Fysik // Physics
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Explores and uses physics to understand the world, and provide applications, new materials and innovations that meet today's needs, and the challenges of the future.
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Browsar Fysik // Physics efter Program "Fundamental physics, MSc"
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- PostA Tensor Formalism for Exceptional Geometry(2014) Edlund, Joakim; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsToroidal compactification of M-theory and its low energy limit, eleven-dimensional supergravity, possess hidden symmetries giving fields additional degrees of freedom. By extending the space-time to accomodate these extra degrees of freedom and constructing a generalised geometry on this space, the U-duality symmetry can be made manifest. The local diffeomorphism invariance is replaced by the larger exceptional groups which also happens to include gauge transformations. In this thesis, a tensor calculus for the exceptional generalised geometry is constructed. The geometrical concepts of diffeomorphisms, torsion, curvature, reducibility, tensors and tensor fields are given a generalised, covariant construction in the toroidally compactified, enhanced space-directions.
- PostChiral Perturbation Theory,Weak Interactions and the Nuclear Two-body Axial Vector Current(2012) Karlsson, Jonathan; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsIn this thesis I give a practical introduction to chiral perturbation theory. This is an effective field theory of pions and nucleons. It is governed by the chiral symmetry stemming from the lightness of the up- and down quarks in quantum chromodynamics. The validity region comprises energies up to the rho meson mass. The theory is expressed as an infinite series of chiral invariant interactions, whose strengths are expressed in an infinite number of low energy constants. The interactions can be ordered and I identify the most important ones. Special care has to be taken when including nucleons in chiral perturbation theory because of the scale introduced by the nucleon mass. To facilitate straightforward calculations I work in heavy-baryon chiral perturbation theory. In this formalismthe nucleons are considered to be very heavy and the nucleon mass only appears in next-to-leading order corrections. The pions and nucleons are coupled to the charged vector bosons of the weak interactions. This interaction is determined entirely by the chiral symmetry. As an example, I compute the decay rate of charged pions. Experimental data for this observable can be used to fix one low energy constant. Finally, I compute the two-body axial vector current of nucleons in heavybaryon chiral perturbation theory with the long wavelength approximation. This current complements the leading order one-body current operator and gives the first correction to the Gamow-Teller operator from the nuclear environment. I provide both a detailed derivation and an explicit expressions for this two-body current operator.
- PostData Analysis of Resonant Proton Scattering in Inverse Kinematics(2013) Strannerdahl, Fredrik; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsThis thesis aims to study a resonant proton scattering experiment performed at CERNISOLDE,Geneva, during the summer of 2012. The main focus is detector calibration, data analysis and interpretation of the experimental data. A radioactive beam of 21Na at 3 MeV/u was impinging on a 5.6 mg/cm2 polyethylene,(CH2)n, target in vacuum. Ejectile protons from nuclear reactions of the beam and the target were analyzed by two silicon strip detectors used in a telescope configuration. The resonant elastic scattering reaction 21Na(p,p)21Na is of particular interest due to the importance of 22Mg in stellar nucleosynthesis. Several previously known excited states of 22Mg have been identified at somewhat higher energies than previously reported. Also some, possibly new, states have been observed.
- PostEisenstein Series and Instantons in String Theory(2013) Gustafsson, Henrik P. A.; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsIn this thesis we review U-duality constraints on corrections to the type IIB supergravity effective action on torus compactifications. The U-duality invariant corrections are described by automorphic forms whose construction and Fourier expansion we explain. The latter enables us to extract physical information about instanton states in the theory. In particular, we discuss the first non-vanishing higher-derivative correction to the Einstein-Hilbert action in ten dimensions, for which there is a unique automorphic form incorporating all the perturbative and non-perturbative corrections in the string coupling constant.
- PostHolographic Superconductivity(2012) Wenger, Tobias; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsIn this thesis we apply the AdS/CFT conjecture to condensed matter physics and more specifically we consider the application to layered superconductors. In this thesis we apply the AdS/CFT conjecture to condensed matter physics and more specifically we consider the application to layered superconductors. We start by analysing the "ordinary" 2+1 dimensional holographic superconductor where we only have a scalar field coupled to an Einstein-Maxwell theory in the bulk. We then proceed to add first order corrections to the theory by higher derivative terms in the action. This is initially done by adding a Weyl correction which allows us to interpolate between vortex- and quasi particle excitations in the superconductor. We then generalise this to adding all possible first order correction terms to the theory, this amounts to adding non-linear Maxwell terms to the bulk Lagrangian. The stability of the theory is considered and we also explore the parameter space and in particular we find that we are able to tune the energy gap 2 Tc, which in the weakly coupled BCS-case is 3:5. The range of the values for the energy gap we find matches nicely with the experimentally obtained range of energy gaps for high-Tc cuprates. By tuning the coupling strength of the non-linear Maxwell terms we find that we can produce Drude behaviour at low frequencies.
- PostMajorana Fermions in Topological Quantum Matter(2012) Laurell, Pontus; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsTwo-dimensional topological insulators coupled to s-wave superconductors and external magnetic fields have been predicted to support Majorana edge states. The stability of these states against electron-electron interactions and spin-orbit interactions of Rashba and Dresselhaus type are studied using bosonization and renormalization group analysis. To extend an earlier model, a local Umklapp interaction, corresponding to isolated impurities, is first studied. It is shown that the local Umklapp interaction is less relevant than the global Umklapp interaction, and that the Majorana states are stable against this disorder effect. The model is then extended to also include Rashba and Dresselhaus spin-orbit interactions of constant interaction strength. It is shown that the Majorana states are stable also against the Rashba effect, but may be destabilized by the Dresselhaus effect. The Luttinger parameter is found to be a function of the Rashba interaction strength. The thesis also contains an introduction to the theory of topological insulators, with focus on the field theoretical description and interaction processes.
- PostNeutron detection with the Miniball germanium array(2015) Andersson, Daniel; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsIn experiment IS430 at Rex-Isolde, Cern, transfer reactions of neutron-rich beryllium isotopes on deuterated targets were studied with the segmented germanium detector array Miniball, detecting electromagnetic radiation, and the silicon-based T-Rex detector for charged particles. This thesis investigates signals in Miniball following inelastic scattering of neutrons on 72Ge, populating its first excited state which decays through ejecting a monoenergetic electron — a technique to detect neutrons in germanium detectors based on a proof-of-concept article. By correlating these neutron signals with additional event information, there is a possibility to draw a more complete picture of the reactions involved without the need to add additional detection equipment. Monitoring of these events could also have possible uses in online analysis of the neutron rate hitting the detectors, possibly degrading their function. This work investigates to which extent this process can be of help in the T-Rex and Miniball configuration at Isolde in particular, and for germanium detectors in general.
- PostOptimised Use of Detector Systems for Relativistic Radioactive Beams(2013) Lindberg, Simon; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsEver since the discovery of the atomic nucleus, the exploration and understanding of its properties has been a frontier of physics research. Such investigations are still ongoing at different research facilities around the world. One of these places is the GSI accelerator laboratory where experiments with unstable heavy ions are performed. To obtain high-quality results from the experiments, it is essential that the detectors used are performing at their maximum. Hence it is important to understand the characteristics of the detectors to be able to find and correct errors. In this thesis, the response of two different detector systems in the LAND-setup at GSI is investigated. The first detector system is called the Crystal Ball, a γ-detector, which is also able to detect high-energy protons. The second detector type is used for detecting ions. It consists of a long plastic scintillator which is very common in nuclear physics experiments and is used in several different detector systems in the LAND-setup. For the Crystal Ball an evaluation of different addback routines were performed. An addback routine is a method to recreate the multiplicity and energy of γ-rays and protons hitting the Crystal Ball detectors. This was done based on simulations of different scenarios. For the scintillator, experimental data were used. The motivation to investigate the behaviour of the scintillator is a feature causing the detector to respond differently depending on the position of a hit in the paddle. The origin of this behaviour was found and different methods for correction are suggested and evaluated. The third and last topic of this thesis is a brief analysis of data collected by a detector system constructed to find a relation between energies deposited by cosmic muons and protons in the Crystal Ball. With this relation it is possible to calibrate the Crystal Ball for a range of proton energies, using cosmic muons. The results from the experiment agree with expectations, however to find the relation, a more thorough analysis is needed.
- PostSupersymmetric Gauge Theory, Wall-Crossing and Hyperkähler Geometry(2013) Till, Oskar; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsIn this thesis we study moduli spaces of four-dimensional N = 2 supersymmetric gauge theories. We focus on the vector multiplet moduli space and describe how the rigid special geometry of the Coulomb branch determines the couplings in the effective Lagrangian. Compactication to three dimensions gives rise to an N = 4 theory whose moduli space is hyperkähler. The twistor space construction of this hyperkähler metric is presented and put in the context of Gaiotto, Moore and Neitzke's physical interpretation of the solution by Kontsevich and Soibelman of the wall-crossing problem.
- PostThe Similarity Renormalization Group for three bosons in a momentum-space partial-wave basis(2012) Carlsson, Boris; Chalmers tekniska högskola / Institutionen för fundamental fysik; Chalmers University of Technology / Department of Fundamental PhysicsThe Similarity Renormalization Group (SRG) flow equation is explored for systems of two and three spinless bosons in a momentum-space partial-wave basis. The two- and three-body binding energies as well as the phaseshifts are used to gauge that the transformation is unitary and to study how well the SRG decouples high- and low-energy physics. I consider four different potentials with different characteristics: Two simplied nucleon potentials and two inter-atomic helium potentials (a soft-core potential and the state-of-the-art LM2M2 potential that is fitted to a wealth of experimental data). An initial three-body force is included for two of these potentials. Even with only two-body terms in the initial hamiltonian, SRG induced many-body forces are shown to arise during the transformation. These induced forces are computed for the three-body system and their evolution is studied as a function of the flow parameter. In all cases the SRG transformed potentials display greatly improved decoupling. This is achieved with a three-body binding-energy deviation of less than 0.1% in all cases except for the soft-core helium potential.