Axion Cosmology

17 February - 13 March 2020

Bjoern Garbrecht, Bela Majorovits, David Marsh, Javier Redondo

What’s the nature of dark matter? has become one of the most important questions in modern particle physics and cosmology. The QCD axion, hypothetical particle arising in the Peccei-Quinn-Weinberg-Wilczek “mechanism” to explain the shocking absence of CP violation in the strong interactions (“strong-CP problem”) is one of the leading candidates. Unfortunately, so far it has received comparatively less attention than the “weakly-interacting-massive-particles” WIMPs. The QCD axion, as a very weakly interacting and small-mass particle, behaves in very different ways than a WIMP promising very distinct phenomenology and demanding extraordinarily different experimental searches.

In the last decade there has been a steady increase in the study of the theory and phenomenology of axion dark matter and a parallel interest has grown in the experimental community. The QCD axion has been generalised to axion-like particles (ALPs) and more broadly to weakly-interacting-slim particles (WISPs). Many new experimental techniques have been proposed and R&D projects have been launched to test them. With such a strain, important aspects of the theory of axion DM lag behind the experimental developments and will not be ready to interpret accurately the results of axion DM searches expected during the next decade. Furthermore, certain ranges of parameter space are currently untargeted by any realistic experimental technique.

In this workshop we will address the most relevant questions still open today in axion dark matter phenomenology by putting together scientists with the relevant expertise.


The workshop will concentrate on 5 basic aspects:

• Axions radiated from cosmic strings and the axion DM mass.

We will discuss current simulation techniques and future avenues, extrapolations to physical values of string tension, effective tension simulations, the local-string limit ...

• Bose-condensation of Axion DM; Quantum vs. classical behaviour Theoretical description, phenomenological implications, like in structure formation, galactic and subgalactic features...

• Small scale behaviour of axion DM: Miniclusters, Bose stars

We will discuss numerical simulations of minicluster formation, evolution until today, survival in the galaxy, morphology, density profiles, formation of axion stars and axitons, indirect and direct detection...

• Direct searches for axion DM

We will focus on DM searches above an below the vanilla haloscope micro-eV masses, theory, technical challenges, future investments required; coupling of multiple cavities, MADMAX and new open resonators, topological insulators and other novel concepts...

• Indirect searches for axion DM

We will discuss observation of axion DM spontaneous/stimulated decay, targets (compact objects with large B-fields, quiet dwarf-spheroidals...), theory, astrophysical models, potential reach...


The workshop will seek the active collaboration of its participants and will foster a multidisciplined environment by combining theorists, phenomenologists, observers and experimentalists to maximise the awareness of the severe issues and develop new ideas and strategies to tackle the unsolved problems.

Register here


(Deadline: 16 May 2019)

Technische Universitaet Muenchen
Exzellenzcluster Universe

Boltzmannstr. 2
D-85748 Garching

Tel. + 49 89 35831 - 7100
Fax + 49 89 3299 - 4002