arXiv subjects

Vivian Miranda

Publications and source records attributed to Vivian Miranda.

At least 19 recordsLinked to original sources

arXiv2026

Accurate modeling for 3$\times$2pt analyses in Roman and Rubin: a study of model approximations

One of the pillars of modern cosmology is the use of galaxy imaging surveys to extract information from the large-scale structure. In recent surveys, this measurement is typically performed through a 3$\times$2pt analysis, which combines auto- and cross-correlations between galaxy density and galaxy weak lensing. In this paper, we carry out a systematic study of three modeling approximations commonly used in such analyses: 1) applying the Limber approximation, 2) neglecting redshift-space distortions, and 3) using less accurate models for the nonlinear matter power spectrum. We carry out the study in the context of the final data from two major Stage-IV galaxy imaging surveys: the Nancy Grace Roman Space Telescope's High Latitude Imaging Survey and the Vera C. Rubin Observatory's Legacy Survey of Space and Time. To do this, we first validate our modeling pipeline, implemented in the software package CoCoA, against an established code base, CCL. Next, we perform a simulated likelihood analysis to assess the impact of these approximations on the cosmological constraints. We find all three effects to be important; neglecting any of them can induce biases in cosmological constraints approaching or exceeding $1\sigma$, and exceeding $2\sigma$ for Rubin in several cases. Moreover, we explore how the lens-galaxy sample configuration and scale-cut choice can influence the constraints.

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arXiv2026

Raising the reionization optical depth with inflationary CMB features

Within the highly successful $\Lambda$CDM paradigm established with cosmic microwave background (CMB) anisotropy measurements, the optical depth through reionization $\tau$ is the most uncertain due both to the difficulty in measuring large-angle polarization and the assumptions made in their interpretation. Currently, for the Planck primary data in the flat $\Lambda$CDM cosmology with slow-roll inflation and standard reionization, the one-sided 95% upper limit for $\tau$ is $\tau_{\rm max}=0.0696$. Yet when all current CMB measurements excluding large-angle polarization are combined with baryon acoustic oscillation (BAO) measurements, the one-sided 95% lower limit is an incompatible $\tau_{\rm min}=0.074$. If the long-standing low-power feature of the temperature measurements is interpreted as physically originating from inflation then $\tau$ inferred from large-angle polarization becomes larger. Marginalizing over templates of the low-power feature based on the generalized slow-roll formalism of inflation raises the Planck maximum to a more compatible $\tau_{\rm max}=0.075$ which further increases to $\tau_{\rm max} = 0.082$ with the inclusion of all CMB+BAO data. This marginalization does not assess the statistical significance of the low-power feature itself; rather, it shows that allowing a higher $\tau$ is a consequence of interpreting the anomaly as a physical feature instead of a statistical fluctuation.

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arXiv2026

The sound of dynamical dark energy and modified gravity

Different candidate models are able to reproduce the dynamical dark energy signal preferred by combinations of recent distance measurements. These models may be distinguished by the behavior of their perturbations, which are controlled by the effective sound speed $c_s^2(k,a)$. To explore correlations between the dark energy sound speed and perturbative behavior, we test modified gravity (MG) scenarios in which the dark energy equation of state and sound speed determine modifications to the clustering of matter. We investigate the impact of varying the dark energy sound speed on several cosmological quantities in both General Relativity (GR) and MG. We constrain the dark energy and modified gravity parameters using measurements of the Cosmic Microwave Background (CMB) from Planck PR4, type Ia supernova luminosity distances (SN) from Pantheon+, Baryon Acoustic Oscillations (BAO) from DESI DR2, and cosmic shear from DES-Y3. Using the combination of CMB+BAO+SN, we find that, in the MG scenarios, the preference for dynamical dark energy is correlated with deviations from GR over redshifts $z < 2$ at over 95\% confidence level. The significance of these deviations is not degraded when considering a dynamical or superluminal sound speed, but vanishes if we assume a cosmological constant. The inclusion of cosmic shear and CMB lensing data significantly shifts the constraints towards GR. Our framework enables the exploration of modified gravity models using the dark energy sound speed as a physically meaningful free parameter.

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arXiv2026

Towards the Two-Loop EFTofLSS in Galaxy Lensing Surveys

Extracting cosmological information from Stage IV weak lensing surveys requires non-linear modelling of the matter power spectrum that is accurate across a broad range of scales and redshifts and robust to baryonic feedback. We forecast the application of the two-loop effective field theory of large-scale structure (EFTofLSS) to Roman Space Telescope, carefully considering parameterization, scale cuts, and priors. We develop neural network emulators for the two-loop integrals, allowing rapid evaluation of the likelihood. Weak lensing demands a continuous-in-redshift description of the EFT, potentially introducing tens of nuisance parameters. We address this by calibrating the counterterm redshift evolution against the Euclid Emulator 2 and accounting for the residual freedom in redshift with spline functions. A principal component analysis of the free parameters reduces the dimensionality to a few degrees of freedom that the data can constrain. Next, we calibrate the priors on those degrees of freedom by using a suite of hydrodynamical simulations. We forecast the $S_8$ constraints as a function of scale cuts, showing that the two-loop EFT with Roman cosmic shear provides unbiased $S_8=\sigma_8\sqrt{\Omega_{\rm m}/0.3}$ constraints with relative errors of about $0.9\%$ and $1.4\%$ when allowing for $5\%$ and $1\%$ contamination from ultraviolet modes, respectively. The two-loop EFT improves the scale reach beyond the one-loop EFT and non-linear dark matter-only models when baryonic effects are included. This framework provides a robust path for extracting small-scale information from future cosmic shear data.

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arXiv2026

Modeling Redshift Uncertainties in Roman Weak Lensing Cosmology

Cosmological constraints using weak gravitational lensing measurements from the Roman Space Telescope will require a powerful method for modelling uncertainties in the galaxy redshift distribution. In this work, we use an optimized version of the principal component analysis (PCA) to model uncertainties in the full shape of the redshift distributions, a method proposed by \cite{pca_method} and recently used in the Dark Energy Survey Y6 analysis. Here, we implement this new approach within the Roman High Latitude Imaging Survey (HLIS) Cosmology Project Infrastructure Team (PIT) pipeline, namely Cobaya-Cosmolike Joint Architecture (\texttt{CoCoA}). To validate the PCA in mitigating biases on cosmological parameters, $S_8$ and $\Omega_m$, we use a set of redshift distributions from \texttt{Cardinal} generated for a variety of Roman configurations. Overall, when the simulated cosmic shear data vector is not strongly miscalibrated relative to the fiducial one, both the mean-shift and the PCA-based approaches produce consistent cosmological constraints when marginalizing over nuisance parameters. For mild to strong miscalibration, including additional PCs progressively mitigates biases in $S_8$ and $\Omega_m$, and can achieve comparable performance with fewer parameters than the nine tomographic-bin mean-shift model.

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arXiv2026

Fisher Forecasts for Cosmological Yields from $3\!\times\!2$pt Analysis of the Roman Space Telescope High Latitude Imaging Survey

The High Latitude Imaging Survey (HLIS) of NASA's Nancy Grace Roman Space Telescope will provide powerful tests of cosmological models through sensitive measurements of cosmic shear, galaxy-galaxy lensing (GGL), and galaxy clustering. As part of the HLIS Project Infrastructure Team's Data Challenge 1 (DC1), we carry out Fisher forecasts of cosmological parameter constraints from combinations of these probes, focusing on inverse-variance figures of merit (FoMs) for the parameters $\sigma_8$ and $\Omega_{\rm{m}}$, which scale the amplitude of weak lensing signals. We find good agreement between Fisher analysis and Markov chain Monte Carlo (MCMC) analysis of the DC1 baseline data vector, and we investigate varied priors on cosmological parameters and on nuisance parameters describing unknown biases in photometric redshifts or shear measurements. The DC1 benchmark modeling assumes a ``lens $=$ source'' analysis with linear galaxy bias and no marginalization over baryonic physics. Under these assumptions, the forecast constraints from GGL+clustering are substantially stronger than those from cosmic shear, with the combination of all three probes (``$3\!\times\!2$pt'') providing moderate further improvement. Adding tight external priors on the power spectrum shape parameters $n_{\rm{s}}$, $\Omega_{\rm{b}}$, and $h_0$ can improve the $(\sigma_8, \Omega_{\rm{m}})$ FoMs by factors of $1.2$--$3.5$. The smallest scale angular bins provide much more information than the largest scale bins, and the highest redshift tomographic bins provide more information than the lowest redshift bins. Factor-of-two changes in the priors on photo-$z$ and shear biases, relative to the benchmark values based on anticipated calibration accuracy, produce changes of $\lesssim 20\%$ in FoMs.

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arXiv2025

Constraining baryonic feedback and cosmology from DES Y3 and Planck PR4 6$\times$2pt data. I. $\Lambda$CDM models

We combine weak lensing, galaxy clustering, cosmic microwave background (CMB) lensing, and their cross-correlations (so-called 6$\times$2pt) to constrain cosmology and baryonic feedback scenarios using data from the Dark Energy Survey (DES) Y3 Maglim catalog and the Planck satellite PR4 data release. We include all data points in the DES Y3 cosmic shear two-point correlation function (2PCF) down to 2.$^\prime$5 and model baryonic feedback processes via principal components (PCs) that are constructed from the ANTILLES simulations. We find a tight correlation between the amplitude of the first PC $Q_1$ and mean normalized baryon mass fraction $\bar{Y_\mathrm{b}}=\bar{f}_\mathrm{b}/(\Omega_\mathrm{b}/\Omega_\mathrm{m})$ from the ANTILLES simulations and employ an independent $\bar{Y_\mathrm{b}}$ measurement from Akino et al. (2022) as a prior of $Q_1$. We train a neural network $6\times2$pt emulator to boost the analysis speed by $\mathcal{O}(10^3)$, which enables us to run an impressive number of simulated analyses to validate our analysis against various systematics. For our 6$\times$2pt analysis, we find $S_8=0.8073\pm0.0094$ when including a $Q_1$ prior from $\bar{Y_\mathrm{b}}$ observations. This level of cosmological constraining power allows us to put tight constraints on the strength of baryonic feedback. We find $Q_1=0.025^{+0.024}_{-0.029}$ for our 6$\times$2pt analysis and $Q_1=0.043\pm{0.016}$ when combining with external information from Planck, ACT, DESI. All these results indicate weak feedback, e.g., the tensions to Illustris ($Q_1=0.095$) and OWLS AGN T8.7 ($Q_1=0.137$) are 2.9$\sigma$-3.3$\sigma$ and 4.7$\sigma$-5.9$\sigma$, respectively.

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arXiv2025

Modeling nonlinear scales for dynamical dark energy cosmologies with COLA

Upcoming galaxy surveys will bring a wealth of information about the clustering of matter, but modeling small-scale structure beyond $\Lambda$CDM remains computationally challenging. While accurate N-body emulators exist to model the matter power spectrum for $\Lambda$CDM and some limited extensions, it's unfeasible to generate N-body simulation suites for all candidate models. Motivated by recent hints of an evolving dark energy equation of state, we assess the viability of employing the COmoving Lagrangian Acceleration (COLA) method to generate simulation suites assuming the $w_0w_a$ dark energy model. We combine COLA simulations with an existing high-precision $\Lambda$CDM emulator to extend its predictions into new regions of parameter space. We assess the precision of our emulator at the level of the matter power spectrum, finding that our emulator can reproduce the nonlinear boosts from EuclidEmulator2 at less than $2\%$ error. Moreover, we perform an analysis of a simulated cosmic shear survey akin to the Legacy Survey of Space and Time (LSST) first year of observations, assessing the differences in parameter constraints between our COLA-based emulator and the benchmark emulator. We find our emulator to be in excellent agreement with the benchmark, achieving less than $0.3\sigma$ shifts in cosmological parameters. We compare our emulator's performance to a commonly used approach: assuming the $\Lambda$CDM boost can be employed for extended parameter spaces without modification. We find that our emulator yields a significantly smaller $\Delta\chi^2$ distribution, parameter constraint biases, and a more accurate figure of merit compared to this second approach. Our results demonstrate that COLA emulators provide a computationally efficient path forward for modeling nonlinear structure in extended cosmologies, offering a practical alternative to full N-body suites.

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arXiv2025

Phantom Mirage from Axion Dark Energy

Supernova (SN) and baryon acoustic oscillation (BAO) distance measures have recently provided hints that the dark energy is not only dynamical but apparently evolves from normal to phantom dark energy between redshifts $0<z<1$. A normal axion dark energy component in the mass range just below the Hubble scale can mimic a phantom component by appearing as dark energy at $z=1$ and dark matter at $z=0$, raising the possibility of a phantom mirage. We show that there is a wide range of axion dark energy contributions that can resolve the SN-BAO tension as well as thawing quintessence does, leaving BAO tension with the cosmic microwave background (CMB) for the distance measures from $z\sim 1$ to recombination to be resolved at high redshifts. With axions, raising the optical depth to reionization to $\tau \approx 0.1$ works essentially as well as $w_0-w_a$ phantom dark energy for all but the lowE CMB data, with a remaining $\Delta\chi^2\sim -16$ compared with $\Lambda$CDM, whereas a small spatial curvature of $\Omega_K \sim 0.003$ can largely relax the full SN-BAO-CMB tension with a total $\Delta\chi^2 \sim -12$.

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arXiv2025

Cosmology Constraints from Type Ia Supernova Simulations of the Nancy Grace Roman Space Telescope Strategy Recommended by the High Latitude Time Domain Survey Definition Committee

Within the next few years, the upcoming Nancy Grace Roman Space Telescope will be gathering data for the High Latitude Time Domain Survey (HLTDS) that will be used to significantly improve the Type Ia supernova measurement of the dark energy equation of state parameters w0 and wa. Here we generate a catalog-level simulation of the in-guide strategy recommended by the HLTDS definition committee, and determine dark energy parameter constraints using a detailed analysis that includes light curve fitting, photometric redshifts and classification, BEAMS formalism, systematic uncertainties, and cosmology fitting. After analysis and selection requirements, the sample includes 10,000 Roman SNe Ia that we combine with 4,400 events from LSST. The resulting dark energy figure of merit is well above the NASA mission requirement of 326, with the caveat that SN Ia model training systematics have not been included.

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arXiv2025

Attention-based Neural Network Emulators for Multi-Probe Data Vectors Part III: Modeling The Next Generation Surveys

Machine learning can accelerate cosmological inferences that involve many sequential evaluations of computationally expensive data vectors. Previous works in this series have examined how machine learning architectures impact emulator accuracy and training time for optical shear and galaxy clustering 2-point function. In this final manuscript, we explore neural network performance when emulating Cosmic Microwave Background temperature and polarization power spectra. We maximize the volume of applicability in the parameter space of our emulators within the standard $\Lambda$-cold-dark-matter model while ensuring that errors are below cosmic variance. Relative to standard multi-layer perceptron architectures, we find the dot-product-attention mechanism reduces the number of outliers among testing cosmologies, defined as the fraction of testing points with $\Delta \chi^2 > 0.2$ relative to \textsc{CAMB} outputs, for a wide range of training set sizes. Such precision enables attention-based emulators to be directly applied to real data without requiring any additional correction via importance sampling. Combined with pre-processing techniques and optimized activation and loss functions, attention-based models can meet the precision criteria set by current and future CMB and lensing experiments. For each of Planck, Simons Observatory, CMB S4, and CMB HD, we find the fraction of outlier points to be less than $10\%$ with around $2\times10^5$ to $4\times10^5$ training data vectors. We further explore the applications of these methods to supernova distance, weak lensing, and galaxy clustering, as well as alternative architectures and pre-processing techniques.

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arXiv2024

Uniting the Observed Dynamical Dark Energy Preference with the Discrepancies in $\Omega_m$ and $H_0$ Across Cosmological Probes

Recent results from Type Ia Supernovae (SNe), baryon acoustic oscillations (BAO), and the cosmic microwave background (CMB) indicate 1) potentially discrepant measurements of the matter density $\Omega_m$ and Hubble constant $ H_0 $ in $\Lambda$CDM model when analyzed individually, and 2) hints of dynamical dark energy in a $w_0w_a$CDM model when data are combined in a joint analysis. We examine whether underlying dynamical dark energy cosmologies favored by data would result in biases in $\Omega_m$ and $ H_0 $ for each probe when analyzed individually under $\Lambda$CDM. We generate mock datasets in $w_0w_a$CDM cosmologies, fit the individual probes under the $\Lambda$CDM model, and find expected biases in $\Omega_m$ are $\sim 0.03$. Notably, the $\Omega_m$ differences between probes are consistent with values observed in real datasets. We also observe that mock DESI-BAO datasets generated in the $w_0w_a$CDM cosmologies will lead to a biased measurement of $H_0$ higher by ($\sim1.2$km/s/Mpc) when fitted under $\Lambda$CDM, appearing to mildly improve the Hubble tension, but as the true underlying $H_0$ is lower, the tension is in fact worsened. We find that the $\Omega_m$ discrepancies, the high BAO $ H_0 $ relative to CMB, and the joint dynamical dark energy signal are all related effects that could be explained \textit{simultaneously} with either new physics or new systematics. While it is possible to unite many of the discrepancies seen in recent analyses along a single axis, our results underscore the importance of understanding systematic differences in datasets, as they have unique impacts in different cosmological parameter spaces.

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arXiv2024

Quantifying Scalar Field Dynamics with DESI 2024 Y1 BAO measurements

Quintessence scalar fields are a natural candidate for evolving dark energy. Unlike the phenomenological $w_0w_a$ parameterization of the dark energy equation of state, they cannot accommodate the phantom regime of dark energy $w(z) < -1$, or crossings into the phantom regime. Recent baryon acoustic oscillation (BAO) measurements by the Dark Energy Spectroscopic Instrument (DESI) indicate a preference for evolving dark energy over a cosmological constant, ranging from $2.6σ-3.9σ$ when fitting to $w_0w_a$, and combining the DESI BAO measurements with other cosmological probes. In this work, we directly fit three simple scalar field models to the DESI BAO data, combined with cosmic microwave background anisotropy measurements and supernova data sets. We find the best fit model to include a $2-4\%$ kinetic scalar field energy $Ω_{\rm scf,k}$, for a canonical scalar field with a quadratic or linear potential. However, only the DESY-Y5 supernova data set combination shows a preference for quintessence over $Λ$CDM at the $95\%$ confidence level. Fitting to the supernova data sets Pantheon, Pantheon+, DES-Y5, and Union3, we show that the mild tension ($n_σ< 3.4 $) under $Λ$CDM emerges from a BAO preference for smaller values of fractional mass-energy density $Ω_m < 0.29$, while all supernova data sets, except for Pantheon, prefer larger values, $Ω_m > 0.3$. The tension under $Λ$CDM remains noticeable ($n_σ <2.8$), when replacing two of the DESI BAO redshift bins with effective redshifts $z_{\text{eff}} =0.51$, and $z_{\text{eff}}= 0.706$ with comparable BOSS DR 12 BAO measurements at $z_{\text{eff}} =0.51$, and $z_{\text{eff}}= 0.61$. Canonical scalar fields as dark energy are successful in mitigating that tension.

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arXiv2024

Sound Horizon Independent Constraints on Early Dark Energy: The Role of Supernova Data

We assess the consistency of cosmological models that alter the size of the sound horizon at last scattering to resolve the Hubble tension with data from ACT + Planck CMB lensing, Big Bang Nucleosynthesis, and supernova data from Pantheon or Pantheon+. We use early dark energy (EDE) as an example model but conclude that the results apply to other similar models. We constrain $Λ$CDM and EDE with these data finding that while they can constrain $Λ$CDM very tightly, EDE opens up the parameter space significantly and allows $H_0 > 72$ km s$^{-1}$ Mpc$^{-1}$. We combine these data with measurements from ACT + Planck TT650TEEE CMB primary anisotropy and galaxy baryon acoustic oscillations, and find that overall, EDE fits these data better than $Λ$CDM at $\approx 2σ$. However, the fit to specifically the sound-horizon-independent measurements is worse for EDE than $Λ$CDM. We assess this increase in $χ^2$ coming from the sound-horizon-independent measurements and find that the best-fit model is still consistent with a random statistical fluctuation even with $H_0$ values around $72$ km s$^{-1}$ Mpc$^{-1}$. We conclude that these specific sound-horizon-independent data cannot rule out the possibility of a miscalibration of the size of the sound horizon, but leave open the possibility that other current or future sound-horizon-independent data sets could rule out such a miscalibration.

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arXiv2024

Cosmology from weak lensing, galaxy clustering, CMB lensing and tSZ: II. Optimizing Roman survey design for CMB cross-correlation science

We explore synergies between the Nancy Grace Roman Space Telescope High Latitude Wide Area Survey (HLWAS) and CMB experiments, specifically Simons Observatory (SO) and CMB-Stage4 (S4). Our simulated analyses include weak lensing, photometric galaxy clustering, CMB lensing, thermal SZ, and cross-correlations between these probes. While we assume the nominal 16,500 square degree area for SO and S4, we consider multiple survey designs for Roman that overlap with Rubin Observatory's Legacy Survey of Space and Time (LSST): the 2000 square degree reference survey using four photometric bands, and two shallower single-band surveys that cover 10,000 and 18,000 square degree, respectively. We find a ~2x increase in the dark energy figure of merit when including CMB-S4 data for all Roman survey designs. We further find a strong increase in constraining power for the Roman wide survey scenario cases, despite the reduction in galaxy number density, and the increased systematic uncertainties assumed due to the single band coverage. Even when tripling the already worse systematic uncertainties in the Roman wide scenarios, which reduces the 10,000 square degree FoM from 269 to 178, we find that the larger survey area is still significantly preferred over the reference survey (FoM 64). We conclude that for the specific analysis choices and metrics of this paper, a Roman wide survey is unlikely to be systematics-limited (in the sense that one saturates the improvement that can be obtained by increasing survey area). We outline several specific implementations of a two-tier Roman survey (1000 square degree with 4 bands, and a second wide tier in one band) that can further mitigate the risk of systematics for Roman wide concepts.

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arXiv2024

Mitigation of nonlinear galaxy bias with a theoretical-error likelihood

Stage-IV galaxy surveys will measure correlations at small cosmological scales with high signal-to-noise ratio. One of the main challenges of extracting information from small scales is devising accurate models, as well as characterizing the theoretical uncertainties associated with any given model. In this work, we explore the mitigation of theoretical uncertainty due to nonlinear galaxy bias in the context of photometric 2$\times$2-pt analyses. We consider linear galaxy bias as the fiducial model and derive the contribution to the covariance matrix induced by neglected higher-order bias. We construct a covariance matrix for the theoretical error in galaxy clustering and galaxy-galaxy lensing using simulation-based relations that connect higher-order parameters to linear bias. We test the modified likelihood in 2$\times$2-pt analyses based on two sets of mock data vectors: (1) simulated data vectors, constructed from those same relations between bias parameters, and (2) data vectors based on the AbacusSummit simulation suite. We then compare the performance of the theoretical-error approach to the commonly employed scale cuts. We find most theoretical-error configurations yield results equivalent to the scale cuts in terms of precision and accuracy, in some cases producing significantly stronger bounds on cosmological parameters. These results are independent of the maximum scale $k_\mathrm{max}$ in the analysis with theoretical error. The scenarios where linear bias supplemented by theoretical error is unable to recover unbiased cosmology are connected to inadequate modeling of the $gg$-$g\kappa$ covariance of theoretical error. In view of its removing the ambiguity in the choice of $k_\mathrm{max}$, as well as the possibility of attaining higher precision than the usual scale cuts, we consider this method to be promising for analyses of LSS in upcoming photometric galaxy surveys.

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arXiv2024

Modeling nonlinear scales with COLA: preparing for LSST-Y1

Year 1 results of the Legacy Survey of Space and Time (LSST) will provide tighter constraints on small-scale cosmology, beyond the validity of linear perturbation theory. This heightens the demand for a computationally affordable prescription that can accurately capture nonlinearities in beyond-$Λ$CDM models. The COmoving Lagrangian Acceleration (COLA) method, a cost-effective \textit{N}-body technique, has been proposed as a viable alternative to high-resolution \textit{N}-body simulations for training emulators of the nonlinear matter power spectrum. In this study, we evaluate this approach by employing COLA emulators to conduct a cosmic shear analysis with LSST-Y1 simulated data across three different nonlinear scale cuts. We use the $w$CDM model, for which the \textsc{EuclidEmulator2} (\textsc{ee2}) exists as a benchmark, having been trained with high-resolution \textit{N}-body simulations. We primarily utilize COLA simulations with mass resolution $M_{\rm part}\approx 8 \times 10^{10} ~h^{-1} M_{\odot}$ and force resolution $\ell_{\rm force}=0.5 ~h^{-1}$Mpc, though we also test refined settings with $M_{\rm part}\approx 1 \times 10^{10} ~h^{-1}M_{\odot}$ and force resolution $\ell_{\rm force}=0.17 ~h^{-1}$Mpc. We find the performance of the COLA emulators is sensitive to the placement of high-resolution \textit{N}-body reference samples inside the prior, which only ensure agreement in their local vicinity. However, the COLA emulators pass stringent criteria in goodness-of-fit and parameter bias throughout the prior, when $Λ$CDM predictions of \textsc{ee2} are computed alongside every COLA emulator prediction, suggesting a promising approach for extended models.

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arXiv2024

Investigating Late-Time Dark Energy and Massive Neutrinos in Light of DESI Y1 BAO

Baryonic Acoustic Oscillation (BAO) data from the Dark Energy Spectroscopic Instrument (DESI), in combination with Cosmic Microwave Background (CMB) data and Type Ia Supernovae (SN) luminosity distances, suggests a dynamical evolution of the dark energy equation of state with a phantom phase ($w < -1$) in the past when the so-called $w_0w_a$ parametrization $w(a) = w_0 + w_a(1-a)$ is assumed. In this work, we investigate more general dark energy models that also allow a phantom equation of state. We consider three cases: an equation of state with a transition feature, a model-agnostic equation of state with constant values in chosen redshift bins, and a k-essence model. Since the dark energy equation of state is correlated with neutrino masses, we reassess constraints on the neutrino mass sum focusing on the model-agnostic equation of state. We find that the combination of DESI BAO with Planck 2018 CMB data and SN data from Pantheon, Pantheon+, or Union3 is consistent with an oscillatory dark energy equation of state, while a monotonic behavior is preferred by the DESY5 SN data. Performing model comparison techniques, we find that the $w_0w_a$ parametrization remains the simplest dark energy model that can provide a better fit to DESI BAO, CMB, and all SN datasets than $\Lambda$CDM. Constraints on the neutrino mass sum assuming dynamical dark energy are relaxed compared to $\Lambda$CDM and we show that these constraints are tighter in the model-agnostic case relative to $w_0w_a$ model by $70\%-90\%$.

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