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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Utrecht Spring 2021

April 9 @ 14:00 - 17:00

Utrecht, April 9th.

This meeting will take place via remote connection. Here the information for connecting:

Time: April 9, 2021 02:00 PM Amsterdam Time

Join Zoom Meeting
Zoom Link
Meeting ID: 843 3902 4566
Password: a149bz

14:00-14:50 CET: Talk by Enis Belgacem (Utrecht)

Title: Anisotropies and chirality of the GW background with pulsar timing arrays


Gravitational waves affect the regularity of radiation emission from pulsars. Monitoring pulsar timing arrays (PTAs) gives access to very low GW frequencies and can provide informations on the properties of the stochastic GW background expected, for instance, from inspiraling supermassive black hole binaries. After a general introduction to the subject, I will explain some recent advances in the characterization of the signatures imprinted by intensity anisotropies and circular polarization of the GW background on the timing residuals at PTAs, obtained within a convenient harmonic space treatment. I will then discuss ongoing work on the comparison with previous studies in configuration space.

15:00-15:50 CET: Talk by Marc Kamionkowski (JHU)

Title: The Hubble tension and early dark energy 


We have known since the late 1920s that the Universe is expanding. However, the expansion rate currently inferred from measurements of the cosmic microwave background now disagrees with that obtained from supernova measurements. Over the past few years, theorists have been exploring the possibility that this Hubble tension is explained by some new “early dark energy”: a new component of matter that may have been dynamically important several hundred thousand years after the Big Bang.

16:00-16:50 CET: Talk by Georgios Valogiannis (Harvard)

Title: Testing gravity with cosmology: efficient simulations, novel statistics and analytical approaches


The nature of the accelerated expansion of the universe is arguably the biggest open question in modern cosmology. One of the competing candidates for its explanation claims that what we observe might be the signal of a fundamental deviation from Einstein’s General Relativity (GR) at large scales, instead of dark energy. Such a breakdown of the laws of gravity would however manifest itself in the observed clustering pattern of the Large-Scale Structure (LSS) of the Universe. In this era of precision cosmology, the current and next stage of LSS surveys such as DESI, the V. Rubin Observatory and Euclid will thus offer an unprecedented opportunity to perform precise cosmological tests of gravity. The optimal interpretation of this vast amount of upcoming data is, however, contingent upon our ability to make efficient and reliable theoretical predictions of LSS observables, a task that proves to be particularly challenging in such modified theories of gravity (MG). In this talk I will discuss how we can overcome these challenges by utilizing a combination of analytical, semi-analytical and hybrid simulation techniques, as well as a suite of novel statistics that will allow us to comfortably differentiate between competing scenarios in future analysis pipelines.

17:00 CET: social virtual borrel


April 9
14:00 - 17:00
Event Category:


Tomislav Prokopec
Elisa Chisari