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In this thesis we investigate various aspects of ux compactications in six-dimensionalquantum eld theories. After introducing the internal geometries, i.e. [...]

A combination is presented of all previously published deep inelastic neutral and charged current $e^{\pm}p$ scattering measurements at HERA for zero beam polarisation.The ZEUS and H1 collaborations have collected data at electron beam energy of $27.5$ GeV and proton beam energies of $920$, $820$, $575$ and $460$ GeV.The combined data correspond to an integrated luminosity of about $1$ fb$^{-1}$ and cover a kinematic range in the negative four-momentum-transfer squared from $Q^{2} = 0.045$ GeV$^{2}$ to $Q^{2} = 50000$ GeV$^{2}$ and in Bjorken $x$ from $x_{\rm Bj} = 6 \times 10^{-7}$ to $x_{\rm Bj} = 0.65$.The correlations of systematic uncertainties between different sets of data were taken into account, resulting in significantly improved precision.The combined $e^{\pm}p$ cross sections were used in a QCD analysis at next-to-leading order, providing a set of parton distribution functions, called ZCIPDF.The combined measurements were also used in an analysis beyond the Standard Model using a new approach, performing simultaneous fits on large sets of Monte Carlo replicas of parton distribution functions, PDFs, together with the parameters of "new physics" processes.A simplified approach to reduce the calculation time was developed and extensively tested.It allowed the calculation time to be reduced by about a factor of 50.The resulting $95\,\%$ C.L. upper limit on the effective quark radius is $0.43 \cdot 10^{-16}$ cm and the limits on the mass scales for different contact interaction scenarios extend up to $10$ TeV.The analyses have shown that taking into account the possible influence of processes beyond the Standard Model on the PDF parameters is necessary, since the limits that would be obtained using PDFs from QCD analysis within the Standard Model are too strong by about $10\,\%$.Studies of the surface quality of 28 Niobium superconducting radio frequency, SRF, cavities and development of a controllable cooling system for Niobium samples are also reported.The SRF cavities are the core of the accelerating technology for the future International Linear Collider, ILC; the reported studies are part of an ongoing research and development program..

The determination of the injection composition of cosmic ray nuclei within astrophysical sources requires sufficiently accurate descriptions of the source physics and the propagation – apart from controlling astrophysical uncertainties. We therefore study the implications of nuclear data and models for cosmic ray astrophysics, which involves the photo-disintegration of nuclei up to iron in astrophysical environments. [...]

We study the production of high energy neutrinos in jets from the tidal disruption of stars by supermassive black holes. The diffuse neutrino flux expected from these tidal disruption events (TDEs) is calculated both analytically and numerically, taking into account the dependence of the rate of TDEs on the redshift and black hole mass. [...]

Ultra high energy cosmic rays (UHECRs) are expected to be accelerated inastrophysical sources and to travel through extragalactic space before hitting the Earth atmosphere.They interact both with the environment in the source and with the intergalacticphoton fields they encounter, causing different processes at various scales dependingon the photon energy in the nucleus rest frame. UHECR interactions are sensitive touncertainties in the extragalactic background spectrum and in the photo-disintegrationmodels..

In this thesis, we propose and demonstrate a novel approach to power scaling of DFG-based ultrafast mid-IR laser sources. The essence of this novel approach is the generation of a high-energy signal beam. [...]

S5 0716+714 is a well known BL Lac object, and one of the brightest and most active blazars. The discovery in the Very High Energy band (VHE, E > 100 GeV) by MAGIC happened in 2008. [...]