Category Archives: Cosmology

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At a recent DESY (Hamburg) colloquium, I gave a review talk on “Resolving the Hubble Tension with New Early Dark Energy.”

I explained how the DESI anomaly might be connected to the Hubble tension and have an early-universe explanation in terms of dark acoustic oscillations. 

Slides + full video: https://physikseminar.desy.de/hamburg/colloquia_in_2025/16_december_2025/

The paper mentioned in the video clip below (now online): arXiv:2512.15870 — https://arxiv.org/abs/2512.15870

This builds on earlier work on New Early Dark Energy, with excellent collaborators: Florian Niedermann, Mathias Garny, Henrique Rubira, Aleksandr Chatrchyan, Juan Cruz, Emil Brinch Holm, Vivian Poulin, Thomas Tram, Steen Hannestad …

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A new early-universe explanation of the DESI anomaly connecting to the predictions of our solution to the Hubble tension in collaboration with Mathias Garny and Florian Niedermann: https://arxiv.org/abs/2512.15870

The presence of a Dark Acoustic Oscillation (DAO) near the actual BAO may appear as a single BAO-only feature with a slightly shifted peak position, which could bias the DESI BAO measurements, thereby explaining the anomaly in the DESI DR2 data without invoking late-time-evolving Dark Energy. The DAO predicted in our model for solving the Hubble tension, Hot New Early Dark Energy (Hot NEDE) with Dark Radiation Matter Decoupling (DRMD), also meets the requirements for explaining the DESI results, as shown in the leftmost panel of the figure below. The green curve is the favoured DAO position by the DESI DR2 data on small scales, and the dotted black line is the prediction of DRMD in Hot NEDE, when solving the Hubble tension.

Screenshot 2025-12-19 at 07.52.54.png

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New community report today uses different methods and techniques to establish the value of the Hubble constant to 1% precision, H0=73.50+/-0.81 km/s/Mpc, confirming the Hubble tension at more than 5-sigma.

This means that our current standard model of the Universe, the ΛCDM model, can not describe the real Universe as we observe it, and we must move to finding the correct model of our Universe replacing ΛCDM.

New Early Dark Energy (NEDE) has proven itself to be a promising framework in which to search for the solution to the Hubble tension (see previous posts), and we will keep intensifying our efforts to explore NEDE.

See the community report here: https://arxiv.org/abs/2510.23823

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To make sense of the Hubble tension, it is essential to have a simple (in terms of ideas), convincing solution. In a new paper, we present a new microscopic Hot NEDE model of the dark sector based on well-known fundamental principles, gauge symmetry, and spontaneous symmetry breaking, which resolves the Hubble tension. We also discuss how this solution can be further tested with future precision data.

Profile likelihood curves for the model from our paper can be seen below.  

Work in collaboration with Mathias Garny, Florian Niedermann and Henrique Rubira.

The paper is on arXiv: https://arxiv.org/abs/2508.03795.

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“Simplicity is part of what I mean by beauty, but it is a simplicity of ideas, not simplicity of a mechanical sort that can be measured by counting equations or symbols.”

— Steven Weinberg

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In a new paper, “I demonstrate that soft graviton modes in de Sitter are the Goldstone modes of the spontaneously broken asymptotic symmetry group of de Sitter. I then show that any local measurement, including the effects of the environment, will collapse the symmetric state onto the broken state in the large volume limit. In any discussion involving observers, de Sitter is, therefore, best described globally by the broken phase, while local observers, in the small volume limit, can not discriminate between different degenerate global vacuum states, and are therefore best described by the symmetric state. This illuminates the physical nature of soft graviton modes in de Sitter.”

As a bonus, I also speculate about the possibility that a new type of crystals, with the same symmetry-breaking pattern as discussed in the paper, could be realized in the laboratory as an analog system of de Sitter and eternal inflation.

The paper is on arXiv:  https://arxiv.org/abs/2502.03520