For decades, two research activities related to particle physics and astrophysics have been at the core of cosmic ray (CR) studies.

CRs played a significant role in the development of particle physics. In particular, several elementary particles (positron, muons, mesons) have been discovered in CRs. Positrons, gamma rays and neutrinos as secondary products of ko decay or annihilation of Dark Matter have been often invoked for explanation of different CR ‘anomalies’. These non-standard scenarios give a certain particle physics and cosmological ‘flavor’ to CR studies.

Presently, the cosmic ray community is focused more on the astrophysical aspect. Often, the main goal of the field is reduced to the question of identification of major contributors to the ‘local fog’ – directly detected fluxes of CRs in Earth’s neighborhood. However, the term ‘Cosmic Rays’ has much broader implications linked to exploration of the non-thermal Universe and the locations where the relativistic matter is produced – the Cosmic Ray Factories. These perfectly designed machines are sites of production of the fourth substance of the visible Universe – after matter, radiation and magnetic fields. They appear in a wide diversity of forms on different scales – from compact relativistic objects to large cosmological structures. They are unique laboratories to explore how the combination of processes related to electrodynamics, magnetohydrodynamics, plasma physics, gravity, particle physics, etc., provide transformation of the available thermal and electromagnetic energy into non-thermal particles. The transformation efficiency in some objects approaches 100%. Moreover, in some objects the acceleration of individual CRs proceeds at a rate close to the theoretical limit determined by the electrodynamics and magnetohydrodynamics. These machines are called Extreme Accelerators.

We will try cover all aspects of physics and astrophysics of Extreme Accelerators, including the acceleration mechanisms, observational signatures, the astronomical objects and scenarios: Proton PeVatrons as contributors to highest energy Galactic CRs around and beyond the “knee”, Crab Nebula and other PWNe as absolute extreme accelerators, ZeVatrons as factories of highest energy Extragalactic CRs reported up to 10^{20} eV and beyond. The talks dedicated to these objects will constitute the core of the program of the CDY Initiative in general, and the Seminars, in particular. Of course, the substantial fraction of the talks will be devoted to the recent observations relevant to the Extreme Accelerators. In addition to the on-going high energy GeV/TeV observations conducted with Fermi-LAT and the Imaging Atmospheric Cherenkov Telescope Arrays (H.E.S.S., MAGIC, VERITAS), we will discuss the detections of Ultra High Energy gamma rays above 100 TeV recently reported by the HAWC, ASg, and especially LHAASO collaborations. Of course, the TeV/PeV/EeV neutrino results, as well as GW events which could potentially have a link to Extreme accelerators (e.g. through Gamma Ray Bursts) will be thoroughly covered as well.

In summary, we hope that this new initiative will help to integrate the expertise of different physics/ astrophysics communities towards the understanding of the nature of Extreme Accelerators.


The Initiative will consist of three components:

  • Introductory lectures on current topics
    • Formal talks followed by an informal discussion led by the speaker and one of the members.
    • Duration: talk – 45 min., followed by an informal discussion of 30 min.
    • These lectures will be open and recorded.
  • Seminars and Workshops (Extreme Accelerators)
    • Focused seminars and workshops on selected topics will start in the fall of 2021.
  • High-Energy Astrophysics Summer School
    • The first summer school will be held in Dublin (DIAS) in the summer of 2022. Details will be provided.


The CDY website header combines a number of relevant images from our field of research. From left to right: