DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2026

 

    • Tuesday 21 April 2026 at 10:15 in A315 and using Zoom:  Antonino Salvino Midiri (University of Geneva) Onsite Cosmo Seminar
      Fluid perturbations from expanding bubbles in first-order phase transitions
      Abstract:       In this talk I am going to focus on the power spectrum of the velocity field induced in the primordial plasma by expanding scalar-field bubbles during a first-order phase transition occurring in the radiation-dominated era. Contrary to previous expectations, we find that the breaks in the velocity spectrum are not associated to the bubble size and the sound shell thickness, but to the position of the discontinuities of the velocity profiles. This distinction is particularly relevant for supersonic deflagrations, as it implies that the intermediate slope is more pronounced and the two breaks are more separated when the wall velocity approaches the Chapman-Jouget speed, instead of the sound speed. Moreover, we find that the asymptotic branches of the velocity power spectrum are determined by an integral over the velocity profiles at large scales, and by the discontinuities of the profiles at small scales. Furthermore, the position of the two breaks and the intermediate slope depend on the distribution function of the times of bubble nucleation. The main result is a refined template for the velocity spectrum at the beginning of the sound-wave phase, which can be used for studying the resulting anisotropic stresses and gravitational wave production.
    • Thursday 21 May 2026 at 10:15 in A315 and using Zoom: Michal Heller (Ghent)
      TBA
      Abstract:       TBA
    • Tuesday 26 May 2026 at 10:15 in A315 and using Zoom: Mika Nurmela (Helsinki)
      TBA
      Abstract:       TBA
    • Thursday 6 June 2026 at 10:15 in A315 and using Zoom: Andrea Olzi (Paris)
      TBA
      Abstract: TBA
    • Tuesday 11 August 2026 at 10:15 in A315 and using Zoom: Christophe Royon (CMS)
      TBA
      Abstract:       TBA

Hopefully the up to 50 min + 10 min discussion long seminar/colloquium will be understandable to a wide audience.
Contacts: Keijo Kajantie (keijo kajantie at helsinki fi) [ HIP seminar],
Tushar Gupta  (tushar.gupta at helsinki fi) [cosmo seminar]

Other related seminars

Friday 10-12 seminar series in D114: Astrophysics seminar
Mathematical Physics Seminar and Workshop series Wed 14-16 in Exactum C123.
InstituteQ Events and Seminars