Category Archives: NEDE

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We might have observed “the end of the first act” of the universe’s evolution in recent high-precision CMB observations. In a new paper, we show that ACT DR6 data provide evidence for an accelerated running of the primordial spectral index, which would imply a breakdown of the first stage of inflation and, at the same time, resolve the Hubble tension in the DRMD Hot NEDE model (see previous posts). 

Inflation occurs during the first period of the universe’s evolution after the Big Bang, and observing the breakdown in the first stage of inflation therefore amounts to observing the end of the first act of the universe’s evolution. The accelerated running compensates for the increased damping at small scales in the CMB and therefore allows for a larger N_eff in models with self-interacting dark radiation, such as Hot NEDE with DRMD. The idea that inflation occurred in several acts (or stages) has long been considered more natural than 60 e-folds of single-field slow-roll inflation. In our paper, we also discuss how the end of the first act could occur through gauge-field production in axion monodromy-like inflation or through a tachyonic instability. For more details, see our new paper: https://arxiv.org/abs/2604.26541

Work in collaboration with Mathias Garny (Technical University of Munich) and Florian Niedermann (Nordita).

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The Hubble tension and the DESI anomaly are considered to both seriously challenge the standard model of cosmology (the ΛCDM model).

In a new paper, we predict Dark Acoustic Oscillations (DAO) as the fingerprint of new dark forces required to resolve the Hubble tension in the Dark Radiation-Matter Decoupling (DRMD) model, naturally realised within the Hot New Early Dark Energy (Hot NEDE) setup. DAOs, with the same properties required to solve the Hubble tension, can independently explain the DESI anomaly.

Using an inference independent of large-scale structure data, relying only on Planck measurements of the cosmic microwave background and SH0ES-calibrated supernova data, we find evidence for a DAO signal with drag-horizon scale rd,DAO ∈[54,65] Mpc/h (68% C.I.) and amplitude ADAO ∈[0.02,0.05] (68% C.I.). These predictions provide a concrete target for current and upcoming large-scale structure surveys, including DESI, Euclid, and the Roman Space Telescope.

It is remarkable that the scale and amplitude of the DAO required for solving the Hubble tension using only CMB and supernova data (no DESI BAO data), overlaps with the DAO scale and an amplitude independently preferred by the DESI BAO data (see my two previous posts), when the DESI anomaly is interpreted as being due to a DAO bias (as an alternative to the evolving dark energy interpretation) — providing a preliminary independent verification of DRMD’s relevance for solving the Hubble tension.

The work in collaboration with Mathis Garny and Florian Niedermann is on arXiv: https://arxiv.org/abs/2602.23895

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Below is a cartoon illustration of the negative branch versus the positive branch discussed in the video linked in the previous post and in our paper: https://arxiv.org/abs/2512.15870

As we discuss in the paper:

On the positive branch, the DAO is almost on top of the BAO but at a slightly larger scale, and it will shift the perceived peak of the BAO slightly to the positive side of the DAO.

On the negative branch, the BAO and the DAO peaks are well separated, but close; the characteristic tail of the DAO can shift the perceived position of the BAO in the opposite
direction away from the DAO. In this case, the main peak of the DAO is assumed to be at a sufficiently small scale where it could be hidden by non-linear systematics in currently publicly available DESI DR2 data.

Both the positive and negative branches could potentially be discoverable in future DESI data releases or upcoming surveys like Euclid, by either resolving the DAO peak that overlaps closely with the BAO, or identifying a shallow DAO peak on scales∼50Mpc/h somewhat smaller than the BAO, consistent with our predictions in our earlier work as a result of solving the Hubble tension: https://arxiv.org/abs/2508.03795

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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. 

Link to: Slides + full video

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 an update of our recent paper with Aleksandr Chatrchyan, Florian Niedermann, and Vivian Poulin, we have included fits of Cold New Early Dark Energy (Cold NEDE) to the DESI BAO data. 

Using  CMB Planck Plik data, DESI BAO, and Pantheon+ data, we find around 2-sigma evidence for NEDE (see upper left panel below), which is enhanced to 6-sigma evidence when including SH0ES supernovae data (see upper right panel below). 

Without including SH0ES data, a value of H0=73 km/s/Mpc, compatible with SH0ES findings, is allowed within 2-sigma using Planck Plik, DESI BAO, and Pantheon+ data (see lower left panel below). Including SH0ES data, the Lambda-CDM preferred value of H0 less than 68 km/s/Mpc is excluded at 6-sigma in the Cold NEDE model.

For likelihoods with other dataset combinations, parameters, and discussion, see our full paper: https://arxiv.org/abs/2408.14537.