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 Late-Spring 2022

June 3 @ 13:15 - 17:00

Leiden, June 3rd.

Here the remote connection for who is joining online:

Time: June 3rd, 2022 01:00 PM Amsterdam Time

Join Zoom Meeting
Zoom Link
Meeting ID: 626 2471 2286
Passcode: H1vHVuR?

In the following the program of the day:

13:15-14:00 CET: Talk by Natalie B. Hogg (IPhT CEA Paris-Saclay)

Title: Dancing in the dark: detecting a population of distant primordial black holes


Primordial black holes (PBHs) are compact objects proposed to have formed in the early Universe from the collapse of small-scale over-densities. Their existence may be detected from the observation of gravitational waves (GWs) emitted by PBH mergers, if the signals can be distinguished from those produced by the merging of astrophysical black holes (ABHs). In this talk, I will present a new mock-data-based forecast of the capability of the Einstein Telescope (a proposed third-generation GW observatory) to identify and measure the abundance of a subdominant population of distant PBHs, using the difference in the redshift evolution of the merger rate of the two populations as a discriminant. I will describe the careful modelling of the merger rates and observational uncertainties that we followed to create the mock data and present the two independent statistical methods we used to analyse it. I will show how the more powerful, likelihood-based method revealed that PBH abundances as small as fPBH≈7×10−6 (fPBH≈2×10−6) will be distinguishable from fPBH=0 at the level of 3σ with a one year (ten year) observing run of the Einstein Telescope, a roughly 2 orders of magnitude improvement on current bounds.

14:00 – 14:15 CET : Coffee Break

14:15-15:00 CET: Talk by Cliff Burgess (McMaster University and Perimeter Institute)

Title: RG Modulus Stabilization, de Sitter vacua and the inflationary eta problem 


This talk describes a new mechanism for stabilizing moduli in supergravity theories without leaving the domain of perturbative control. The only required nonperturbative information (as required by the ‘Dine-Seiberg’ problem) comes from the standard renormalization-group resummation of leading logarithms. The resulting potential is naturally minimized for exponentially large moduli even given input parameters that involve only hierarchies that are O(10). The resulting compactifications generically break supersymmetry and de Sitter vacua are relatively easy to achieve without the usual uplifting problems encountered in other stabilization methods (like KKLT or LVS scenarios). Variations
on the theme lead to inflationary scenarios for which the size of the stabilized moduli differ significantly before and after inflation and so provide a dynamical mechanism whereby inflationary scales are much larger than late-time physical (e.g. supersymmetry breaking) scales. When applied to warped D3-D3 inflation this stabilization mechanism evades the eta-problem that usually preventjustify slow roll in this scenario.

15:00-15:15 CET: Coffee Break

15:15-16:00 CET: Talk by Gustavo Salinas (Stockholm University)

Title: Flashes from collisions of axion clumps with neutron stars 


Abstract: Axions are being searched for intensively by experiments, as they might constitute dark matter. Apart from a smooth component, some of the axion dark matter might bound to clumps, miniclusters and axion stars, with unique observational signatures. In this talk I describe in detail the collision of such an axion clump with a neutron star, with results from simulations of the axion-photon conversion on the neutron star magnetosphere and the subsequent propagation of the photons. I also briefly discuss the sensitivity of current and future experiments to such signals.

16:00 CET: Borrel


June 3
13:15 - 17:00
Event Category:


Fabrizio Renzi
Guadalupe Cañas Herrera


Room HL207 – 2° floor of Huygens building
Leiden, + Google Map