CDHY Initiative

Working together to understand the sites of extreme acceleration

About

Motivation

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

Cosmic rays and particle physics

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

Beyond the local fog: Cosmic Ray Factories and Extreme Accelerators

Presently, the cosmic ray community is focused more on the astrophysical aspect. Often, the main goal of the field is reduced to identifying the major contributors to the ‘local fog’ – directly detected fluxes of CRs in Earth’s neighbourhood. 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., provides 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.

What the programme covers

We 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 the highest-energy Galactic CRs around and beyond the ‘knee’, Crab Nebula and other PWNe as absolute extreme accelerators, ZeVatrons as factories of the highest-energy Extragalactic CRs reported up to 1020 eV and beyond. The talks dedicated to these objects constitute the core of the programme of the CDHY Initiative in general, and the seminars, in particular. Of course, a substantial fraction of the talks is devoted to the recent observations relevant to the Extreme Accelerators. In addition to the ongoing high-energy GeV/TeV observations conducted with Fermi-LAT and the Imaging Atmospheric Cherenkov Telescope arrays (H.E.S.S., MAGIC, VERITAS), we discuss the detections of ultra-high-energy gamma rays above 100 TeV recently reported by the HAWC, ASγ, and especially LHAASO collaborations. Of course, the TeV/PeV/EeV neutrino results, as well as GW events that could have a link to Extreme Accelerators (e.g. through gamma-ray bursts) are thoroughly covered.

In summary, this initiative integrates the expertise of different physics/astrophysics communities towards understanding the nature of Extreme Accelerators.

Format

The Initiative consists 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 are open and recorded.
  • Seminars and Workshops (Extreme Accelerators)
    • Focused seminars and workshops on selected topics started in the autumn of 2023.
  • High-Energy Astrophysics Summer School
    • See the Workshops page for information on the summer school.

Header image credits

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