chengzor

• Vikenes, Vetle Amundsen; Ruan, Cheng-Zong & Mota, David (2025). An emulation-based model for the projected correlation function. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 696. doi: 10.1051/0004-6361/202452174. Full text in Research Archive Show summary

  Data from the ongoing Euclid survey will map out billions of galaxies in the Universe, covering more than a third of the sky. This data will provide a wealth of information about the large-scale structure of the Universe and will have a significant impact on cosmology in the coming years. In this paper we introduce an emulator-based halo model approach to forward-modeling the relationship between cosmological parameters and the projected galaxy-galaxy two-point correlation function (2PCF). Utilizing the large A BACUS S UMMIT simulation suite, we emulated the 2PCF by generating mock-galaxy catalogs within the halo occupation distribution (HOD) framework. Our emulator is designed to predict the 2PCF over scales 0.1 ≤  r /( h −1  Mpc)≤105, from which we derived the projected correlation function, independent of redshift space distortions. We demonstrate that the emulator accurately predicts the projected correlation function over scales 0.5 ≤  r ⊥ /( h −1  Mpc)≤40 given a set of cosmological and HOD parameters. We then employed this model in a parameter inference analysis, showcasing its ability to constrain cosmological parameters. Our findings indicate that the projected correlation function places only weak constraints on several cosmological parameters due to its intrinsic lack of information; additional clustering statistics are necessary to better probe the underlying cosmology. Despite the simplified covariance matrix used in the likelihood model, the posterior distributions of several cosmological parameters remain broad, underscoring the need for a more comprehensive approach.

• Vogt, S.M.L.; Bocquet, S.; Davies, C.T.; Mohr, J.J.; Schmidt, F. & Ruan, Cheng-Zong [Show all 55 contributors for this article] (2025). Constraints on f (R) gravity from thermal-Sunyaev-Zel'dovich-effect-selected SPT galaxy clusters and weak lensing mass calibration from DES and HST. Physical Review D. ISSN 2470-0010. 111(4). doi: 10.1103/PhysRevD.111.043519. Full text in Research Archive Show summary

  We present constraints on the 𝑓⁡(𝑅) gravity model using a sample of 1005 galaxy clusters in the redshift range 0.25–1.78 that have been selected through the thermal Sunyaev-Zel’dovich effect from South Pole Telescope data and subjected to optical and near-infrared confirmation with the multicomponent matched filter algorithm. We employ weak gravitational lensing mass calibration from the Dark Energy Survey Year 3 data for 688 clusters at 𝑧 <0.95 and from the Hubble Space Telescope for 39 clusters with 0.6 <𝑧 <1.7. Our cluster sample is a powerful probe of 𝑓⁡(𝑅) gravity, because this model predicts a scale-dependent enhancement in the growth of structure, which impacts the halo mass function (HMF) at cluster mass scales. To account for these modified gravity effects on the HMF, our analysis employs a semianalytical approach calibrated with numerical simulations. Combining calibrated cluster counts with primary cosmic microwave background temperature and polarization anisotropy measurements from the Planck 2018 release, we derive robust constraints on the 𝑓⁡(𝑅) parameter 𝑓𝑅⁢0. Our results, log10⁡|𝑓𝑅⁢0| <−5.32 at the 95% credible level, are the tightest current constraints on 𝑓⁡(𝑅) gravity from cosmological scales. This upper limit rules out 𝑓⁡(𝑅)-like deviations from general relativity that result in more than a ∼20% enhancement of the cluster population on mass scales 𝑀200⁢c>3×1014⁢𝑀⊙.

• Mauland-Hus, Renate; Winther, Hans Arnold & Ruan, Cheng-Zong (2024). Sesame: A power spectrum emulator pipeline for beyond-ΛCDM models. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 685. doi: 10.1051/0004-6361/202347892. Full text in Research Archive Show summary

  The mysterious nature of the dark sector of the Λ-cold-dark-matter (ΛCDM) model is one of the main motivators behind the study of alternative cosmological models. A central quantity of interest for these models is the matter power spectrum, which quantifies structure formation on various scales and can be cross-validated through theory, simulations, and observations. Here, we present a tool that can be used to create emulators for the non-linear matter power spectrum, and similar global clustering statistics, for models beyond ΛCDM with very little computation effort and without the need for supercomputers. We use fast approximate N-body simulations to emulate the boost, B(k, z) = Pbeyond − ΛCDM(k, z)/PΛCDM(k, z), and then rely on existing high-quality emulators made for ΛCDM to isolate Pbeyond − ΛCDM(k, z). Since both the ΛCDM and beyond-ΛCDM models are simulated in our approach, some of the lack of power on small scales due to the low force-resolution in the simulations is factored out, allowing us to extend the emulator to k ∼ 3 − 5 h Mpc−1 and still maintain good accuracy. In addition, errors from the simulation and emulation process can easily be estimated and factored into the covariance when using the emulator on data. As an example of using the pipeline, we create an emulator for the well-studied f(R) model with massive neutrinos, using approximately 3000 CPU hours of computation time. Provided with the paper is a fully functioning pipeline that generates parameter samples, runs a Boltzmann solver to produce initial conditions, runs the simulations, and then gathers all the data and runs it through a machine learning module to develop the emulator. This tool, named Sesame, can be used by anyone to generate a power spectrum emulator for the cosmological model of their choice.

• Bose, B.; Gupta, A. Sen; Fiorini, B.; Brando, G.; Hassani, Farbod & Baker, T. [Show all 12 contributors for this article] (2024). Matter power spectra in modified gravity: a comparative study of approximations and N-body simulations. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 536(1), p. 664–683. doi: 10.1093/mnras/stae2562. Full text in Research Archive
• Rodriguez-Meza, Mario A.; Aviles, Alejandro; Noriega, Hernan E.; Ruan, Cheng-Zong; Li, Baojiu & Vargas-Magaña, Mariana [Show all 7 contributors for this article] (2024). fkPT: constraining scale-dependent modified gravity with the full-shape galaxy power spectrum. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(3). doi: 10.1088/1475-7516/2024/03/049. Full text in Research Archive Show summary

  Modified gravity models with scale-dependent linear growth typically exhibit an enhancement in the power spectrum beyond a certain scale. The conventional methods for extracting cosmological information usually involve inferring modified gravity effects via Redshift Space Distortions (RSD), particularly through the time evolution of fσ8. However, classical galaxy RSD clustering analyses encounter difficulties in accurately capturing the spectrum's enhanced power, which is better obtained from the broad-band power spectrum. In this sense, full-shape analyses aim to consider survey data using comprehensive and precise models of the whole power spectrum. Yet, a major challenge in this approach is the slow computation of non-linear loop integrals for scale-dependent modified gravity, precluding the estimation of cosmological parameters using Markov Chain Monte Carlo methods. Based on recent studies, in this work we develop a perturbation theory tailored for Modified Gravity, or analogous scenarios introducing additional scales, such as in the presence of massive neutrinos. Our approach only needs the calculation of the scale-dependent growth rate f(k,t) and the limit of the perturbative kernels at large scales. We called this approximate technique as fk-Perturbation Theory and implemented it into the code fkpt, capable of computing the redshift space galaxy power spectrum in a fraction of a second. We validate our modeling and code with the f(R) theory MG-GLAM and General Relativity NSeries sets of simulations.

• Song, Yanling; Hu, Bin; Ruan, Cheng-Zong; Moretti, Chiara & Monaco, Pierluigi (2024). An implementation of nDGP gravity in Pinocchio. Journal of Cosmology and Astroparticle Physics (JCAP). 2024(7). doi: 10.1088/1475-7516/2024/07/093. Full text in Research Archive Show summary

  In this paper we investigate dark matter structure formation in the normal branch of the Dvali-Gabadadze-Porrati (nDGP) model using the PINOCCHIO algorithm. We first present 2nd order Lagrangian perturbation theory for the nDGP model, which shows that the 1st- and 2nd-order growth functions in nDGP are larger than those in ΛCDM. We then examine the dynamics of ellipsoidal collapse in nDGP, which is accelerated compared to ΛCDM due to enhanced gravitational interactions. Running the nDGP-PINOCCHIO code with a box size of 512 Mpc h^(−1) and 1024^3 particles, we analyze the statistical properties of the output halo catalogs, including the halo power spectrum and halo mass function. The calibrated PINOCCHIO halo power spectrum agrees with N-body simulations within 5% in the comoving wavenumber range k < 0.3 (h Mpc^(−1)) at redshift z = 0. The agreement is extended to smaller scales for higher redshifts. For the cumulative halo mass function, the agreement between N-body and PINOCCHIO is also within the simulation scatter.

• Ruan, Cheng-Zong; Cuesta-Lazaro, Carolina; Eggemeier, Alexander; Li, Baojiu; Baugh, Carlton M. & Arnold, Christian [Show all 10 contributors for this article] (2023). An emulator-based halo model in modified gravity -I. The halo concentration-mass relation and density profile. Monthly notices of the Royal Astronomical Society. ISSN 0035-8711. 527(2), p. 2490–2507. doi: 10.1093/mnras/stad3021. Full text in Research Archive

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