Cosmological Parameters from the BOSS Galaxy Power Spectrum

Abstract: We present cosmological parameter measurements from the publicly available Baryon Oscillation Spectroscopic Survey (BOSS) data on anisotropic galaxy clustering in Fourier space. Compared to previous studies, our analysis has two main novel features. First, we use a complete perturbation theory model that properly takes into account the non-linear effects of dark matter clustering, short-scale physics, galaxy bias, redshift-space distortions, and large-scale bulk flows. Second, we employ a Markov-Chain Monte-Carlo technique and consistently reevaluate the full power spectrum likelihood as we scan over different cosmologies. Our baseline analysis assumes minimal $\Lambda$CDM, varies the neutrino masses within a reasonably tight range, fixes the primordial power spectrum tilt, and uses the big bang nucleosynthesis prior on the physical baryon density $\omega_b$. In this setup, we find the following late-Universe parameters: Hubble constant $H_0=(67.9\pm 1.1)$ km$\,$s$^{-1}$Mpc$^{-1}$, matter density fraction $\Omega_m=0.295\pm 0.010$, and the mass fluctuation amplitude $\sigma_8=0.721\pm 0.043$. These parameters were measured directly from the BOSS data and independently of the Planck cosmic microwave background observations. Scanning over the power spectrum tilt or relaxing the other priors do not significantly alter our main conclusions. Finally, we discuss the information content of the BOSS power spectrum and show that it is dominated by the location of the baryon acoustic oscillations and the power spectrum shape. We argue that the contribution of the Alcock-Paczynski effect is marginal in $\Lambda$CDM, but becomes important for non-minimal cosmological models.

• The paper introduces a perturbation theory model that integrates non-linear galaxy clustering, redshift-space distortions, and dark matter dynamics.
• It applies IR resummation and MCMC techniques to yield precise estimates of the Hubble constant, matter density, and mass fluctuation amplitude.
• The study offers new constraints on neutrino masses and expands the cosmological parameter space beyond standard ΛCDM models.

Analysis of Cosmological Parameters from the BOSS Galaxy Power Spectrum

The paper tackles the estimation of cosmological parameters derived from the Baryon Oscillation Spectroscopic Survey (BOSS) data, focusing on anisotropic galaxy clustering in Fourier space. The authors introduce advanced methodological improvements, primarily through the utilization of a comprehensive perturbation theory model which encompasses non-linear effects related to dark matter clustering, galaxy bias, redshift-space distortions, and large-scale flows. They supplement theoretical modeling with the Markov Chain Monte Carlo (MCMC) technique, enhancing the estimation process by meticulously reevaluating the full power spectrum likelihood across various cosmologies.

Methodological Advancements

1. Perturbation Theory Model: The authors apply a perturbation theory framework that incorporates a detailed understanding of galaxy clustering non-linearities, vicinity-space distortions, and underlying dark matter behavior. This comprehensive approach allows the derivation of power spectrum data to be more accurate and reliable, compensating for what previous studies might have averaged out as noise or systemic errors.
2. IR Resummation: The paper introduces infrared (IR) resummation techniques to counteract bulk motion damplings, critical in accurately predicting baryon acoustic oscillations (BAO). This technique aligns with Eulerian Perturbation Theory (EPT) to coherently model the displacement fields.
3. MCMC and Neutrino Mass Constraints: By incorporating MCMC techniques, the paper not only reevaluates the likelihood with varying cosmologies but also addresses the longstanding issues regarding neutrino mass measures and significance within the power spectrum.

Empirical Findings

From the baseline analysis utilizing $\Lambda$CDM, key cosmological parameters are derived:

• The Hubble constant is estimated at $H_0 = 67.9 \pm 1.1$ km/s/Mpc.
• The matter density fraction is determined at $\Omega_m = 0.295 \pm 0.010$.
• The mass fluctuation amplitude is $\sigma_8 = 0.721 \pm 0.043$.

These baseline results, achieved through the multi-environment study of BOSS data, show consistency and competitiveness compared to alternatives like the Planck cosmic microwave background (CMB) observations.

Discussion on Potential and Future Scope

The paper initiates a reevaluation of fixed cosmological shape parameters, departing from traditional strict uniform priors. The outcome is the derivation of constraints on neutrino masses in a minimally biased framework. The robustness of these findings indicates potential applications in future large-scale surveys, enabling more precise measurements of cosmological phenomena like dark energy dynamics.

Furthermore, the analytical techniques refined within the paper allow for expansion into models considering early and late-Universe deviations from $\Lambda$CDM. Such analysis could prove instrumental as more high-resolution survey data becomes attainable, broadening the understanding of non-linear structures and BAO on characterizing cosmic expansion and matter distribution.

Overall, by extending the perturbation theory and resummation methodologies, the paper sets a new precedent in accurately capturing cosmological parameters, promising advancements for upcoming astronomical datasets and theoretical physics models.