Journal Club

Seminar Room

Friday 26th of September, 2025

Hour: 11:00

Title: Domain walls seeding the electroweak phase transition

Presented by: Luis Gil Martín

Ref: https://arxiv.org/abs/2203.16450

Abstract:

Topological defects can act as local impurities that seed cosmological phase transitions. In this paper we study the case of domain walls, and how they can affect the electroweak phase transition in the Standard Model extended with a Z2-odd scalar singlet. When the transition is two-step, the early breaking of the Z2 symmetry implies the formation of domain walls which can then act as nucleation sites for the second step. We develop a method based on dimensional reduction to calculate the rate of the catalyzed phase transition within the 3d theory on the domain wall surface. By comparison with the standard homogeneous rate, we conclude that the seeded phase transition is generically faster and it ultimately determines the way the phase transition is completed. We comment on the phenomenological implications for gravitational waves and baryogenesis.

Hour: 11:30

Title: News from the light ion runs at the LHC

Presented by: Alba Soto Ontoso

Ref: https://cms.cern/news/collective-motion-tiny-systems-oxygen-and-neon-collisions-window-nuclear-structure

Abstract:

For the first time, the CMS experiment has measured how particles flow in collisions of oxygen-oxygen (OO) and neon-neon (NeNe) ions at the Large Hadron Collider (LHC). These small, but powerful, collisions reveal clear signs of collective behavior, similar to what is seen in much larger systems such as lead-lead (PbPb) collisions. The results provide robust evidence for how the initial geometry of colliding nuclei translates into final particle flow – a key step toward understanding collectivity in small collision systems and its possible connection to a hot and exotic state of matter called the quark-gluon plasma (QGP).