An iterative AI reasoning process proposes new dynamical dark energy equations of state that are competitive with traditional forms on supernova, BAO, and Planck data.
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The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes
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abstract
Boltzmann codes are used extensively by several groups for constraining cosmological parameters with Cosmic Microwave Background and Large Scale Structure data. This activity is computationally expensive, since a typical project requires from 10'000 to 100'000 Boltzmann code executions. The newly released code CLASS (Cosmic Linear Anisotropy Solving System) incorporates improved approximation schemes leading to a simultaneous gain in speed and precision. We describe here the three approximations used by CLASS for basic LambdaCDM models, namely: a baryon-photon tight-coupling approximation which can be set to first order, second order or to a compromise between the two; an ultra-relativistic fluid approximation which had not been implemented in public distributions before; and finally a radiation streaming approximation taking reionisation into account.
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representative citing papers
Bayesian reconstruction and exhaustive symbolic regression on CMB, BAO, and supernova data yield the one-parameter dark energy parametrization w(a) = w0 / sqrt(a) that fits observations comparably to CPL and better than LambdaCDM.
Derives exact rational-plus-π² closed forms for every multipole coefficient α_ℓ in the neutrino collision kernel by rewriting the kernel as angular derivatives of a Yukawa potential and reducing the integrals via a first-order recurrence.
Control variates with Zeldovich mocks reduce covariance matrix variance by up to an order of magnitude on large scales in DESI-like mocks.
The work demonstrates that multi-tracer field-level SBI on galaxy and HI maps yields 2-7 times better constraints on Omega_m and sigma_8 than single-tracer or summary-statistic approaches, with 3D maps performing best.
Any unified early and late dark energy scenario with a single tracking scalar field requires a potential with three distinct slopes arranged in a steep-steeper-shallow hierarchy.
A Newtonian Motion Gauge found via Einstein-Boltzmann solver maps linear dynamics with scale-dependent growth and GR corrections to Newtonian equations, enabling consistent nonlinear EFT calculations that are transformed back for accuracy in real and redshift space.
Second-order relativistic corrections to the redshift drift are derived; the dominant sub-Hubble term is the squared radial velocity gradient, producing a bispectrum that can exceed the squared power spectrum at low z.
DESI DR1 Lyman-alpha data yields Δ²★=0.379±0.032 and n★=-2.309±0.019 at k★=0.009 km⁻¹s and z=3, sharpening N_eff, α_s, and β_s constraints by factors of 1.18-1.90 when combined with other probes.
Derives the power spectrum evolution and cross-spectra for arbitrary multi-species wave and particle dark matter, incorporating free-streaming, Jeans scales, and intrinsic fluctuations.
The paper calculates multifrequency angular power spectra of the 21 cm line for models with primordial magnetic fields of strength 4 nG and spectral indices -2.9 and -2.5, then estimates signal-to-noise ratios for uGMRT, MeerKAT and SKA1-MID.
Λ_s VCDM is a predictive model combining Λ_s CDM with VCDM gravity via an auxiliary scalar field and sigmoid-smoothed potentials to enable stable mirror AdS-to-dS transitions with possible transient acceleration.
Cobaya is a modular Bayesian analysis code that exploits model interdependencies via automatic caching and a novel parameter-blocking algorithm to minimize sampling cost.
Neglecting linear GR effects biases f_NL at 1–3σ for Euclid/SPHEREx in SFB forecasts; multi-tracer improves Doppler detection and weakly breaks b_ϕ f_NL degeneracy.
Optimal redshift weighting on eBOSS QSO full-shape data reduces uncertainties on H0 by 43.3%, σ8 by 19.7%, w0 by 20.5% and produces a bounded posterior on wa in the CPL model.
HIcosmo is a new JAX-based differentiable framework for background cosmology inference that matches Cobaya results while delivering 8.7x CPU and up to 20x GPU speedups.
A geometric invariance makes the BAO-SN Ω_m gap invariant under sound-horizon rescaling α and requires opposite w(z) deformations for the two datasets, so their combination cannot reach the local H0 value.
iDCDM adds two parameters to LambdaCDM so that dark matter decay produces late-time interacting radiation, yielding a distinctive low-redshift suppression of structure growth while leaving BBN and primary CMB unchanged.
An interacting sterile neutrino component via pseudoscalar mediator reconciles CMB and DESI DR2 BAO measurements with 2.7 sigma preference and reduces H0 tension to 2.4 sigma.
First UVLF-based constraints on model-agnostic isocurvature power spectra for CDM, baryon, neutrino, and dark radiation modes yield consistent 95% credible envelopes over k ~ 0.5-10 Mpc^{-1}.
Planck CMB data set upper limits on vector and axial-vector dark matter-electron couplings for masses 100 eV to 100 keV via energy injection from inelastic scattering and hydrogen absorption.
Develops a short-timescale injection formalism for post-recombination fluctuations, derives CMB impacts from scalar/vector/tensor perturbations, and constrains sequestered dark sector phase transitions to permille-level fractional energy injections.
Model-independent reconstruction shows that early-universe modifications resolving the Hubble tension exist at the background level, requiring a smooth ~15% pre-recombination expansion rate enhancement.
Future global 21-cm observations could beat CMB limits on TeV-scale decaying dark matter for lifetimes ≳10^15 s, especially for decays into neutrinos.
citing papers explorer
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Physics-guided discovery of dynamical dark-energy equations of state through iterative AI reasoning
An iterative AI reasoning process proposes new dynamical dark energy equations of state that are competitive with traditional forms on supernova, BAO, and Planck data.
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Data-Driven Discovery of a Simple Phantom-Crossing Dark Energy Parametrization
Bayesian reconstruction and exhaustive symbolic regression on CMB, BAO, and supernova data yield the one-parameter dark energy parametrization w(a) = w0 / sqrt(a) that fits observations comparably to CPL and better than LambdaCDM.
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Self-interacting neutrinos in cosmological perturbation theory -- integrating the collision kernel
Derives exact rational-plus-π² closed forms for every multipole coefficient α_ℓ in the neutrino collision kernel by rewriting the kernel as angular derivatives of a Yukawa potential and reducing the integrals via a first-order recurrence.
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Fewer simulations, sharper covariances: Reducing mock covariance noise with Zeldovich approximation control variates
Control variates with Zeldovich mocks reduce covariance matrix variance by up to an order of magnitude on large scales in DESI-like mocks.
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Field-level multi-tracers simulation-based inference of cosmological parameters from 3D maps
The work demonstrates that multi-tracer field-level SBI on galaxy and HI maps yields 2-7 times better constraints on Omega_m and sigma_8 than single-tracer or summary-statistic approaches, with 3D maps performing best.
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Unifying Early and Late Dark Energy: Dynamical Requirements and Obstructions
Any unified early and late dark energy scenario with a single tracking scalar field requires a potential with three distinct slopes arranged in a steep-steeper-shallow hierarchy.
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Effective Field Theory of Large Scale Structure and Newtonian Motion Gauges
A Newtonian Motion Gauge found via Einstein-Boltzmann solver maps linear dynamics with scale-dependent growth and GR corrections to Newtonian equations, enabling consistent nonlinear EFT calculations that are transformed back for accuracy in real and redshift space.
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Nonlinear Relativistic Effects on Cosmological Redshift Drift
Second-order relativistic corrections to the redshift drift are derived; the dominant sub-Hubble term is the squared radial velocity gradient, producing a bispectrum that can exceed the squared power spectrum at low z.
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Cosmological analysis of the DESI DR1 Lyman alpha 1D power spectrum
DESI DR1 Lyman-alpha data yields Δ²★=0.379±0.032 and n★=-2.309±0.019 at k★=0.009 km⁻¹s and z=3, sharpening N_eff, α_s, and β_s constraints by factors of 1.18-1.90 when combined with other probes.
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Growth of Structure in Multi-species Wave Dark Matter
Derives the power spectrum evolution and cross-spectra for arbitrary multi-species wave and particle dark matter, incorporating free-streaming, Jeans scales, and intrinsic fluctuations.
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Effects of primordial magnetic fields on 21 cm multifrequency angular power spectra
The paper calculates multifrequency angular power spectra of the 21 cm line for models with primordial magnetic fields of strength 4 nG and spectral indices -2.9 and -2.5, then estimates signal-to-noise ratios for uGMRT, MeerKAT and SKA1-MID.
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$\Lambda_{\rm s}$CDM cosmology from a type-II minimally modified gravity
Λ_s VCDM is a predictive model combining Λ_s CDM with VCDM gravity via an auxiliary scalar field and sigmoid-smoothed potentials to enable stable mirror AdS-to-dS transitions with possible transient acceleration.
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Cobaya: Code for Bayesian Analysis of hierarchical physical models
Cobaya is a modular Bayesian analysis code that exploits model interdependencies via automatic caching and a novel parameter-blocking algorithm to minimize sampling cost.
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Impact and measurability of linear relativistic effects in galaxy surveys
Neglecting linear GR effects biases f_NL at 1–3σ for Euclid/SPHEREx in SFB forecasts; multi-tracer improves Doppler detection and weakly breaks b_ϕ f_NL degeneracy.
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Cosmological inference from the eBOSS QSO full-shape analysis with optimal redshift weights
Optimal redshift weighting on eBOSS QSO full-shape data reduces uncertainties on H0 by 43.3%, σ8 by 19.7%, w0 by 20.5% and produces a bounded posterior on wa in the CPL model.
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HIcosmo: a differentiable JAX-based framework for cosmology inference
HIcosmo is a new JAX-based differentiable framework for background cosmology inference that matches Cobaya results while delivering 8.7x CPU and up to 20x GPU speedups.
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Geometric obstruction to resolving the Hubble tension: orthogonality of scale and shape in distance measurements
A geometric invariance makes the BAO-SN Ω_m gap invariant under sound-horizon rescaling α and requires opposite w(z) deformations for the two datasets, so their combination cannot reach the local H0 value.
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Dark Matter with a Drag at Low Redshift
iDCDM adds two parameters to LambdaCDM so that dark matter decay produces late-time interacting radiation, yielding a distinctive low-redshift suppression of structure growth while leaving BBN and primary CMB unchanged.
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Recoupled Dark Radiation reconciling CMB and DESI BAO measurements
An interacting sterile neutrino component via pseudoscalar mediator reconciles CMB and DESI DR2 BAO measurements with 2.7 sigma preference and reduces H0 tension to 2.4 sigma.
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New Isocurvature Constraints from JWST UV Luminosity Function
First UVLF-based constraints on model-agnostic isocurvature power spectra for CDM, baryon, neutrino, and dark radiation modes yield consistent 95% credible envelopes over k ~ 0.5-10 Mpc^{-1}.
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CMB Limits on the Absorption of Light Vector and Axial-Vector Dark Matter
Planck CMB data set upper limits on vector and axial-vector dark matter-electron couplings for masses 100 eV to 100 keV via energy injection from inelastic scattering and hydrogen absorption.
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Post-Recombination Fluctuations from a Sequestered Dark Sector
Develops a short-timescale injection formalism for post-recombination fluctuations, derives CMB impacts from scalar/vector/tensor perturbations, and constrains sequestered dark sector phase transitions to permille-level fractional energy injections.
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Geometric Constraints on the Pre-Recombination Expansion History from the Hubble Tension
Model-independent reconstruction shows that early-universe modifications resolving the Hubble tension exist at the background level, requiring a smooth ~15% pre-recombination expansion rate enhancement.
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Cosmological constraints on TeV-scale dark matter subcomponents decaying between recombination and reionisation
Future global 21-cm observations could beat CMB limits on TeV-scale decaying dark matter for lifetimes ≳10^15 s, especially for decays into neutrinos.
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Double the axions, half the tension: multi-field early dark energy eases the Hubble tension
Two-field axion-like early dark energy reduces Hubble tension to 1.5 sigma residual and improves high-ell CMB fits over single-field models.
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Into the Gompverse: A robust Gompertzian reionization model for CMB analyses
A Gompertzian reionization model with three nuisance parameters demotes optical depth to a derived quantity, reducing its uncertainty by a factor of three and revealing potential neutrino mass tension in CMB analyses.
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A unified harmonic framework for dark siren cosmology
The GW-galaxy cross-correlation method, unified with spectral sirens in a harmonic framework, can measure H0 to 1% and Omega_m to 5% precision with 2 years of data from next-generation detectors like Einstein Telescope and Cosmic Explorer.
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Observational constraints on Luciano-Saridakis entropic cosmology
First background-level constraints on Luciano-Saridakis entropic cosmology using CC, Pantheon+ with SH0ES, DESI DR2 BAO and compressed Planck data show robust fit, 2sigma exclusion of LambdaCDM, and potential Hubble tension alleviation.
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Nonlinear Matter Power Spectrum from relativistic $N$-body Simulations: $\Lambda_{\rm s}$CDM versus $\Lambda$CDM
Relativistic N-body simulations of Lambda_s CDM produce a redshift-dependent crest in the matter power spectrum ratio, peaking at 20-25% near the transition and leaving a 15-20% uplift at z=0 on group scales.
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Modeling nonlinear scales for dynamical dark energy cosmologies with COLA
COLA-based hybrid emulator reproduces nonlinear power spectrum boosts in w0wa models to <2% error vs EuclidEmulator2 and produces <0.3σ shifts in LSST-like cosmic shear parameter constraints.
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Impact of projection-induced optical selection bias on the weak lensing mass calibration of galaxy clusters
Projection-induced selection bias causes 20-50% overestimation of weak lensing masses for optically selected galaxy clusters, larger on scales >3 Mpc.
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Parity Violation in Galaxy Shapes: Primordial Non-Gaussianity
The parity-odd intrinsic alignment power spectrum probes the collapsed limit of the parity-odd primordial trispectrum and can tighten constraints on parity-violating PNG when bias parameters are calibrated from N-body simulations.
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Generalized neutrino isocurvature
Generalizes neutrino isocurvature by introducing a mixing angle for the neutrino-matter perturbation ratio and derives first Planck limits on the angle.
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The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and its Implications for Structure Growth
ACT DR6 yields a 2.3% precise CMB lensing power spectrum with A_lens = 1.013 ± 0.023 relative to Planck 2018 Lambda CDM, giving S8 = 0.818 ± 0.022 and no evidence for suppressed structure growth.
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Dark Energy Survey Year 3 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing
DES Y3 3x2pt analysis constrains S8=0.776±0.017 and Ωm=0.339±0.032 in flat ΛCDM, consistent with Planck CMB results at p=0.13-0.48.
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Exploring the interplay of late-time dynamical dark energy and new physics before recombination
Under standard recombination, phantom-crossing dynamical dark energy is preferred at ~97–98.5% probability; early-time fixes to the Hubble tension erase that preference while creating severe ω_m tension with CMB.
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A hidden reionization prior biases cosmological inference
No monotonic reionization history fits Planck τ, patchy kSZ from SPT/ACT, and Lyα endpoint; an early ionization phase at z≳12 relaxes ∑mν<0.39 eV and shifts σ8 via As-τ degeneracy.
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Spherical Collapse and Halo Formation in a Cosmology with Decaying Dark Matter and a Semi-Cosmographic Dark Energy
In a decaying dark matter plus semi-cosmographic dark energy cosmology constrained by DESI BAO and ShapeFit, the spherical collapse threshold stays close to the ΛCDM value while massive halo abundance shows pronounced deviations that enable joint constraints on DDM lifetime and dark energy parameter
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Late-Time Oscillating Quintessence in Light of DESI
A late-onset oscillating quintessence model improves the fit to DESI plus supernova and CMB data by Delta chi squared of about 9 over Lambda CDM, driven by background expansion.
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Are Cosmological Data Excluding Sterile Neutrinos or Only the Fully Thermalized Limit?
Cosmological observations constrain the effective abundance of light sterile neutrinos tightly while allowing non-fully-thermalized realizations to remain viable across LambdaCDM and CPL models.
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Evolving Dark Energy Is Vacuum Energy After All
A QCD-vacuum dark-energy model with a two-parameter switch reproduces the DESI-preferred late-time expansion and is mildly favoured over ΛCDM by Bayesian evidence (lnB≈2.7).
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Impact of lensing magnification on the power spectrum turnover
Lensing magnification biases the recovered turnover scale k0 by up to 3.6 sigma in high-z mocks, vanishing above z~3.7 for MegaMapper-like surveys and requiring modeling above z~2.9.
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Constraints on the Sum of Neutrino Masses from ACT DR6 and DESI DR2 Considering Isocurvature Initial Conditions
Including neutrino density isocurvature in fits to ACT DR6, DESI DR2, and DES data yields ∑m_ν < 0.057 eV at 95% CL in ΛCDM with no detection of the isocurvature mode.
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Compressed Gaussian likelihood for the Planck low-$\ell$ data
A compressed Gaussian likelihood for Planck low-ℓ data is built from SRoll2 via offset log-normal functions for Fisher compatibility and validated against the original via MCMC.
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Late-time Quantum Vacuum Decay and its Cosmological Implications
Phenomenological late-time vacuum-tunneling models are fit to DESI DR2, supernova, and CMB data, allowing up to 50% vacuum-energy drop for z_t < 1 and a preferred z_t ~7 model that converts ~10% dark matter while easing cosmological tensions.
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Exploring the Dark Sector: Interacting Radiation in Light of Modern Cosmological Probes
New constraints on dark radiation parameters from recent cosmological datasets show the model alleviates the Hubble tension with SH0ES inclusion while remaining consistent with standard expectations without it.
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Negative neutrino mass or negative dark energy?
A sign-switching dark energy model (Λ_s CDM) recovers positive effective neutrino masses (0.055 ± 0.050 eV) consistent with oscillation data, unlike ΛCDM which prefers negative values (-0.075 eV), for DESI DR2 + CMB + supernova fits with z_† > 2.4.
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Primordial Magnetic Fields at Cosmic Dawn: 21-cm Forecasts with HERA and SKA
Primordial magnetic fields enhance low-mass halo abundance at Cosmic Dawn, advancing Lyman-alpha coupling, X-ray heating and reionization and imprinting detectable signatures on global and fluctuating 21-cm signals observable by HERA and SKA.
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Alleviating the Hubble Tension Using $\Lambda$sCDM Model: A Coupled Dark Energy - Dark Matter Interaction
The ΛsCDM model with coupled dark sectors reduces the Hubble tension to 1.2σ via late-time expansion changes while keeping the early-universe sound horizon nearly unchanged.
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A barotropic alternative to Early Dark Energy for alleviating the $H_0$ tension
A barotropic fluid with ω_s ≈ 0.29 and Ω_s ≈ 1.5×10^{-5} raises the inferred H0 to match SH0ES while remaining consistent with Planck CMB, DESI BAO, and Pantheon data.