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Newsletter December 2025

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Description

This is December’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

 

Ultralight Dark Matter from the Edge of Field Space

Mathias Becker, Francesco D'Eramo, Ville Vaskonen

https://arxiv.org/abs/2511.09622

 

We introduce a novel class of bosonic dark matter candidates that we dub wallions, featuring boundaries in field space. The wallion mass is exponentially suppressed when the separation between boundaries far exceeds their intrinsic width and remains radiatively stable under self-interactions. We study the early-universe evolution of wallions and the associated cosmological signatures. Finally, we show that instanton effects can dynamically generate field-space boundaries and discuss possible experimental probes once the wallion couples to Standard Model fields.



Stellar Bounds on Light Spin-2 Particles in Bimetric Theories

Camilo García-Cely, Andreas Ringwald

https://arxiv.org/abs/2511.03707

 

Using the bimetric formalism, we compute the production and emission rates of light spin-2 particles in non-degenerate stellar interiors through photoproduction and bremsstrahlung processes, including the effects of plasma screening. By comparing the resulting energy-loss rates with observational limits on stellar cooling, we derive bounds on the coupling strength and mass of the spin-2 particle. Assuming these particles are the dark matter of the Universe, the obtained constraints are competitive with existing astrophysical and cosmological limits, excluding a wide region of parameter space in the mass range 5-30 eV.



Demonstration of an interferometric technique for measuring vacuum magnetic birefringence with an optical cavity 

Aaron D. Spector, Todd Kozlowski, Laura Roberts

https://arxiv.org/abs/2510.14064v1

 

We present a scheme to measure vacuum magnetic birefringence for the first time, by sensing the changes in the frequencies of laser fields stabilized to the resonances of a 245 m long optical cavity whose eigenmode propagates through a string of 24 superconducting magnets arranged for the ALPS II experiment. Results from a prototype setup using a 19 m test cavity without a magnetic field are presented and projected in terms of the sensitivity of the proposed full-scale experiment.



New Massless Spectra from Cosmic String Cusps

Amelia Drew and Ivan Rybak

https://arxiv.org/pdf/2512.12258

 

Cosmic strings cusps are generic features of Nambu–Goto loops where the string momentarily reaches the speed of light. They have a characteristic sharp profile and produce strong gravitational-wave (GW) bursts with frequency-domain strain κ˜(ω) ∝ ω −4/3 , making them key targets for current and future GW searches. However, under certain conditions, this generic picture can differ. We identify cusp solutions with different, including smooth, shapes, and compute their massless GW and axion spectra, deriving a novel general expression for the spectrum κ˜(ω) ∝ ω −n/(2n−1)ω −m/(2m−1) where n, m ≥ 2. We also investigate the effect of realistic corrections to the Nambu-Goto description which can introduce a high frequency cutoff.



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@ba.infn.it

Damiano Fiorillo damianofg@gmail.com

with subject: preprint summary for Cosmic WISPers newsletter.



PhD/Postdoc/Junior Positions

  • December

    • Two Postdoctoral Fellowships in Machine Learning for Astrophysics & Cosmology, Stockholm University link

    • Post-doctoral position in particle cosmology, Warsaw University link

    • Faculty position in nuclear and astro-particle physics theory and experiment, T.-D. Lee Institute, Shanghai link

    • Ayudas para contratos Juan de la Cierva 2025 link

    • Postdoctoral fellowship in theoretical physics at Zaragoza University link

    • PhD opportunities in theoretical physics at Zaragoza University link

    • Research Associate for the Project “Cluster of Excellence Quantum Universe” : Signatures of BSM physics in neutron star mergers at University of Hamburg link

    • PhD position in Physics of Compact Stars and Dark Matter, IST Lisbon & University of Southampton link

    • PhD student position in theoretical physics, Barcelona, IFAE link

    • Postdoctoral position in particle and astroparticle theoretical physics, Brussels University link

    • Postdocs in theoretical particle physics and cosmology, King’s College London link

    • PhD position “Signatures of beyond-standard-model physics in neutron star mergers”, Hamburg University link

  • January

    • Postdoctoral positions in theoretical nuclear and particle astrophysics, Taiwan Institute link

    • Postdoctoral positions in theoretical particle physics, INFN Padua link

    • Postdoctoral positions in theoretical particle physics, INFN Frascati link

    • Postdoctoral positions in theoretical astroparticle physics, INFN Bari link

    • Several postdoctoral positions in theoretical astroparticle physics (expression of interest), University of Padua link

    • Postdoctoral research associate, Durham University link

    • Postdoc positions in theoretical astroparticle physics, University of Bologna link

    • Postdoctoral position in astroparticle and gravitational physics, SISSA, Trieste link

    • Postdoctoral research associate, Fermilab link

    • Postdoctoral positions in theoretical particle physics, KIT Karlsruhe link

 

Conferences

  • January

    • New Windows on Fundamental Physics: from tabletop devices to large scale detectors link
    • High Energy, Cosmology, and Astroparticle Physics Conference link

  • Febuary

    • Cosmic WIPSers Working Group Meeting link

  • 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

  • May

    • SCALE 2026: Strings & Cosmology – All Lengths Explored (SCALE) link
    • Planck2026 & 6th EuCAPT Symposium 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
    • Invisibles 26 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

  • August

    • XVI International Conference on Gravitation, Astrophysics and Cosmology (ICGAC16) link
    • Invisibles 26 link