iTHEMS Cosmology Forum n°5 - Effective Field Theory approaches across the Universe

Thursday 29 Jan 2026, 09:30 → 23:45 Asia/Tokyo

Okochi Hall (RIKEN Wako Campus)

This fifth workshop will bring together researchers exploring the effective field theory (EFT) framework in diverse cosmological contexts. Topics will include EFT formulations of interacting dark matter and dark energy, open EFTs for gravity, and multi-field inflationary dynamics. By highlighting recent progress and open questions, the workshop seeks to bridge insights from the early and late universe through the unifying language of EFT. In addition to the invited talks, the workshop will feature a panel discussion designed to promote interaction between the speakers and participants.

One of the key goals of this event is to foster collaboration among researchers working in neighboring fields, and to encourage participation from young and early-career researchers who are interested in, but may not yet have worked on, these themes. The workshop welcomes a broad audience with an interest in theoretical cosmology, gravitation, and quantum field theory.

This forum will consist of 1 day. 

The workshop will be in English.

The workshops are organised by the Cosmology Study Group at RIKEN iTHEMS.

Important dates:

Jan. 13th - Registration deadline 

Jan. 29th - Workshop Day 

Invited Speakers:

Katuski Aoki (Yukawa Institute for Theoretical Physics, Kyoto)

Toshifumi Noumi (Tokyo University, Tokyo)

Lucas Pinol (LPENS, Paris)

Organisers:

Shuntaro Aoki, Nagisa Hiroshima, Derek Inman, Amaury Micheli, Hironao Miyatake, Kai Murai, Ryo Namba

Hosted by:

RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)

Support:

No VISA support can be provided.

Limited support for local expenses may be available for postdocs and non-permanent faculty members. Students may be supported if presenting a poster. Please contact us directly.

10:00 Coffee and Opening Remarks

1 Keynote Talk - EFTs across the Universe: inflation, dark energy, dark matter, and gravitational waves

Our Universe is spatially homogeneous and isotropic on large scales. This high symmetry of the Universe enables us to systematically investigate various possibilities of cosmological scenarios using the powerful tool from high-energy physics, namely, effective field theory (EFT). In this approach, the difference in field contents is translated into the difference in symmetry-breaking patterns, encapsulating phenomenological features of each scenario into effective operators in a model-independent manner. In this talk, starting with a brief review of the so-called EFT of inflation/dark energy, I will talk about how we can extend this framework to different phenomena of cosmology, such as vector dark energy, interacting dark matter and dark energy, and chiral gravitational waves.

Speaker: Katsuki Aoki (Yukawa Institute for Theoretical Physics, Kyoto University)

EFTs_Aoki@RIKEN.pdf

11:45 Lunch

2 Effective field theories of inflationary fluctuations beyond single field and tree level

Effective field theory techniques provide an efficient way to enumerate the allowed operators in various physical systems based on their symmetries. Moreover, they allow for a systematic classification of these operators in decreasing order of relevance based on a derivative expansion. These tools are powerful in guiding us towards the construction of a realistic inflationary scenario with few model assumptions. In this presentation, I will guide the audience towards more general effective field theories of inflationary fluctuations than what is usually considered. In particular, I will show how nonlinearly realised symmetries play a key role in multifield inflation, and I will make the explicit link with the theory for fluctuations in nonlinear sigma models. Finally, I will present a few interesting features at the one-loop level, where symmetries beautifully restore the conservation of the primordial curvature perturbation on super-Hubble scales.

Speaker: Lucas Pinol (LPENS, Paris)

EFTs of inflationary fluctuations-1.pdf

14:00 Group Photo

3 Poster session (with coffee)

4 Open system EFT for cosmologists

I will give an introduction to the effective field theory (EFT) of open systems aimed at cosmologists. After motivating why open systems are relevant in cosmology, I will discuss Brownian motion as the simplest illustrative example. I will then present the EFT construction for open systems with spontaneous symmetry breaking and in the presence of gravity, with cosmological applications in mind.

Speaker: Toshifumi Noumi (Tokyo University, Tokyo)

Noumi.pdf

16:00 Break - Setting up for Panel

5 Panel Discussion

Speakers: Katsuki Aoki (Yukawa Institute for Theoretical Physics, Kyoto University), Lucas Pinol (LPENS, Paris), Toshifumi Noumi (Tokyo University, Tokyo)