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Newsletter March 2026

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This is March’s edition of the newsletter of the COST action. The aim is to keep you updated on recent and upcoming conferences and postdoc positions on subjects related to WISPs.

 

Cosmic Wispers preprints

 

Black hole scalar sirens in the Milky Way

Daniel Gavilan-Martin, Olivier Simon, Dhashin Krishna, Derek F. Jackson Kimball, Dmitry Budker, Arne Wickenbrock

https://arxiv.org/abs/2602.23415

Light scalar particles trigger the superradiant instability around spinning black holes (BHs), causing clouds of scalars to grow around the BH. In the presence of sufficiently strong particle self-interactions, scalars are ejected from BH orbits, resulting in coherent, non-relativistic emissions that continuously carry away the BH's angular momentum. Parameters exist for which cloud growth is much faster, and scalar depletion is much slower, than the age of the Galaxy. This defines a distinct class of astrophysical sources of scalars, which we call BH scalar sirens -- BHs that persistently emit scalars effectively forever. We compute the scalar background from the expected population of isolated stellar-mass BHs in the Milky Way. This provides a detection target independent of early-universe scalar production or cosmological initial conditions. The generated observable signals are up to two orders-of-magnitude larger than those expected from a misaligned cosmic scalar.  While stellar-mass Milky Way BHs are our primary target, our framework extends to supermassive, intermediate-mass and light BHs. Given the difficulty of directly observing populations of isolated BHs, scalar emissions offer a novel probe of these otherwise invisible objects, highlighting the potential for joint discovery between scalars and BHs, and broadly motivating searches for scalars over many orders-of-magnitude in mass.



Axions at the meV Crossroads: Theory, Cosmology, Astrophysics, and Experiments

Michele Cicoli, Francesco D'Eramo, Luca Di Luzio, Damiano F. G. Fiorillo, Maurizio Giannotti, Alicia Gomez, Diego Guadagnoli, Mathieu Kaltschmidt, Bradley J. Kavanagh, Alessandro Lella, Giuseppe Lucente, David J. E. Marsh, Federico Mescia, Alessandro Mirizzi, Javier Redondo, Nicole Righi, Jaime Ruz, Ken'ichi Saikawa, Elisa Todarello, Edoardo Vitagliano, Su-Yang Xu

https://arxiv.org/abs/2603.18167

The meV mass range has emerged as a focal point in axion physics, where advances in theory, cosmology, astrophysics, and experimental techniques converge. Axions in this mass range are theoretically well motivated, can arise in ultraviolet-complete models, and can have significant cosmological impacts as dark matter or dark radiation. In parallel, their efficient production in stellar and supernova environments provides powerful astrophysical probes. Here, we provide a comprehensive overview of meV axions across these domains, highlighting both established results and open questions. We discuss the theoretical underpinnings of meV axions, their cosmological and astrophysical signatures, and the diverse experimental strategies -- ranging from helioscopes and haloscopes to quasiparticle systems and large-volume Cherenkov detectors -- that aim to explore this regime. The convergence of these approaches emphasizes the pivotal role of the meV mass range for axion discovery in the coming years, identifying meV axions as a key probe for testing beyond-Standard-Model physics. This review document is the direct outcome of the discussions at the dedicated workshop "The meV Mass Axion Frontier: Challenges and Opportunities", held at Laboratori Nazionali di Frascati (IT) on 27--28 October 2025, and organized by the EU funded COST Action "Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments" (CA21106). Its aim is to provide an overview of current efforts in meV axion research, their motivations, and the research goals that animate the community involved in this search.



The COSMIC WISPers White Paper: The physics case for Weakly Interacting Slim Particles

Ariel Arza et al.

https://arxiv.org/abs/2603.03433

Axions and other very weakly interacting slim particles (WISPs), with masses below 1 GeV, arise naturally in many extensions of the Standard Model of particle physics. In particular, they could offer a new framework to explain the nature of dark matter and may help address a range of puzzling observations in astrophysics and particle physics. This review provides an overview of ongoing WISP searches and outlines the prospects for the next decade, spanning their theoretical motivation, indirect signatures in astrophysical observations, and dedicated laboratory experiments. It is based on the work carried on by the EU-funded COST Action ``Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments'' (CA21106). This network plays a key role in coordinating and supporting WISP searches across Europe, while also contributing to the development of a roadmap aimed at securing European leadership in this research area. It is emphasized that Europe is currently pursuing a rich, diverse, and cost-effective experimental program, with the potential to deliver one or more transformative discoveries.

 

We encourage participants in the COST action to send us a small summary, typically smaller than the abstract, of their own articles that will appear in the arXiv (after they appear, with their arXiv numbers). The summary will be disseminated in the newsletter.

Send email to 

Alessandro Lella alessandro.lella@unipd.it

Damiano Fiorillo damianofg@gmail.com

with subject: preprint summary for Cosmic WISPers newsletter.






PhD/Postdoc/Junior Positions

  • March

    • Postdoctoral positions, University of Minnesota, Minneapolis link

  • April

    • Postdoctoral positions in supernova neutrino physics, Beijing link

    • Postdoctoral positions for cosmic exotic particle search, USTC, Hefei link

  • May

    • PhD positions in Astrophysics, Cosmology and Gravitation, Espirito Santo University, South America. link

  • August

    • Postdoctoral researcher positions in theoretical astroparticle physics and axion phenomenology, Annecy LAPTH link




Conferences

  • March

    • GGI PhD School on "Theoretical Aspects of Astroparticle Physics, Cosmology and Gravitation" link
    • 60th Rencontres de Moriond on Very High Energy Phenomena in the Universe: Moriond VHEPU 2026 link
    • 2nd UNDARK School link

  • April

    • 7th Edition of the international conference Progress on Old and New Themes in cosmology (PONT 2026) link
    • Dark Energy from Home 2026 (DEfH26) link

  • May

    • UniVersum VII -- Naples 2026 link
    • SCALE 2026: Strings & Cosmology – All Lengths Explored (SCALE) link
    • Planck2026 & 6th EuCAPT Symposium link
    • 6th New Physics Opportunities at Neutrino Facilities Workshop (NPN 2026) link

  • June

    • 16th International Workshop on the Identification of Dark Matter 2026 (IDM 2026) link
    • 32nd International Conference on Neutrino Physics and Astrophysics (Neutrino 2026) link
    • PASCOS 2026: The 31st International Symposium on Particles, Strings, and Cosmology (PASCOS2026) link
    • Black Holes & Cosmology 2026 (BHCos26) link
    • 4th Training School of the COST Action CA21106: Cosmic WISPers link
    • 4th General Meeting of the COST Action: Cosmic WISPers (CA21106) link
    • Primordial Cosmology: Novel Perspectives from Scattering Amplitudes, Holography and the Bootstrap link

  • July

    • Exploring New Frontiers in Cosmology: GGI Workshop link
    • Dark Matter and Stars: Multi-Messenger Probes of Dark Matter and Modified Gravity (icdms2026) link
    • Axions in Seoul 2026: Frontiers in Theory, Cosmology, and Experiment (AiS 2026) link
    • New Frontiers in Strong gravity link

  • August

    • XVI International Conference on Gravitation, Astrophysics and Cosmology (ICGAC16) link
    • Invisibles 26 link
    • Listening to the Cosmos: New Frontiers in Gravitational Wave Physics link
    • COSMO-26: 29th International Conference on Particle Physics & Cosmology link
    • Neutrino Oscillation Workshop 2026 (NOW 2026) link

  • September

    • Erice International School/Workshop of Nuclear Physics, 47th course on 'Neutrinos in Cosmology, in Astro-, Particle- and Nuclear Physics' link

  • November

    • 21st Patras Workshop on Axions, WIMPs and WISPs link

  • December

    • 4th International Conference on Neutrinos and Dark Matter (NuDM- 2026) link