arXiv subjects

Théo Simon

Publications and source records attributed to Théo Simon.

At least 19 recordsLinked to original sources

arXiv2026

Preference for evolving dark energy in light of the galaxy bispectrum

We analyse pre-DESI clustering data using a dark energy equation of state $w(z)$ parametrised by $(w_0, w_a)$, finding a $2.8-3.9σ$ preference for evolving dark energy over the cosmological constant $Λ$ when combined with cosmic microwave background data from \textit{Planck} and supernova data from Pantheon+, Union3, or DESY5. Our constraints, consistent with DESI Y1 results, are derived from the power spectrum and bispectrum of SDSS/BOSS galaxies using the Effective Field Theory of Large Scale Structure (EFTofLSS) at one loop. The evidence, estimated as the Gaussian-equivalent significance from the $Δχ^2$-statistics to $(w_0, w_a) = (-1, 0)$ for two degrees of freedom, remains robust across analysis variations but disappears without the one-loop bispectrum. When combining DESI baryon acoustic oscillations with BOSS full-shape data, while marginalising over the sound horizon in the latter to partially mitigate potential correlations, the significance increases to $3.7-4.4σ$, depending on the supernova dataset. Using instead a data-driven reconstruction of $w(z)$, we show that deviations from $Λ$ can be observed at multiple redshifts, though at a low level of significance: only when imposing the specific parametrisation implied by $(w_0, w_a)$ the above evidence emerges. In addition, our findings are interpreted within the Effective Field Theory of Dark Energy (EFTofDE), from which we explicitly track the non-standard time evolution in EFTofLSS predictions. For perturbatively stable theories in the $w < -1$ regime, the preference for $w_0w_a$CDM persists notably in the clustering limit $(c_s^2 \rightarrow 0)$ when higher-derivative corrections are present.

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arXiv2026

The $H_0$ World Cup. I. Summary of the baseline group stage results

The Hubble tension has reached a nominal significance above $7σ$, while new high-precision measurements of the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO) sharpen the test of proposed solutions. Using a common framework, we compare fourteen representative alternatives to the standard $Λ$ Cold Dark Matter ($Λ$CDM) model in light of up-to-date CMB, BAO and supernovae data to gauge their ability to resolve the tension. The models span late-time modifications, modified recombination, and exotic pre-recombination expansion histories driven by additional radiation or a localized dark energy injection. We evaluate each proposal with complementary frequentist and Bayesian measures of the residual calibration tension and of the improvement in the joint fit. Both approaches identify the same broad hierarchy. Early dark energy and early modified gravity models perform best, shifting the $H_0$ inference without local measurement priors toward $70\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$ and reducing the residual discrepancy with SH0ES to approximately $2.5-3.6σ$, depending on the model and statistic, while receiving strong support over $Λ$CDM in the combined fit. Varying the electron mass at recombination yields an intermediate improvement, whereas the enhanced-radiation and late-time scenarios do not improve over $Λ$CDM. This Letter summarizes the group stage of the competition; in a companion paper (Paper II) we present the results of an exhaustive set of analyses and assess their robustness to variations in modeling assumptions and datasets.

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arXiv2026

The $H_0$ world cup. II. A comprehensive competition between proposed Hubble tension solutions

Cosmology stands at a crossroads. The Hubble tension has reached a nominal significance above $7σ$, while analyses combining DESI BAO and Type Ia supernova data show emerging hints of departures from $Λ$CDM. Meanwhile, high-precision CMB measurements from ACT and SPT enable a timely and more stringent reassessment of proposed solutions to the tension. In this paper, we revisit the $H_0$ Olympics, a systematic contest comparing proposed alternatives to $Λ$CDM using common datasets, likelihoods, and statistical criteria. In this updated edition, the $H_0$ World Cup, we subject fourteen representative solutions to a common analysis of current CMB, BAO, and SN data. The contenders span four broad mechanisms: late-time modifications of the expansion history, modified recombination, additional pre-recombination radiation, and early non-radiative energy injection. Relative to the original analysis, the present competition includes models and mechanisms proposed in the intervening years and evaluates all contenders using both Bayesian and Frequentist tests of tension and model performance, letting the neutrino mass sum vary. We further test if late-time extensions through curvature or the Chevallier-Polarski-Linder (CPL) dark energy parametrization can aid the success of the models. Finally, we subject the leading contenders to dedicated robustness tests involving alternative CMB likelihoods and multipole cuts, supernova samples, large-scale-structure information, and big-bang nucleosynthesis constraints. This framework assesses both the ability of each mechanism to ease the Hubble tension and the robustness of our conclusions to datasets and analysis choices.

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arXiv2026

A sound horizon independent measurement of $H_0$ from BOSS, DESI and DES Y3

We present a sound horizon independent measurement of the Hubble parameter using a multiprobe large-scale structure analysis. Removing the dependency on the sound horizon with a rescaling procedure at the matter power spectrum level, we analyse the BOSS full-shape power spectrum and bispectrum (for the first time) using the effective field theory of large-scale structure up to one loop. We combine this analysis with the auto- and cross-angular power spectra from the DESI Legacy Imaging Survey DR9, the $3 \times 2$pt analysis from DES Y3, and the CMB gravitational lensing power spectrum from Planck PR3. Our baseline analysis, that does not rely on supernovae data, yields $h = 0.702^{+0.022}_{-0.024}$, $Ω_m = 0.310 \pm 0.013$, and $σ_8 = 0.799 \pm 0.020$, corresponding to $3-4 \%$ precision measurements. When adding supernovae data from Pantheon+, we obtain a $2.6 \%$ measurement of $h$, with $h = 0.686 \pm 0.018$. We further note that our EFTBOSS analysis indicates a slight deviation of the BAO scale parameter (at $1.8 σ$) from its $Λ$CDM value, caused by the small scales of the bispectrum. We finally use the sound horizon-free EFTBOSS analysis as a diagnosis for the presence of new physics, finding that our results are consistent with the recent hints of evolving dark energy.

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arXiv2026

New multiprobe analysis of modified gravity and evolving dark energy

We study the $(w_0, \, w_a)$ parametrization of the dark energy (DE) equation of state, with and without the effective field theory of dark energy (EFTofDE) framework to describe the DE perturbations, parametrized here by the braiding parameter $α_B$ and the running of the Planck mass $α_M$. We combine the EFTofLSS full-shape analysis of the power spectrum and bispectrum of BOSS data with the tomographic angular power spectra $C_\ell^{gg}$, $C_\ell^{κg}$, $C_\ell^{Tg}$ and $C_\ell^{Tκ}$, where $g$, $κ$ and $T$ stand for the DESI luminous red galaxy map, Planck PR4 lensing map and Planck PR4 temperature map, respectively. To analyze these angular power spectra, we go beyond the Limber approximation, allowing us to include large-scale data in $C_\ell^{gg}$. The combination of all these probes with Planck PR4, DESI DR2 BAO and DES Y5 improves the constraint on the 2D posterior distribution of $\{w_0, \, w_a\}$ by $\sim 50 \%$ and increases the preference for evolving dark energy over $Λ$ from $3.8 σ$ to $4.6 σ$. When we remove BAO and supernovae data, we obtain a hint for evolving dark energy at $2.3 σ$. Regarding the EFTofDE parameters, we improve the constraints on $α_B$ and $α_M$ by $\sim 40 \%$ and $50 \%$ respectively, finding results compatible with general relativity at $\sim 2 σ$. We show that these constraints do not depend on the choice of the BAO and supernovae likelihoods.

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arXiv2025

Impact of ACT DR6 and DESI DR2 for Early Dark Energy and the Hubble tension

The data release six of the Atacama Cosmology Telescope (ACT DR6) and the second data release from the Dark Energy Spectroscopic Instrument (DESI DR2) recently became available. In light of these data, we update constraints on the Early Dark Energy (EDE) resolution to the Hubble tension. While ACT DR6 does not favor EDE over the core cosmological model $Λ$CDM, it allows for a significantly larger maximum contribution of EDE, $f_{\rm EDE}$, in the pre-recombination era than the latest analysis of {\it Planck} NPIPE despite increased precision at small angular scales. Moreover, EDE rises the value of $H_0r_s$, improving consistency between CMB and DESI DR2 data. We find a residual tension with SH0ES of $\sim 2 σ$ for the combination of {\it Planck} at $\ell <1000$ + ACT DR6 + lensing + Pantheon-plus + DESI DR2, a significant decrease from $3.7 σ$ for analyses that use NPIPE and SDSS BAO data. A profile likelihood analysis reveals significant prior-volume effects in Bayesian analyses which do not include SH$0$ES, with confidence intervals of $f_{\rm EDE}=0.09\pm 0.03$ and $H_0= 71.0\pm1.1$ km/s/Mpc. When including DESI data, the EDE model with $H_0=73$ km/s/Mpc provides a better fit than the $Λ$CDM model with $H_0=68.4$ km/s/Mpc. The inclusion of SH$0$ES data rises the preference well above $5σ$, with $Δχ^2=-35.4$. Our work demonstrates that after ACT DR6 and DESI DR2, EDE remains a potential resolution to the Hubble tension.

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arXiv2025

Primordial Features in light of the Effective Field Theory of Large Scale Structure

While the simplest inflationary models predict a power-law form of the primordial power spectrum (PPS), various UV complete scenarios predict features on top of the standard power law that leave characteristic imprints in the late-time distribution of matter, encoded in the galaxy power spectrum. In this work, we assess the validity of the Effective Field Theory of Large Scale Structure (EFTofLSS) and the IR-resummation scheme of PyBird in the context of primordial (oscillatory) features. We find an excellent agreement at the level of the matter power spectrum between N-body simulations and the one-loop EFT predictions, for models commonly studied in the literature. We then apply the EFTofLSS to the galaxy power spectrum measurements from BOSS LRG and eBOSS QSO to constrain specific global and local features in the PPS. We demonstrate that while such features can improve the fit to cosmic microwave background (CMB) data, they may result in a poorer fit to clustering measurements at low redshift. The resulting constraints on the amplitude of the primordial oscillations are competitive with those obtained from CMB data, despite the well-known damping of oscillations due to non-linear structure formation processes. For the first time in this context, we jointly analyze the galaxy power spectrum (monopole and quadrupole) in combination with Planck CMB data to derive strong constraints on the amplitude of primordial features. This work highlights the EFTofLSS as a powerful tool for testing early universe scenarios on scales that complement CMB observations.

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arXiv2025

Self-interacting neutrinos in light of recent CMB and LSS data

We update constraints on a simple model of self-interacting neutrinos involving a heavy scalar mediator with universal flavor coupling. According to past literature, such a model is allowed by Cosmic Microwave Background (CMB) data, with some CMB and large-scale structure data even favoring a strongly-interacting neutrino (SI$ν$) scenario over $Λ$CDM. In this work, we re-evaluate the constraints on this model in light of the new Planck NPIPE data, DESI BAO data, and the Effective Field Theory of Large Scale Structures (EFTofLSS) applied to BOSS data. We find that Planck NPIPE are more permissive to the SI$ν$ scenario and that DESI data favor the SI$ν$ over $Λ$CDM. However, when considering EFTofBOSS data, this mode is no longer preferred. Therefore, new DESI data analyzed under the EFTofLSS are particularly awaited to shed light on this disagreement.

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arXiv2025

Probing Dark Relativistic Species and Their Interactions with Dark Matter through CMB and 21cm surveys

We investigate the sensitivity of the 21cm power spectrum from cosmic dawn and the epoch of reionization to models of free-streaming dark radiation (parameterized through $N_{\rm eff}$) and interacting dark radiation-dark matter models (DM-DR). The latter models have gained attention for their potential in addressing recent cosmological tensions and structure formation challenges. We perform a Fisher matrix analysis under different assumptions regarding the astrophysical modeling, and forecast the sensitivity of HERA observations, combined with CMB data from Planck and the Simons Observatory (SO), to $N_{\rm eff}$ and DM-DR interaction modeled using the ETHOS framework assuming a constant scattering rate between the two components. Most importantly, we find that 21cm observations can improve the sensitivity to the DM-DR interaction rate by up to four order of magnitude compared to Planck and SO. Conversely, in the limit of low interaction rate (which asymptotically matches $N_{\rm eff}$), CMB data dominates the constraining power, but the inclusion of HERA data can provide a $\sim 20\%$ improvement in sensitivity over CMB data alone. Moreover, we find that HERA observations will be able to probe a region of the DM-DR interaction parameter space which is promising to explain the weak lensing amplitude `$S_8$' tension. Our results demonstrate the complementarity of 21cm and CMB data in exploring dark sector interactions.

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arXiv2024

Towards alleviating the $H_0$ and $S_8$ tensions with Early Dark Energy - Dark Matter drag

Early dark energy, an additional component of dark energy active in the decade of redshift before recombination, has emerged as one of the most effective models at reducing the $H_0$ tension between direct measurement of the Hubble parameter $H_0$ in the late-universe and the $Λ$CDM prediction when calibrated on Planck. However, it requires a slight increase in the dark matter density $ω_{\rm cdm}$ and primordial tilt $n_s$ that worsens the $S_8$ tension between measurements of weak gravitational lensing at low redshifts and the Planck/$Λ$CDM prediction. Using a phenomenological fluid model, we investigate whether the inclusion of a drag term between dark matter and early dark energy can compensate for the effect of the increase in power at small-scales, such that both $H_0$ and $S_8$ tensions are simultaneously alleviated. We find that this works if the drag term is dynamically relevant in the post-recombination universe. However, a drag term active before or just around the time at which the early dark energy contribution to the energy density is maximum is significantly constrained due to its impact on the matter perturbations before recombination, and the subsequent modifications to the cosmic microwave background power spectra.

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arXiv2024

On the implications of the `cosmic calibration tension' beyond $H_0$ and the synergy between early- and late-time new physics

The `cosmic calibration tension' is a $> 5σ$ discrepancy between the cosmological distance ladder built from baryonic acoustic oscillations (BAO) calibrated by the Planck/$Λ$CDM sound horizon ($r_s$) and Type Ia supernovae (SN1a) calibrated instead with the S$H_0$ES absolute magnitude, assuming the distance-duality relationship (DDR) holds. In this work, we emphasize the consequences of this tension beyond the value of the Hubble constant $H_0$, and the implications for physics beyond $Λ$CDM. Of utmost importance, it implies a larger physical matter density $ω_m\equiv Ω_m h^2$, as both the fractional matter density $Ω_m$ and $h\equiv H_0/100$ km/s/Mpc are well constrained from late-time data. New physics in the pre-recombination era must thus be able to decrease $r_s$ while either reducing the value of $Ω_m$, or increasing the value of $ω_m$. Assuming a $Λ$CDM-like primordial power spectrum, this necessarily results in an increase in the clustering amplitude $σ_8$. Deviations from $Λ$CDM in the late-time expansion history cannot resolve the calibrator tension but can help relax the required shifts to the matter density and $σ_8$: it is in that sense that a combination of early and late-time new physics may help alleviate the tension. More precisely, models that modify the pre-recombination expansion history can accommodate the increase in $ω_m$ without the need for additional modifications. It is those models which only affect recombination that require additional deviations at late-times to be successful. Hence, the `cosmic calibration tension' points either to a targeted modification of the pre-recombination expansion history, or to a broader change affecting multiple cosmic epochs.

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arXiv2024

Can acoustic and axion-like early dark energy still resolve the Hubble tension?

In this paper, we reassess the ability of the acoustic early dark energy (ADE) and axion-like early dark energy (EDE) models to resolve the Hubble tension in light of the new Pantheon+ and S$H_0$ES data on the one hand, and the BOSS LRG and eBOSS QSO data, analyzed under the effective field theory of large-scale structures (ETFofLSS) on the other hand. We find that the Pantheon+ data, which favor a larger $Ω_m$ value than the Pantheon data, have a strong constraining power on the ADE model, while the EFTofLSS analysis of the BOSS and eBOSS data only slightly increases the constraints. We establish that the ADE model is now strongly disfavored as a solution to the Hubble tension, with a remaining tension of $3.6σ$ (according to the $Q_{\rm DMAP}$ metric). In addition, we find that the axion-like EDE model performs better when confronted to the same datasets, with a residual tension of $2.5σ$. This work shows that the Pantheon+ data can have a decisive impact on models which aim to resolve the Hubble tension.

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arXiv2024

The weak, the strong and the ugly -- A comparative analysis of interacting stepped dark radiation

Models which address both the Hubble and $S_8$ tensions with the same mechanism generically cause a pre-recombination suppression of the small scale matter power spectrum. Here we focus on two such models. Both models introduce a self-interacting dark radiation fluid scattering with dark matter, which has a step in its abundance around some transition redshift. In one model, the interaction is weak and with all of the dark matter whereas in the other it is strong but with only a fraction of the dark matter. The weakly interacting case is able to address both tensions simultaneously and provide a good fit to a the Planck measurements of the cosmic microwave background (CMB), the Pantheon Type Ia supernovae, and a combination of low and high redshift baryon acoustic oscillation data, whereas the strongly interacting model cannot significantly ease both tensions simultaneously. The addition of high-resolution cosmic microwave background (CMB) measurements (ACT DR4 and SPT-3G) slightly limits both model's ability to address the Hubble tension. The use of the effective field theory of large-scale structures analysis of BOSS DR12 LRG and eBOSS DR16 QSO data additionally limits their ability to address the $S_8$ tension. We explore how these models respond to these data sets in detail in order to draw general conclusions about what is required for a mechanism to address both tensions. We find that in order to fit the CMB data the time dependence of the suppression of the matter power spectrum plays a central role.

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arXiv2023

Bayesian and frequentist investigation of prior effects in EFTofLSS analyses of full-shape BOSS and eBOSS data

Previous studies based on Bayesian methods have shown that the constraints on cosmological parameters from the Baryonic Oscillation Spectroscopic Survey (BOSS) full-shape data using the Effective Field Theory of Large Scale Structure (EFTofLSS) depend on the choice of prior on the EFT nuisance parameters. In this work, we explore this prior dependence by adopting a frequentist approach based on the profile likelihood method, which is inherently independent of priors, considering data from BOSS, eBOSS and Planck. We find that the priors on the EFT parameters in the Bayesian inference are informative and that prior volume effects are important. This is reflected in shifts of the posterior mean compared to the maximum likelihood estimate by up to 1.0 σ (1.6 σ) and in a widening of intervals informed from frequentist compared to Bayesian intervals by factors of up to 1.9 (1.6) for BOSS (eBOSS) in the baseline configuration, while the constraints from Planck are unchanged. Our frequentist confidence intervals give no indication of a tension between BOSS/eBOSS and Planck. However, we find that the profile likelihood prefers extreme values of the EFT parameters, highlighting the importance of combining Bayesian and frequentist approaches for a fully nuanced cosmological inference. We show that the improved statistical power of future data will reconcile the constraints from frequentist and Bayesian inference using the EFTofLSS.

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arXiv2023

Cosmological inference from the EFTofLSS: the eBOSS QSO full-shape analysis

We present cosmological results inferred from the effective-field theory (EFT) analysis of the full-shape of eBOSS quasars (QSO) power spectrum. We validate our analysis pipeline against simulations, and find overall good agreement between the analyses in Fourier and configuration space. Keeping the baryon abundance and the spectral tilt fixed, we reconstruct at $68\%$ CL the fractional matter abundance $Ω_m$, the reduced Hubble constant $h$, and the clustering amplitude $σ_8$, to respectively $Ω_m=0.327\pm 0.035$, $h=0.655\pm 0.034$, and $σ_8=0.880\pm 0.083$ from eBOSS QSO alone. These constraints are consistent at $\lesssim 1.8σ$ with the ones from Planck and from the EFT analysis of BOSS full-shape. Interestingly $S_8$ reconstructed from eBOSS QSO is slightly higher than that deduced from Planck and BOSS, although statistically consistent. In combination with the EFT likelihood of BOSS, supernovae from Pantheon, and BAO from lyman-$α$ and 6dF/MGS, constraints improve to $Ω_m = 0.2985\pm 0.0069$ and $h = 0.6803\pm 0.0075$, in agreement with Planck and with similar precision. We also explore one-parameter extensions to $Λ$CDM and find that results are consistent with flat $Λ$CDM at $\lesssim 1.3σ$. We obtain competitive constraints on the curvature density fraction $Ω_k=-0.039\pm 0.029$, the dark energy equation of state $w_0=-1.038\pm 0.041$, the effective number of relativistic species $N_{\rm eff}=3.44^{+0.44}_{-0.91}$ at $68\%$ CL, and the sum of neutrino masses $\sum m_ν<0.274e$V at $95\%$ CL, without Planck data. Including Planck data, contraints significantly improve thanks to the large lever arm in redshift between LSS and CMB measurements. In particular, we obtain the stringent constraint $\sum m_ν<0.093e$V, competitive with recent lyman-$α$ forest power spectrum bound.

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arXiv2023

Consistency of effective field theory analyses of the BOSS power spectrum

We assess the robustness of $Λ$CDM results from the full-shape analysis of BOSS power spectrum using the one-loop prediction of the Effective Field Theory of Large-Scale Structure (EFTofLSS). The public likelihoods PyBird and CLASS-PT lead to results in agreement only at the $1σ$ level, despite the fact that they are derived from the same BOSS dataset and theory model. We perform a thorough comparison of the various analyses choices made between the two pipelines, and identify that the differences come from the choice of prior on the EFT parameters, dubbed "West-coast" (WC) and "East-coast" (EC) prior, respectively associated to PyBird and CLASS-PT. In particular, because posteriors are non-Gaussian, projection effects from the marginalization over the EFT parameters shift the posterior mean of the cosmological parameters with respect to the best-fit up to $1σ$ in the WC prior and up to $2σ$ in the EC prior. We quantify that best-fit cosmological parameters extracted from BOSS given the two prior choices are consistent at $\sim 1σ$. The consistency improves to $\sim 0.5σ$ when doubling the prior widths. While this reveals that current EFT analyses are subject to prior effects, we show that cosmological results obtained in combination with CMB, or from forthcoming large-volume data, are less sensitive to those effects. In addition, we investigate differences between BOSS measurements. We find broad agreements across all pre-reconstructed measurements considered ($<0.6σ$), but the two available BOSS post-reconstructed measurements in Fourier space, once combined with the EFT full-shape analysis, lead to discrepant Hubble parameter $H_0$ at $\sim 0.9σ$. Given the various effects we discuss, we argue that the clustering amplitude $σ_8$ measured with BOSS is not in statistical tension with that inferred from Planck under $Λ$CDM.

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arXiv2023

Updated constraints from the effective field theory analysis of BOSS power spectrum on Early Dark Energy

Analyses of the full shape of BOSS DR12 power spectrum using the one-loop prediction from the Effective Field Theory of Large-Scale Structure (EFTBOSS) have led to new constraints on extensions to the $Λ$CDM model, such as Early Dark Energy (EDE) which has been suggested as a resolution to the "Hubble tension". In this paper, we re-assess the constraining power of the EFTBOSS on EDE in light of a correction to the normalization of BOSS window functions. Overall we find that constraints from EFTBOSS on EDE are weakened, and represent a small change compared to constraints from Planck and the conventional BAO/$fσ_8$ measurements. The combination of Planck data with EFTBOSS provides a bound on the maximal fractional contribution of EDE $f_{\rm EDE}<0.083$ at 95% C.L. (compared to $<0.054$ with the incorrect normalization, and $<0.088$ without full-shape data) and the Hubble tension is reduced to $2.1σ$. However, the more extreme model favored by an analysis with just data from the Atacama Cosmology Telescope is disfavored by the EFTBOSS data. We also show that the updated Pantheon+ Type Ia supernova analysis can slightly increase the constraints on EDE. Yet, the inclusion of the SN1a magnitude calibration by SH0ES strongly increases the preference for EDE to above $5σ$, yielding $f_{\rm EDE}\sim 0.12^{+0.03}_{-0.02}$ around the redshift $z_c=4365^{+3000}_{-1100}$. Our results demonstrate that EFTBOSS data (alone or combined with Planck data) do not exclude the EDE resolution of the Hubble tension.

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arXiv2022

Constraining decaying dark matter with the effective field theory of large-scale structure

I present the first constraints on decaying cold dark matter (DCDM) models thanks to the effective field theory of large-scale structure (EFTofLSS) applied to BOSS-DR12 data. I consider two phenomenological models of DCDM: i) a model where a fraction $f_{\rm dcdm}$ of cold dark matter (CDM) decays into dark radiation (DR) with a lifetime $τ$; ii) a model (recently suggested as a potential resolution to the $S_8$ tension) where all the CDM decays with a lifetime $τ$ into DR and a massive warm dark matter (WDM) particle, with a fraction $\varepsilon$ of the CDM rest mass energy transferred to the DR. I discuss the implications of the EFTofLSS constraints for the DCDM model suggested to resolve the $S_8$ tension.

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