CosmoBrainstorm 2026

Friday 24 Apr 2026, 10:00 → 22:25 Europe/Stockholm

Oksana Iarygina (Stockholm University, Nordita), Jens Jasche (Stockholm University), David Marsh (Stockholm University), Florian Niedermann (Stockholm University, Nordita)

Venue

Nordita: 4205, floor 4 (conference room), Stockholm, Sweden

Scope

This workshop brings together experts in theory, cosmological data analysis, and particle cosmology to explore how fundamental physics can be probed with current and upcoming observations. Hosted at the Oskar Klein Centre in collaboration with Nordita, the meeting aims to foster close interaction between theory and data, with a strong emphasis on open questions and emerging methodologies. The program is designed to be of particular interest to both communities, encouraging exchange between observational and theoretical perspectives.

A central goal of the workshop is to stimulate collaboration and brainstorming on recent and future developments in cosmology.

The program will feature contributions from local researchers, and will be structured around thematic discussion sessions rather than traditional long talks.

Special Guests

• Eiichiro Komatsu (MPA Munich)
• Takeshi Kobayashi (SISSA, Trieste)
• Chiara Animali (Louvain U. and LPENS, Paris)

Schedule

10:00-12:20	Talks by local researchers
12:20-14:00	Lunch
14:00-16:00	Moderated discussion session with Chiara Animali, Azi Fattahi, Ariel Goobar, Takeshi Kobayashi, and Eiichiro Komatsu
16:00-18:00	Social event (pizza and beer)

 

Panel Discussion

In the discussion session, the panelists will provide us with their take on the "Most exciting or controversial developments in cosmology for the next 5-10 years", followed by a general discussion involving both the panel and the audience.

Panel discussion moderators: Oksana Iarygina, Jens Jasche

Registration

The registration and abstract submission is currently open. We highly encourage early-career researchers to submit an abstract for a contributed short talk (10 minutes + 5 minutes for questions).

The deadline for abstract submission is 10 April (and full consideration will be given to all abstracts received by that date).
The registration closes on April 17.

Organizers

Oksana Iarygina
Jens Jasche
David Marsh
Florian Niedermann

Sponsored by:

 

EventPosterCosmoBrain22026.pdf

Talks: Part 1

1 Illuminating the Local Universe: Large-Scale Structure from ZTF Type Ia Supernovae

Large-scale structure in the nearby Universe is traditionally traced by galaxies and clusters, but wide-field time-domain surveys now allow Type Ia supernovae (SNe Ia) to serve as an additional probe of the cosmic web. Using the second Type Ia supernova data release from the Zwicky Transient Facility (ZTF), I show that SNe Ia exhibit significant spatial clustering, with overdensities closely tracing known galaxy clusters and large-scale structures at low redshift. These inhomogeneities enable direct tests of environmental dependencies in SN Ia light-curve properties, including correlations in stretch and color, while also introducing additional covariance in cosmological analyses through shared bulk flows and common environments. At the same time, the high concentration of SNe Ia within individual structures provides new opportunities to constrain the mass and dynamics of nearby large-scale structures.

Speaker: Antoine Gilles Lordet (Stockholm University / Oskar Klein Center)

CosmoBrainstorm 2026 - Illuminating the Local Universe.pdf

2 The Nature of Dark Matter with Dwarf Galaxies

Dwarf galaxies can serve as powerful probes of the nature of dark matter, but this requires a robust understanding of how baryonic feedback reshapes their dark matter halos. The stellar-to-halo mass ratio is often treated as the primary parameter governing feedback-driven core formation in cold dark matter halos. Using the state-of-the-art EDGE simulations of dwarf galaxies, I will show that the stellar-to-halo mass ratio is only partially correlated with the central dark matter density at z=0, which instead is highly sensitive to a galaxy’s formation history. I will introduce a new quantity that can more accurately predict the impact of baryonic feedback on dark matter halos. I will finish with a look at ongoing work using the LYRA simulations, exploring which properties of the ultra-faint regime are most sensitive to the underlying dark matter model.

Speaker: Claudia Muni (Stockholm University)

Cosmobrainstorm_2026.pdf

3 Gamma Rays and Dark Matter: Status and Prospects

I will review the current status of gamma-ray searches for dark matter, highlighting how space-based observations have opened a powerful window onto particle interactions in astrophysical environments. I will discuss key results from wide-field gamma-ray surveys of targets such as dwarf spheroidal galaxies and the Galactic Center, and how these have shaped constraints on both WIMP and non-WIMP dark matter scenarios. I will also touch upon the broader landscape of gamma-ray astronomy, including the complementarity between space-based instruments and next-generation ground-based observatories.

Speaker: Milena Crnogorcevic (Stockholm University)

2026_CosmoBrainStorm.pdf

4 Gravity beyond a single metric: Ghost-free interactions of spin-2 fields

Some of the most pressing open questions in modern physics, such as dark matter, dark energy, and the Hubble tension, point towards the gravitational sector, making it natural to explore alternative formulations of gravity rather than only modifying the Standard Model matter sector. Both General Relativity and the Standard Model admit formulations in terms of fields of fixed mass and spin. From this perspective, gravity is mediated by spin-2 fields, yet theories with multiple interacting spin-2 fields remain far less understood than their lower-spin counterparts, where, for instance, Yang–Mills theory is essentially the unique theory of interacting spin-1 fields. The central obstacle to consistent spin-2 interactions is the generic appearance of ghosts, pathological modes with negative kinetic energy. In this talk, I will introduce multi-gravity, explain its theoretical and phenomenological interest, and outline how the requirement of ghost-freedom singles out a unique interaction.

Speaker: Joakim Flinckman (Stockholm University)

CosmoBrainstorm_v2.pdf

11:05 Break

Talks: Part 2

5 Magnetic fields as a probe of the first microseconds

The primordial magnetic field can be traced in an evolutionary diagram of comoving magnetic field strength versus comoving length scale, where it follows a characteristic path. Relating the start- and endpoints to each other is an important theoretical accomplishment. At the same time, observational constraints in radio and gamma ray frequencies begin to narrow down the allowed parameter space in this evolutionary diagram. I will highlight several of the theoretical and observational discoveries that make primordial magnetic fields and gravitational waves powerful probes of the first microseconds of the universe, when important beyond standard model physics processes have occurred.

Speaker: Axel Brandenburg (Stockholm University, Nordita)

Brandenburg.pdf

6 A dilaton induced first order QCD phase transition and phenomenology of axion relic pockets

We show that a `QCD dilaton' field, whose vacuum expectation value sets the strong coupling, can render the Quantum Chromodynamic (QCD) confinement transition first-order. The QCD dilaton is cosmologically attracted to a false vacuum at weak coupling in the early universe. Quantum tunnelling towards the true vacuum triggers prompt chiral symmetry breaking and confinement of QCD, leading to detonating bubbles of the hadronic phase. We find that plasma sound waves produced by this dilaton-induced, first-order QCD phase transition generate a stochastic gravitational wave signal strikingly similar to the recently detected gravitational wave background from Pulsar Timing Arrays. We briefly mention how a similar dilaton transition can confine axions into stabilised pockets of false vacuum and outline a way they could generate detectable signals in terrestrial detectors.

Speaker: Charalampos Nikolis (Stockholm University)

cosmo-brainstorm-final.pdf

7 Phase transitions and topological defects

Phase transitions play an important role in cosmology. In this talk I will explore the interplay between first-order phase transitions and topological defects. I will also discuss how late-time symmetry-restoring transitions can generate gravitational waves, relevant for pulsar timing arrays, and at the same time impact the Hubble tension.

Speaker: Aleksandr Chatrchyan (Stockholm University)

COSMOBRAIN.pdf

12:05 Group Photo

12:20 Lunch

Moderated discussion session

Moderated discussion session with Chiara Animali, Azi Fattahi, Ariel Goobar, Takeshi Kobayashi, and Eiichiro Komatsu.

Moderators: Oksana Iarygina and Jens Jasche

Social event (pizza and beer)