arXiv subjects

Yann Rasera

Publications and source records attributed to Yann Rasera.

At least 19 recordsLinked to original sources

arXiv2026

PySCo-EFT and ECOSMOG-EFT: a tandem of N-body simulation codes for the Effective Field Theory of Dark Energy

Modified gravity theories constitute viable alternatives to the standard cosmological model for explaining the observed late-time accelerated expansion of the Universe. The Effective Field Theory of Dark Energy (EFTofDE) is an efficient framework to describe a wide range of such theories with a limited number of parameters. To robustly constrain them by comparison with clustering and weak lensing data from upcoming large-scale structure surveys, high-resolution cosmological N-body simulations are required to obtain accurate predictions for the matter distribution on non-linear scales. We introduce two new N-body simulation codes for EFTofDE cosmologies: PySCo-EFT, a Python-based particle mesh code, and ECOSMOG-EFT, a RAMSES-based code with adaptive mesh refinement. We consider Horndeski models with a luminal gravitational wave speed. We use iterative solvers and multigrid schemes to solve for the additional scalar field equation in both codes, incorporating the non-linear Vainshtein screening mechanism. We present validation and convergence tests of the codes. We obtain a sub-0.5 percent agreement with linear theory on large scales and a similar agreement between the two codes on non-linear scales. The dominant numerical effects on the matter-power-spectrum boost are mass resolution, finite-volume effects, refinement threshold, and starting redshift, but they are limited to below 2% at the largest wavenumbers (k=10 h/Mpc) for the range of tested values. We investigate the impact of the EFTofDE parameters on the matter-power-spectrum ratios between EFTofDE and $\Lambda$CDM cases. Depending on the EFTofDE parameters, the screening plays a negligible or dominant role compared to the linearised field equations. Our codes provide tools for generating fast and accurate predictions of the impact of the EFTofDE on the clustering of matter, incorporating non-linear screening.

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arXiv2023

The e-MANTIS emulator: fast predictions of the non-linear matter power spectrum in $f(R)$CDM cosmology

In order to probe modifications of gravity at cosmological scales, one needs accurate theoretical predictions. N-body simulations are required to explore the non-linear regime of structure formation but are very time consuming. In this work, we release a new public emulator, dubbed e-MANTIS, that performs an accurate and fast interpolation between the predictions of $f(R)$ modified gravity cosmological simulations, run with ECOSMOG. We sample a wide 3D parameter space given by the current background scalar field value $10^{-7}<\left|f_{R_0}\right|<10^{-4}$, matter density $0.24<\Omega_\mathrm{m}<0.39$, and primordial power spectrum normalisation $0.6<\sigma_8<1.0$, with 110 points sampled from a Latin Hypercube. For each model we perform pairs of $f(R)$CDM and $\Lambda$CDM simulations covering an effective volume of $\left(560 \, h^{-1}\mathrm{Mpc}\right)^3$ with a mass resolution of $\sim 2 \times 10^{10} h^{-1} M_\odot$. We build an emulator for the matter power spectrum boost $B(k)=P_{f(R)}(k)/P_{\Lambda\mathrm{CDM}}(k)$ using a Gaussian Process Regression method. The boost is mostly independent of $h$, $n_{s}$, and $\Omega_{b}$, which reduces the dimensionality of the relevant cosmological parameter space. Additionally, it is more robust against statistical and systematic errors than the raw power spectrum, thus strongly reducing our computational needs. According to our dedicated study of numerical systematics, the resulting emulator has an estimated maximum error of $3\%$ across the whole cosmological parameter space, for scales $0.03 \ h\mathrm{Mpc}^{-1} < k < 7 \ h\mathrm{Mpc}^{-1}$, and redshifts $0 < z < 2$, while in most cases the accuracy is better than $1\%$. Such an emulator could be used to constrain $f(R)$ gravity with weak lensing analyses

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arXiv2022

The short ionizing photon mean free path at z=6 in Cosmic Dawn III, a new fully-coupled radiation-hydrodynamical simulation of the Epoch of Reionization

Recent determinations of the mean free path of ionising photons (mfp) in the intergalactic medium (IGM) at $\rm z=6$ are lower than many theoretical predictions. To gain insight into this issue, we investigate the evolution of the mfp in our new massive fully coupled radiation hydrodynamics cosmological simulation of reionization: Cosmic Dawn III (CoDaIII). CoDaIII's scale ($\rm 94^3 \, cMpc^3$) and resolution ($\rm 8192^3$ grid) make it particularly suitable to study the evolution of the IGM during Reionization. The simulation was performed with RAMSES-CUDATON on Summit, and used 131072 processors coupled to 24576 GPUs, making it the largest Reionization simulation, and largest RAMSES simulation ever performed. A superior agreement with global constraints on Reionization is obtained in CoDaIII over CoDaII especially for the evolution of the neutral hydrogen fraction and the cosmic photo-ionization rate, thanks to an improved calibration, later end of reionization ($\rm z=5.6$), and higher spatial resolution. Analyzing the mfp, we find that CoDaIII reproduces the most recent observations very well, from $\rm z=6$ to $\rm z=4.6$. We show that the distribution of the mfp in CoDaIII is bimodal, with short (neutral) and long (ionized) mfp modes, respectively, due to the patchiness of reionization and the co-existence of neutral versus ionized regions during Reionization. The neutral mode peaks at sub-kpc to kpc scales of mfp, while the ionized mode peak evolves from $\rm 0.1 Mpc/h$ at $\rm z=7$ to $\sim 10$ Mpc/h at $\rm z=5.2$. Computing the mfp as the average of the ionized mode provides the best match to the recent observational determinations. The distribution reduces to a single neutral (ionized) mode at $\rm z>13$ ($\rm z<5$).

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arXiv2022

Detectability of the gravitational redshift effect from the asymmetric galaxy clustering

It has been recently recognized that the observational relativistic effects, mainly arising from the light propagation in an inhomogeneous universe, induce the dipole asymmetry in the cross-correlation function of galaxies. In particular, the dipole asymmetry at small scales is shown to be dominated by the gravitational redshift effects. In this paper, we exploit a simple analytical description for the dipole asymmetry in the cross-correlation function valid at quasi-linear regime. In contrast to the previous model, a new prescription involves only one dimensional integrals, providing a faster way to reproduce the results obtained by Saga et al. (2020). Using the analytical model, we discuss the detectability of the dipole signal induced by the gravitational redshift effect from upcoming galaxy surveys. The gravitational redshift effect at small scales enhances the signal-to-noise ratio (S/N) of the dipole, and in most of the cases considered, the S/N is found to reach a maximum at $z\approx0.5$. We show that current and future surveys such as DESI and SKA provide an idealistic data set, giving a large S/N of $10\sim 20$. Two potential systematics arising from off-centered galaxies are also discussed (transverse Doppler effect and diminution of the gravitational redshift effect), and their impacts are found to be mitigated by a partial cancellation between two competitive effects. Thus, the detection of the dipole signal at small scales is directly linked to the gravitational redshift effect, and should provide an alternative route to test gravity.

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arXiv2021

Cosmological test of local position invariance from the asymmetric galaxy clustering

The local position invariance (LPI) is one of the three major pillars of Einstein equivalence principle, ensuring the space-time independence on the outcomes of local experiments. The LPI has been tested by measuring the gravitational redshift effect in various depths of gravitational potentials. We propose a new cosmological test of the LPI by observing the asymmetry in the cross-correlation function between different types of galaxies, which predominantly arises from the gravitational redshift effect induced by the gravitational potential of halos at which the galaxies reside. We show that the ongoing and upcoming galaxy surveys can give a fruitful constraint on the LPI-violating parameter, $\alpha$, at distant universes (redshift $z\sim0.1-1.8$) over the cosmological scales (separation $s\sim5-10\, {\rm Mpc}/h$) that have not yet been explored, finding that the expected upper limit on $\alpha$ can reach $0.03$.

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arXiv2021

Gravitation And the Universe from large Scale-Structures: The GAUSS mission concept

Today, thanks in particular to the results of the ESA Planck mission, the concordance cosmological model appears to be the most robust to describe the evolution and content of the Universe from its early to late times. It summarizes the evolution of matter, made mainly of dark matter, from the primordial fluctuations generated by inflation around $10^{-30}$ second after the Big-Bang to galaxies and clusters of galaxies, 13.8 billion years later, and the evolution of the expansion of space, with a relative slowdown in the matter-dominated era and, since a few billion years, an acceleration powered by dark energy. But we are far from knowing the pillars of this model which are inflation, dark matter and dark energy. Comprehending these fundamental questions requires a detailed mapping of our observable Universe over the whole of cosmic time. The relic radiation provides the starting point and galaxies draw the cosmic web. JAXA's LiteBIRD mission will map the beginning of our Universe with a crucial test for inflation (its primordial gravity waves), and the ESA Euclid mission will map the most recent half part, crucial for dark energy. The mission concept, described in this White Paper, GAUSS, aims at being a mission to fully map the cosmic web up to the reionization era, linking early and late evolution, to tackle and disentangle the crucial degeneracies persisting after the Euclid era between dark matter and inflation properties, dark energy, structure growth and gravitation at large scale.

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arXiv2020

Cosmological Model Parameter Dependence of the Matter Power Spectrum Covariance from the DEUS-PUR $Cosmo$ Simulations

Future galaxy surveys will provide accurate measurements of the matter power spectrum across an unprecedented range of scales and redshifts. The analysis of these data will require one to accurately model the imprint of non-linearities of the matter density field. In particular, these induce a non-Gaussian contribution to the data covariance that needs to be properly taken into account to realise unbiased cosmological parameter inference analyses. Here, we study the cosmological dependence of the matter power spectrum covariance using a dedicated suite of N-body simulations, the Dark Energy Universe Simulation - Parallel Universe Runs (DEUS-PUR) {\it Cosmo}. These consist of 512 realizations for 10 different cosmologies where we vary the matter density $Ω_m$, the amplitude of density fluctuations $σ_8$, the reduced Hubble parameter $h$ and a constant dark energy equation of state $w$ by approximately $10\%$. We use these data to evaluate the first and second derivatives of the power spectrum covariance with respect to a fiducial $Λ$CDM cosmology. We find that the variations can be as large as $150\%$ depending on the scale, redshift and model parameter considered. By performing a Fisher matrix analysis we explore the impact of different choices in modelling the cosmological dependence of the covariance. Our results suggest that fixing the covariance to a fiducial cosmology can significantly affect the recovered parameter errors and that modelling the cosmological dependence of the variance while keeping the correlation coefficient fixed can alleviate the impact of this effect.

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arXiv2020

Modelling the asymmetry of the halo cross-correlation function with relativistic effects at quasi-linear scales

The observed galaxy distribution via galaxy redshift surveys appears distorted due to redshift-space distortions (RSD). While one dominant contribution to RSD comes from the Doppler effect induced by the peculiar velocity of galaxies, the relativistic effects, including the gravitational redshift effect, are recently recognized to give small but important contributions. Such contributions lead to an asymmetric galaxy clustering along the line of sight, and produce non-vanishing odd multipoles when cross-correlating between different biased objects. However, non-zero odd multipoles are also generated by the Doppler effect beyond the distant-observer approximation, known as the wide-angle effect, and at quasi-linear scales, the interplay between wide-angle and relativistic effects becomes significant. In this paper, based on the formalism developed by Taruya et al., we present a quasi-linear model of the cross-correlation function taking a proper account of both the wide-angle and gravitational redshift effects, as one of the major relativistic effects. Our quasi-linear predictions of the dipole agree well with simulations even at the scales below $20\,h^{-1}\,$Mpc, where non-perturbative contributions from the halo potential play an important role, flipping the sign of the dipole amplitude. When increasing the bias difference and redshift, the scale where the sign flip happens is shifted to a larger scale. We derive a simple approximate formula to quantitatively account for the behaviors of the sign flip.

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arXiv2020

Phase-space structure of cold dark matter halos inside splashback: multi-stream flows and self-similar solution

Using the motion of accreting particles onto halos in cosmological $N$-body simulations, we study the radial phase-space structures of cold dark matter (CDM) halos. In CDM cosmology, formation of virialized halos generically produces radial caustics, followed by multi-stream flows of accreted dark matter inside the halos. In particular, the radius of the outermost caustic called the splashback radius exhibits a sharp drop in the slope of the density profile. Here, we focus on the multi-stream structure of CDM halos inside the splashback radius. To analyze this, we use and extend the SPARTA algorithm developed by Diemer. By tracking the particle trajectories accreting onto the halos, we count their number of apocenter passages, which is then used to reveal the multi-stream flows of the dark matter particles. The resultant multi-stream structure in radial phase space is compared with the prediction of the self-similar solution by Fillmore & Goldreich for each halo. We find that $\sim30\%$ of the simulated halos satisfy our criteria to be regarded as being well fitted to the self-similar solution. The fitting parameters in the self-similar solution characterizes physical properties of the halos, including the mass accretion rate and the size of the outermost caustic (i.e., the splashback radius). We discuss in detail the correlation of these fitting parameters and other measures directly extracted from the $N$-body simulation.

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arXiv2020

Ray tracing the integrated Sachs-Wolfe effect through the light cones of the Dark Energy Universe Simulation -- Full Universe Runs

The late integrated Sachs-Wolfe (ISW) effect correlates the Cosmic Microwave Background (CMB) temperature anisotropies with foreground cosmic large-scale structures. As the correlation depends crucially on the growth history in the era of dark energy, it is a key observational probe for constraining the cosmological model. Here we present a detailed study based on full-sky and deep light cones generated from very large volume numerical N-body simulations, which allow us to avoid the use of standard replica techniques, while capturing the entirety of the late ISW effect on the large scales. We post-process the light cones using an accurate ray-tracing method and construct full-sky maps of the ISW temperature anisotropy for three different dark energy models. We quantify in detail the extent to which the ISW effect can be used to discriminate between different dark energy scenarios when cross-correlated with the matter distribution or the CMB lensing potential. We also investigate the onset of non-linearities, the so-called Rees-Sciama effect which provides a complementary probe of the dark sector. We find the signal of the lensing-lensing and ISW-lensing correlation of the three dark energy models to be consistent with measurements from the Planck satellite. Future surveys of the large-scale structures may provide cross-correlation measurements that are sufficiently precise to distinguish the signal of these models. Our methodology is very general and can be applied to any dark energy or modified gravity scenario as long as the metric seen by photons can still be characterized by a Weyl potential.

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arXiv2019

Wide-angle redshift-space distortions at quasi-linear scales: cross-correlation functions from Zel'dovich approximation

Redshift-space distortions (RSD) in galaxy redshift surveys generally break both the isotropy and homogeneity of galaxy distribution. While the former aspect is particularly highlighted as a probe of growth of structure induced by gravity, the latter aspect, often quoted as wide-angle RSD but ignored in most of the cases, will become important and critical to account for as increasing the statistical precision in next-generation surveys. However, the impact of wide-angle RSD has been mostly studied using linear perturbation theory. In this paper, employing the Zel'dovich approximation, i.e., first-order Lagrangian perturbation theory for gravitational evolution of matter fluctuations, we present a quasi-linear treatment of wide-angle RSD, and compute the cross-correlation function. The present formalism consistently reproduces linear theory results, and can be easily extended to incorporate relativistic corrections (e.g., gravitational redshift).

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arXiv2019

Average Dark Matter Halo Sparsity Relations as Consistency Check of Mass Estimates in Galaxy Cluster Samples

The dark matter halo sparsity provides a direct observational proxy of the halo mass profile, characterizing halos in terms of the ratio of masses within radii which enclose two different overdensities. Previous numerical simulation analyses have shown that at a given redshift the halo sparsity carries cosmological information encoded in the halo mass profile. Moreover, its ensemble averaged value can be inferred from prior knowledge of the halo mass function at the overdensities of interest. Here, we present a detailed study of the ensemble average properties of the halo sparsity. In particular, using halo catalogs from high-resolution N-body simulations, we show that its ensemble average value can be estimated from the ratio of the averages of the inverse halo masses as well as the ratio of the averages of the halo masses at the overdensity of interests. This can be relevant for galaxy clusters data analyses. As an example, we have estimated the average sparsity properties of galaxy clusters from the LoCuSS and HIFLUGCS datasets respectively. The results suggest that the expected consistency of the different average sparsity estimates can provide a test of the robustness of mass measurements in galaxy cluster samples.

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arXiv2018

Imprints of relativistic effects on the asymmetry of the halo cross-correlation function: from linear to non-linear scales

The apparent distribution of large-scale structures in the universe is sensitive to the velocity/potential of the sources as well as the potential along the line-of-sight through the mapping from real space to redshift space (redshift-space distortions, RSD). Since odd multipoles of the halo cross-correlation function vanish when considering standard Doppler RSD, the dipole is a sensitive probe of relativistic and wide-angle effects. We build a catalogue of ten million haloes (Milky-Way size to galaxy-cluster size) from the full-sky light-cone of a new "RayGalGroupSims" N-body simulation which covers a volume of ($2.625~h^{-1}$Gpc)$^3$ with $4096^3$ particles. Using ray-tracing techniques, we find the null geodesics connecting all the sources to the observer. We then self-consistently derive all the relativistic contributions (in the weak-field approximation) to RSD: Doppler, transverse Doppler, gravitational, lensing and integrated Sachs-Wolfe. It allows us, for the first time, to disentangle all contributions to the dipole from linear to non-linear scales. At large scale, we recover the linear predictions dominated by a contribution from the divergence of neighbouring line-of-sights. While the linear theory remains a reasonable approximation of the velocity contribution to the dipole at non-linear scales it fails to reproduce the potential contribution below $30-60~h^{-1}$Mpc (depending on the halo mass). At scales smaller than $\sim 10~h^{-1}$Mpc, the dipole is dominated by the asymmetry caused by the gravitational redshift. The transition between the two regimes is mass dependent as well. We also identify a new non-trivial contribution from the non-linear coupling between potential and velocity terms.

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arXiv2018

The environmental dependence of the baryon acoustic peak in the Baryon Oscillation Spectroscopic Survey CMASS sample

The environmental dependence of galaxy clustering encodes information about the physical processes governing the growth of cosmic structure. We analyze the baryon acoustic peak as a function of environment in the galaxy correlation function of the Baryon Oscillation Spectroscopic Survey CMASS sample. Dividing the sample into three subsets by smoothed local overdensity, we detect acoustic peaks in the six separate auto-correlation and cross-correlation functions of the sub-samples. Fitting models to these correlation functions, calibrated by mock galaxy and dark matter catalogues, we find that the inferred distance scale is independent of environment, and consistent with the result of analyzing the combined sample. The shape of the baryon acoustic feature, and the accuracy of density-field reconstruction in the Zeldovich approximation, varies with environment. By up-weighting underdense regions and down-weighting overdense regions in their contribution to the full-sample correlation function, by up to 50%, we achieve a fractional improvement of a few per cent in the precision of baryon acoustic oscillation fits to the CMASS data and mock catalogues: the scatter in the preferred-scale fits to the ensemble of mocks improves from 1.45% to 1.34% (pre-reconstruction) and 1.03% to 1.00% (post-reconstruction). These results are consistent with the notion that the acoustic peak is sharper in underdense environments.

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arXiv2017

Precision cosmology with redshift-space bispectrum: a perturbation theory based model at one-loop order

The large-scale matter distribution in the late-time Universe exhibits gravity-induced non-Gaussianity, and the bispectrum, three-point cumulant is expected to contain significant cosmological information. In particular, the measurement of the bispectrum helps to tighten the constraints on dark energy and modified gravity through the redshift-space distortions (RSD). In this paper, extending the work by Taruya, Nishimichi & Saito (2010, Phys.Rev.D 82, 063522), we present a perturbation theory (PT) based model of redshift-space matter bispectrum that can keep the non-perturbative damping effect under control. Characterizing this non-perturbative damping by a univariate function with single free parameter, the PT model of the redshift-space bispectrum is tested against a large set of cosmological $N$-body simulations, finding that the predicted monopole and quadrupole moments are in a good agreement with simulations at the scales of baryon acoustic oscillations (well beyond the range of agreement of standard PT). The validity of the univariate ansatz of the damping effect is also examined, and with the PT calculation at next-to-leading order, the fitted values of the free parameter is shown to consistently match those obtained from the PT model of power spectrum by Taruya, Nishimichi & Saito (2010).

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arXiv2015

Small scale clustering of late forming dark matter

We perform a study of the nonlinear clustering of matter in the late-forming dark matter (LFDM) scenario in which dark matter results from the transition of a nonminimally coupled scalar field from radiation to collisionless matter. A distinct feature of this model is the presence of a damped oscillatory cutoff in the linear matter power spectrum at small scales. We use a suite of high-resolution N-body simulations to study the imprints of LFDM on the nonlinear matter power spectrum, the halo mass and velocity functions and the halo density profiles. The model largely satisfies high-redshift matter power spectrum constraints from Lyman-$α$ forest measurements, while it predicts suppressed abundance of low-mass halos ($\sim 10^{9}-10^{10}$ h$^{-1}$ M$_\odot$) at all redshifts compared to a vanilla $Λ$CDM model. The analysis of the LFDM halo velocity function shows a better agreement than the $Λ$CDM prediction with the observed abundance of low-velocity galaxies in the local volume. Halos with mass $M\gtrsim 10^{11}$ h$^{-1}$ M$_\odot$ show minor departures of the density profiles from $Λ$CDM expectations, while smaller-mass halos are less dense, consistent with the fact that they form later than their $Λ$CDM counterparts.

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arXiv2014

Matter Power Spectrum Covariance Matrix from the DEUS-PUR ΛCDM simulations: Mass Resolution and non-Gaussian Errors

The upcoming generation of galaxy surveys will probe the distribution of matter in the universe with unprecedented accuracy. Measurements of the matter power spectrum at different scales and redshifts will provide stringent constraints on the cosmological parameters. However, on non-linear scales this will require an accurate evaluation of the covariance matrix. Here, we compute the covariance matrix of the 3D matter density power spectrum for the concordance $Λ$CDM cosmology from an ensemble of N-body simulations of the Dark Energy Universe Simulation - Parallel Universe Runs (DEUS-PUR). This consists of 12288 realisations of a $(656\,h^{-1}\,\textrm{Mpc})^3$ simulation box with $256^3$ particles. We combine this set with an auxiliary sample of 96 simulations of the same volume with $1024^3$ particles. We find N-body mass resolution effect to be an important source of systematic errors on the covariance at high redshift and small intermediate scales. We correct for this effect by introducing an empirical statistical method which provide an accurate determination of the covariance matrix over a wide range of scales including the Baryon Oscillations interval. Contrary to previous studies that used smaller N-body ensembles, we find the power spectrum distribution to significantly deviate from expectations of a Gaussian random density field at $k\gtrsim 0.25\,h\,\textrm{Mpc}^{-1}$ and $z<0.5$. This suggests that in the case of finite volume surveys an unbiased estimate of the ensemble averaged band power at these scales and redshifts may require a careful assessment of non-Gaussian errors more than previously considered.

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arXiv2014

Probing dark energy models with extreme pairwise velocities of galaxy clusters from the DEUS-FUR simulations

Observations of colliding galaxy clusters with high relative velocity probe the tail of the halo pairwise velocity distribution with the potential of providing a powerful test of cosmology. As an example it has been argued that the discovery of the Bullet Cluster challenges standard $Λ$CDM model predictions. Halo catalogs from N-body simulations have been used to estimate the probability of Bullet-like clusters. However, due to simulation volume effects previous studies had to rely on a Gaussian extrapolation of the pairwise velocity distribution to high velocities. Here, we perform a detail analysis using the halo catalogs from the Dark Energy Universe Simulation Full Universe Runs (DEUS-FUR), which enables us to resolve the high-velocity tail of the distribution and study its dependence on the halo mass definition, redshift and cosmology. Building upon these results we estimate the probability of Bullet-like systems in the framework of Extreme Value Statistics. We show that the tail of extreme pairwise velocities significantly deviates from that of a Gaussian, moreover it carries an imprint of the underlying cosmology. We find the Bullet Cluster probability to be two orders of magnitude larger than previous estimates, thus easing the tension with the $Λ$CDM model. Finally, the comparison of the inferred probabilities for the different DEUS-FUR cosmologies suggests that observations of extreme interacting clusters can provide constraints on dark energy models complementary to standard cosmological tests.

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