# Zooming in on Axions in the Early Universe

Europe/Zurich
Virtual only (CERN)

### Virtual only

#### CERN

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Description

Update: This event was a big experiment to try and test a couple of different ideas aiming at making virtual workshops as interesting and stimulating as possible. These ideas included: virtual poster sessions, virtual coffee breaks (including coffee break presentations), a Virtual Axion Institute on Mattermost (including a coffee room, a pinboard for all posters, and virtual guest offices), and a virtual guestbook. We learned a lot from this experiment, so if you are interested in organizing a "Zooming in on ..." workshop yourself, please contact us---we'd be happy to share our experience with you. We also believe that our experiment was more or less successful. Here's some of the feedback that we received:

"Many thanks for the nice workshop! I really wish we had more events like this in our community, even after the pandemics is handled properly. The main positive aspect I would like to highlight is the inclusiveness that a virtual workshop promotes. Everybody from around the world is able to participate without spending stratospheric amounts of money on travel, accommodation, meals etc. This is especially true for overseas participants, but also within Europe the available budget may be prohibitive. So congrats and many thanks to the organizers, and I do hope the idea is spread and widely adopted from now on."

"Thanks for the really nice workshop! I think it was a brilliant idea to use the mattermost channels in this manner. It allows for organized discussion. I hope this platform goes on and seeds tons of future projects! Thanks for organizing it!!!"

"Thanks a lot for organizing this fantastic online workshop. I really enjoyed the talks and the overall atmosphere. What I liked was the possibility to chat afterwards in the mattermost, and having the possibility to directly ask questions. Thanks a lot !!!"

"Thanks so much for organizing this workshop. It was awesome to be able to participate even across different time zones. The communication was great and it was very well organized."

"I like the policy that you provide the video recordings only during the workshop and remove it later. This provides some incentive to really participate during the "workshop dates" but still gives flexibility in watching the talks. There is some imbalance for talks in the beginning/end of the workshop. So maybe an alternative policy would be to provide each talk for a fixed amount of time, e.g., 72 hrs?"

Overview: The goal of this virtual Zoom workshop is to focus on the role of axions in the early universe, zooming in on intriguing aspects of their interplay with cosmological dynamics and evolution. Topics covered include axions + (Monday) dark matter / (Tuesday) gauge fields / (Wednesday) baryogenesis / (Thursday) naturalness / (Friday) gravitational waves. On each day, we will have a number of invited expert talks, which will be scheduled so as to make them accessible across as many time zones as possible. Each talk will consist of 40 minutes presentation and 20 minutes discussion. In addition, we will provide ample opportunity for informal discussions and social interactions.

Zoom meeting ID:
Main room: 793 019 0483

Seminars:
(1) Wednesday 2PM: TH Colloquium, Robert Brandenberger
https://indico.cern.ch/event/925915/
(2) Thursday 2PM: BSM Forum, Luca Di Luzio
https://indico.cern.ch/event/917072/
https://cern.zoom.us/j/99113688676
(3) Friday 6 PM: Special XENON1T Seminar, Michelle Galloway

Talks:
- Neil Barrie
- Kim Berghaus
- Aleksandr Chatrchyan
- Daniel Figueroa
- Tomohiro Fujita
- Keisuke Harigaya
- Benedict von Harling
- Anson Hook
- Matthew Kleban
- David J. E. Marsh
- Leila Mirzagholi
- Kyohei Mukaida
- Mauro Pieroni
- Géraldine Servant
- Oleksandr Sobol
- Ben Stefanek
- Fuminobu Takahashi
- Ira Wolfson

Posters:
- James Alvey
- Fernando Arias Aragón
- Raymond Co
- Michael Alan Fedderke
- Sang Hui Im
- Ashu Kushwaha
- Jacob Leedom
- Enrico Morgante
- Ogan Ozsoy
- Alexandros Papageorgiou
- Alexis Plascencia
- Tanmay Poddar
- Pablo Quílez
- Mario Reig
- Thomas Schwetz
- Caner Ünal
- Yuki Watanabe

Virtual Axion Institute: We created the Mattermost workspace "Axions",

https://mattermost.web.cern.ch/axions

which we will use as a virtual institute during the workshop and where we will meet during the virtual coffee breaks. All speakers and everyone who is presenting a poster will have their own virtual guest office in this institute.

Poster sessions: At the end of each day, we will have a poster session, where everyone who is interested can present their work on axions in the early Universe on a "poster", i.e., one slide. These poster presentations can be followed up by more detailed presentations (e.g., via Zoom) in the virtual guest offices. Please contact the organizers if you are interested in presenting a poster.

Participants
• Abu Ubaidah Amir Bin Ab Maalek
• Alejo Nahuel Rossia
• Aleksandr Chatrchyan
• Alexander Panin
• Alexandros Papageorgiou
• Alexey Kivel
• Alexis Plascencia
• Aline Favero
• Alvaro De Rujula
• Alvise Raccanelli
• Anastasia Sokolenko
• Andreas Ringwald
• Andrew Long
• Andrii Lapiuk
• Anne Davis
• Anson Hook
• Antoine Depasse
• Anton Sokolov
• Antonio Walter Riotto
• Aoibheann Margalit
• archana sangwan
• Arindam Chatterjee
• Arindam Mazumdar
• Ashu Kushwaha
• Avik Banerjee
• Benedict von Harling
• Benjamin A. Stefanek
• Benoit Assi
• Bibhushan Shakya
• Bihag Dave
• Bruce Campbell
• Bruno Valeixo Bento
• Caner Unal
• Carlo Tasillo
• Carlos Tamarit
• Catarina Cosme
• Cem Eröncel
• Chakrit Pongkitivanichkul
• Charanjit Kaur
• Chengcheng Han
• Chiara Animali
• Christian Gross
• Christophe Grojean
• claudio corianò
• Daniel G. Figueroa
• Daniele Barducci
• Daria Prokhorova
• David G. Cerdeño
• David Marsh
• David Marsh
• Davide Lai
• Davide Racco
• Davood Rafiei
• Debajit Bose
• Debasish Borah
• Debtosh Chowdhury
• Devarshee sandilya
• DI XU
• Dibya Chakraborty
• Diego Redigolo
• Dipan Sengupta
• Dmitri Grigoriev
• Dmitriy Konarev
• Doojin Kim
• Eduard Masso Soler
• Edward Wang
• Eiichiro Komatsu
• Elisa Ferreira
• Elisa Todarello
• Emilio Torrente Lujan
• Enrico Morgante
• Eugene Lim
• Evgueni Alexeev
• Fang Ye
• Fatih Ertas
• Fazlollah Hajkarim
• Felix Giese
• Felix Yu
• Fernando Arias-Aragón
• Florian Goertz
• Francesco D'Eramo
• Francesco Muia
• Francesco Schiavone
• Francisco Torrenti
• Fuminobu Takahashi
• Fumio Uchida
• Gabriele Franciolini
• Gabriele Veneziano
• Gaetano Fiore
• Gaia Lanfranchi
• Georg Raffelt
• Geraldine Servant
• Gianmassimo Tasinato
• Gioacchino Piazza
• GIUSEPPE LUCENTE
• Glauber Dorsch
• Guillermo Ballesteros
• Gustavo Marques Tavares
• hani maalouf
• Hans Peter Nilles
• Heliudson Bernardo
• Henrique Rubira
• Hilberto Silva
• Hoa Vuong
• Hyun Min Lee
• Ignacy Sawicki
• Ilias Kyritsis
• Ippei Obata
• Ira Wolfson
• Isak Stomberg
• Ivonne Zavala
• Jacob Leedom
• James Alvey
• Jamie Davies
• Jamie McDonald
• Jan Schuette-Engel
• Jean-René Cudell
• Jesús Bonilla García
• Jinsu Kim
• Joao Rosa
• Joerg Jaeckel
• Jonathan Blazek
• Jorge Martin Camalich
• Jorge Terol Calvo
• Jorinde van de Vis
• Juhi Dutta
• Julien Laux
• Jérémie Quevillon
• Kai Schmitz
• Keiko Nagao
• Keisuke Harigaya
• Kenneth Marschall
• Kenny Chun Yu Ng
• KHURSID ALAM
• Kim Berghaus
• Koichi Hirano
• Koushik Dutta
• Kyohei Mukaida
• larry bloxham
• Laura Baudis
• Leila Mirzagholi
• Lennert Thormaehlen
• Ling-Xiao Xu
• Lorenzo Marafatto
• Lorenzo Sorbo
• Luca Di Luzio
• Luca Merlo
• Luca Visinelli
• Luís Ventura
• Maggie Kou
• Manu Srivastava
• Marco Calza
• Marco Chianese
• Marco Peloso
• Marco Scalisi
• Marek Lewicki
• Maria Archidiacono
• Maria Mylova
• Marieke Postma
• Marija Blinova
• Mario Reig
• Marko Simonovic
• Masahito Yamazaki
• Massimo Giovannini
• Matthew Kleban
• Matthew Kleban
• Mauro Pieroni
• Mesbah Alsarraj
• Michael Fedderke
• Michael Maxim Matlis
• Michele Frigerio
• Michiyasu Nagasawa
• Miguel Escudero
• Miguel Sánchez-Conde
• Mikhail Shaposhnikov
• Mohamed Younes Sassi
• Nagisa Hiroshima
• Naoki Yamamoto
• Neil Barrie
• Nicholas Benoit
• Nicola Bellomo
• Nicole Righi
• Ogan Ozsoy
• Oindrila Ghosh
• Oksana Iarygina
• Oleg Ruchayskiy
• Oleksandr Sobol
• Oriol Pujolas Boix
• Osra Hemmati
• Pablo Quilez Lasanta
• Patipan Uttayarat
• Patrick Valageas
• Pedro Klaus Schwaller
• Peera Simakachorn
• Percy Alexander Cáceres Tintaya
• Philip Sørensen
• Pranjal Trivedi
• Praphanon Samitayothin
• Quentin BONNEFOY
• Rachel Houtz
• Raghavan Rangarajan
• Rajeev Singh
• Ranjan Laha
• Raymond Co
• Ricardo Zambujal Ferreira
• Robert Brandenberger
• Roberto Franceschini
• Robin Fynn Diedrichs
• ryan plestid
• Ryosuke Sato
• Samuel Witte
• Sang Hui Im
• Sarif Khan
• Sebastian Hoof
• Sebastian Trojanowski
• Sebastian Zell
• Seodong Shin
• Seokhoon Yun
• Sergey Troitsky
• Shafiq Rasulan
• Shigemi Ohta
• Shota Nakagawa
• Shuichiro Yokoyama
• Simon Knapen
• Sohyun Park
• Soroush Shakeri
• Sotiris Loucatos
• Stefan Antusch
• Stefan Sandner
• Sukkasam Sukngam
• Susan van der Woude
• Syed Mohamed Syakir Syed Omar
• Syksy Räsänen
• Tako Meshveliani
• Takuya Okawa
• Talal Ahmed Chowdhury
• Tanmay Kumar Poddar
• Tevong You
• Thaisa Guio
• Thomas Schwetz
• Théo Moretti
• Tirtha Sankar Ray
• Toby Opferkuch
• Tommi Tenkanen
• Tomoaki Murata
• Tomohiro Fujita
• Tsutomu Yanagida
• Valentin Brunn
• Valerie Domcke
• Valerio De Luca
• varvara konovalova
• Vasja Susič
• Victor Danescu
• Viraf Mehta
• Viviana Niro
• Wei Xue
• Wolfram Ratzinger
• Yash Arya
• Yifan Chen
• Yining You
• Yohei Ema
• Yong Du
• Yong Xu
• Yuki Watanabe
• Yuko Urakawa
• Yvette Welling
• Zhi-Wei Wang
• Monday, 22 June
• 9:45 AM 10:00 AM
Welcome & Introduction 15m

Welcome and introduction to the workshop. I explain our motivation for organizing a virtual workshop, outline the workshop program, introduce our Virtual Axion Institute on Mattermost, and explain our poster sessions.

Speaker: Kai Schmitz (CERN)
• 10:00 AM 12:00 PM
Dark matter: Morning session
• 10:00 AM
1. QCD axion dark matter and PBH, 2. Anomaly-free ALP DM and XENON1T 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Fuminobu's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/fuminobu-takahashi

Abstract: In the first part, I will present a scenario in which PBHs are formed from the QCD axion. If I have time, I will touch on anomaly-free ALP DM (2006.10035, 1403.7390) as well.

Speaker: Fuminobu Takahashi (Tohoku University)
• 11:00 AM
Morning coffee in the Virtual Axion Institute 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

• 12:00 PM 1:00 PM
Lunch break 1h
• 1:00 PM 5:00 PM
Dark matter: Afternoon session
• 1:00 PM
Fragmentation of axion-like particle dark matter and observational signatures 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Aleksandr's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/aleksandr-chatrchyan

Abstract: Light scalar fields, such as axion-like particles, are appealing candidates for dark matter, if produced via the vacuum misalignment mechanism. Due to their small mass, they usually feature large field values, which can give rise to nonperturbative dynamics and fragmentation of the field soon after the onset of oscillations. We investigate this process on the example of monodromy axions, where the discrete shift symmetry is explicitly broken. We confirm the viability of such fields as dark matter for a wide range of masses. Fragmentation imprints strong overdensities in the spatial distribution of the field and we demonstrate that the small size of these fluctuations prevents their collapse into miniclusters. We also calculate the stochastic gravitational wave background that is produced from this process. In some cases the resulting signal may be within reach of future detectors, allowing a complementary probe of this type of dark matter.

Speaker: Aleksandr Chatrchyan (ITP Heidelberg)
• 2:00 PM
Afternoon coffee in the Virtual Axion Institute 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

• 3:00 PM
Phenomenology of the meV QCD axion 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in David's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/david-j-e-marsh

Abstract: If the Peccei-Quinn symmetry is broken after inflation, then the preferred axion mass required for the DM relic density is of order 1 meV. In this scenario, "axion miniclusters” form in the early Universe, and have potentially observable effects in microlensing. I will describe a new method to compute the mass function and radial distribution function of miniclusters based on the excursion set. The meV axion is particularly challenging for direct detection. I will outline progress on the “TOORAD” proposal to detect meV axions with topological insulators.

Speaker: David J. E. Marsh (University of Goettingen)
• 4:00 PM
Axion kinetic misalignment and baryogenesis 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Keisuke's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/keisuke-harigaya

Abstract: We will introduce a new cosmological evolution of the QCD axion and an axion-like particle, where the axion field circulates in the potential. Axion dark matter is produced by kinetic misalignment, which allows for a decay constant much below the prediction of the conventional evolutions. The new axion dynamics creates the baryon asymmetry of the universe. In the minimal scenario, which we call axiogenesis, the coupling strength of the axion to standard model particles is predicted as a function of the axion mass. The predicted range is within reach of future experimental axion searches. The lepton number violation by Majorana neutrino masses may aid the baryogenesis scheme. In this scenario, which we call lepto-axiogenesis, we instead obtain a prediction on the mass of the Peccei-Quinn symmetry breaking field, which, in supersymmetric theories, is tied with the masses of super partners.

Speaker: Keisuke Harigaya (Institute for Advaned Study)
• 5:00 PM 6:00 PM
Posters
• Tuesday, 23 June
• 10:00 AM 12:00 PM
Gauge fields: Morning session
• 10:00 AM
Lattice formulation of axion inflation: application to preheating 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Daniel's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/daniel-figueroa

Abstract: I will present a lattice formulation of an interaction $\phi F\tilde F$ between an axion and a $U(1)$ gauge sector, with the following properties: it reproduces the continuum theory up to $\mathcal{O}(dx_\mu^2)$, it preserves exact gauge invariance and shift symmetry on the lattice, and it is suitable for self-consistent expansion of the Universe. I will discuss an implicit method to solve the lattice equations of motion, which preserves the relevant system constraints down to arbitrary (tunable) precision. We then apply our formalism to study the last efolds of axion-inflation with quadratic potential, and the preheating stage following afterwards. We fully account for the inhomogeneity and non-linearity of the system, including the gauge field contribution to the expansion rate of the Universe and its backreaction into the axion dynamics. We characterize in detail, as a function of the coupling, the energy transfer from the axion to the gauge field, identifying two coupling regimes: sub- and super-critical, depending on whether the final energy fraction stored in the gauge field is below or above $\sim 50\%$ of the total energy. The Universe is very efficiently reheated for super-critical couplings, reassuring previous results with less advanced lattice techniques.

Speaker: Daniel G. Figueroa (IFIC, Valencia)
• 11:00 AM
Morning coffee in the Virtual Axion Institute 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

• 12:00 PM 1:00 PM
Lunch break 1h
• 1:00 PM 5:00 PM
Gauge fields: Afternoon session
• 1:00 PM
Equilibration of the chiral asymmetry due to finite electron mass 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Oleksandr's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/oleksandr-sobol

Abstract: One of the possible ways to generate the comological magnetic fields is based on the chiral magnetic effect. In plasma with chiral imbalance, it drives the instability which leads to the enhancement of some long-range magnetic modes of one helicity. In this respect, a very important question for magnetogenesis is how does this chiral imbalance evolve in time. In particular, how fast does it decay due to the chirality flipping processes in plasma? We calculate this rate due to nonzero electron mass in hot electron-positron plasma at temperatures well below the electroweak crossover. We consider the electron mass as a perturbation and apply the linear response formalism in order to extract the leading (quadratic in mass) contribution to the chirality-flipping rate. We show that this rate appears already in the first order in EM coupling constant and the numerical result is three orders of magnitude greater than the previous naive estimates.

Speaker: Oleksandr Sobol (EPFL)
• 2:00 PM
Afternoon coffee in the Virtual Axion Institute 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

• 3:00 PM
Two talks on axion-SU(2) inflation (Ira Wolfson, Leila Mirzagholi) 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 20 minutes talk + 10 min discussion + 20 minutes talk + 10 min discussion

Virtual Axion Institute: The discussion on both talks can be continued in Ira's and Leila's virtual guest offices.
https://mattermost.web.cern.ch/axions/channels/ira-wolfson
https://mattermost.web.cern.ch/axions/channels/leila-mirzagholi

Ira Wolfson: "Here be dragons": no-go areas in the axion-SU(2) chromo-natural model, and the spectator model solution
Abstract: The axion-SU(2) chromo-natural model, proposed in [1,2] presents an attractive phenomenological inflationary model. Unlike other such models it is more stable due to the SU(2)~SO(3) homomorphism, that in some cases allows the generation of 60 efolds or more. These models are interesting since they produce a distinct chiral tensor radiation signature, while also possibly explaining the matter-antimatter disparity in the early universe. Previous works [3,4] have probed part of its initial condition phase space, and shown a significant basin of attraction to an attractor solution. This brings up the question: How attractive is the isotropic attractor solution of axion-SU(2) inflation? We probe a previously unexplored part of the initial condition phase space and reveal regions where the system fails to converge on the attractor solution. We call this area the "no-go" area, and we study its characteristics. We continue to study a version of the axion-SU(2) model in which the axion and gauge sectors are demoted to spectator status. We show that while the basin of attraction to the attractor solution becomes larger with further dominance of the inflaton sector over the axion's and gauge fields', the "no-go" area persists albeit in a more contained fashion. The talk is based on I.W., Azadeh Maleknejad, and Eiichiro Komatsu, 2003.01617.

Leila Mirzagholi: Effects of gravitational Chern-Simons term during axion-SU(2) inflation
Abstract: I discuss the effect of the gravitational Chern-Simons term coupled to the axion field on the production and propagation of gravitational waves during inflation with the spectator axion-SU(2) sector. Both parity-violating terms RR-tilde and FF-tilde exist simultaneously and should be effectively considered on the same level in the theory. Using the existing bounds on the parameters of the spectator axion-SU(2) gauge field sector and choosing reasonable cut-off scales, we put constraints on the new free parameter in our model to remain in the ghost-free regime.

[1] A. Maleknejad and M. M. Sheikh-Jabbari, Phys. Lett. B 723 (2013) 224 [1102.1513].
[2] A. Maleknejad and M. M. Sheikh-Jabbari, Phys. Rev. D 84 (2011) 043515 [1102.1932].
[3] E. Dimastrogiovanni and M. Peloso, Phys. Rev. D 87 (2013) 103501 [1212.5184].
[4] P. Adshead, E. Martinec and M. Wyman, Phys. Rev. D 88 (2013) 021302 [1301.2598].

Speakers: Ira Wolfson (Max-Planck-Institute for Astrophysics, Garching) , Leila Mirzagholi (Max Planck Institute for Astrophysics, Garching)
• 4:00 PM
Thermal friction in early cosmology 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Kim's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/kim-berghaus

Abstract: Rolling scalar fields play an important role in understanding cosmology within a particle physics framework. Coupling a rolling scalar field to light degrees of freedom gives rise to a thermal friction which, if large enough, induces a thermal bath. In the context of inflation the presence of such a thermal bath has compelling consequences as it significantly alters the usual observables, leading to a suppression of the tensor-to-scalar ratio r and a unique prediction for non-gaussianities. In my talk, I will illuminate why the axion of a non-Abelian gauge group is the ideal candidate for generating the thermal friction and how it sets the stage for a minimal setup of warm inflation, as well as a potential solution to the Hubble tension.

Speaker: Kim Berghaus (Johns Hopkins University)
• 5:00 PM 6:00 PM
Posters
• Wednesday, 24 June
• 10:00 AM 12:00 PM
Baryogenesis: Morning session
• 10:00 AM
Big bounce baryogenesis 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Neil's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/neil-barrie

Abstract: We explore the possibility of an Ekpyrotic contraction phase harbouring a mechanism for Baryogenesis. A Chern-Simons coupling between the fast-rolling Ekpyrotic scalar and the Standard Model Hypercharge gauge field enables the generation of a non-zero helicity during the contraction phase. The baryon number subsequently produced at the Electroweak Phase Transition is consistent with observation for a range of couplings and bounce scales. Simultaneously, the gauge field production during the contraction provides the seeds for galactic magnetic fields and sources gravitational waves, which may provide additional avenues for observational confirmation.

Speaker: Neil Barrie (Kavli IPMU)
• 11:00 AM
Morning coffee in the Virtual Axion Institute 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

• 12:00 PM 1:00 PM
Lunch break 1h
• 1:00 PM 2:00 PM
Baryogenesis: Afternoon session 1
• 1:00 PM
Towards a robust estimate for gravitational leptogenesis 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Kohei's virtual guest office.

Abstract: In axion inflation, we can consider the anomalous coupling between the axion and gravity through the Chern-Simons term, which can generate chiral gravitational waves. Lepton asymmetry is also produced via the gravitational chiral anomaly at the same time, with which we can expect for the explanation of the present matter-anti matter asymmetry of the Universe. However, there still remain unclear issues in this model, such as the ghost-like degree of freedom and the UV divergences. In this talk, I will explain these issues in depth and determine with which conditions the present baryon asymmetry is explained.

Speaker: Kohei Kamada (Research Center for the Early Universe, University of Tokyo)
• 2:00 PM 3:00 PM
Seminar: TH Colloquium
• 2:00 PM
A unfied model of dark energy, dark matter and baryogenesis (TH Colloquium) 1h

TH Colloquium: https://indico.cern.ch/event/925915/

Virtual Axion Institute: The discussion on this talk can be continued in Robert's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/robert-brandenberger

Abstract: I discuss a model involving a self-interacting complex axion field whose imaginary part, a pseudo-scalar axion, couples to the instanton density of gauge fields including the hypermagnetic field. This coupling may give rise to baryogenesis in the early universe. After tracing out the gauge and matter degrees of freedom, a non-trivial effective potential for the imaginary part of the axion field is obtained. It is proposed that oscillations of this component around a minimum of its effective potential can be interpreted as Dark Matter. The absolute value of the axion field rolls slowly towards infinity. At late times, it can give rise to Dark Energy.

Speaker: Robert Brandenberger (McGill University)
• 3:00 PM 5:00 PM
Baryogenesis: Afternoon session 2
• 3:00 PM
Afternoon coffee in the Virtual Axion Institute (Tanmay Poddar, Raymond Co) 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

Presentations in virtual guest offices (in parallel):

(*) Tanmay Poddar
Virtual guest office: https://mattermost.web.cern.ch/axions/channels/tanmay-poddar
Zoom meeting: https://us04web.zoom.us/j/71066215138 (details: see guest office)

(*) Raymond Co
Virtual guest office: https://mattermost.web.cern.ch/axions/channels/raymond-co
Zoom meeting: https://umich.zoom.us/j/98155673494 (details: see guest office)

Speakers: Tanmay Poddar (Physical Research Laboratory) , Raymond Co (University of Michigan)
• 4:00 PM
Baryogenesis from axion inflation 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Benedict's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/benedict-von-harling

Abstract: The coupling of an axion-like particle driving inflation to the Standard Model particle content through a Chern-Simons term generically sources a dual production of massless helical gauge fields and chiral fermions. We demonstrate that the interplay of these two components results in a highly predictive baryogenesis model, which requires no further ingredients beyond the Standard Model. If the helicity stored in the hyper magnetic field and the effective chemical potential induced by the chiral fermion production are large enough to avoid magnetic diffusion from the thermal plasma but small enough to sufficiently delay the chiral plasma instability, then the non-vanishing helicity survives until the electroweak phase transition and sources a net baryon asymmetry which is in excellent agreement with the observed value. If any of these two conditions is violated, the final baryon asymmetry vanishes. The observed baryon asymmetry can be reproduced if the energy scale of inflation is around H_inf ∼ 10^10 - 10^12 GeV with a moderate dependence on inflation model parameters.

Speaker: Benedict von Harling (IFAE)
• 5:00 PM 6:00 PM
Posters
• Thursday, 25 June
• 10:00 AM 12:00 PM
Naturalness: Morning session
• 10:00 AM
Probing the relaxed relaxion with luminosity & S1 and S2 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Gilad's virtual guest office.

Abstract: Cosmological relaxation of the electroweak scale is an attractive scenario addressing the gauge hierarchy problem. Its main actor, the relaxion, is a light spin-zero field which dynamically relaxes the Higgs mass with respect to its natural large value. We show that the relaxion is generically stabilized at a special position in the field space, which leads to suppression of its mass and potentially unnatural values for the model's effective low-energy couplings. In particular, we find that the relaxion mixing with the Higgs can be several orders of magnitude above its naive naturalness bound. Low energy observers may thus find the relaxion theory being fine-tuned although the relaxion scenario itself is constructed in a technically natural way. More generally, we identify the lower and upper bounds on the mixing angle. We examine the experimental implications of the above observations at the luminosity and solar-direct-detection frontiers.

• 11:00 AM
Morning coffee in the Virtual Axion Institute (Thomas Schwetz) 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

Presentations in virtual guest offices:

(*) Thomas Schwetz
Virtual guest office: https://mattermost.web.cern.ch/axions/channels/thomas-schwetz
Zoom meeting: https://zoom.us/j/92414190410 (password: see guest office)

Speaker: Thomas Schwetz (Karlsruhe Institute of Technology)
• 12:00 PM 1:00 PM
Lunch break 1h
• 1:00 PM 2:00 PM
Naturalness: Afternoon session 1
• 1:00 PM
Revisiting the relaxion mechanism 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Geraldine's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/geraldine-servant

Abstract: Five years ago, a new mechanism was proposed to address the Higgs mass hierarchy problem through the cosmological evolution of an axion particle, the "relaxion". I will discuss several stopping mechanisms for the relaxion, in particular the effect of axion fragmentation that was omitted in the former literature. I will present the implications for the relaxion parameter space and which new opportunities for model building are opened.

Speaker: Geraldine Servant (DESY and U. Hamburg)
• 2:00 PM 3:00 PM
Seminar: BSM Forum
• 2:00 PM
Pati-Salam axion (BSM Forum) 1h

BSM Forum: https://indico.cern.ch/event/917072

Zoom meeting: https://cern.zoom.us/j/99113688676

Virtual Axion Institute: The discussion on this talk can be continued in Luca's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/luca-di-luzio

Abstract: I discuss the physics case for the GUT axion, motivated by the fact that the GUT axion window could be completely explored by the late phases of the axion Dark Matter experiments CASPEr-Electric and ABRACADABRA. This connection is exemplified for the case of the Pati-Salam partial unification scheme, in which the axion mass is predicted as a function of a sliding Left-Right symmetry breaking scale.

Speaker: Luca Di Luzio (DESY)
• 3:00 PM 6:00 PM
Naturalness: Afternoon session 2
• 3:00 PM
Afternoon coffee in the Virtual Axion Institute (Alexandros Papageorgiou) 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

(*) Alexandros Papageorgiou (Office hours / Q&A session)
Virtual guest office: https://mattermost.web.cern.ch/axions/channels/alexandros-papageorgiou
Zoom meeting ID: 927 1806 9143 (details: see guest office)

Speaker: Alexandros Papageorgiou (University of Minnesota)
• 4:00 PM
A CMB Millikan experiment with cosmic axiverse strings 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Anson's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/anson-hook

Abstract: We study axion strings of hyperlight axions coupled to photons. These axions strings produce a distinct quantized polarization rotation of CMB photons which is O(1%). As the CMB light passes many strings, this polarization rotation converts E-modes to B-modes and adds up like a random walk. Using numerical simulations we show that the expected size of the final result is well within the reach of current and future CMB experiments through the measurement of correlations of CMB B-modes with E- and T-modes. The quantized polarization rotation angle is topological in nature and its value depends only on the anomaly coefficient, independent of other details such as the axion decay constant. Measurement of the anomaly coefficient provides information about the UV theory, such as the quantization of electric charge and the value of the fundamental unit of charge. The presence of axion strings in the universe relies only on a phase transition in the early universe after inflation, after which the string network rapidly approaches an attractor scaling solution. The existence of these strings could also be probed by measuring the relative polarization rotation angle between different images in gravitationally lensed quasar systems.

Speaker: Anson Hook (University of Maryland)
• 5:00 PM
The axidental Universe 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Matthew's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/matthew-kleban

Abstract: Theories of N axion fields with random potentials have a number of distinct meta-stable minima that scales super-exponentially with N. This makes large N axion theories extremely complex “landscapes” that are could provide a solution to the cosmological constant problem. Despite this extraordinary complexity, novel techniques exist that make these theories analytically and computationally tractable. For N~100s and with Planckian or GUT/string energy scales and random parameters, there are many minima with vacuum energy consistent with observed dark energy (as well as very many more with larger positive or negative values). These minima are long-lived, and decay via thin-wall Coleman de Luccia phase transitions only to ~N nearby neighbors. This landscape supports a variety of types of slow-roll inflation, and tunneling can be followed by inflation of roughly quadratic type, with density perturbations that have amplitude ~10^{-5} in this same random parameter regime. They naturally contain one or more light fields that can solve the strong CP problem and serve as fuzzy or QCD axion dark matter. The minimal anthropic requirement that structure forms somewhere/sometime singles out cosmological histories that tunnel and then undergo ~60 efolds of inflation post-tunneling. Hence, a theory of ~100s axions, without model building and with only GUT-scale random parameters, naturally produces large universes with histories very much like that of our own, including a big bang (tunneling), slow-roll inflation, dark matter, and dark energy.

Speaker: Matthew Kleban (New York University)
• 6:00 PM 7:00 PM
Posters
• Friday, 26 June
• 10:00 AM 12:00 PM
Gravitational waves: Morning session
• 12:00 PM 1:00 PM
Lunch break 1h
• 1:00 PM 5:00 PM
Gravitational waves: Afternoon session
• 1:00 PM
Primordial GWs from the axion-SU(2) gauge fields during inflation 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Tomohiro's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/tomohiro-fujita

Abstract: Having on-going and upcoming experiments to detect them, we hope primordial gravitational waves (PGW) will be observed in the near future. PGWs produced during inflation are the unique probe for very high energy physics beyond the reach of particle accelerators, and now is the time to study what we can learn from PGWs. In this talk, I will demonstrate that much more information than the energy scale of inflation can be extracted from PGWs by using a model as an example. In the model, SU(2) gauge fields coupled to a rolling axion during inflation generate detectable PGWs, which are non-gaussian, maximally chiral, and may have non-trivial spectral shape depending on the axion potential.

Speaker: Tomohiro Fujita (ICRR, Tokyo University)
• 2:00 PM
GWs from axion preheating and SGWB reconstruction at LISA 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Mauro's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/mauro-pieroni

Abstract: The talk is divided in two independent parts. I will first discuss models in which a pseudoscalar (axion) inflaton is non-minimally coupled with some (Abelian) gauge fields. In particular, I will show that the efficiency of gravitational wave production during preheating can be used to set stringent constraints on the axion/gauge field coupling. In the second part of the talk I will discuss model independent reconstruction of stochastic gravitational wave backgrounds (SGWB) at LISA. After a brief introduction of the topic, I will discuss a recently proposed approach based on principal components analysis.

Speaker: Mauro Pieroni (Imperial College London)
• 3:00 PM
Afternoon coffee in the Virtual Axion Institute (Sang Hui Im, Alexis Plascencia, Ogan Ozsoy) 1h

(*) Stay in the main Zoom room and have a face-to-face chat with the other participants.

(*) Visit our Virtual Axion Institute and have a chat with the other participants in the coffee room:
https://mattermost.web.cern.ch/axions/

(*) Have a look at the posters on our pinboard:
https://mattermost.web.cern.ch/axions/channels/pinboard

(*) Visit the speakers and poster presenters in their virtual guest offices and continue the discussion on their presentations.

(*) Start your own Zoom meeting, announce it in the Virtual Axion Institute, and invite other participants.

Presentations in virtual guest offices (in parallel):

(*) Sang Hui Im
Virtual guest office: https://mattermost.web.cern.ch/axions/channels/sang-hui-im
Zoom meeting: https://us04web.zoom.us/j/6220520198 (password: see guest office)

(*) Alexis Plascencia
Virtual guest office: https://mattermost.web.cern.ch/axions/channels/alexis-plascencia
Zoom meeting: https://cwru.zoom.us/j/93939002270 (password: see guest office)

(*) Ogan Ozsoy
Virtual guest office: https://mattermost.web.cern.ch/axions/channels/ogan-ozsoy
Zoom meeting: https://us04web.zoom.us/j/2406288112 (password: see guest office)

Speakers: Sang Hui Im (IBS-CTPU) , Alexis Plascencia (Case Western Reserve University) , Ogan Ozsoy (University of Warsaw)
• 4:00 PM
Gravitational wave probes of axion-like particles 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Format: 40 minutes talk + 20 min discussion

Virtual Axion Institute: The discussion on this talk can be continued in Benjamin's virtual guest office.
https://mattermost.web.cern.ch/axions/channels/benjamin-stefanek

Abstract: Conventional approaches to probing axions and axion-like particles (ALPs) typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. Such particles, which are viable candidates for dark matter, can also produce a stochastic gravitational wave (GW) background in the early universe. This occurs if the axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. This instability exponentially amplifies vacuum fluctuations of a single dark photon helicity, resulting in a rapidly time-varying, anisotropic energy distribution that sources chiral GWs. We identify the regions of ALP parameter space which may be probed by future GW detectors, including ground- and space-based interferometers and pulsar timing arrays. Interestingly, these experiments have the ability to probe axions from the bottom up, i.e. in the very weakly coupled regime which is otherwise unconstrained. A smoking gun for the model is the completely chiral nature of the GW peak, which could be detected by LISA or Einstein Telescope if the signal amplitude is large. (40 minutes talk + 20 min discussion)

Speaker: Benjamin A. Stefanek (JGU Mainz)
• 5:00 PM 6:00 PM
Posters
• 6:00 PM 7:00 PM
Seminar
• 6:00 PM
Search for axions and axion-like particles with XENON1T 1h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Speaker: Michelle Galloway on behalf of the XENON1T Collaboration

Abstract: We present the latest results from a search for QCD axions from the Sun as well as axion-like particles of solar and dark matter origins. With an unprecedented low background of 76 ± 2 stat events/(tonne × year × keV) between 1–30 keV, XENON1T is uniquely poised to explore new parameter space for these electronic-recoil channels via the axio-electric effect. Our search revealed an excess of events in the (1 - 7) keV region, favoring these channels over background with significances of 3.5 sigma for solar axions/ALPs and 3.0 sigma global (4.0 local) for ALP dark matter with a peak at 2.3 +- 0.2 keV (68% C.L.). We review the detection principles, cross checks of our results, discrepancy with stellar constraints, and present a hypothesis of a new background from a previously undetected tritium component.

Speaker: Michelle Galloway (University of Zurich)
• 7:00 PM 9:00 PM
Happy Hour 2h

Zoom meeting: https://cern.zoom.us/j/7930190483 (password: see email)

Informal Happy Hour for everyone who wants to stick around. We won't provide any specific program; the idea simply is to chat a bit and have a drink together. However, if you wish to contribute to this Happy Hour in a particular way, e.g., by playing something on your guitar, teaching us your favorite cocktail recipe, or organizing a little pub quiz, please feel free to do so.