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Working Group Meeting of COST Action COSMIC WISPers (CA21106)

→ Europe/Zurich
01.403-01.404 (Kirchhoff Institute for Physics)

01.403-01.404

Kirchhoff Institute for Physics

Im Neuenheimer Feld 227 69120 Heidelberg
Alexander Stoll (Kirchhoff-Institute for Physics, Heidelberg University), Loredana Gastaldo (Kirchhoff Institute for Physics, Heidelberg University)
Description

Axions and other very weakly interacting slim (m << GeV) particles (WISPs) are easily accommodated in several  extensions of the Standard Model of Particle Physics. Searches for WISPs are strongly motivated by our attempts  to understand the nature of the dark matter and puzzling astrophysical and particle physics observations.

The Working Group Meeting will shape the activities of the COST Action "COSMIC WISPers in the Dark Universe: Theory, astrophysics, experiments" (CA21106). The objective of the meeting is to promote a discussion among the different communities involved in the project,  with the immediate aim of reviewing the present experimental and theoretical status of WISP searches and plan further directions of investigation. Highlights related to the different Working Groups will be presentes as well as status report of each Working Group.

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Participants
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  • Thu, February 13
    • Registration
      Conveners: Alessandro Mirizzi, Dr Loredana Gastaldo (Kirchhoff Institute for Physics, Heidelberg University)
    • Welcome
    • Talks: WG1
      • 1
        Quantum sensors for axion dark matter
        Speaker: Prof. MARTIN BAUER (IPPP Durham)
        CosmicWimpers25.pdf
      • 2
        Testing the far UV with an axion coupled to photons

        After a brief introduction to axions in string theory, discussing their quality and the origin of their couplings, I will review recent progress in understanding their properties in different string theories from type IIB to heterotic string theories. I will show how the discovery of a light ALP — that is, above the QCD line — is incompatible with unification and heterotic string theory. Finally I will discuss our limitations and the questions that remain open.

        Speaker: Mario Reig Lopez (University of Oxford)
        Cosmic wispers Heidelberg_final.pdf
    • Coffee Break
    • Talks: WG2
      • 3
        Scaling in axion string networks

        In the post-inflationary axion scenario, axions are produced by axion strings. A crucial parameter for the prediction of the axion dark matter mass is the length per unit volume of axion strings at the time of the QCD transition. This can be established only by numerical simulations, which are limited in volume and time, and must be extrapolated to physical values. After a brief history of simulations and the standard extrapolation method (“scaling”), I show results from our latest campaign of simulations. When analysed in the scaling framework, quite precise results are obtained: as measured in the string rest frame, the length density in the radiation era is $1.491(93)/(ct)ˆ2$. The importance for extrapolation of measuring the RMS velocity is emphasised. The much larger values for the string density obtained by other groups are due to extrapolations of the slow approach towards the inferred scaling value. Work in progress towards an axion mass prediction in the scaling framework is outlined.

        Speaker: Prof. Mark Hindmarsh (University of Helsinki, University of Sussex)
        axion_string_scaling_250213_CW_Heidelberg.pdf
      • 4
        General WISP

        Ref: https://inspirehep.net/literature/2176766

        Speaker: Dr Ville Vaskonen
        WISP.pdf
    • Coffee Break: Lunch
    • Talks: WG3
      • 5
        Astrophysical signatures of accreting axion stars
        Speaker: Guenter Sigl
        axion-stars.pdf
      • 6
        High-frequency gravitational waves shining in photons in Astrophysical magnetic fields

        High-frequency gravitational waves (f\gtrsimf≳~MHz) are a smoking gun for the existence of exotic physics. In particular, GW backgrounds lying in the high-frequency would allow one to probe inflation, first-order phase transitions, topological defects and primordial black holes. The lack of current and future gravitational wave experiments sensitive at those frequencies leads to the need of employing different indirect techniques. Notably, one of the most promising one is constituted by graviton-photon conversions in magnetic fields. In this talk, I will discuss possible signature of gravitational wave conversions within astrophysical magnetic fields, focusing on the case Galactic B-fields. In this regard, I will illustrate how graviton-to-photon conversions may lead to unexpected imprints in gamma-ray observations in the range of frequencies f\sim10^{9}-10^{26}\,\Hz. Hence, the absence of any significant evidence for a diffuse photon flux induced by gravitational-wave conversions places stringent constraints on the gravitational-wave strain h_c
        ​
        .

        Speaker: Alessandro Lella
        2025_3_Working_Group_Meeting_Heidelberg.pdf
    • Coffee Break
    • Talks: WG4
      • 7
        NA62: new results
        Speaker: Babette Dobrich (Max Planck Society (DE))
        recentNA62.pdf
      • 8
        GravNet - A global network for the search of high frequency gravitational waves
        Speaker: Claudio Gatti (INFN e Laboratori Nazionali di Frascati (IT))
        Gravnet-Gatti.pdf
    • Dinner
  • Fri, February 14
    • Highlights from CA 21106 Community
    • Coffee Break
    • WG Reports
      • 11
        WG 1 Report
      • 12
        WG 2 Report
      • 13
        WG 3 Report
      • 14
        WG 4 Report
        WG4Report.pdf
      • 15
        WG 5 Report
    • Coffee Break: Lunch
    • Round table and closing
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