Anton Chudaykin’s research while affiliated with Cañada College and other places

We present updated constraints on modified gravity by including the Integrated Sachs-Wolfe (ISW) effect from CMB lensing-CMB temperature cross-correlations, based on the latest Planck PR4 maps. Utilizing the Effective Field Theory of dark energy approach and adopting the $w_0w_a$CDM background cosmological model, we find that including the CMB ISW lensing cross-correlations tighten constraints on the modified gravity parameters by approximately $20\%$, reducing the viable parameter space by 50-$80\%$. We derive constraints from Planck CMB, Planck and ACT CMB lensing, DESI DR1 BAO, CMB ISW-lensing, and type Ia supernovae (SN Ia) data. Our results are consistent with General Relativity (GR) at the $95\%$ CL. The modified gravity model shows a mild preference for an evolving dark energy at the $1.8\sigma$, $2.6\sigma$ and $3.2\sigma$ levels for the combinations with Pantheon+, Union3 and DESY5 supernova datasets. We find that using the latest likelihoods $\texttt{HiLLiPoP}+\texttt{LoLLiPoP}$ alleviates the departure of modified gravity parameters from the GR-values compared to results using Planck 2018 data. This paper underlines the importance of the ISW lensing probe in constraining late-time modifications of gravity.

We provide a perturbative effective field theory (EFT) description for anisotropic (redshift-space) correlations between the Lyman alpha forest and a generic biased tracer of matter, which could be represented by quasars, high-redshift galaxies, or dark matter halos. We compute one-loop EFT power spectrum predictions for the combined analysis of the Lyman alpha and biased tracers' data and test them on the publicly available high fidelity Sherwood simulations. We use massive and light dark matter halos at redshift z=2.8 as proxies for quasars and high-redshift galaxies, respectively. In both cases, we demonstrate that our EFT model can consistently describe the complete data vector consisting of the Lyman alpha forest auto spectrum, the halo auto spectrum, and the Lyman alpha -- halo cross spectrum. We show that the addition of cross-correlations significantly sharpens constraints on EFT parameters of the Lyman alpha forest and halos. In the combined analysis, our EFT model fits the simulated cross-spectra with a percent level accuracy at $k_{\rm max}= 1~h$Mpc$^{-1}$, which represents a significant improvement over previous analytical models. Thus, our work provides precision theoretical tools for full-shape analyses of Lyman alpha - quasar cross-correlations with ongoing and upcoming spectroscopic surveys.

Parameter estimation from galaxy survey data from the full-shape method depends on scale cuts and priors on EFT parameters. The effects of priors, including the so-called "prior volume" phenomenon have been originally studied in Ivanov et al. (2019) and subsequent works. In this note, we repeat and extend these tests and also apply them to the priors used by D'Amico et al. (2019). We point out that in addition to the "prior volume" effect there is a much more dangerous effect that is largely overlooked: a systematic bias on cosmological parameters due to overoptimistic scale cuts. Unlike the "prior volume" effect, this is a genuine systematic bias due to two-loop corrections that does not vanish with better priors or with larger data volumes. Our study is based on the high fidelity BOSS-like PT Challenge simulation data which offer many advantages over analyses based on synthetic data generated with fitting pipelines. We show that the analysis choices of D'Amico et al.~(2019), especially their scale cuts, significantly bias parameter recovery, overestimating $\sigma_8$ by over $5\%$ (equivalent to $1\sigma$). The bias on measured EFT parameters is even more significant. In contrast, the analysis choices associated with the CLASS-PT code lead to a negligible ($\lesssim 1\%$) bias in the recovery of cosmological parameters based on their best-fit values.

The Dark Energy Spectroscopic Instrument (DESI) collaboration has recently released measurements of baryon acoustic oscillation (BAO) from the first year of observations. A joint analysis of DESI BAO, CMB, and SN Ia probes indicates a preference for time-evolving dark energy. We evaluate the robustness of this preference by replacing the DESI distance measurements at $z<0.8$ with the SDSS BAO measurements in a similar redshift range. Assuming the $w_0w_a$CDM model, we find an evolution of the dark energy equation of state parameters consistent with $\Lambda$CDM. Our analysis of $\chi^2$ statistics across various BAO datasets shows that DESI's preference for evolving dark energy is primarily driven by the two LRG samples at $z_{\rm eff}=0.51$ and $z_{\rm eff}=0.71$, with the latter having the most significant impact. Taking this preference seriously, we study a general Horndeski scalar-tensor theory, which provides a physical mechanism to safely cross the phantom divide, $w=-1$. Utilizing the Effective Field Theory of dark energy and adopting the $w_0w_a$CDM background cosmological model, we derive constraints on the parameters $w_0=-0.856\pm0.062$ and $w_a=-0.53_{-0.26}^{+0.28}$ at $68\%$ CL from Planck CMB, Planck and ACT CMB lensing, DESI BAO, and Pantheon+ datasets, showing good consistency with the standard $w_0w_a$CDM model. The modified gravity model shows a preference over $\Lambda$CDM at the $2.4\sigma$ level, while for $w_0w_a$CDM it is at $2.5\sigma$. We conclude that modified gravity offers a viable physical explanation for DESI's preference for evolving dark energy.

We study the one-point probability distribution function (PDF) for matter density averaged over spherical cells. The leading part to the PDF is defined by spherical collapse dynamics, whereas the next-to-leading part comes from the integration over fluctuations around the saddle-point solution. The latter calculation receives sizable contributions from short modes and must be renormalized. We propose a new approach to renormalization by modeling the effective stress-energy tensor for short perturbations. The model contains three free parameters. Two of them are related to the counterterms in the one-loop matter power spectrum and bispectrum, one more parameterizes their redshift dependence. This relation can be used to impose priors in fitting the model to the PDF data. We confront the model with the results of high-resolution N-body simulations and find excellent agreement for cell radii r * ≥ 10 Mpc/ h at all redshifts down to z = 0. Discrepancies at a few per cent level are detected at low redshifts for r * ≤ 10 Mpc/ h and are associated with two-loop corrections to the model.

We present the effective-field theory (EFT-)based cosmological full-shape analysis of the anisotropic power spectrum of eBOSS quasars at the effective redshift zeff=1.48. We perform extensive tests of our pipeline on simulations, paying particular attention to the modeling of observational systematics, such as redshift smearing, fiber collisions, and the radial integral constraint. Assuming the minimal Λ cold dark matter model, and fixing the primordial power spectrum tilt and the physical baryon density, we find the Hubble constant H0=(66.7±3.2) km s−1 Mpc−1, the matter density fraction Ωm=0.32±0.03, and the late-time mass fluctuation amplitude σ8=0.95±0.08. These measurements are fully consistent with the Planck cosmic microwave background results. Our eBOSS quasar S8 posterior, 0.98±0.11, does not exhibit the so-called S8 tension. Our work paves the way for systematic full-shape analyses of quasar samples from future surveys like DESI.

We study the one-point probability distribution function (PDF) for matter density averaged over spherical cells. The leading part to the PDF is defined by the dynamics of the spherical collapse whereas the next-to-leading part comes from the integration over fluctuations around the saddle-point solution. The latter calculation receives sizable contributions from unphysical short modes and must be renormalized. We propose a new approach to renormalization by modeling the effective stress-energy tensor for short perturbations. The model contains three free parameters related to the counterterms in the one-loop matter power spectrum and bispectrum, as well as their redshift dependence. This relation can be used to impose priors in fitting the model to the PDF data. We confront the model with the results of high-resolution N-body simulations and find excellent agreement for cell radii $r_*\geq 10\,{\rm Mpc}/h$ at all redshifts up to z=0. Discrepancies at a few per cent level are detected at low redshifts for $r_*\leq 10\,{\rm Mpc}/h$ and are associated with two-loop corrections to the model.

We present the effective-field theory (EFT)-based cosmological full-shape analysis of the anisotropic power spectrum of eBOSS quasars at the effective redshift $z_{\rm eff}=1.48$. We perform extensive tests of our pipeline on simulations, paying a particular attention to the modeling of observational systematics, such as redshift smearing, fiber collisions, and the radial integral constraint. Assuming the minimal $\Lambda$CDM model, and fixing the primordial power spectrum tilt and the physical baryon density, we find the Hubble constant $H_0=(66.7\pm 3.2)~$km~s$^{-1}$Mpc$^{-1}$, the matter density fraction $\Omega_m=0.32\pm 0.03$, and the late-time mass fluctuation amplitude $\sigma_8=0.95\pm 0.08$. These measurements are fully consistent with the Planck cosmic microwave background results. Our eBOSS quasar $S_8$ posterior, $0.98\pm0.11$, does not exhibit the so-called $S_8$ tension. Our work paves the way for systematic full-shape analyses of quasar samples from future surveys like DESI.

The standard Λ Cold Dark Matter (ΛCDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant H0, the σ8–S8 tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the 5.0σ tension between the Planck CMB estimate of the Hubble constant H0 and the SH0ES collaboration measurements. After showing the H0 evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density Ωm, and the amplitude or rate of the growth of structure (σ8,fσ8). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the H0–S8 tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questions.