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Theoretical Astro-Particle Physics: Student Projects

For more information contact: O. Scholten

Particle Accelerators in Space.

Question: Is shock-wave acceleration a realistic possibility to create Ultra High Energy cosmic rays?

In a combination of a strong magnetic field and a strong shock wave charged particles can be accelerated by the so-called Fermi acceleration mechanism. The conditions for Fermi acceleration may occur in supernova explosions but also in the shock wave of the Big Bang. Is it possible to make estimates of fluxes and energies of cosmic rays based on this mechanism.
What do the magnetic fields which are necessary for Fermi Acceleration imply for the average magnetic fields in space and how does this influence the transport of charged particles through space?
Importance: This research is done as part of the Pierre Auger and the LOFAR-cosmic ray collaborations which aim at measuring the flux of UHE cosmic rays.
Background reading:

  • UHE cosmic rays: NuMoon
  • 'Astrophysical Origins of Ultrahigh Energy Cosmic Rays.', Diego F. Torres and Luis A. Anchordoqui, Astro-ph/0402371 . [Tor04-02371]
  • 'Particle acceleration by ultrarelativistic shocks: theory and simulations.', Abraham Achterberg, et al., Mon. Not. R. Astron. Soc. 328, 393 (2001). [Ach01-MNRAS328p393]

Super massive particles.

Question: Is it realistic to assume that Ultra High Energetic cosmic rays are the result of the decay of super massive particles?

Extremely-massive super-symmetric particles are sometimes suggested as the solution to the dark matter problem. Due to their symmetry properties they may couple weakly to normal matter but if they are very massive they may have a finite, but small, probability to decay. These decay products are seen as cosmic rays. What are the limits one can impose on such an model. What are the possible decays of such particles, in neutrinos or in hadrons?
Importance: This research is done as part of the Pierre Auger and the LOFAR-cosmic ray collaborations which aim at measuring the flux of UHE cosmic rays.
Background reading:
  • UHE cosmic rays: NuMoon
  • 'Astrophysical Origins of Ultrahigh Energy Cosmic Rays.', Diego F. Torres and Luis A. Anchordoqui, Astro-ph/0402371 . [Tor04-02371]
  • 'The high energy cosmic ray spectrum from relic particle decay.', Subir Sarkar and Ramon Toldrà, Nucl. Phys. B, hep-ph/0108098 .[Sar01-08098]
  • 'Ultrahigh energy neutrinos from hidden-sector topological defects.', V. Berezinsky and A. Vilenkin, Phys. Rev. D 62, 083512 (2000), Astro-ph/0604311, Astro-ph/0409222. [Ber00-PRD62p083512]

NuMoon-Direction Sensitivity.

Question: Can one distinguish hadrons and neutrinos in the NuMoon experiment and is it possible to have direction sensitivity?

In the NuMoon experiment the impact of Ultra High Energy cosmic rays and neutrinos on the moon are detected through the radio waves that are emitted by the particle showers that are induced in the lunar regolith. Calculations show that through this mechanism the flux of UHE particles can be determined with un-precedented accuracy. Open questions are whether one can distinguish between neutrinos and hadrons and if one is also sensitive to the original direction of the UHE particles. This might be possible through the polarization and the frequency spectrum of the emitted pulse. Of particular interest is here the transmission of electromagnetic signal through an in-homogeneous layer of lunar rock and regolith.
Importance: This research is done as part of the NuMoon collaborative effort.
Background reading:

NuMoon-Shallow Showers.

Question: Do shallow showers in the lunar regolith emit Cherenkov radiation through the surface?

When an ultra-high energetic proton (UHE-cosmic ray) hits the lunar surface, as shower of particles is produces at a very short distance below the surface. The leading part of this shower, moving with the velocity of light (c), has an excess of electrons. Since this velocity is larger that the velocity of electromagnetic waves in the medium (=c/n, where n is the index of refraction) Cherenkov radiation will be emitted. If the distance of the shower to the surface is considerably less than the wave-length of the radiation, once should question if this radiation can ever be emitted through the surface, after all, if this charge was moving in vacuum instead of in the regolith, no Cherenkov radiation would be emitted.
Importance: This question is of central importance for the calculation of the sensitivity of the NuMoon experiment to cosmic rays.
Background reading:

  • UHE cosmic rays: NuMoon
  • Paper on the NuMoon project astro-ph/0508580
  • 'FORTE satellite constraints on ultrahigh energy cosmic particle fluxes.', N.G. Lehtinen et al., Phys. Rev. D 69, 013008 (2004), astro-ph/0309656. [Lei04-PRD69p13008]

LPM effect in hadronic and neutrino showers.

Question: What is the length of UHE neutrino and Cosmic-ray induced showers?

At ultra high energies, due to the Landau-Pomerancuk-Migdal (LPM) effect, the effective cross section of particles in a medium decreases, giving much larger path lengths. The LPM is due to quantum-coherence between successive scatterings in a medium. The path length of particles is an essential ingredient for the calculation of the length showers which in turn determine the angular spread of the emitted radiation.
Importance: This research is done as part of the Pierre Auger and the LOFAR-cosmic ray collaboration.
Background reading:

  • UHE cosmic rays: NuMoon
  • 'The LPM effect for EeV hadronic showers in ice: implications for radio detection of neutrinos.', J. Alvarez-Muñiz, E. Zas, Phys. Lett. B 434, 396 (1998), astro-ph/9806098, , astro-ph/9901278. [Alv98-PLB434p396]
  • 'Electromagnetic cascade showers in lead with the Landau-Pomeranchuk-Migdal effect included: Average behavior of the one-dimensional LPM shower in lead.', A. Misaki, Phys. Rev. D 40, 3087 (1998). [Mis98-PRD40p3087]

Collective Geo-Magnetic Radiation.

Question: can geo-synchrotron radiation also be understood from a macroscopic picture?

Radio detection of cosmic rays in the Earth atmosphere is possible through the so-called geo-synchrotron effect. The is a description of this effect based on the synchrotron motion of the individual charged particles in the shower induced by the cosmic ray. To obtain a better insight in the relation between the structure of the cosmic ray shower (which has information on the mass and charge of the initiating cosmic ray) and the structure of the electromagnetic pulse it is desirable to develop a description which is based on the gross structure of the shower rather than the motion of separate electrons.
Importance: This research is done as part of the Pierre Auger and the LOFAR-cosmic ray collaboration.
Background reading:

  • UHE cosmic rays: NuMoon
  • 'Radio emission from cosmic ray air showers: simulation results and parametrization.', T. Huege and H. Falcke, astro-ph/0501580 . [Hue05-01580]
  • 'Synchrotron radiation at radio frequencies from cosmic ray air showers.', Denis A. Suprun, Peter W. Gorham, Jonathan L. Rosner, Astropart. Phys. 20, 157 (2003), astro-ph/0211273. [Sup03-ApP20p157]
Laatst gewijzigd:19 februari 2018 13:52