arXiv subjects

Lukas Tobias Hergt

Publications and source records attributed to Lukas Tobias Hergt.

5 recordsLinked to original sources

arXiv2026

Is DESI Seeing Dynamical Dark Energy, or a Cosmic Glitch in Gravity?

Combined baryon acoustic oscillation and cosmic microwave background data have begun to mildly favor departures from $Λ\mathrm{CDM}$. This is usually framed as 2-parameter dynamical dark energy. However, a 1-parameter "cosmic glitch in gravity" model, whose cosmological gravitational coupling differs from Newton's constant as in Hořava gravity, fits at least as well. $\textit{Planck}$+ACT+SPT and DESI~DR2 give $G_\mathrm{cosmo}/G_\mathrm{N}=0.9920\pm0.0025$, a $3.3\,σ$ preference for weaker cosmological gravity, robust to adding CMB lensing and supernovae. Fitted to the CMB alone, the glitch predicts DESI distances; $w_0w_a$CDM does not.

astro-ph.CO↗

arXiv2026

Consistency of standard cosmologies using Bayesian model comparison and tension quantification

We present a unified Bayesian assessment of model comparison and data-set consistency for LCDM (cold dark matter plus a cosmological constant) and minimal extensions (neutrino mass, spatial curvature, constant or evolving dark energy) using cosmic microwave background (CMB), baryon acoustic oscillation (BAO), and type Ia supernova (SN) data. The major results are summarized in the first three figures. We quantify model preference with Bayesian evidence and assess consistency with complementary evidence- and likelihood-based diagnostics applied uniformly across data-set combinations. For the models considered, updated Planck processing systematically improves internal CMB consistency (low-$\ell$ versus high-$\ell$, and primary CMB versus CMB lensing). The preference for a closed geometry and an associated ``curvature tension'' with BAO and/or CMB lensing are largely confined to earlier Planck likelihood implementations and weaken substantially when using updated CMB processing and more recent BAO measurements. Apparent evidence for evolving dark energy in CMB+BAO+SN combinations depends sensitively on the specific pairing of CMB and SN likelihoods: plausible alternatives shift inferred tensions by more than $1\,σ$ and can completely reverse the preferred model. Allowing a free neutrino mass tends to absorb residual shifts without introducing new inconsistencies, and we do not find robust evidence for a standalone $τ$-driven discrepancy once the full likelihood context is accounted for. We conclude that claims of a required update of our standard cosmological model from LCDM to $w_0w_a$CDM are premature.

astro-ph.CO↗

arXiv2025

Planck PR4 (NPIPE) map-space cosmic birefringence

Cosmic birefringence is an effect where the plane of polarisation of the cosmic microwave background (CMB) is rotated by an angle $β$ through coupling to a hypothetical parity-violating field. We analyse the Planck Public Release 4 (PR4 or NPIPE) data using a map-space analysis method and find $β=0.46^\circ\pm 0.04^\circ(\mathrm{stat.})\pm0.28^\circ(\mathrm{syst.})$ for SEVEM CMB maps and $β=0.48^\circ\pm 0.04^\circ(\mathrm{stat.})\pm 0.28^\circ(\mathrm{syst.})$ for Commander CMB maps. These values are slightly higher than previously published results, which may be explained by the fact that we have not attempted to remove any potential bias from miscalibration of the Planck polarimeters. The uncertainty in this miscalibration dominates the systematic uncertainty, which also means that our results are consistent with no parity violation. An advantage of the map-space analysis is that it is easy to investigate any variations on the sky, for example caused by foreground contamination. Our results for isotropic birefringence are fairly robust against different spatial data cuts, but there may be hints of a foreground systematic (north versus south hemispheres) or uncontrolled miscalibration effect (T peaks versus E peaks) that should be followed up in future studies. We additionally find no evidence of a cosmic birefringence dipole (anisotropic birefringence).

astro-ph.CO↗

arXiv2024

Methods for CMB map analysis

This introductory guide aims to provide insight to new researchers in the field of cosmic microwave background (CMB) map analysis on best practices for several common procedures. We will discuss common map-modifying procedures such as masking, downgrading resolution, the effect of the beam and the pixel window function, and adding white noise. We will explore how these modifications affect the final power spectrum measured from a map. This guide aims to describe the best way to perform each of these procedures, when the different steps and measures should be carried out, and the effects of incorrectly performing or applying any of them.

astro-ph.CO↗

arXiv2024

Some Times in Standard Cosmology

The standard cosmological model is sufficiently well constrained that precise estimates can be provided for the redshift of various physically defined times in the chronology of the Universe. For example, it is well known that matter-radiation equality, recombination and reionisation happen at redshifts of around 3000, 1000 and 10, respectively, and these can be specified more precisely by fitting to data. What is less well known are the times in years (and their uncertainties) for these and other epochs in the history of the Universe. Here we provide precise time determinations for six epochs in cosmological history within the standard model, using data from the Planck satellite. Our main results are illustrated in a figure.

astro-ph.CO↗