Day 1275

Thursday.


1706.06593
Integrated cosmological probes: concordance quantified
Nicola, Amara, Refregier

Assessing the consistency of parameter constraints derived from different cosmological probes is an important way to test the validity of the underlying cosmo model.  An earlier work computed constraints on cosmo parameters for LCDM from an integrated analysis of CMB temperature anisotropies and CMB lensing from Planck, galaxy clustering and WL from SDSS, WL from DES SV as well as Type Ia SNe and Hubble parameter measurements.  In this work, extend this analysis and quantify the concordance between the derived constraints and those derived by the Planck Collaboration as well as WMAP9, SPT and ACT.  As a measure for consistency, use the Surprise statistic (Seehars+2014), which is based on the relative entropy.  In the framework of a flat LCDM cosmo model, find all datasets to be consistent with one another at a level of less than 1 sigma.  Highlight that the relative entropy is sensitive to inconsistencies in the models that are used in different parts of the analysis.  In particular, inconsistent assumptions for the neutrino mass break its invariance on the parameter choice.  When consistent model assumptions are used, the data sets considered in this work all agree with each other and LCDM, without evidence for tensions.


1706.06645
Towards optimal extraction of cosmological information from nonlinear data
Seljak, et al

One of the main unsolved problems of cosmology is how to maximize the extraction of information from nonlinear data.  If the data are NL the usual approach is to employ a sequence of statistics (N-point statistics, counting statistics of clusters, density peaks or voids etc.), along with the corresponding covariance matrices.  However, this approach is computationally prohibitive and has not been shown to be exhaustive in terms of information content.  Instead, develop a Bayesian approach, expanding the likelihood around the maximum posterior of linear modes, which is solved using optimization methods.  By integrating out the modes using perturbative expansion of the likelihood, construct an initial power spectrum estimator, which for a fixed forward model contains all the cosmo information if the initial modes are gaussian distributed.  Develop a method to construct the window and covariance matrix such that the estimator is explicitly unbiased and nearly optimal.  Then generalize the method to include the forward mode parameters, including cosmo and nuisance parameters, and primordial non-gaussianity.  Apply the method in the simplified context of NL structure formation, using either simplified 2-LPT dynamics or N-body sims as the nonlinear mapping between linear and nonlinear density, and 2-LPT dynamics in the optimization steps used to reconstruct the initial density modes.  Demonstrate that the method gives an unbiased estimator of the initial PS, providing among others a near optimal reconstruction of linear baryonic acoustic oscillations.


1706.06842
A warm or cold early Earth?  New insights from a 3-D climate-carbon model
Charnay, et al

Oxygen isotopes in marine cherts have been used to infer hot oceans during the Archean with temperatures between 60 deg C (333K) and 80 deg C (353K).  Such climates are challenging for the early Earth warmed by the faint young Sun.  The interpretation of the data has therefore been controversial.  1D climate modeling inferred that such hot climates would require very high levels of CO2 (2-6 bars).  Previous carbon cycle modeling concluded that such stable hot climates were impossible and that the carbon cycle should lead to cold climates during the Hadean and the Archean.  Here, revisit the climate and carbon cycle of the early Earth at 3.8 Ga using a 3D climate-carbon model.  Find that CO2 partial pressures of around 1 bar could have produced hot climates given a low land fraction and cloud feedback effects.  However, such high CO2 partial pressures should not have been stable because of the weathering of terrestrial and oceanic basalts, producing an efficient stabilizing feedback.  Moreover, the weathering of impact ejecta during the Late Heavy Bombardment (LHB) would have strongly reduced the CO2 partial pressure leading to cold climates and potentially snowball Earth events after large impacts.  The results therefore favor cold or temperate climates with global mean temperatures between around 8 deg C (281K) and 30 deg C (303 K) and with 0.1-0.36 bar of CO2 for the late Hadean and early Archean.  Finally, the model suggests that the carbon cycle was efficient for preserving clement conditions on the early Earth without necessarily requiring any other greenhouse gas or warming process.