The non-trivial structure of the QCD vacuum gives rise to a P and CP violating term in the QCD Lagrangian. The fact that we do not see an observable CP violation in the strong interaction despite this CP violating theta term is called the Strong CP Problem. In this thesis, we analyze an observable consequence of this theta vacuum term in the decay of the ground state neutral Sigma hyperon. Due to the SU(3) flavor symmetry, the current upper bound of the neutron electric dipole moment can be translated to an angular asymmetry in the decay distribution of the Σ0 particle. The selfanalyzing weak decay of the Λ hyperon means that any P violation in the initial Σ0 → Λγ decay will result in an asymmetry in the angular distribution of the final decay products. Studying the Sigma and anti-Sigma hyperon decays, we get an idea of C and CP violation in the decay chain. The effect of the production process of the Σ0 hyperon on the angular distribution of the final products is also worked out. A significant angular asymmetry in the decay will mean not only physics beyond the Standard Model, but also physics beyond the CP violating term in the QCD Lagrangian

The description of a black hole in the limit of very large number of spacetime dimensions D simplifies considerably. When D approaches infinity, the gravitational field lines of force are infinitely dispersed among the infite number of spacetime directions. This implies that outside the near-horizon region of the black hole the background spacetime will be flat, while the gravitational field will be strongly localized near the horizon. Thus, we can attempt to replace the black hole by a sphere cut off at the horizon in an empty background. In this project we attempt to obtain the physical conditions that the sphere has to meet in order to be able to reproduce the dynamics of the black hole when embedded in the empty background. This is described in the effective equation that we derive starting from the Einstein equations. Finally, we apply our results to take a look at ’black droplets’, black holes localized at the boundary of AdS and extending a finite distance into the bulk.

ChemCam, mounted on the mast of the Mars Science Laboratory (MSL) rover, uses Laser-Induced Breakdown Spectroscopy (LIBS) to perform remote-sensing science on Mars. ChemCam’s telescope is used to simultaneously focus the laser on martian rocks up to 7 meters away from the rover and collect the light emitted as the plasma plume created on the target cools down. The light is then transmitted to three spectrometers located in the body of the rover, providing spectra from which the composition of the samples is inferred on the ground. Context images of the sampled targets are captured by the Remote Micro Imager (RMI) that completes the instrument. A hardware failure that occurred a bit more than two years into the mission caused the ChemCam instrument to lose its original autofocus ability. This resulted in a degraded performance mode for several months while the ChemCam team developed a new autofocus algorithm based on the RMI images. During this period of degraded performance, several observations with different focus conditions were made on each target.  This unusual set of data provides the opportunity to study the influence of less-than-optimal focus conditions on the LIBS signal created on the target and analyzed by ChemCam. To this purpose, we look at both raw ChemCam spectra and  post-processed products used for scientific analysis to investigate how the quality of the focus influences the LIBS signal and the quantitative predictions of the composition of the observed targets.

No description available.

The MAX phase family is a set of nanolaminated, hexagonal materials typically comprised of three elements: a transition metal (M), an A-group element (A), and carbon and/or nitrogen (X). In this thesis, first-principles based methods have been used to investigate the phase stability and physical properties of a number of MAX and MAX-like phases. Most theoretical work on MAX phase stability use the constraint of 0 K conditions, due to the very high computational cost of including temperature dependent effects such as lattice vibrations and electronic excitations for all relevant competing phases in the ternary or multinary chemical space. Despite this, previous predictions of the existence of new MAX phases have to a large extent been experimentally verified. In an attempt to provide a possible explanation for this consistency, and thus help strengthen the confidence in future predictions, we have calculated the temperature dependent phase stability of Tin+1AlCn, to date the most studied MAX phases. We show that both the electronic and vibrational contribution to the Gibbs free energies of the MAX phases are  cancelled by the corresponding contributions to the Gibbs free energies of the competing phases. We further show that this is the case even when thermal expansion is considered. We have also investigated the stability of two hypothetical MAX-like phases, V2Ga2C and (Mo1-xVx)2Ga2C, motivated by a search for ways to attain new two-dimensional MAX phase derivatives, so-called MXenes. We predict that it is possible to synthesize both phases. For x≤0.25, stability of (Mo1-xVx)2Ga2C is indicated for both ordered and disordered solid solutions on the M sublattice. For x=0.5 and x≥0.75, stability is only indicated for disordered solutions. The ordered solutions are stable at temperatures below 1000 K, whereas stabilization of the disordered solutions requires temperatures of up to 2100 K, depending on the V concentration. Finally, we have investigated the electronic, vibrational, and magnetic properties of the recently synthesized MAX phase Mn2GaC. We show that the electronic band structure is anisotropic, and determine the bulk, shear, and Young’s modulus to be 157, 93, and 233 GPa, respectively, and Poisson’s ratio to be 0.25. We further predict the magnetic critical order-disorder temperature of Mn2GaC to be 660 K. We base the predictions on Monte Carlo simulations of a bilinear Heisenberg Hamiltonian constructed from magnetic exchange interaction parameters derived using two different supercell methods: the novel magnetic direct cluster averaging method (MDCA), and the Connolly-Williams method (CW). We conclude that CW is less computationally expensive than MDCA for chemically and topologically ordered phases such as Mn2GaC.

The Standard Model (SM) of particle physics describes the elementary particles that constitute matter and their interactions. The predictions of the SM have been confirmed by numerous experimental results. However, several questions of particle phenomena in the Universe remain unaddressed by the Standard Model, which suggests that the SM can be extended to a more complete theory. One approach to search for extensions of the SM is to test the predictions of the Standard Model in high precision measurements and see whether the results falsify the SM. For this reason, production of the ttZ and ttW processes at the ATLAS experiment at CERN is studied. It is investigated whether the SM gives correct predictions for these processes and how much room there is for contributions from new physics that give similar final states. Three measurements of ttZ and ttW production are performed. The first measurement is performed at 8 TeV collision energy. The next measurement uses data collected in 2015 at 13 TeV collision energy, when the production cross sections for these processes are considerably larger. The third measurement uses ten times as much data at 13 TeV collision energy. This analysis is not public at the time of writing, so only preliminary results for the expected sensitivity are presented. The new physics affecting ttZ production is parametrised in the model-independent framework of Effective Field Theory. Five effective operators that can affect ttZ production are studied and their coefficients are constrained in a fit to simulated data for the third measurement. The major background process tWZ is modelled at NLO in QCD. In order to avoid overlaps with ttZ, the Diagram Removal (DR) method is employed in two versions: one where the quantum interference is neglected (DR1) and another where it is modelled (DR2). The differences between the two predictions are explored and enter the measurement as a modelling uncertainty.

Fission yields represent the probability of producing a certain nuclide in a fission event, and are important observables for fission research. For applications, accurate knowledge of the yields is fundamental at all stages of the fuel cycle of nuclear reactors, e.g., for reactivity calculations, or to estimate (spent) fuel inventory. Fission yields also help in the basic understanding of the fission process, for nucleosynthesis models, and for radioactive ion beam production. This thesis was developed in the framework of the AlFONS project, the objective of which was to measure neutron-induced fission yields of relevance for partitioning and transmutation of spent fuel. The work is performed at the IGISOL-4 facility in JYFL (University of Jyväskylä). The first part of this thesis work is dedicated to the development and characterisation of a suitable 9Be(p(30MeV),nx) neutron source for IGISOL-4. The neutron energy spectrum and the neutron yield from a 5mm thick converter were studied with Monte Carlo simulations. Two characterisation campaigns that validated the MCNPX code were also performed. At the maximum current available from the cyclotron at JYFL, a total neutron yield between 2 and 5×1012 neutrons/(sr s) can be obtained. This satisfies the design goal for studies of fission yields. The neutron source was used in the measurement of fission yields from high-energy neutron-induced fission of natU at IGISOL-4, discussed in the second part of this thesis. The fission products were online-separated with a dipole magnet. The isobars, with masses in the range A = 128-133, were identified using γ-spectroscopy. Data for the relative yields of tin and antimony, as well as isomeric yield ratios for five nuclides will be reported. The yields show trends not observed in the ENDF/B-VII.1 evaluation, and only in part confirmed by the GEF model. The final part of this thesis concerns a study of the performance of different nuclear model codes, that aim at describing the states of the fission fragments right after scission. Reproduction of experimental data serves to benchmark the models and it indicates, to some extent, how reliably the results can be extrapolated to regions where no data exist. A methodology to compare and test these models has been developed, which was implemented in the DEℓFIN code. DEℓFIN takes the excited fission fragments, defined by the model under test, and de-excites them in a standardised way using the nuclear model code TALYS. Eliminating any variability in the way the final observables are extracted helps focusing on each model's assumptions. DEℓFIN was tested on five models, and interesting features in the prompt neutron multiplicity were found for some of them. This study will promote a better understanding of the ideas used in the development of fission models.

No description available.

For an idealized one-dimensional crystal it is possible to have energy levels whose wave functions are localized at the surface. These states are called surface states. There is one surface state for each energy gap between the ordinary allowed bands of energies. These electron states are called Tamm states. This Tamm state has an energy that lies almost at the middle of the energy gap and is mainly localized at the surface atomic layer. The image potential states are generated by a potential well formed by the Coulomb-like image potential barrier. These image states that are also called Shockley states are localized in a slowly decaying tail in the vacuum. I also studied the lateral (in-plane) motion of electrons confined to terraces between steps on a vicinal Cu (111) surface. The local density of states showed a number of peaks at energies where electrons can occupy new quantum-well states on a step. I also tested the influence of the electron lifetime on the local density of states.

Brownian motion conned in a two dimensional channel with varying crosssectionunder the inuence of an external force eld is examined. In particular,a one dimensional equation approximately describing the dynamics of the Brownianparticles is derived, a generalization of the well known Fick-Jacobs equation.This generalized Fick-Jacobs equation is numerically veried by Browniandynamics simulations for a special case of the external force eld. Furthermorethe generalized Fick-Jacobs equation is investigated in the context of stochasticthermodynamics.