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Research interests

I am interested in the emission of (extremely) energetic particles by astrophysical sources. In particular:

• The relation between cosmic neutrinos and cosmic rays

  Many models for the production of ultra-high energy cosmic rays (UHECRs) predict an accompanying flux of neutrinos. But what are the prospects of detecting these neutrinos? And how do current bounds on neutrino fluxes constrain UHECR models? An interesting insight that we obtained recently is that the experimental upper limit on the diffuse neutrino flux (i.e., the total flux from all unresolved sources) constrains models of joint UHECR and neutrino production in the close-by active galaxy Centaurus A (see: "Relation between the neutrino flux from Centaurus A and the associated diffuse neutrino flux", H. B. J. Koers & P. Tinyakov, Phys. Rev. D78: 083009, 2008).

• Ultra-high energy cosmic ray anisotropy tests

  The discovery of the GZK cutoff provides strong evidence that the sources of observed UHECRs are within 100-200 Mpc. The Universe is not homogeneous on these length scales, being organized into galaxy clusters, superclusters, and voids. Because of this large-scale structure, the flux of UHECRs at Earth is expected to exhibit (small) anisotropies that can tell us something about their sources and their propagation through the Universe. Because of limited statistics, however, powerful statistical tests have to be developed for this purpose. We have proposed such a test in a recent publication ("Testing large-scale (an)isotropy of ultra-high energy cosmic rays", H. B. J. Koers & P. Tinyakov, JCAP 0904: 003, 2009) and are currently applying it to data obtained by the HiRes and Telescope Array experiments.

• Neutrinos as probes of gamma-ray bursts

  Gamma-ray bursts (GBRs) are extremely powerful stellar explosions, releasing vast amounts of energy in a very short time. The exact mechanism responsible for this energy release is however still unclear. Neutrinos may provide unique insights because they can be emitted from regions that are opaque to photons and because - unlike photons - they are predominantly created by hadronic interactions. One mechanism I have studied in detail is neutrino production in nucleonic interactions in GRB plasmas ("Neutron-rich gamma-ray burst flows: dynamics and particle creation in neutron - proton collisions", H. B. J. Koers & D. Giannios, Astron. Astrophys. 471: 395, 2007). Another ongoing project is to pin down how the energy spectrum of neutrinos can tell us something about magnetic fields generated by GRB shock waves.

Publications

• Analysis of Large-scale Anisotropy of Ultra-high Energy Cosmic Rays in HiRes Data

  R. U. Abbasi et al. (The HiRes collaboration together with H. B. J. Koers & P. Tinaykov)
  arXiv: 1002.1444 [astro-ph.HE]
  ApJ 713: L64, 2010

• Note on galaxy catalogues in UHECR flux modelling

  H. B. J. Koers & P. Tinyakov
  arXiv: 0909.3010 [astro-ph.CO]
  MNRAS 403: 2131, 2010

• Flux calculations in an inhomogeneous Universe: weighting a flux-limited galaxy sample

  H. B. J. Koers & P. Tinyakov
  arXiv: 0909.0121 [astro-ph.CO]
  MNRAS 399: 1005, 2009

• Testing large-scale (an)isotropy of ultra-high energy cosmic rays

  H. B. J. Koers & P. Tinyakov
  arXiv: 0812.0860 [hep-ph]
  JCAP 0904: 003, 2009

• Neutrino production in nucleonic interactions in gamma-ray bursters

  H. B. J. Koers
  arXiv: 0805.2514 [astro-ph]
  Proceedings of Rencontres de Moriond 2008 (Electroweak session), La Thuile, Italy, 1-8 March 2008

• Relation between the neutrino flux from Centaurus A and the associated diffuse neutrino flux

  H. B. J. Koers & P. Tinyakov
  arXiv: 0802.2403 [astro-ph]
  Phys. Rev. D78: 083009, 2008

• Enhanced high-energy neutrino emission from choked gamma-ray bursts due to meson and muon acceleration

  H. B. J. Koers & R. A. M. J. Wijers
  arXiv: 0711.4791 [astro-ph]
  

• The astrophysical herald: neutrinos as probes for particle physics and astronomy (PhD thesis)

  H. B. J. Koers
  DARE digital repository: 228805
  

• Neutron-rich gamma-ray burst flows: dynamics and particle creation in neutron - proton collisions

  H. B. J. Koers & D. Giannios
  arXiv: astro-ph/0703719
  Astron. Astrophys. 471: 395, 2007

• Parameterization of the energy and rapidity distributions of secondary pions and kaons produced in energetic proton-proton collisions

  H. B. J. Koers, A. Pe'er & R. A. M. J. Wijers
  arXiv: hep-ph/0611219
  

• Thermal neutrinos from hot GRB fireballs

  H. B. J. Koers & R. A. M. J. Wijers
  arXiv: astro-ph/0511071
  Proceedings of the International Europhysics Conference on High Energy Physics 2005

• The effect of neutrinos on the initial fireballs in gamma-ray bursts

  H. B. J. Koers & R. A. M. J. Wijers
  arXiv: astro-ph/0505533
  MNRAS 364: 934, 2005

• Perturbative neutrino pair creation by an external source

  H. B. J. Koers
  arXiv: hep-ph/0409259
  Phys. Lett. B605: 384, 2005

Selected presentations

• Seminar: Testing (an)isotropy of ultra-high energy cosmic rays

  University of Utah, Salt Lake City, USA (Aug 2009)

• Seminar: Astronomy with cosmic rays and cosmic neutrinos

  Université Catholique de Louvain-la-Neuve, Louvain-la-Neuve, Belgium (Oct 2008)

• Presentation: Neutrino emission from cosmic-ray sources: the odds for a smoking gun

  Annual meeting of the Belgian Physical Society, Brussels, Belgium (May 2008)

• Seminar: Unravelling the nature of GRB outflows through nucleonic interactions?

  Radboud University, Nijmegen, The Netherlands (Dec 2007)

• Seminar: Neutron-rich GRB outflows

  Max-Planck-Institut für Astrophysik, Garching, Germany (Jan 2007)

• Seminar: The effect of neutrinos on the initial fireballs in GRBs

  University of Oxford, Oxford, UK (Sep 2006)

• Presentation: Low- and high-energy neutrinos from gamma-ray bursts

  Annual NIKHEF meeting, NIKHEF, Amsterdam, The Netherlands (Dec 2005)

• Presentation: Thermal neutrinos from hot GRB fireballs

  HEP2005 Europhysics Conference, Lisbon, Portugal (Jul 2005)

• Presentation: Neutrino pair creation

  Antares collaboration meeting, CERN, Geneva, Switzerland (Mar 2004)