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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Grongingen Fall 2019

04/10/2019 @ 08:00 - 17:00

Groningen,  October 4th. The meeting will take place in room A8 of the Academy Building, downtown Groningen (10min walk from the central station, 4min by bike). Coffee and tea will be available prior to the first talk (at 11.45) and in between both afternoon sessions (at 15.00).

12:00 – 13:00: Talk by Subodh Patil (Bohr Institute)

Title:Tensor bounds on the hidden universe (and a 1PI coda on loops in inflation)


In this talk, we present the observation that primordial gravitational waves, if ever observed, can be used to bound
the hidden field content of the universe. This is because a large number of hidden fields can resum to potentially observable logarithmic runnings for the graviton two-point function in the context of single field inflation, courtesy of a `large N’ resummation. This allows one to translate ever more precise bounds on the tensor to scalar consistency relation into bounds on the hidden field content of the universe, with potential implications for phenomenological constructions that address naturalness with a large number of species. Along the way, we need to address certain subtleties regarding loop corrections on cosmological backgrounds, especially with regards to the correct implementation of dimensional regularization. We find a pleasing confirmation of our understanding by directly reproducing our results from the 1PI effective action (as one must) and present a simplified prescription to calculate loop corrections to certain correlation functions in inflation.

13:00 – 14:00: Lunch Break

14:00 – 14:30: Talk by Alba Kalaja(Groningen University)

Title: From Primordial Black Holes Abundance to Primordial Curvature Power Spectrum (and back).


In the model where Primordial Black Holes (PBHs) form from large primordial curvature perturbations, in principle constraints on PBH abundance provide a powerful probe of the early Universe. In this presentation, I will discuss updated constraints on the primordial curvature power spectrum obtained from the latest limits on PBH abundance taking into account all the steps from gravitational collapse in real space to PBH formation.
In particular, I will show how to combine results from numerical relativity simulations and peak theory to study the conditions for PBH formation including non-linearity terms, perturbation profile details and a careful treatment of smoothing scales, and how to translate such conditions into primordial spectrum constraints for a wide range of shapes and abundances.
Our results show that the correct and accurate modelling of non-linearities, filtering and typical perturbation profile, is crucial for deriving meaningful cosmological implications.

14:30 – 15:00: Talk by Horng Sheng Chia(Amsterdam Univerisity)

Title: Gravitational wave signatures of ultralight bosons in binary systems


Ultralight boson fields exist in various proposed extensions to the Standard Model, and can form boson clouds around rapidly-rotating black holes through a process called superradiance. In this talk, I will describe how various properties of these clouds, such as their shapes and energy spectra, depend on the masses and intrinsic spins of the boson fields. I will then discuss that how the dynamics of the clouds are greatly enriched when they are in binary black hole systems. Finally, I will sketch how the dynamical evolution of the clouds backreact on the orbit, thereby leaving their imprints in the gravitational waves emitted by the binary system.

15:00 – 15:30: Coffee Break

15:30 – 16:30: Talk by Elisa Chisari(Utrecht University)

Title: Galaxy shapes as a cosmological tool


Two phenomena contribute to correlating galaxy shapes across the Universe: the deviation of photons from a straight path due to the spacetime curvature (“gravitational lensing”), and tidal interactions (“intrinsic alignments”). Modelling both accurately is crucial to obtaining unbiased constraints on the cosmological model from forthcoming surveys, particularly in the context of elucidating the origin of accelerated expansion of the Universe. In this talk, I will cover recent advances in our understanding of the intrinsic alignments of galaxies. While these alignments are typically regarded as a contaminant to weak gravitational lensing, I will also discuss how they might become a cosmological probe in their own right in the near future.



08:00 - 17:00
Event Category:


Daan Meerburg


Academy Building
Broerstraat 5
Groningen, 9712CP
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