Analysis of first KATRIN data and searches for keV-scale sterile neutrinos

The phenomenon of neutrino oscillation stands in contradiction with the Standard Model of Particle Physics (SM) where neutrinos are formulated as massless particles. One way to introduce a non-zero neutrino mass to the SM is the so-called see-saw-mechanism. It adds at least one sterile neutrino to the particle framework. A sterile neutrino would not participate in any SM interaction, only interact gravitationally and would be of arbitrary mass-scale. These unique properties make a sterile neutrino an interesting Dark Matter candidate. The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to determine the effective electron anti-neutrino mass with a sensitvity of $0.2\, \mathrm{eV}/c^{2}$ (90 $\%$ C.L.) by observing the tritium $\beta$-decay close to its kinematic endpoint. Studies show that the experiment can be additionally extended to search for a sterile neutrino, for example on the keV mass-scale. This thesis specifies how the KATRIN experiment can be operated to search for keV-scale sterile neutrinos without any significant hardware modifications. It presents a first comprehensive overview of all yet known systematic effects that occur in such a measurement. This information is used for a first keV-scale sterile neutrino measurement with KATRIN data. By analyzing 82 KATRIN $\beta$-spectrum scans wit a total measurement time of approximately 160 hours, the current laboratory limit on the active-to-sterile mixing angle could be improved by up to a factor of eight on a mass scale of $0.10 \, \mathrm{keV} \leq m_{\nu_\mathrm{s}} \leq 0.76 \, \mathrm{keV}$ with a resolution on the mixing amplitude of up to $\sin^2 \theta < 2.33 \cdot 10^{-3}$

A Dyson-Schwinger study of the four-gluon vertex

We present a self-consistent calculation of the four-gluon vertex of Landau gauge Yang--Mills theory from a truncated Dyson--Schwinger equation. The equation contains the leading diagrams in the ultraviolet and is solved using as the only input results for lower Green functions from previous Dyson--Schwinger calculations that are in good agreement with lattice data. All quantities are therefore fixed and no higher Green functions enter within this truncation. Our self-consistent solution resolves the full momentum dependence of the vertex but is limited to the tree-level tensor structure at the moment. Calculations of selected dressing functions for other tensor structures from this solution are used to exemplify that they are suppressed compared to the tree-level structure except for possible logarithmic enhancements in the deep infrared. Our results furthermore allow one to extract a qualitative fit for the vertex and a running coupling.Comment: 23 pages, 14 figs.; more detailed discussion of renormalization, version accepted by EPJ

Entangled Singularity patterns of Photons in Ince-Gauss modes

Photons with complex spatial mode structures open up possibilities for new fundamental high-dimensional quantum experiments and for novel quantum information tasks. Here we show for the first time entanglement of photons with complex vortex and singularity patterns called Ince-Gauss modes. In these modes, the position and number of singularities vary depending on the mode parameters. We verify 2-dimensional and 3-dimensional entanglement of Ince-Gauss modes. By measuring one photon and thereby defining its singularity pattern, we non-locally steer the singularity structure of its entangled partner, while the initial singularity structure of the photons is undefined. In addition we measure an Ince-Gauss specific quantum-correlation function with possible use in future quantum communication protocols

Site-resolved imaging of a fermionic Mott insulator

The complexity of quantum many-body systems originates from the interplay of strong interactions, quantum statistics, and the large number of quantum-mechanical degrees of freedom. Probing these systems on a microscopic level with single-site resolution offers important insights. Here we report site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators using ultracold atoms in a square lattice. For strong repulsive interactions we observe two-dimensional Mott insulators containing over 400 atoms. For intermediate interactions, we observe a coexistence of phases. From comparison to theory we find trap-averaged entropies per particle of $1.0\,k_{\mathrm{B}}$. In the band-insulator we find local entropies as low as $0.5\,k_{\mathrm{B}}$. Access to local observables will aid the understanding of fermionic many-body systems in regimes inaccessible by modern theoretical methods.Comment: 6+7 page

Rococo Möbel : entwürfe für moderne Möbel im Style des 18 Jahrhunderts : 20 Tafeln

Copia digital. España : Ministerio de Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 2018Fecha 1890 tomada del catálogo Copa