The Effective Field Theory of Cosmological Large Scale Structures (1206.2926v2)

Abstract: Large scale structure surveys will likely become the next leading cosmological probe. In our universe, matter perturbations are large on short distances and small at long scales, i.e. strongly coupled in the UV and weakly coupled in the IR. To make precise analytical predictions on large scales, we develop an effective field theory formulated in terms of an IR effective fluid characterized by several parameters, such as speed of sound and viscosity. These parameters, determined by the UV physics described by the Boltzmann equation, are measured from N-body simulations. We find that the speed of sound of the effective fluid is c_s^2 10^-6 and that the viscosity contributions are of the same order. The fluid describes all the relevant physics at long scales k and permits a manifestly convergent perturbative expansion in the size of the matter perturbations \delta(k) for all the observables. As an example, we calculate the correction to the power spectrum at order \delta(k)^4. The predictions of the effective field theory are found to be in much better agreement with observation than standard cosmological perturbation theory, already reaching percent precision at this order up to a relatively short scale k \sim 0.24 h/Mpc.

• The paper develops an effective field theory framework that models large-scale cosmic structures by encapsulating small-scale physics into effective fluid parameters.
• It rigorously measures parameters like the effective speed of sound from N-body simulations, achieving percent-level precision in power spectrum predictions.
• The study refines standard perturbation theory by incorporating non-linear corrections, significantly enhancing agreement with observational data.

Overview of the Effective Field Theory of Cosmological Large Scale Structures

The paper "The Effective Field Theory of Cosmological Large Scale Structures" by Carrasco, Hertzberg, and Senatore addresses the complexity inherent in cosmological large-scale structure (LSS) formation, particularly due to the non-linear dynamics predominantly influenced by gravitational interactions beyond linear regimes. The authors propose an effective field theory (EFT) approach to accurately predict the statistical properties of cosmic structures on large scales, working within a framework that is perturbative yet accounts for non-linear contributions by integrating out the small-scale physics.

Key Contributions

1. EFT Framework: The authors develop an EFT for the large-scale structures by considering the long-wavelength perturbations in the universe as an effective fluid. Instead of directly dealing with the complex interactions of smaller scales, they define parameters such as speed of sound and viscosity which encapsulate the impact of small-scale physics on large-scale behavior.
2. Parameter Estimation: The effective parameters in this theory are not directly deduced from the theoretical model but are instead rigorously measured using $N$-body simulations. Notably, the paper identifies the effective speed of sound $c_s^2 \approx 10^{-6}c^2$, signifying the theory's capability to provide continuity with real-world observations from simulations.
3. Perturbation Theory: By utilizing a perturbative approach, the paper explores corrections to the power spectrum, analyzing contributions up to fourth order. These corrections notably improve the precision of model predictions when compared to standard linear perturbation theory.
4. Comparative Analysis: The effective theory's predictions exhibit much closer alignment with observational data than the standard cosmological perturbation theory, achieving percent-level precision up to $k\simeq 0.24 h \text{ Mpc}^{-1}$.

Observations and Implications

The results presented assert the critical role of EFT in describing the large-scale structures of the universe. The effective parameters, extracted from simulations, facilitate an accurate reconstruction of the power spectrum up to scales previously dominated by non-linear effects. This advancement underscores the potential of EFT in astrophysical contexts, specifically where direct simulation of every scale is computationally prohibitive.

Theoretical Implications:

EFT provides a systematic and robust framework that ties together different scales of the cosmic structure, offering theoretical insights into the nature of dark energy and the primordial universe's initial conditions. This approach promises further refinement in placing constraints on dark matter interactions and modifications to general relativity on cosmological scales.

Practical Applications:

Looking ahead, the precision of EFT applied to LSS data showcases tremendous implications for upcoming surveys, potentially exceeding the data richness explored by the Cosmic Microwave Background (CMB) observations. As observational tools improve, such a structured analytical framework becomes invaluable in propelling the accuracy of cosmological parameters derived from LSS measurements.

Future Directions

Given the demonstrated success, future research can extend this framework beyond $\Lambda$CDM models to probe alternative cosmologies or incorporate baryonic effects more comprehensively. The paper paves the way for subsequent studies to build upon this foundational EFT, pushing towards two-loop or higher order corrections to further refine the agreement between theory and observation.

In conclusion, the research presented in this paper exemplifies a pivotal step in understanding cosmological structures through the lens of effective field theory, promising heightened accuracy and a robust platform for interpreting future astronomical data.