Sound-Horizon-Agnostic Forecast for Constraints on H 0 and m nu from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing

arXiv:2610.31660 · astro-ph.CO · Submitted 2026-10-22 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "Sound-Horizon-Agnostic Forecast for Constraints on H 0 and m nu from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing".

Jocelyn: Here's the gist of the paper. The gist The method presents a sound-horizon-agnostic forecast for constraints on H0 and Σmν from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing.

Vera: This research is significant because it provides a consistency test of ΛCDM without relying on the standard early-Universe calibration of the sound horizon at recombination rd.

Jocelyn: How it works The core methodology involves treating the sound horizon at baryon drag rd as a free parameter and inferring it jointly with other cosmological parameters <ref:2610.31660#pg5> This approach avoids the need for standard early-Universe calibration of rd by treating it as a free parameter <ref:2610.31660#pg5>.

Vera: The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>.

Paper summary: Vera: To recap, this paper "Sound-Horizon-Agnostic Forecast for Constraints on H zero and m nu from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing" presents a forecast combining several major probes. The core idea is treating the sound horizon at baryon drag rd as a free parameter instead of using its standard early-Universe calibration >

Jocelyn: So they use LSST-like galaxy weak lensing and Simons Observatory-like CMB lensing alongside the DESI BAO program and expanded supernova samples to constrain H0 and Σmν jointly <ref:2610.31660#pg1>.

Subrahmanyan: The significance is that this method provides a consistency test of ΛCDM without relying on the standard early-Universe calibration of rd, which is what makes it different from traditional methods >

Vera: But they are upfront about the limitations too. They mention that because rd is left free, the resulting framework isn't fully model-independent, and they interpret their forecasts within standard ΛCDM supplemented by a free rd >

Jocelyn: And they acknowledge that this approach remains sensitive to the assumed early-time cosmology, specifically how theta* combined with CMB lensing and galaxy-lensing information describes both the physics around recombination and the subsequent evolution <ref:2610.31660#pg3>.

Subrahmanyan: So, they’re essentially saying this is a statement about sound-horizon calibration, not about model independence >

Conclusion: Vera: Thinking about the title of "Sound-Horizon-Agnostic Forecast for Constraints on H zero and m nu from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing," it really sums up the ambition of this work. It’s a forecast that tries to get robust constraints on H0 and neutrino masses without being tied down by one specific early-Universe value for the sound horizon >

Jocelyn: And what it implies is that we have a way to test ΛCDM consistency using these diverse measurements, even when we don't rely on the standard calibration of rd >

Subrahmanyan: It means that if our constraints come out and they are consistent across all these probes, it gives us confidence in the structure of ΛCDM across different cosmological scales >

Seyed Hamidreza Mirpoorian, Helena García Escudero, Levon Pogosian, Amy Wayland, David Alonso

Department of Physics, Simon Fraser University · Laboratoire de Univers et Particules de Montpellier, UMR5299-CNRS · Department of Physics and Astronomy, University of Southern California · Department of Physics, University of Oxford

astro-ph.CO

Submitted: 2026-10-22

Updated: 2026-10-22

Comments: 11 pages, 3 figures, 3 tables

Code: https://github.com/hamidmirpoorian/4modrec

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

The gist: The gist The method presents a sound-horizon-agnostic forecast for constraints on H0 and Σmν from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing.

Key concepts

Sound Horizon at Baryon Drag ($r_d$): $r_d$ is the characteristic distance sound waves traveled in the primordial plasma before baryon drag occurred. Instead of fixing this value based on standard early-universe physics, this method treats $r_d$ as a free parameter to test $\Lambda$CDM consistency.
Sound-Horizon-Agnostic Forecast: This is a forecasting technique that derives cosmological constraints without needing to assume the standard calibration for the sound horizon. By treating $r_d$ as a free variable, the analysis tests whether $\Lambda$CDM holds true across different assumptions about early-universe physics.
Systematic Marginalization: The analysis explicitly accounts for realistic observational errors and biases, such as photometric redshift calibration issues, shear biases in galaxy lensing, intrinsic alignments of galaxies, and baryonic feedback effects. This ensures the constraints on $H_0$ and $\Sigma m_{\nu}$ are robust against these known systematics.
Joint Parameter Inference: The method simultaneously infers cosmological parameters like $H_0$, $\Sigma m_{\nu}$, and the free parameter $r_d$. This joint inference allows for a more comprehensive consistency check of the $\Lambda$CDM model by exploring the parameter space without relying on a single, potentially inaccurate, early-universe calibration.

Summary

The gist The method presents a sound-horizon-agnostic forecast for constraints on H0 and Σmν from BAO, CMB Lensing, Supernovae and LSST-like Galaxy Lensing. This research is significant because it provides a consistency test of ΛCDM without relying on the standard early-Universe calibration of the sound horizon at recombination rd.

How it works

The core methodology involves treating the sound horizon at baryon drag rd as a free parameter and inferring it jointly with other cosmological parameters <ref:2610.31660#pg5> This approach avoids the need for standard early-Universe calibration of rd by treating it as a free parameter <ref:2610.31660#pg5>. The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>.

The analysis combines several probes to constrain the parameters <ref:2610.31660#pg5>. These probes include:

**: LSST-like galaxy weak lensing <ref:2610.31660#pg5> and SimonsObservatory-like CMB lensing <ref:2610.31660#pg5>. 5) The completed DESI BAO program <ref:2610.31660#pg5> and expanded supernova samples <ref:2610.31660#pg5>. 7) This method provides a consistency test of ΛCDM without relying on the standard early-Universe calibration of rd <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating the sound horizon at baryon drag rd as a free parameter provides a consistency test of ΛCDM without relying on the standard early-Universe calibration of rd <ref:2610.31660#pg5>. 8) Allowing Σmν to vary weakens the H0 constraints, while still yielding a forecast 95% CL upper limit of about 0.4 eV on Σmν <ref:2610.31660#pg5>. 5) We treat rd as a free parameter and infer it jointly with other cosmological parameters <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>. 5) Treating rd as a free parameter removes the explicit assumption of a standard early-Universe calibration <ref:2610.31660#pg5>. 8) We also extend the CMB-lensing analysis to Lmax = 5000 <ref:2610.31660#pg5>. 9) The analysis incorporates realistic galaxy weak-lensing systematics, explicitly marginalizing over photometricredshift calibration, multiplicative shear biases, intrinsic alignments, and baryonic feedback <ref:2610.31660#pg5>.

Improvements for AI systems

Sound Horizon Agnostic Constraint Calculation: The improved system can calculate constraints on H0 and sum of neutrino masses from combined BAO, CMB lensing, galaxy weak lensing, and supernova data by treating the sound horizon at baryon drag rd as a free parameter rather than relying on standard early-Universe calibration.
Systematics Marginalization: The AI system can incorporate realistic galaxy weak-lensing systematics such as photometric redshift calibration errors, multiplicative shear biases, intrinsic alignments, and baryonic feedback explicitly into the analysis likelihoods to produce unbiased constraints.
Prior Sensitivity Testing: The system can perform sensitivity tests by varying the prior choice for As (e.g., uniform versus informative Gaussian) and Sigma m nu (uniform versus logarithmic) to quantify how these choices affect H0 and Sigma m nu forecasts, as demonstrated in Table III of the paper.
Modified Universe Validation: The improved system can validate its method by testing it on mock data from modified recombination and early dark energy models, allowing for a direct comparison of unbiased recovery against models that modify the matter and lensing power spectra beyond just the sound horizon.
Uncertainty Quantification: The system can forecast uncertainties for H0, such as sigma(H0) approximately 1.3 km/s/Mpc with the least informative prior set or 0.69 km/s/Mpc with an informative prior on As, providing a direct measure of constraint precision for future surveys like LSST and Simons Observatory.