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Register a new userTowards Precision Constraints on Gravity with the Effective Field Theory of Large-Scale Structure
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Added by
Matthew Lewandowski
Publication date
2018
fields
Physics
and research's language is
English
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We compare analytical computations with numerical simulations for dark-matter clustering, in general relativity and in the normal branch of DGP gravity (nDGP). Our analytical frameword is the Effective Field Theory of Large-Scale Structure (EFTofLSS), which we use to compute the one-loop dark-matter power spectrum, including the resummation of infrared bulk displacement effects. We compare this to a set of 20 COLA simulations at redshifts $z = 0$, $z=0.5$, and $z =1$, and fit the free parameter of the EFTofLSS, called the speed of sound, in both $Lambda$CDM and nDGP at each redshift. At one-loop at $z = 0$, the reach of the EFTofLSS is $k_{rm reach}approx 0.14 , h { rm Mpc^{-1}}$ for both $Lambda$CDM and nDGP. Along the way, we compare two different infrared resummation schemes and two different treatments of the time dependence of the perturbative expansion, concluding that they agree to approximately $1%$ over the scales of interest. Finally, we use the ratio of the COLA power spectra to make a precision measurement of the difference between the speeds of sound in $Lambda$CDM and nDGP, and verify that this is proportional to the modification of the linear coupling constant of the Poisson equation.
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We develop an approach to compute observables beyond the linear regime of dark matter perturbations for general dark energy and modified gravity models. We do so by combining the Effective Field Theory of Dark Energy and Effective Field Theory of Large-Scale Structure approaches. In particular, we parametrize the linear and nonlinear effects of dark energy on dark matter clustering in terms of the Lagrangian terms introduced in a companion paper, focusing on Horndeski theories and assuming the quasi-static approximation. The Euler equation for dark matter is sourced, via the Newtonian potential, by new nonlinear vertices due to modified gravity and, as in the pure dark matter case, by the effects of short-scale physics in the form of the divergence of an effective stress tensor. The effective fluid introduces a counterterm in the solution to the matter continuity and Euler equations, which allows a controlled expansion of clustering statistics on mildly nonlinear scales. We use this setup to compute the one-loop dark-matter power spectrum.
An accurate theoretical template for the galaxy power spectrum is a key for the success of ongoing and future spectroscopic surveys. We examine to what extent the Effective Field Theory of Large Scale Structure is able to provide such a template and correctly estimate cosmological parameters. To that end, we initiate a blinded challenge to infer cosmological parameters from the redshift-space power spectrum of high-resolution mock catalogs mimicking the BOSS galaxy sample but covering a hundred times larger cumulative volume. This gigantic simulation volume allows us to separate systematic bias due to theoretical modeling from the statistical error due to sample variance. The challenge task was to measure three unknown input parameters used in the simulation: the Hubble constant, the matter density fraction, and the clustering amplitude. We present analyses done by two independent teams, who have fitted the mock simulation data generated by yet another independent group. This allows us to avoid any confirmation bias by analyzers and pin down possible tuning of the specific EFT implementations. Both independent teams have recovered the true values of the input parameters within sub-percent statistical errors corresponding to the total simulation volume.
We present constraints on Horndeski gravity from a combined analysis of cosmic shear, galaxy-galaxy lensing and galaxy clustering from $450,mathrm{deg}^2$ of the Kilo-Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey. The Horndeski class of dark energy/modified gravity models includes the majority of universally coupled extensions to $Lambda$CDM with one scalar field in addition to the metric. We study the functions of time that fully describe the evolution of linear perturbations in Horndeski gravity. Our results are compatible throughout with a $Lambda$CDM model. By imposing gravitational wave constraints, we fix the tensor speed excess to zero and consider a subset of models including e.g. quintessence and $f(R)$ theories. Assuming proportionality of the Horndeski functions $alpha_B$ and $alpha_M$ (kinetic braiding and the Planck mass run rate, respectively) to the dark energy density fraction $Omega_{mathrm{DE}}(a) = 1 - Omega_{mathrm{m}}(a)$, we find for the proportionality coefficients $hat{alpha}_B = 0.20_{-0.33}^{+0.20} ,$ and $, hat{alpha}_M = 0.25_{-0.29}^{+0.19}$. Our value of $S_8 equiv sigma_8 sqrt{Omega_{mathrm{m}}/0.3}$ is in better agreement with the $Planck$ estimate when measured in the enlarged Horndeski parameter space than in a pure $Lambda$CDM scenario. In our joint three-probe analysis we report a downward shift of the $S_8$ best fit value from the $Planck$ measurement of $Delta S_8 = 0.016_{-0.046}^{+0.048}$ in Horndeski gravity, compared to $Delta S_8 = 0.059_{-0.039}^{+0.040}$ in $Lambda$CDM. Our constraints are robust to the modelling uncertainty of the non-linear matter power spectrum in Horndeski gravity. Our likelihood code for multi-probe analysis in both $Lambda$CDM and Horndeski gravity is publicly available at http://github.com/alessiospuriomancini/KiDSHorndeski .
The Effective Field Theory of Large-Scale Structure (EFTofLSS) is a formalism that allows us to predict the clustering of Cosmological Large-Scale Structure in the mildly non-linear regime in an accurate and reliable way. After validating our technique against several sets of numerical simulations, we perform the analysis for the cosmological parameters of the DR12 BOSS data. We assume $Lambda$CDM, a fixed value of the baryon/dark-matter ratio, $Omega_b/Omega_c$, and of the tilt of the primordial power spectrum, $n_s$, and no significant input from numerical simulations. By using the one-loop power spectrum multipoles, we measure the primordial amplitude of the power spectrum, $A_s$, the abundance of matter, $Omega_m$, and the Hubble parameter, $H_0$, to about $13%$, $3.2%$ and $3.2%$ respectively, obtaining $ln(10^{10}As)=2.72pm 0.13$, $Omega_m=0.309pm 0.010$, $H_0=68.5pm 2.2$ km/(s Mpc) at 68% confidence level. If we then add a CMB prior on the sound horizon, the error bar on $H_0$ is reduced to $1.6%$. These results are a substantial qualitative and quantitative improvement with respect to former analyses, and suggest that the EFTofLSS is a powerful instrument to extract cosmological information from Large-Scale Structure.
The precision of the cosmological data allows us to accurately approximate the predictions for cosmological observables by Taylor expanding up to a low order the dependence on the cosmological parameters around a reference cosmology. By applying this observation to the redshift-space one-loop galaxy power spectrum of the Effective Field Theory of Large-Scale Structure, we analyze the BOSS DR12 data by scanning over all the parameters of $Lambda$CDM cosmology with massive neutrinos. We impose several sets of priors, the widest of which is just a Big Bang Nucleosynthesis prior on the current fractional energy density of baryons, $Omega_b h^2$, and a bound on the sum of neutrino masses to be less than 0.9 eV. In this case we measure the primordial amplitude of the power spectrum, $A_s$, the abundance of matter, $Omega_m$, the Hubble parameter, $H_0$, and the tilt of the primordial power spectrum, $n_s$, to about $19%$, $5.7%$, $2.2%$ and $7.3%$ respectively, obtaining $ln ( 10^{10} A_s) =2.91pm 0.19$, $Omega_m=0.314pm 0.018$, $H_0=68.7pm 1.5$ km/(s Mpc) and $n_s=0.979pm 0.071$ at $68%$ confidence level. A public code is released with this preprint.
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