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Register a new userImpact of theoretical priors in cosmological analyses: the case of single field quintessence
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We investigate the impact of general conditions of theoretical stability and cosmological viability on dynamical dark energy models. As a powerful example, we study whether minimally coupled, single field Quintessence models that are safe from ghost instabilities, can source the CPL expansion history recently shown to be mildly favored by a combination of CMB (Planck) and Weak Lensing (KiDS) data. We find that in their most conservative form, the theoretical conditions impact the analysis in such a way that smooth single field Quintessence becomes significantly disfavored with respect to the standard LCDM cosmological model. This is due to the fact that these conditions cut a significant portion of the (w0;wa) parameter space for CPL, in particular eliminating the region that would be favored by weak lensing data. Within the scenario of a smooth dynamical dark energy parametrized with CPL, weak lensing data favors a region that would require multiple fields to ensure gravitational stability.
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We investigate the cosmological observational test of the extended quintessence model, i.e. a scalar-tensor gravity model with a scalar field potential serving as dark energy, by using the Planck 2018 cosmic microwave background (CMB) data, together with the baryon acoustic oscillations (BAO) and redshift-space distortion (RSD) data. As an example, we consider the model with a Brans-Dicke kinetic term $frac{omega(phi)}{phi} phi_{;mu} phi^{;mu} $ and a quadratic scalar potential $V (phi) = A + B (phi - phi_0) + frac{C}{2} (phi - phi_0)^2$, which reduces to general relativity (GR) in the limit $omega(phi) to infty$, and the cosmological constant in the limit $B=C=0$. In such a model the scalar field typically rolls down the potential and oscillates around the minimum of $V (phi)$. We find that the model parameter estimate for the CMB+BAO+RSD data set is given by $lg alpha = -3.6 _{-0.54}^{+0.66}~ (68%)$, corresponding to $ 3.8 times 10^5 < omega_0 < 9.5 times 10^7~ (68%)$, and $lg C = 4.9 pm 1.4~ (68%) $. However, the GR $Lambda$CDM model can fit the data almost as good as this extended quintessence model, and is favored by the Akaike information criterion (AIC). The variation of the gravitational constant since the epoch of Recombination is constrained to be $0.97 < G_{rm rec}/G_0 < 1.03~ (1 sigma)$. In light of recent report that the CMB data favors a closed universe, we consider the case with non-flat geometry in our fit, and find that the mean value of $Omega_k$ shifts a little bit from $-0.049$ to $-0.036$, and the parameters in our model are not degenerate with $Omega_k$.
Attempts at constraining theories of late time accelerated expansion often assume broad priors for the parameters in their phenomenological description. Focusing on shift-symmetric scalar-tensor theories with standard gravitational wave speed, we show how a more careful analysis of their dynamical evolution leads to much narrower priors. In doing so, we propose a simple and accurate parametrisation of these theories, capturing the redshift dependence of the equation of state, $w(z)$, and the kinetic braiding parameter, $alpha_{rm B}(z)$, with only two parameters each, and derive their statistical distribution (a.k.a. theoretical priors) that fit the cosmology of the underlying model. We have considered t
We examine the plausibility of crossing the cosmological constant ($L$) barrier in a two-field quintessence model of dark energy, involving a kinetic interaction between the individual fields. Such a kinetic interaction may have its origin in the four dimensional effective two-field version of the Dirac-Born-Infeld action, that describes the motion of a D3-brane in a higher dimensional space-time. We show that this interaction term could indeed enable the dark energy equation of state parameter $wx$ to cross the $L$-barrier (i.e., $wx = -1$), keeping the Hamiltonian well behaved (bounded from below), as well as satisfying the condition of stability of cosmological density perturbations, i.e., the positivity of the squares of the sound speeds corresponding to the adiabatic and entropy modes. The model is found to fit well with the latest Supernova Union data and the WMAP results. The best fit curve for $wx$ crosses -1 at red-shift $z$ in the range $sim 0.215 - 0.245$, whereas the transition from deceleration to acceleration takes place in the range of $z sim 0.56 - 0.6$. The scalar potential reconstructed using the best fit model parameters is found to vary smoothly with time, while the dark energy density nearly follows the matter density at early epochs, becomes dominant in recent past, and slowly increases thereafter without giving rise to singularities in finite future.
We present a detailed analysis of the impact of $H_0$ priors from recent surveys in the literature on the late time cosmology of five $f(T)$ cosmological models using cosmic chronometers, the Pantheon data set, and baryonic acoustic oscillation data. In this work, we use three recently reported values of $H_0$ that have contributed to the recent $H_0$ tension problem. We find that these priors have a strong response in these analyses in terms of all the cosmological parameters. In general, our analyses gives much higher values of $H_0$ when considered against equivalent analyses without priors while, by and large, giving lower values of the matter density parameter. We close with a cross-analysis of each of our model, data set and prior combination choices.
We investigate observational constraints on cosmological parameters combining 15 measurements of the transversal BAO scale (obtained free of any fiducial cosmology) with Planck-CMB data to explore the parametric space of some cosmological models. We investigate how much Planck + transversal BAO data can constraint the minimum $Lambda$CDM model, and extensions, including neutrinos mass scale $M_{ u}$, and the possibility for a dynamical dark energy (DE) scenario. Assuming the $Lambda$CDM cosmology, we find $H_0 = 69.23 pm 0.50$ km s${}^{-1}$ Mpc${}^{-1}$, $M_{ u} < 0.11$ eV and $r_{rm drag} = 147.59 pm 0.26$ Mpc (the sound horizon at drag epoch) from Planck + transversal BAO data. When assuming a dynamical DE cosmology, we find that the inclusion of the BAO data can indeed break the degeneracy of the DE free parameters, improving the constraints on the full parameter space significantly. We note that the model is compatible with local measurements of $H_0$ and there is no tension on $H_0$ estimates in this dynamical DE context. Also, we discuss constraints and consequences from a joint analysis with the local $H_0$ measurement from SH0ES. Finally, we perform a model-independent analysis for the deceleration parameter, $q(z)$, using only information from transversal BAO data.
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