Novel strategies for new low-mass particles searches at colliders and from stellar objects

par Mael Cavan (Lapth - USMB)

vendredi 10 oct. 2025, 14:00 → 16:30 Europe/Paris

Auditorium (Annecy-le-Vieux)

The Standard Model (SM) of particle physics is an extremely successful theoretical framework that
precisely describes the electromagnetic, weak, and strong interactions between the fundamental
constituents of matter. Its predictions have been confirmed by numerous experiments, notably the
discovery of the Higgs boson in 2012. However, several indications suggest the existence of physics
beyond the SM (BSM), such as the origin of dark matter, the matter-antimatter asymmetry, neutrino
masses, and the strong CP problem. The latter can be elegantly addressed by the Peccei–Quinn mechanism, which predicts the existence
of a pseudo-scalar particle: the QCD axion. This particle is also a promising candidate for dark
matter. In its "invisible" version, the axion interacts very weakly with matter; its couplings are
inversely proportional to $f_a$, typically greater than $10^9$ GeV, making it difficult to detect.
Similar particles, called ALPs (Axion-Like Particles), have also been proposed. Unlike the QCD
axion, ALPs allow for a lower $f_a$, making them potentially accessible in collider experiments.
This manuscript adopts a multi-environmental approach to study axion physics, combining
astrophysical phenomena, Cherenkov detection, and collider searches. After introducing the
theoretical framework of the QCD axion, an effective description of its interactions is developed
using chiral perturbation theory (ChPT) to study low-energy hadronic phenomena.
The first study focuses on axion emission in supernovae, particularly SN 1987A. The cooling of the
stellar core via axion emission provides an indirect detection channel. By extending the calculations
to strange baryons and mesons, we present the first quantitative study of axionic emissivity beyond
the first generation and establish the strongest constraint on the axion–strange–down coupling, as
well as a novel constraint on the axion–strange–strange coupling.

The second study investigates the detection of an astrophysical axion flux on Earth in water
Cherenkov detectors such as Hyper-Kamiokande. We compute the spectra of the processes $a + N \
to N + \gamma$ and $a + N \to N + \pi^0$. Even for the QCD axion, detectable signals may arise,
particularly through $\pi^0$ production, which exhibits a more favorable spectrum. An extension to
strange matter yields weaker signatures but potentially observable ones if the couplings to the first
generation are suppressed.
Finally, the last part is devoted to axion searches at colliders. After reviewing existing constraints,
we propose exploring new three-body decay channels such as $K \to \pi \pi a$ and $K \to \mu \mu
a$, leveraging the capabilities of the LHCb detector. A method is presented to study, from a
theoretical perspective, processes that could be of experimental interest.
This work thus highlights the value of combining different experimental environments to probe
axion properties across various energy scales using complementary methods