3rd Training School COST Action COSMIC WISPers (CA21106)

16 sept. 2025, 06:23 → 19 sept. 2025, 22:30 Europe/Paris

Auditorium Vivargent (Campus du CNRS)

 

 

The COST Action CA21106 3rd Training School will be held in Annecy (France) at the LAPTh, a world-class research laboratory just 40 km away from CERN.

 

 

We will support travel and accommodation expenses of up to 30 participants.  

 

The goal is to start training a generation of young scientists in the interdisciplinary expertise on WISPs, ranging from theoretical and experimental approaches to multi-messenger astroparticle physics and cosmology. For this purpose, the Training School will offer lectures from experts on different aspects of WISPs physics. The School is aimed at PhD students, as well as at early-career postdocs.

The European COST Action CA21106 "Cosmic WISPers in the Dark Universe: Theory, astrophysics and experiments" is an initiative funded by the COST Association, whose goal is to study axions and other very weakly interacting slim particles (WISPs) emerging 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.

 

 

Local organising committee:

F. Calore (Chair)

Y. Genolini 

P. D. Serpico 

R. Zatini

 

 

mar. 16 septembre

Registration and welcome coffee

1 Welcome and presentation of the School

Lectures: WG1 lecture I

2 Non-axionic WISP theory

Orateur: Mark Goodsell

10:40 Coffe break

Lectures: WG4 lecture I

3 Probing ultralight axion-like particles with quantum technology

Orateur: Sreemanti Chakraborti

12:30 Lunch break

Tutorial Exp: WG4 tutorial I

Tutorial TH/Pheno: WG1 tutorial

16:00 Coffee break

Students presentations

4 Flash talk: QCD Sum Rules: Basis and applications. Carlos Albarrán Calvo

The QCD sum rules technique is a very useful tool in order to analytically calculate a series of hadronic parameters. I will explain the concept, basis and development of the method, illustrating a practical example meanwhile and one of its many applications.

5 Flash talk: Searching for the unique signature of ALPs using radio telescopes. David Alonso-López

Radio-loud strong gravitational lensed quasars are a robust probe of axion-like particles (ALPs), one of the most promising dark matter candidates. The coupling of a pseudoscalar field (the ALP) with the electromagnetic field (EM), via a Chern-Simons type term, produces achromatic birefringence, i.e., a rotation of the polarisation angle independent of frequency. In the geometric optics regime, the propagation of light in the presence of an ALP field does not suffer any other deviation from the standard propagation of light in curved spacetimes. This birefringence effect can be used to probe the parameter space of the ALP field with radio polarimetry observations. In particular, the LOFAR-VLBI pipeline is capable to produce sub-arcsecond resolution images of the lensed systems, whose typical size is ~1 arcsec. If polarisation is detected in these lensed quasars, the time delay between the images provides a net difference in the polarisation angle (∆θ) that only depends on the ALP field mass and coupling to the EM field, cancelling out other effects such as Faraday Rotation and systematics or calibration errors. By detecting just a single lensed quasar in polarisation with LOFAR, even a non-detection of the birefringence effect (∆θ=0) would improve by a factor of 10 current constraints on the ALP field's mass and coupling to the EM field in the ultra-light regime (<10^-18 eV).

6 Flash talk: Neutrino Oscillations: Global Fit and implications on DM searches. Martina Beccaria

In this talk I will present the Neutrino Global Fit, obtained from results of different neutrino oscillations experiments, and the possibility in the future to use its methodology to gain information about ultra light Dark Matter.

7 Flash talk: Dark Photon Search at the Short Baseline Near Detector. Gaetano Fricano

This study presents a search for Dark Photon signals at the Short-Baseline Near Detector (SBND), recently commissioned at Fermilab. Dark Photons, predicted in minimal extensions of the Standard Model with an extra U(1) gauge symmetry, can be a source of electron positron pairs, producing broader and more energetic shower topologies than neutrino-induced backgrounds. Exploiting SBND’s excellent imaging capabilities, kinematic and timing-based discriminants are investigated to suppress backgrounds and probe a previously unexplored region of the dark photon parameter space.

8 Flash talk: Optomechanical Particle Detection with a Membrane-Based Interferometer network. Karlo Veličan

We present an optomechanical approach to particle detection using a modified Michelson interferometer, where one mirror is replaced by a thin silicon nitride membrane. The membrane’s mechanical motion, induced by particle interactions, is read out via homodyne detection of the optical signal. This setup provides high sensitivity and paves the way for a scalable network of mechanical particle detectors. Such a platform could open new opportunities for precision sensing in dark matter sector.

9 Searching for the Dark Photon with PADME. Kalina Dimitrova

The PADME Experiment at Laboratori Nationali di Frascati is designed to search for the Dark Photon, a hypothetical gauge boson, responsible for the interaction between the visible and the hidden sector. PADME explores the process of annihilation of beam positrons with the electrons in a fixed target, employing the missing mass technique: in case the annihilation results in the associate production of one visible and one Dark photon, the first can be registered by the experiment's electromagnetic calorimeter and the Dark Photon mass can be reconstructed knowing the beam energy. This talk presents the analysis techniques that are being employed for the PADME data, as well as the background composition and rejection procedure.

10 QCD axions at finite density. Vincenzo Fiorentino

Providing an elegant solution to the strong CP problem, and representing a promising candidate for cold dark matter, the QCD axion is one of the best motivated light BSM particles. For this reason, the experimental effort in the search for the axion has increased drastically in recent times, with new experimental proposals like IAXO at DESY, and FLASH at the INFN. This makes it necessary to provide highly precise and reliable bounds on the axion parameter space. In this talk I will give an introduction to the supernova axion bound, focusing in particular on the role of finite density corrections, which are important in the supernova and have been neglected in the past. Additionally, I will describe how the so-called nucleophobic axion models, for which the supernova bound gets sizeably relaxed, survive finite density effects. Finally, I will provide some insight on more recent developments.

11 Axion domain walls and thermal friction. Amedeo Maria Favitta

Cosmological models with QCD axions and/or ALPs can be affected by a domain wall (DW) problem. We review and propose solutions, beyond proposing a biased axion potential, taking into account thermal plasma friction: we evaluate the plasma pressure acting on a DW with velocity v taking into account the relevant particle processes, deriving and studying the relative VOS model and obtaining relative bounds and cosmological BSM observables under such hypotheses.

12 Probing self interacting dark matter with inverse bremsstrahlung of gravitational waves. Víctor Fonoll Rubio

We present the inverse bremsstrahlung (IB) absorption of GWs as a novel approach to GWs physics that can help set constraints on different physical models. The observation of GWs of a given frequency sets constraints on its absorption efficiency, which depends on the characteristics of the medium of propagation. In the case of interacting dark matter, this can translate to constraints on its mass-coupling space. For this, we present a novel approach to parametrize the absorption of GWs in DM halos and in IGM. We find the arising constraints to be less stringent than existing ones.

13 Tackling ALP searches in meson decays with ALPaca: a phenomenological approach. Marta Fuentes Zamoro

Part of the community has intensively searched for ALP signals, as well as conducted dedicated data analyses to identify potential evidence of New Physics compatible with an ALP, resulting in constraints on the ALP parameter space. Therefore, it is now the time to present a tool, ALPaca, that facilitates the combination among the different information on ALP physics. The focus of this talk will be on a phenomenological analysis of the ALP theory using the most up-to-date data from flavour facilities, to show both the latest constraints and the potential of ALPaca.

14 Influence of Quadratic Axion-Matter Interaction on the Direct Detection of Dark Matter. Yeray Garcia del Castillo

Axions and Axion-Like-Particles (ALPs) are theoretically well-motivated candidates for dark matter that, due to their large occupation number, can be described as oscillating classical fields. These particles may feature a quadratic interaction with ordinary matter which can modify the field's dynamics in the vicinity of such objects, inducing a very interesting phenomenology. In this talk, I will treat in a general setting, how the presence of the Earth can modify the sensitivities of direct detection experiments such as CASPEr. I will show the regions of the parameter space with noticeable effects, where current and future experimental sensitivities can be modified. I will also discuss the applicability of the results when the Earth’s acceleration is taken into account. For this purpose, I will discuss the time dependence of the field and its relaxation times to stationary configurations.

15 Domain wall evolution beyond quartic potentials. Ricarda Heilemann

The Sine-Gordon and Christ-Lee potentials; Abstract: Domain walls are the simplest type of topological defects formed at cosmological phase transitions, and one of the most constrained. Their studies typically assume a quartic double well potential, but this model is not fully representative of the range of known or plausible particle physics models. Here we study the cosmological evolution of domain walls in two other classes of potentials. The Sine-Gordon potential allows several types of walls, interpolating between different pairs of mínima (which demands specific numerical algorithms to separately measure the relevant properties of each type). The Christ-Lee potential parametrically interpolates between sextic and quartic behavior. We use multiple sets of simulations in two and three spatial dimensions, for various cosmological epochs and under various choices of initial conditions, to discuss the scaling properties of these networks. In the Sine-Gordon case, we identify and quantify deviations from the usual scaling behavior. In the Christ-Lee case, we discuss conditions under which walls form (or not), and quantify how these outcomes depend on parameters such as the energy difference between the false and true vacua and the expansion rate of the Universe. Various biased initial conditions are also addressed in fappendices. Finally, we briefly comment on the possible cosmological implications of our results.

16 A combined search for dark matter with COSINE-100 and ANAIS-112. Sophia Hollick

The evidence for the existence of dark matter from astrophysical observations is strong. However, there has not been a conclusive direct detection of dark matter that does not rely on gravitational interaction with visible matter. One experiment, DAMA, claims to have observed an annual modulation signal in a sodium-iodide-based detector consistent with that expected from dark matter. COSINE-100 and ANAIS-112, two leading sodium-iodide dark matter experiments, were designed to test DAMA’s claim directly using the same target material. COSINE-100, located at Yangyang Underground Laboratory in South Korea, and ANAIS-112, located at Canfranc Underground Laboratory, have been taking data since 2016 and 2017, respectively. The two experiments have similar sensitivity and have thus far published results independently. In this talk, I will discuss our efforts to combine the data from the two experiments for increased search sensitivity and share its results.

17 Three-photon annihilation at PADME experiment. Katerina Kostova

The three-photon final state in e+e- annihilation has significantly lower cross-section in comparison to the two-photon annihilation, however, it may provide an indication for the existence of new axion-like particles decaying into a pair of photons produced together with an additional photon. To measure the e+e- to three gamma cross-section, data from the PADME experiment will be utilized. PADME is a fixed-target experiment exploiting the positron beam from the DAΦNE linear accelerator at Laboratori Nazionali di Frascati in Italy. The main goal of the experiment is the search for new light particles that may give an insight for the explanation for the dark matter problem. Based on Monte Carlo simulations accounting for the geometrical and resolution effects, the divergence of the three-photon annihilation process is studied as a function of various final state cuts. The expected acceptance is calculated and optimised and the prospects for the measurement of Br(e+e- → ggg) at PADME are discussed.

18:30 Welcome reception

mer. 17 septembre

Lectures: WG4 lecture II

18 Probing ultralight axion-like particles with quantum technology

Orateur: Sreemanti Chakraborti

10:30 Coffee break

Lectures: WG1 lecture II

19 Non-axionic WISP theory

Orateur: Mark Goodsell

12:30 Lunch break

CERN visit

jeu. 18 septembre

Lectures: WG2 lecture I

20 Ultralight dark matter

Orateur: Elisa Ferreira

10:30 Coffee break

Lectures: WG3 lecture I

21 WISPs and Compact Objects

Orateur: Jamie McDonald

12:30 Lunch break

Tutorial Exp: WG4 tutorial II

Tutorial TH/Pheno: WG3 tutorial

16:00 Coffee break

Students presentations

22 Polarimetric Microlensing as a Tool for Breaking Degeneracies in Compact Object Lensing toward the Galactic Bulge. Marsida Laze

Gravitational microlensing upon passage of compact objects in front of background stars brightens them and provides a way to investigate the lensing bodies. Nonetheless, photometric light curves by themselves are not sufficient to uniquely constrain important parameters such as mass, distance, and velocity because of the degeneracies. Typical second-order effects like parallax and finite-source size improve the situation; however, a quite promising alternative is polarization measurement. In particular, RGB stars can show detectable polarization in microlensing by symmetry-breaking differential magnification. This study explores the detectability of polarization signals using the FORS2 polarimeter at the VLT with an assumed sensitivity of 0.1%. They show that intense polarization in microlensing events among RGB stars and intermediate-distance lenses is imminent, and with polarimetric microlensing being a promising tool for the improvement of lens characterization and degeneracy resolution.

23 Probing axion-like particles with multimessenger observations of neutron star mergers. Francesca Lecce

Axion-like particles (ALPs) can be copiously produced in binary neutron star (BNS) mergers through nucleon-nucleon bremsstrahlung if the ALP-nucleon couplings are sizable. Furthermore, the ALP-photon coupling may trigger conversions of ultralight ALPs into photons in the magnetic fields of the merger remnant and of the Milky Way. This effect would lead to a potentially observable short gamma-ray signal, in coincidence with the gravitational-wave signal produced during the merging process. This event could be detected through multi-messenger observation of BNS mergers employing the synergy between gravitational-wave detectors and gamma-ray telescopes. In this work, we study the sensitivity of current and proposed MeV gamma-ray experiments to detect such a signal. We find that the proposed instruments can reach a sensitivity comparable with the SN 1987A limit.

24 The PADME Run III analysis result. Marco Mancini

The PADME experiment, designed to investigate potential signatures of physics beyond the Standard Model, has conducted a resonant search for a hypothetical X17 particle, potentially linked to the anomaly observed at ATOMKI. During Run III, PADME employed a positron beam impinging on a fixed diamond target to explore resonant electron-positron annihilation processes near 17 MeV, where the new particle is expected to be, aiming to identify deviations in two-body final state yields. The analysis strategy involved comparing observed yields with expected background through Monte Carlo simulations and data-driven techniques. Systematic uncertainties were carefully evaluated, accounting for beam parameters, target thickness and detector efficiencies. A likelihood-based statistical framework, incorporating nuisance parameters, was used to estimate upper limits on coupling strength under the assumption of a signal-plus-background or background-only hypothesis. While no significant excess indicative of new physics was observed, the sensitivity achieved places meaningful constraints on the viable parameter space for the X17 hypothesis.

25 Astrophysical aspects of string compactifications. Mario Ramos-Hamud

A generic aspect of effective field theories coming from string compactifications is the appearance of moduli fields. Among these moduli, the axion and dilaton are present at low energies as (pseudo-)Goldstone bosons from the spontaneous breaking of an exact (or approximate) global symmetry. These moduli have a different microscopic coupling to matter but appear kinetically coupled in such a way that their interaction can compete with gravity at low energies and have an important effect in strong gravity environments. In this talk, we will discuss some of the astrophysical implications of a stringy-inspired multi-scalar-tensor theory. In particular, we show numerically the existence of a screening mechanism that reduces the Brans-Dicke dilaton coupling to macroscopic matter sources such as a neutron star.

26 Interferometric Technique for a Measurement of Vacuum Magnetic Birefringence with the ALPSII Magnet String. Laura Roberts

Vacuum magnetic birefringence (VMB) is a currently undetected con- sequence of quantum electrodynamics (QED) which results from the pre- diction of virtual electron-positron pairs allowing for the polarization of vacuum under the influence of a strong magnetic field. The ALPSII string consists of a 212m, 5.3T magnet string with modulation capabilities cur- rently in the mHz regime, which can produce a strong VMB signal. We propose a sensing scheme which measures the relative frequency changes between orthogonal laser fields frequency stabilized to a single optical cavity. The frequency drifts, which are proportional to the induced bire- fringence from VMB, are sensed with a local oscillator allowing for a heterodyne readout. With a goal of reaching sensitivities on the order of 10−17m√Hz in differential optical path length displacement, we present the ongoing work and initial results for the current prototype experiment, alongside a summary of the ALPSII infrastructure and its ability to measure birefringence on the QED level with the proposed scheme.

27 Axion Searches Using X-ray Telescopes. Francisco Rodríguez Candón

28 Dynamical systems and superstring phases in the early universe. Noelia Maria Sanchez Gonzalez

In this talk, I will present the string theory dynamics of the volume scalar rolling down an exponential potential in a background of cosmic superstring loops. In the context of the LVS potential, we demonstrate the existence of a novel string loop attractor tracker solution, in which 75% of the energy density of the universe is in the form of a gas of fundamental cosmic superstring loops (preferred over the standard radiation tracker). On this tracker, it is the continual reduction in the string tension as the volume evolves that makes the loops stable against decay. For more general non-LVS potentials, mixed radiation-loop trackers can also occur.

29 Multiple mountains on a pulsar: implications for gravitational waves and the spin-down rate. Paritosh Verma

A pulsar, i.e., a spinning neutron star, with a deformation could emit gravitational waves continuously. Such continuous waves, which have not been detected yet, will be very useful to study gravitational physics and to probe the extreme physics of neutron stars. While typically such waves from a pulsar are estimated considering an overall stellar ellipticity, there can be multiple irregularities or mountains in the stellar crust that the gravity of the star cannot smooth. In this paper, we consider this realistic situation and compute the strain, power, torque and the pulsar spin-down rate due to multiple mountains supported by the stellar crust. Here, we consider astronomically motivated mountain distributions and use the Brans-Dicke theory of gravity which has three polarization states: two tensors dominated by the time-varying quadrupole moment and one scalar dominated by the time-varying dipole moment. We also give limiting results for general relativity.

ven. 19 septembre

Lectures: WG3 lecture II

30 WISPs and Compact Objects

Orateur: Jamie McDonald

10:30 Coffee break

Lectures: WG2 Lecture II

31 Ultralight dark matter

Orateur: Elisa Ferreira

12:30 Lunch break

Tutorial Exp: WG4 tutorial III

Tutorial TH/Pheno: WG2 tutorial