DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2026

• • Thursday 16 April 2026 at 10:15 in A315 and using Zoom: Will Barker (Institute of Physics, Prague) Onsite Cosmo Seminar
    Systematic approaches to new physics in cosmology
    The standard model of cosmology, which combines the standard model of particle physics with general relativity and the added ingredients of dark matter and dark energy, is remarkably successful at explaining our observations of the cosmos. Despite this success, the nature of dark matter and dark energy remains a mystery. Meanwhile, subtle and shifting tensions are often used as a pretext for developing new physics models. We outline an approach for the systematic exploration of new physics models in the dark sector. Rather than developing specific models, it is possible to survey the space of possible theories using numerical and symbolic techniques, combined with modern sampling methods and high-performance computing. The current system constrains models based on the stability of the free theory, and we will discuss simple phenomenological constraints against observations of black holes, gravitational waves, pulsars and the distributions of galaxies. We will also discuss ongoing extensions to the automatic reconstruction of interactions and the quantum theory. 
  • 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
  • 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