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 2022

May 6 @ 13:00 - 17:00

Utrecht, May 6th.

This meeting will take place via an hybrid format. Here the information for connecting through Microsoft Teams:

Time: May 6, 2022 01:00 PM Amsterdam Time

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13:00-13:30 CET: Welcome and coffee

13:30-14:30 CET: Talk by Gideon Koekoek (Maastricht)

Title: Gravitational wave frequency shifts & the search for CCC: a selection of results from UM-students


In this talk, I will discuss two recent results obtained by BSc- and MSc-students from Maastricht University’s research group in Gravitational Waves and Fundamental Physics. The first of these concerns the question whether electromagnetic fields around compact objects, such as black holes, quasars, and neutron stars, can be measured by gravitational waves alone. Quantifying such fields by other means tends to be challenging due to the complicated interplay of electromagnetic and gravitational effects. In this talk we will discuss a possibility to quantify the electromagnetic field around a binary system of inspiraling compact objects exclusively by observing shifts in the gravitational wave frequency. We will apply these results to binary systems of 10^1 to 10^3 solar masses, and discuss the measurability for LIGO/Virgo, LISA, and the upcoming Einstein Telescope. The second half of the talk will be about the Cyclic Conformal Cosmology model by Roger Penrose. It proposes that the universe goes through an endless loop of aeons where the end of each is conformally ‘glued’ to the big bang of the next. I will explain how Penrose proposes that his CCC can be tested by looking for remnants of super massive black holes of the previous aeon in the cosmic microwave background, and present our results from the search for these remnants.

14:30-14:45 CET: Break

14:45-15:45 CET: Talk by Sunny Vagnozzi (Cambridge)

Title: Searching for dark energy off the beaten track 


Most of the efforts in searching for dark energy (DE) have focused on its gravitational signatures, and in particular on its equation of state. However, there is a lot to be learned by getting off the beaten track. I will first focus on non-gravitational interactions of (screened) DE with visible matter, leading to the possibility of “direct detection of dark energy”, analogous to direct detection of dark matter: I will argue that such interactions can and potentially may already have been detected in experiments such as XENON1T, while discussing some of their complementary cosmological and astrophysical signatures. I will then discuss early- and late-time consistency tests of LCDM, and how these may shed light on (early and late) DE, particularly in relation to the Hubble tension, presenting two such tests based on the early ISW effect and the ages of the oldest astrophysical objects in the Universe. If time allows, I will present new ways of probing more general ultralight particles (which may be related to either dark matter or DE), using black hole shadows and planetary objects such as asteroids.

15:45-16:00 CET: Break

16:00-17:00 CET: Talk by Diego Cruces (Barcelona)

Title: Gradient expansion and stochastic approach to inflation


Although inhomogeneities during inflation are usually studied in a perturbative way, the knowledge of non-perturbative effects is of great interest, especially in the cases that are relevant for primordial black hole formation, like in ultra-slow-rolling and/or constant-rolling backgrounds. The stochastic approach of inflation aims to study inflationary inhomogeneities in a non-perturbative way by splitting them into an infrared (IR) and an ultraviolet (UV) part. In this talk I will explore the foundations of the stochastic formalism paying special attention to the non-perturbative (in terms of the amplitude of the inhomogeneities) expansion that dictates the evolution of the IR part: the gradient expansion, by doing so, I will identify some important limitations that the current realisation of the stochastic approach to inflation has.

17:00 CET: Borrel


May 6
13:00 - 17:00
Event Category:


Elisa Chisari
Tomislav Prokopec


Buys Ballot Building, 7th floor, room 7.12
Utrecht, Netherlands + Google Map