[en] We apply the relativistic chiral Lagrangian to the nuclear equation of state. An effective chiral power expansion scheme, which is constructed to work around nuclear saturation density, is presented. The leading and subleading terms are evaluated and are shown to provide an excellent equation of state. Our saturation mechanism is found to probe in detail the underlying pion dynamics

[en] In the first phase of the upgrade program of the CERN accelerator complex the proton injector Linac2 will be replaced by a new, normal-conducting H-ion Linac, Linac4, allowing a significant increase of the proton flux intensity along the downstream accelerator complex. In the design of Linac4 three beam transport sections are implemented to match the beam between the different accelerator elements and to model the longitudinal pulse structure. These three beam transport sections, which are the most critical locations in terms of beam quality preservation, are in the focus of this thesis. During the work of this thesis the Low Energy Beam Transport (LEBT), which is required to match the source beam to the radiofrequency quadrupole (RFQ), has been commissioned and its beam dynamics re-constructed. The measurement campaign used to reconstruct the LEBT beam dynamics was performed with the aim to prepare the RFQ commissioning and to maximise the LEBT performance. Downstream of the Linac4 accelerator the beam is transported along a 180 m long transfer line to the Proton Synchrotron Booster (PS-Booster). The transfer line optics was studied, optimised and sections were completely re-designed. The new transfer line optics is characterised by an improved preservation of the beam emittance, higher stability of the optical solution with respect to alignment errors and field jitters of the transfer line magnets and it is matched to each of the PS-Booster injection schemes. In a concluding ''Start-To-End'' simulation based on the measured beam characteristics at the LEBT exit the beam dynamics of the downstream Linac, including the transfer line, was calculated. To minimise particle losses within acceptable emittance preservation the beam optics of the Medium Energy Beam Transport (MEBT) was adapted to the measured beam parameters. This ''Start-To-End'' simulation was performed to identify critical sections of the Linac4 beam dynamics and to adjust the commissioning strategies.

[en] The achievement of a higher proton flux to go beyond the current LHC design luminosity parameters is conditional on an upgrade of the injector chain. Presently the major limitation is given by space charge effects at injection from Linac2 into the PS Booster. These will be overcome by increasing the injection energy from 50 MeV to 160 MeV with the planned replacement of Linac2 with Linac4, a new normal conducting H-linear accelerator presently under construction. Due to the high charge density of the Linac4 bunches space charge will still dominate the beam dynamics in the low energy 3 MeV frontend. In this presentation a short, theoretical introduction to space charge effects is given, and their impact on the beam is illustrated with simulations. Moreover, the latest results of the commissioning of the low energy front end of Linac4 are shown and discussed.

[en] We present a new chiral expansion scheme for the nucleon-nucleon scattering amplitude which preserves unitarity exactly. Our effective field theory builds on the power counting rules for 2-nucleon reducible diagrams. We evaluate the leading order terms of the isospin one scattering amplitude and elaborate in detail on the ¹S₀ phase shift. Our chiral description of the ¹S₀-phase shift does compete in quality with modern phenomenological nucleon-nucleon potentials. We describe elastic and inelastic scattering quantitatively up to laboratory energies of E_lab≅600 MeV

[en] We present a study of Goldstone boson scattering based on the flavor SU(3) chiral Lagrangian formulated with vector mesons in the tensor field representation. A coupled-channel channel computation is confronted with the empirical s- and p-wave phase shifts, where good agreement with the data set is obtained up to about 1.2 GeV. There are two relevant free parameters only, the chiral limit value of the pion decay constant and the coupling constant characterizing the decay of the rho meson into a pair of pions. We apply a recently suggested approach that implements constraints from micro-causality and coupled-channel unitarity. Generalized potentials are obtained from the chiral Lagrangian and are expanded in terms of suitably constructed conformal variables. The partial-wave scattering amplitudes are defined as solutions of non-linear integral equations that are solved by means of an ND ansatz.

[en] We study the quark-mass dependence of baryon masses from the three-flavour chiral Lagrangian formulated for the J = 1/2⁺ and J^P = 3/2⁺ ground states. The available lattice data are used to determine the low-energy parameters relevant for the baryon masses at chiral order 4, where large-N_c sum rules are imposed as to reduce the number of independent low-energy operators. We scrutinize the convergence properties of the three-flavour chiral extrapolation.

[en] The study of the πN→ρ⁰N and πN→ωN amplitudes below and close to the vector meson production threshold (1.4√1.8 GeV) reveals a rich structure arising from the presence of baryon resonances in this energy range. These resonances are reflected in the interference pattern of the e⁺e^- decays of the ρ⁰- and ω-mesons produced in π^-p and π⁺n reactions. We discuss the shape and magnitude of the ρ⁰-ω interference in the π^-p→e⁺e^-n and π⁺n→e⁺e^-p reaction cross sections as functions of the total center of mass energy √s. We find contrasted results: the interference is largely destructive for the π^-p→e⁺e^-n cross section but constructive for the π⁺n→e⁺e^-p cross section. An experimental study of these reactions would provide significant constraints on the coupling of vector meson-nucleon channels to low-lying baryon resonances

[en] We consider the reaction dynamics of bosons with negative parity and spin 0 or 1 and fermions with positive parity and spin (1)/(2) or (3)/(2). Such systems are of central importance for the computation of the baryon resonance spectrum in the hadrogenesis conjecture. Based on a chiral Lagrangian the coupled-channel partial-wave scattering amplitudes have to be computed. We study the generic properties of such amplitudes. A decomposition of the various scattering amplitudes into suitable sets of invariant functions expected to satisfy Mandelstam's dispersion-integral representation is presented. Sets are identified that are free from kinematical constraints and that can be computed efficiently in terms of a novel projection algebra. From such a representation one can deduce the analytic structure of the partial-wave amplitudes. The helicity and the conventional angular-momentum partial-wave amplitudes are kinematically constrained at the Kibble conditions. Therefore an application of a dispersion-integral representation is prohibitively cumbersome. We derive covariant partial-wave amplitudes that are free from kinematical constraints at the Kibble conditions. They correspond to specific polynomials in the 4-momenta and Dirac matrices that solve the various Bethe-Salpeter equations in the presence of short-range interactions analytically. (orig.)

[en] We consider the quark-mass dependence of open-charm meson masses. The chiral Lagrangian formulated with the ground-state mesons with J"P =0"- and J"P = 1"- quantum numbers is applied at the one loop level. The implications of the heavy-quark spin symmetry are worked out. We scrutinize the results from various QCD lattice simulations for the masses of the charmed meson ground-states. Finite volume effects are considered systematically.

[en] We present a pedagogical case study how to combine micro-causality and unitarity based on a perturbative approach. The method we advocate constructs an analytic extrapolation of partial-wave scattering amplitudes that is constrained by the unitarity condition. Suitably constructed conformal mappings help to arrive at a systematic approximation of the scattering amplitude. The technique is illustrated at hand of a Yukawa interaction. The typical case of a superposition of strong short-range and weak long-range forces is investigated.