$CDM model we investigate a number of quintessence and phantom dark energy models, and we study how they would perform when compared to observational data, such as the expansion rate, the angular distance, and the growth rate measurements, from the upcoming Dark Energy Spectroscopic Instrument (DESI) survey. We sample posterior likelihood surfaces of these dark energy models with Monte Carlo Markov Chains while using central values consistent with the Planck $Lambda$CDM universe and covariance matrices estimated with Fisher information matrix techniques. We find that for this setup the Bayes factor provides a substantial evidence in favor of the $Lambda$CDM model over most of the alternatives. We also investigated how well the CPL parametrization approximates various scalar field dark energy models, and identified the location for each dark energy model in the CPL parameter space.
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We constrain spatially-flat tilted and nonflat untilted scalar field ($phi$) dynamical dark energy inflation ($phi$CDM) models by using Planck 2015 cosmic microwave background (CMB) anisotropy measurements and recent baryonic acoustic oscillation distance observations, Type Ia supernovae apparent magnitude data, Hubble parameter measurements, and growth rate data. We assume an inverse power-law scalar field potential energy density $V(phi)=V_0 phi^{-alpha}$. We find that the combination of the CMB data with the four non-CMB data sets significantly improves parameter constraints and strengthens the evidence for nonflatness in the nonflat untilted $phi$CDM case from $1.8sigma$ for the CMB measurements only to more than $3.1sigma$ for the combined data. In the nonflat untilted $phi$CDM model current observations favor a spatially closed universe with spatial curvature contributing about two-thirds of a percent of the present cosmological energy budget. The flat tilted $phi$CDM model is a 0.4$sigma$ better fit to the data than is the standard flat tilted $Lambda$CDM model: current data allow for the possibility that dark energy is dynamical. The nonflat tilted $phi$CDM model is in better accord with the Dark Energy Survey bounds on the rms amplitude of mass fluctuations now ($sigma_8$) as a function of the nonrelativistic matter density parameter now ($Omega_m$) but it does not provide as good a fit to the larger-multipole Planck 2015 CMB anisotropy data as does the standard flat tilted $Lambda$CDM model. A few cosmological parameter value measurements differ significantly when determined using the tilted flat and the untilted nonflat $phi$CDM models, including the cold dark matter density parameter and the reionization optical depth.
We perform Markov chain Monte Carlo analyses to put constraints on the non-flat $phi$CDM inflation model using Planck 2015 cosmic microwave background (CMB) anisotropy data and baryon acoustic oscillation distance measurements. The $phi$CDM model is a consistent dynamical dark energy model in which the currently accelerating cosmological expansion is powered by a scalar field $phi$ slowly rolling down an inverse power-law potential energy density. We also use a physically consistent power spectrum for energy density inhomogeneities in this non-flat model. We find that, like the closed-$Lambda$CDM and closed-XCDM models, the closed-$phi$CDM model provides a better fit to the lower multipole region of the CMB temperature anisotropy data compared to that provided by the tilted flat-$Lambda$CDM model. Also, like the other closed models, this model reduces the tension between the Planck and the weak lensing $sigma_8$ constraints. However, the higher multipole region of the CMB temperature anisotropy data are better fit by the tilted flat-$Lambda$CDM model than by the closed models.
We study Planck 2015 cosmic microwave background (CMB) anisotropy data using the energy density inhomogeneity power spectrum generated by quantum fluctuations during an early epoch of inflation in the non-flat $Lambda$CDM model. Unlike earlier analyses of non-flat models, which assumed an inconsistent power-law power spectrum of energy density inhomogeneities, we find that the Planck 2015 data alone, and also in conjunction with baryon acoustic oscillation measurements, are reasonably well fit by a closed $Lambda$CDM model in which spatial curvature contributes a few percent of the current cosmological energy density budget. In this model, the measured Hubble constant and non-relativistic matter density parameter are in good agreement with values determined using most other data. Depending on parameter values, the closed $Lambda$CDM model has reduced power, relative to the tilted, spatially-flat $Lambda$CDM case, and can partially alleviate the low multipole CMB temperature anisotropy deficit and can help partially reconcile the CMB anisotropy and weak lensing $sigma_8$ constraints, at the expense of somewhat worsening the fit to higher multipole CMB temperature anisotropy data. Our results are interesting but tentative; a more thorough analysis is needed to properly gauge their significance.
We present constraints on extensions to the flat $Lambda$CDM cosmological model by varying the spatial curvature $Omega_K$, the sum of the neutrino masses $sum m_ u$, the dark energy equation of state parameter $w$, and the Hu-Sawicki $f(R)$ gravity $f_{R0}$ parameter. With the combined $3times2$pt measurements of cosmic shear from the Kilo-Degree Survey (KiDS-1000), galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), and galaxy-galaxy lensing from the overlap between KiDS-1000, BOSS, and the spectroscopic 2-degree Field Lensing Survey (2dFLenS), we find results that are fully consistent with a flat $Lambda$CDM model with $Omega_K=0.011^{+0.054}_{-0.057}$, $sum m_ u<1.76$ eV (95% CL), and $w=-0.99^{+0.11}_{-0.13}$. The $f_{R0}$ parameter is unconstrained in our fully non-linear $f(R)$ cosmic shear analysis. Considering three different model selection criteria, we find no clear preference for either the fiducial flat $Lambda$CDM model or any of the considered extensions. Besides extensions to the flat $Lambda$CDM parameter space, we also explore restrictions to common subsets of the flat $Lambda$CDM parameter space by fixing the amplitude of the primordial power spectrum to the Planck best-fit value, as well as adding external data from supernovae and lensing of the CMB. Neither the beyond-$Lambda$CDM models nor the imposed restrictions explored in this analysis are able to resolve the $sim 3sigma$ tension in $S_8$ between the $3times2$pt constraints and Planck, with the exception of $w$CDM, where the $S_8$ tension is resolved. The tension in the $w$CDM case persists, however, when considering the joint $S_8$-$w$ parameter space. The joint flat $Lambda$CDM CMB lensing and $3times2$pt analysis is found to yield tight constraints on $Omega_{rm m}=0.307^{+0.008}_{-0.013}$, $sigma_8=0.769^{+0.022}_{-0.010}$, and $S_8=0.779^{+0.013}_{-0.013}$.
We analyze constraints on parameters characterizing the pre-inflating universe in an open inflation model with a present slightly open $Lambda$CDM universe. We employ an analytic model to show that for a broad class of inflation-generating effective potentials, the simple requirement that some fraction of the observed dipole moment represents a pre-inflation isocurvature fluctuation allows one to set upper and lower limits on the magnitude and wavelength scale of pre-inflation fluctuations in the inflaton field, and the curvature of the pre-inflation universe, as a function of the fraction of the total initial energy density in the inflaton field as inflation begins. We estimate that if the pre-inflation contribution to the current CMB dipole is near the upper limit set by the {it Planck} Collaboration then the current constraints on $Lambda$CDM cosmological parameters allow for the possibility of a significantly open $Omega_{i} le 0.4$ pre-inflating universe for a broad range of the fraction of the total energy in the inflaton field at the onset of inflation. This limit to $Omega_{i}$ is even smaller if a larger dark-flow tilt is allowed.
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