Theoretical Cosmology meetings

To actively encourage the field of theoretical cosmology and to set an informal stage for the exchange of ideas, the Dutch theoretical cosmology community organizes Friday afternoon meetings approximately 6 times a year — usually on the first Friday of the month. The meetings typically start in the afternoon with a main speaker, followed by a short break to continue with another seminar or journal club discussion on some topic of current interest. We end the afternoon with drinks. The supporting institutes in Leiden, Amsterdam, Groningen, Utrecht where recently joined by the strings and cosmology group in Leuven and take turns in hosting the event.

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Leiden Autumn 2021

05/11/2021 @ 13:30 - 16:30

Leiden, November 5th.

This meeting will take place via a mixed in person-zoom session. Please, register your on-site presence at the following google sheet. Here the information for connecting through Zoom:

Time: November 5, 2021 01:30 PM Amsterdam Time

Join Zoom Meeting
Zoom Link
Meeting ID: 691 7900 5101
Password: A9@B?iki

13:30 – 14:15: Talk by Stefano Camera (University of Turin)

Title: Radio cosmology and the SKAO


In this talk, I shall review the most peculiar aspects of cosmology in the radio band, with a special focus on the SKAO radio-telescope and its pathfinders. I shall present the main radio probes that can be exploited for late-time cosmology: continuum and 21-cm line galaxy surveys, neutral hydrogen intensity mapping, and even weak lensing cosmic shear at radio frequencies. Moreover, I shall also discuss the added value of multi-wavelength synergies, presenting some show-case example of the power of radio-optical cross-correlations to test the foundations of the concordance cosmological model, such as the nature of dark matter and dark energy, or tests of inflation and gravity.

14:15 – 14:30: 15 minutes Coffee Break & Discussion

14:30 – 15:15 Talk by Evangelos Sfakianakis (Institut de Física d’Altes Energies – IFAE)

Title: CMB Signatures of Standard Model Higgs Effects during Reheating


I will describe a new way of studying the Higgs potential at extremely high energies. The Standard Model (SM) Higgs boson, as a light spectator field during inflation in the early Universe, can acquire large field values from its quantum fluctuations which vary among different causal (Hubble) patches. Such a space dependence of the Higgs after the end of inflation leads to space-dependent SM particle masses and hence variable efficiency of reheating, when the inflaton decays to Higgsed SM particles. Inhomogeneous reheating results in (observable) temperature anisotropies. I will discuss both perturbative and resonant decay of the inflaton to SM particles. For the case of perturbative decay from coherent oscillations of the inflaton after high scale inflation, I will demonstrate the existence of strong constraints on the reheat temperature for the inflaton decay into heavy SM particles. For the case of resonant particle production (preheating) to (Higgsed) SM gauge bosons, resulting temperature fluctuations are larger than the ones observed in the CMB for a range of gauge coupling that includes those found in the SM and hence such preheating cannot be the main source of reheating the Universe after inflation. Further, due to the non-linear relation between the Higgs value and the reheating efficiency, the resulting temperature spectrum acquires a significant non-Gaussian component, which is constrained by Planck observations of the CMB and is potentially detectable in next-generation experiments. Constraints from non-Gaussianity are stronger than the ones due to the amplitude temperature anisotropies alone. Hence, in principle, observational searches for non-Gaussianity in the CMB can be used to constrain the dynamics of the Higgs boson at very high.

15:15 – 15:45: 30 minutes Coffee Break & Discussion

15:45 – 16:30: Talk by Michael Zantedeschi (Max Planck Institute for Physics – MPI Physics)

Title: Primordial Black Holes from Confinement


Primordial black holes are very interesting candidates for dark matter. However, their formation is still a mystery. In this talk, I will present a generic mechanism in which primordial black holes are formed by the early Universe “ancestor” of the same force that confines quarks inside hadrons. In this scenario, heavy quarks of a confining gauge theory produced by de Sitter fluctuations are diluted by the inflationary expansion and are confined upon horizon re-entry. The large amount of energy stored in the coloured flux tubes connecting the quark pairs leads to black-holes formation. I will discuss phenomenological features of the new mechanism and show that it can account for both the entirety of dark matter and the supermassive black holes in galactic centres. Under proper conditions, the scenario can be realised in a generic confinement theory, including ordinary QCD. Moreover, its gravitational-wave signal could be relevant in view of the recent NANOGrav data.

16:30: Borrel


13:30 - 16:30
Event Category:


Guadalupe Canas, Fabrizio Renzi


Casimir Room, Oort building
Leiden, + Google Map