A5037465199- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Cosmology and Gravitation Theories
- Gamma-ray bursts and supernovae
- Stellar, planetary, and galactic studies
- Dark Matter and Cosmic Phenomena
- Astrophysics and Cosmic Phenomena
- Gaussian Processes and Bayesian Inference
- Radio Astronomy Observations and Technology
- Computational Physics and Python Applications
- Astronomical Observations and Instrumentation
- Geophysics and Gravity Measurements
- Adaptive optics and wavefront sensing
- Scientific Research and Discoveries
- Pulsars and Gravitational Waves Research
- Solar and Space Plasma Dynamics
- Black Holes and Theoretical Physics
- Particle physics theoretical and experimental studies
- Relativity and Gravitational Theory
- Phase Equilibria and Thermodynamics
- CCD and CMOS Imaging Sensors
- Pacific and Southeast Asian Studies
- Earth Systems and Cosmic Evolution
- Particle Detector Development and Performance
- Spatial and Panel Data Analysis
Sejong University
2021-2024
Korea Astronomy and Space Science Institute
2016-2022
Yonsei University
2019-2022
The Ohio State University
2022
Korea Institute for Advanced Study
2011-2017
Observatoire de Paris
2012
Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères
2010-2012
Sorbonne Université
2012
Centre National de la Recherche Scientifique
2012
Abstract Gaussian processes have been widely used in cosmology to reconstruct cosmological quantities a model-independent way. However, the validity of adopted mean function and hyperparameters, dependence results on choice not well explored. In this paper, we study effects underlying hyperparameter selection reconstruction distance moduli from type Ia supernovae. We show that an arbitrary affects reconstruction: zero leads unphysical best-fit ΛCDM biased reconstructions. propose marginalize...
We consider the possibility that dark sector of our Universe contains a negative cosmological constant dubbed $\ensuremath{\lambda}$. For such models to be viable, should contain an additional component responsible for late-time accelerated expansion rate ($X$). explore departure history these from concordance$\mathrm{\ensuremath{\Lambda}}$ cold matter ($\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$) model. large class models, is transient with nontrivial dependence on model parameters. All...
Our current understanding of the Universe is established through pristine measurements structure in cosmic microwave background (CMB) and distribution shapes galaxies tracing large scale (LSS) Universe. One key ingredient that underlies cosmological observables field sources observed assumed to be initially Gaussian with high precision. Nevertheless, a minimal deviation from Gaussianityis perhaps most robust theoretical prediction models explain Universe; itis necessarily present even...
Using measurements of H(z) and dA(z) from the Baryon Oscillation Spectroscopic Survey (BOSS) DR12 luminosity distances Joint Lightcurve Analysis (JLA) compilation supernovae (SN), we measure H0rd without any model assumption. Our measurement H0 rd = (10033.20+333.10−371.81 (SN) ± 128.19 (BAO)) km s−1 is consistent with Planck constrains for flat ΛCDM model. We also report that higher expansion history rates h(z) (among possibilities) as well lower-bound values result in better internal...
We combine model-independent reconstructions of the expansion history from latest Pantheon supernovae distance modulus compilation and measurements baryon acoustic oscillation to test some important aspects concordance model cosmology namely Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) metric flatness spatial curvature. then use reconstructed histories fit growth measurement redshift-space distortion obtain constraints on (${\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}$,...
The hot dense environment of the early universe is known to have produced large numbers baryons, photons, and neutrinos. These extreme conditions may also other long-lived species, including new light particles (such as axions or sterile neutrinos) gravitational waves. effects any such relics can be observed through their unique imprint in cosmic microwave background (CMB), large-scale structure, primordial element abundances, are important determining initial universe. We argue that future...
Analysis of large galaxy surveys requires confidence in the robustness numerical simulation methods. The simulations are used to construct mock catalogs validate data analysis pipelines and identify potential systematics. We compare three $N$-body codes, ABACUS, GADGET, SWIFT, investigate regimes which their results agree. run at different mass resolutions, $6.25\times10^{8}$, $2.11\times10^{9}$, $5.00\times10^{9}~h^{-1}$M$_{\odot}$, matching phases reduce noise within comparisons. find...
Based on a formalism introduced in our previous work, we reconstruct the phenomenological function $G_{\rm eff}(z)$ describing deviations from General Relativity (GR) model-independent manner. In this alternative approach, model $\mu\equiv G_\mathrm{eff}/G$ as Gaussian process and use forecasted growth-rate measurements stage-IV survey to its shape for two different toy models. We follow two-step procedure: (i) first background expansion history Supernovae (SNe) Baryon Acoustic Oscillation...
Galaxies accrete their mass by means of both smooth accretion from the cosmic web, and mergers smaller entities. We wish to quantify respective role these two modes accretion, which could determine morphological types galaxies observed today. Multi-zoom cosmological simulations are used estimate as a function time evolution in bound systems, for dark matter well baryons. The baryonic contents haloes studied. Merger histories followed external density, different ways is assembled stellar...
Reconstructing the expansion history of Universe from type Ia supernovae data, we fit growth rate measurements and put model-independent constraints on some key cosmological parameters, namely, $\Omega_\mathrm{m},\gamma$, $\sigma_8$. The are consistent with those concordance model within framework general relativity, but current quality data is not sufficient to rule out modified gravity models. Adding condition that dark energy density should be positive at all redshifts, independently its...
The Horizon Run 4 is a cosmological $N$-body simulation designed for the study of coupled evolution between galaxies and large-scale structures Universe, test galaxy formation models. Using $6300^3$ gravitating particles in cubic box $L_{\rm box} = 3150 ~h^{-1}{\rm Mpc}$, we build dense forest halo merger trees to trace history with mass resolution scale down $M_s 2.7 \times 10^{11} h^{-1}{\rm M_\odot}$. We set particle data, which can serve as testbeds comparison models gravitational...
The form of the primordial power spectrum (PPS) cosmological scalar (matter density) perturbations is not yet constrained satisfactorily in spite tremendous amount information from Cosmic Microwave Background (CMB) data. While a smooth power-law-like PPS consistent with CMB data, some small non-smooth features at large scales can also fit temperature and polarization data similar statistical evidence. Future surveys cannot help distinguish all such models due to cosmic variance angular...
Abstract We examine the Pantheon supernovae distance data compilation in a model independent analysis to test validity of cosmic history reconstructions beyond concordance ΛCDM cosmology. Strong deviations are allowed by at z ≳ 1 reconstructed Hubble parameter, Om diagnostic, and dark energy equation state. explore three interpretations: 1) possibility true cosmology being far from ΛCDM, 2) property evolution, 3) survey selection effects. The strong (and theoretically problematic) vanish...
Using redshift space distortion data, we perform model-independent reconstructions of the growth history matter inhomogeneity in expanding Universe using two methods: crossing statistics and Gaussian processes. We then reconstruct corresponding background expansion fit it to type Ia supernovae putting constraints on $(\Omega_\mathrm{m,0},\sigma_{8,0})$. The results obtained are consistent with concordance flat-$\Lambda$CDM model General Relativity as gravity theory given current quality data.
We study the properties of dark matter haloes in a wide range modified gravity models, namely, $f(R)$, DGP, and interacting energy models. effects on internal haloes, such as spin structural parameters. find that $f(R)$ enhance median value Bullock parameter, but could not detect for DGP coupled energy. also yields lower sphericity oblateness, while has opposite effect. However, these are very small. then interaction rate different gravity, only strongly models rate. quantify enhancement...
Starting from a very accurate model for density-in-cells statistics of dark matter based on large deviation theory, bias the tracer density in spheres is formulated. It adopts mean relation quadratic to relate log-densities those mass-weighted haloes real and redshift space. The validity parametrised established using parametrisation-independent extraction function. This average then combined with PDF, neglecting any scatter around it: it nevertheless yields an excellent densities-in-cells...
Large deviation statistics is implemented to predict the of cosmic densities in cylinders applicable photometric surveys. It yields few percent accurate analytical predictions for one-point probability distribution function (PDF) concentric or compensated cylinders; and also captures density-dependence their angular clustering (cylinder bias). All are found be excellent agreement with cosmological simulation Horizon Run 4 quasi-linear regime where standard perturbation theory normally breaks...
ABSTRACT Accurate estimation of the Hubble constant, and other cosmological parameters, from distances measured by cosmic gravitational wave sirens requires sufficient allowance for dark energy evolution. We demonstrate how model-independent statistical methods, specifically Gaussian process regression, can remove bias in reconstruction H(z), be combined to model independently with supernova distances. This allows stringent tests both H0 Λ cold matter, detect unrecognized systematics. also...
Combining supernovae, baryon acoustic oscillations, and redshift-space distortions data from the next generation of (stage-IV) cosmological surveys, we aim to reconstruct expansion history up large redshifts using forward-modeling ${f}_{\mathrm{DE}}(z)={\ensuremath{\rho}}_{\mathrm{DE}}(z)/{\ensuremath{\rho}}_{\mathrm{DE},0}$ with Gaussian processes (GP). In order quantities at high where few or no are available, adopt a new approach GP which enforces following minimal assumptions: (a) Our...
Simple parameter-free analytic bias functions for the two-point correlation of densities in spheres at large separation are presented. These generalize so-called Kaiser to mildly non-linear regime arbitrary density contrasts. The derivation is carried out context deviation statistics while relying on spherical collapse model. A logarithmic transformation provides a saddle approximation which valid whole range and shown be accurate against 30 Gpc cube state-of-the-art Horizon Run 4...
We have developed a frequentist approach for model selection which determines the consistency between any cosmological and data using distribution of likelihoods from iterative smoothing method. Using this approach, we shown how confidently can conclude whether support given without comparison to different one. In current work, compare our with conventional Bayesian based on estimation evidence nested sampling. use simulated future Roman (formerly WFIRST)-like type Ia supernovae in analysis....
The expansion of the Universe is understood to have accelerated during two epochs: in its very first moments a period Inflation and much more recently, at $z < 1$, when Dark Energy hypothesized drive cosmic acceleration. undiscovered mechanisms behind these epochs represent some most important open problems fundamental physics. large cosmological volume $2 z 5$, together with ability efficiently target high-$z$ galaxies known techniques, enables gains study Energy. A future spectroscopic...