星空传媒

• Astrophysical magnetic fields and ultra-high-energy cosmic rays. Both Galactic and extragalactic magnetic fields (GMFs and EGMFs) play an important role in many astrophysical processes; they balance the interstellar medium against gravity, they affect gas flows, they influence star and galaxy formation and they accelerate cosmic rays (high-energy atomic nuclei propagating through space). The GMF is believed to consist of a Galactic disc component and a halo component. However, observations of the magnetic fields in the halo component are especially scarce. In addition, the EGMF strength in voids between galaxies is currently hardly constrained at all, with limits spanning many orders of magnitude, 10^-8 < B < 1 nG.
  
  The goal of this project is to utilize arrival-direction measurements of ultra-high-energy cosmic rays (UHECRs, extragalactic cosmic rays with energies E > 10¹⁸ eV) for the determination of magnetic-field properties between the sources of these UHECRs and Earth. Due to the recent advances in UHECR detections, a new way of determining the magnetic-field strengths and directions between the nearest UHECR sources and Earth has become viable. The UHECRs are deflected by the GMF and EGMF on their way from their sources to Earth. The amount of deflection provides a direct measure of the GMF and EGMF properties.

• Modeling the spectrum and composition of ultra-high-energy cosmic rays (UHECRs), including cosmogenic neutrinos. Even though the sources of UHECRs are currently still unknown, we can use the measured energy spectrum and chemical composition of UHECRs at Earth to investigate the properties of UHECR sources. We do this by simulating the propagation of UHECRs from their sources to Earth, taking into account all interactions that can happen on the way. This can give us an indication for the maximum energy that the sources can accelerate UHECRs to, the energy spectrum of UHECRs that the sources emit, the power of the UHECR sources and the chemical composition of the UHECRs when they escape from their sources.
  
  In addition, during the propagation of UHECRs from their sources to Earth, so-called cosmogenic neutrinos are created in UHECR interaction with background light. The simulations of the propagation of UHECRs can, therefore, also be used to predict the expected cosmogenic neutrino flux at Earth.

• Development of CRPropa, a publicly-available simulation framework to study the propagation of UHECRs and their secondaries through (extra)galactic environments. To study the origin of UHECRs and understand what measurements of UHECRs at Earth tell us about their sources, it is essential to have an understanding of what is happening to the UHECRs when they are propagating through the Universe. For this purpose, we are developing CRPropa (https://crpropa.github.io/CRPropa3/), worldwide the most used code for simulations on ultra-high-energy cosmic particles.
  
  When traveling through the extragalactic cosmos, UHECRs can interact with low-energy background light (the cosmic microwave background and the cosmic infrared background) through processes like photopion production, photodisintegration and pair production. In these interactions, unstable nuclei can be created, leading to the nuclear decay of these particles. In addition, secondary electromagnetic particles as well as neutrinos can be created in these processes. Furthermore, as UHECRs are charged particles, they get deflected by extragalactic and Galactic magnetic fields. CRPropa can take into account all these processes and, therefore, give reliable predictions for UHECR energy spectra, chemical compositions and arrival directions as well as secondary gamma-ray and neutrino fluxes for any kind of source realizations and extragalactic and Galactic magnetic field scenarios.

KM3NeT Collaboration: Interpretation of KM3NeT neutrino events. We are part of the Cubic Kilometre Neutrino Telescope (KM3NeT) collaboration. This is a large international collaboration of scientists developing a next-generation neutrino telescope located at the bottom of the Mediterranean Sea. KM3NeT is already operational and collecting data, but it will be extended further in the next few years. 

A new window to the Universe has been opened recently with the first detections of high-energy neutrino sources and a neutrino signal from the Milky Way galaxy. Significant advances in this field of neutrino astronomy are expected in the near future, for example, by KM3NeT. As part of the KM3NeT collaboration, we investigate the origin of high-energy neutrinos through numerical simulations of the propagation of cosmic rays (which create neutrinos when interacting with their environment). These efforts will contribute to solving the century-old question of the origin of cosmic rays and will lead to a better understanding of potential neutrino sources.