Particle Physics in the Early Universe

14 sept. 2026, 09:00 → 18 sept. 2026, 20:00 Europe/Paris

The International conference “Particle Physics in the Early Universe” is  taking place 14–18 September 2026 in Paris and Orsay.

The conference is co-organized by the Polish Academy of Sciences Scientific Center in Paris, the Institute for Advanced Studies of the University of Warsaw, and IJCLab Orsay. The first day of the conference (Sep 14) will take place in the auditorium Joliot Curie, building 100 at  IJCLab in Orsay.  The sessions of September 15-18 will be held at the Polish Academy of Sciences Scientific Center, located in the elegant 16th arrondissement of Paris. 

The scientific program will explore the interplay between elementary particle physics and early-Universe cosmology, covering topics such as cosmological inflation, dark matter, dark energy, baryogenesis and leptogenesis, phase transitions in the early Universe, and their potential observational signatures, particularly gravitational waves. A central focus will be the cosmological implications of theories beyond the Standard Model and their possible experimental tests. Contributions will be published in a special issue of Acta Physica Polonica B. There is  no conference fee for invited participants.

Confirmed speakers include: 

Zurab Berezhiani
Nicolas Bernal
Matteo Braglia
Chiara Caprini
Thomas Colas
Joe Conlon
Ed Copeland
Marco Drewes 
Emilian Dudas
Ruth Durrer
Joulien Froustey
Yann Gouttenoire
Alejandro Ibarra
Ayuki Kamada
Steve King
Will Kinney
Rocky Kolb
Kamila Kowalska
Fotis Koutroulis
Oleg Lebedev
Marek Lewicki
Marta Losada
Matthew McCullough
Kyohei Mukaida
Marek Olechowski
Marco Peloso
Lucas Pinol 
Sébastien Renaux-Petel
Kazuki Sakurai
Mikhail Shaposhnikov
Pedro Schwaller
Pasquale Serpico
Enrico Sessolo
Joe Silk
Juri Smirnov
David Stefanyszyn
Bogumiła Świeżewska 
Xi Tong
David Wands

The Organizing Committee:
Adam Falkowski (IJClab Orsay)
Zygmunt Lalak (University of Warsaw)
Yann Mambrini (IJClab Orsay)
Stefan Pokorski (University of Warsaw and Polish Academy of Science)

 

lun. 14 septembre

09:00 Registration and Coffee

1 Welcome

Orateur: Prof. Yann Mambrini (CNRS, IJCLab, Université Paris-Saclay)

Early Universepdf.pdf

Monday

2 Searching for cosmic superstrings in Gravitational Waves and the CMB

Orateur: Ed Copeland

Paris-2026-Copeland.pdf

3 Dark Matter from a Slightly Broken Mirror

Orateur: Juri Smirnov (University of Liverpool)

1_BrokenMirrorDarkMatter.pdf

11:30 Coffee break

Monday

4 Developments in gravitational particle production

Orateur: Oleg Lebedev (University of Helsinki)

Paris2026-Lebedev-ok.pdf

12:45 Lunch break

Monday

5 Nonthermal leptogenesis via cosmological gravitational particle production

Orateur: Rocky Kolb (The University of Chicago)

Leptogenesis_Paris_26.pptx

Leptogenesis_Paris_26.pptx

6 Geodesic Completeness in General Cosmological Scenarios

The well-known Borde-Guth-Vilenkin Theorem shows that inflationary
spacetimes are generically geodesically past-incomplete, necessitating
the existence of a pre-inflationary boundary of some sort, possibly
singular. In this talk, I discuss the generalization of the BGV theorem
to spactimes beyond inflation, including inhomogeneous and cyclic
models. I argue that the cyclic model proposed by Ijjas and Steinhardt
is geodesically incomplete, and that an asymptotically de Sitter
version of Penrose's Conformal Cyclic Cosmology is either past- or
future-incomplete.

Orateur: William Kinney (Univ. at Buffalo, SUNY)

Kinney.pdf

15:30 Coffee Break

Monday

7 Non-compact QCD axion and its gravitational origin

Orateur: Prof. Mikhail Shaposhnikov (EPFL)

Shaposhnikov-Paris2026.pdf

8 Primordial lepton asymmetries: constraints and consequences

Orateur: Julien Froustey (IFIC, CSIC-UV)

JFroustey_PPEU_Sep2026_compressed.pdf

17:30 Free discussions

19:00 Dinner at "Le Gramophone" in Orsay

27 Bd Dubreuil, 91400 Orsay

mar. 15 septembre

9 Welcome

Tuesday

10 Neutrino mass and gravitational waves from RG fixed points

Orateur: Kamila Kowalska (National Centre for Nuclear Research)

2026.09.15_Paris.pdf

11 Gravitational Waves from Strongly Supercooled Cosmological Phase Transitions

Orateur: Marek Lewicki (University of Warsaw & AstroCeNT)

2026_9_PTGW_Paris_MLewicki.pdf

11:00 Coffee Break

Tuesday

12 (Gravitational) Ultra-relativistic freeze-out during reheating

Orateur: Mathieu Gross (IJCLab)

(gravitational) Ultra-relativistic freeze-out during reheating.pdf

13 Discussion of the LZ event

Orateurs: Juri Smirnov (University of Liverpool), Pedro Schwaller (Mainz University)

Discussion LZ-1.pdf

12:30 Lunch Break

Tuesday

14 TBA: astrophysical and other implications

Orateur: Zurab Berezhiani (University of Aquila)

Berezhiani 2026-Paris.pdf

15 Gravitational Waves from Primordial Black Hole Reheating

I will present the 13 channels of gravitational wave production which are at play when the universe is reheated from the evaporation of a population of primordial black holes dominating the energy density of the universe

Orateur: Yann GOUTTENOIRE (IAP)

Gouttenoire_FrancoPolishConf_2026.pdf

16 Coupled Dark Energy and Dark Matter for DESI: An Effective Guide to the Phantom Divide

Orateur: Stephen King

Paris.pdf

Paris.pptx

15:30 Coffee Break

Tuesday

17 Thermalization Process during Reheating and Gravitational Waves

Orateur: Kyohei Mukaida

reheating_gw.pdf

18 Stabilizing dark matter with quantum scale symmetry

Orateur: Enrico Maria Sessolo (National Centre for Nuclear Research, Warsaw)

Sessolo_Paris_2026.pdf

17:00 Free Discussions

mer. 16 septembre

Wednesday

19 Searching for Primordial Features in the Cosmic Microwave Background

eviations from slow-roll can leave characteristic oscillatory imprints in the spectrum of primordial perturbations, known as primordial features. If detected, such signals could reveal new energy scales during inflation or provide evidence for additional massive degrees of freedom. In this talk, I will review what we can learn from primordial features, discuss the hints currently present in the Cosmic Microwave Background data and the prospects for future detection, and show that these signatures are distinctive and difficult to mimic with other kinds of new physics.

Orateur: Matteo Braglia (CERN)

Particle Physics in the Early Universe.pdf

20 Axion inflation with gauge fields: backreaction and signatures

Orateur: Marco Peloso (University of Padua and INFN, Sezione di Padova)

Peloso parigi26.pdf

Peloso parigi26.pptx

11:00 Coffee Break

Wednesday

21 A unique coupling of the massive spin-2 field to supergravity

Orateur: Emilian Dudas (CPTHE (Ecole polytechnique))

Dudas - ms2-early_universe2026.pdf

Dudas - ms2-early_universe2026.pptx

22 Nouvelle Cuisine

Orateur: Matthew Mccullough (CERN)

Paris.pdf

12:30 Lunch Break

Wednesday

23 Constraining Dissipative Inflation with Open Effective Field Theories

Orateur: Thomas Colas (DAMTP - University of Cambridge)

PPinEU_Thomas_Colas.pdf

24 Primordial black hole formation from self-resonant preheating in single-field inflation?

Orateur: Pasquale SERPICO (LAPTh)

2609_Serpico_Paris.pdf

25 Microcausality and the Cosmological Collider

Orateur: David Stefanyszyn (University of Nottingham)

Stefanyszyn - MicrocausalityTalk.pdf

15:30 Coffee Break

Wednesday

26 Supercooled cosmological phase transitions: precise predictions and particle production

Orateur: Bogumiła Świeżewska (University of Warsaw)

B_Swiezewska.pdf

27 New probes of supercool phase transitions and domain walls at PTA frequencies

Orateur: Pedro Schwaller (Mainz University)

Paris_Particle_Cosmology_PTs_2026.pdf

17:00 Free Discussions

28 Reception in the Polish Embassy

jeu. 17 septembre

Thursday

29 QCD-driven Warm Inflation: A testable mechanism to set the Hot Big Bang initial conditions

Orateur: Marco Drewes (UCLouvain)

1 - Drewes.pdf

30 Gravitational production of Sterile Neutrinos

Orateur: Fotis Koutroulis (IHEP, Beijing)

KOUTROULIS_Paris2026.pdf

11:00 Coffee Break

Thursday

31 A Stochastic Gravitational Wave Background

Gravitational waves (GWs) have a very weak absorption cross section. This makes them difficult to observe on the one hand, but it is also for this reason they carry pristine information from their generation mechanism. Their observation may allow glimpses back to the highest redshifts and energies in the Universe.

After a brief introduction to the significance of the observation of a stochastic gravitational wave background, I shall concentrate on two possibilities: Generating gravitational waves from violent processes in the post-inflationary Universe and generating them during inflation. I shall show that in both cases different universal GW spectra are generated. I shall also discuss what we may learn from their observation.

Orateur: Prof. Ruth Durrer (Université de Genève, DPT)

3 - Durrer.pdf

32 Cosmology with LISA and related Figures of Merit

Orateur: Chiara Caprini (CERN and University of Geneva)

4 - Caprini.pdf

12:30 Lunch break

Thursday

33 A Laplace-space approach to cosmological correlators

Orateur: Sébastien RENAUX-PETEL (IAP - CNRS)

5 - Renaux-Petel.pdf

34 Modelling Ultra-Slow-Roll Inflation

Orateur: David Wands (University of Portsmouth)

6 - Wands.pdf

35 One-loop freezing of the primordial curvature perturbation

Orateur: Lucas PINOL (CNRS, LPENS)

7 - Pinol.pdf

15:30 Coffee Break

Thursday

36 Seesaw cosmology

Orateur: Nicolás Bernal (New York University Abu Dhabi)

8 - Bernal.pdf

37 Self-interacting dark matter: non-perturbative dynamics

Orateur: Ayuki Kamada (University of Warsaw)

kamada0917.pdf

38 New dark matter signals from semiannihilation

Orateur: Alejandro Ibarra (Technical University of Munich)

10 - Ibarra.pdf

17:30 Free Discussions

19:00 Conference dinner in "Piccolino Parigi"

16 Rue Copernic, 75116 Paris

ven. 18 septembre

Friday

39 A review of pheno constraints on EWBAU models

Orateur: Marta Losada (NYU Abu Dhabi)

1 - Losada.pdf

40 Testing α-attractor models of inflation by CMB and reheating temperature

Orateur: Marek Olechowski (University of Warsaw)

2 - Olechowski.pdf

41 Freeze-In Composite Dark Matter

Orateur: Kazuki Sakurai (University of Warsaw)

Freeze-In_Dark_Baryon_Kazuki_Sakurai.pdf

11:00 Coffee Break

Friday

42 Unveiling the Dark Ages

Orateur: JOE Silk (IAP/JHU)

DARKAGESorsayX.pdf

43 Cosmological correlators beyond the symmetric lamppost

Orateur: Xi Tong (DAMTP, University of Cambridge)

5 - Tong.pdf

44 Quantum and classical fluctuations in inflation

Orateur: Guillermo Ballesteros (University of Madrid)

6 - Ballesteros.pdf

13:00 Lunch and Farewell