Global ETD Search

151	On the vector transition form factors in the Ω- → Ξ0 W- decay Bertilsson, Magnus January 2023 (has links) To learn more about the structure of hadrons we study form factors. In the semi-leptonic decay Ω- → Ξ0W- two types of form factors arise namely the vector and axial-vector transition form factors. We focus on the vector transition form factors at next-to-next-to-leading order in the power counting of chiral perturbation theory and study their quark mass dependence. They are related to the scattering amplitude for the transition and therefore we have to calculate Feynman diagrams. Next-to-next-to-leading order Feynman diagrams translate to 1-loop diagrams and at this order there is a substantial amount of them. This study is a feasibility study and therefore we limit this study to diagrams containing the low-energy constants HA and hA from the leading order chiral Lagrangian. There are 5 such diagrams, three with two propagators in the loop (bubble diagrams) and two with three propagators in the loop (triangle diagrams). We derive explicit expressions for all 5 diagrams. To calculate these diagrams numerically we use Mathematica and FeynCalc. We provide numerical results for the three bubble diagrams but not the triangle diagrams due to the long computing time for these diagrams. Therefore, we show that performing form factor calculations at NNLO seems feasible but there needs to be more investment into figuring out the coding aspects regarding the triangle diagrams. QCD Form factors Vector form factors Chiral perturbation theory One-loop diagrams Hadrons Hadron physics Hyperon decay Hadron structure Subatomic Physics Subatomär fysik
152	Total Monte Carlo of the fission model in GEF and its influence on the nuclear evaporation in TALYS Peter, Karlsson January 2023 (has links) Features recently added to the nuclear reaction software TALYS allow the use of the GEF model as a fission fragment generator. GEF generates data for fission fragment yields, total excitation energy (TXE), total kinetic energy (TKE) and individual fragment excitation energies (E*) with their standard deviations through Monte Carlo simulations for TALYS. In this work a framework named McPUFF was developed to couple GEF and TALYS and study the propagation of uncertainties in fission fragment data. The GEF model has a set of 94 parameters which were changed in order to produce perturbed output data. Both GEF and TALYS were modified to allow implementation of the Total Monte Carlo (TMC) method which is a method for handling the propagation of uncertainties throughout the simulation process. The developed framework allows the user to control aspects of the nuclear reaction using a set of input files. It is designed to be fast and memory efficient, performing simulations in parallel and storing all results in an object structure. A demonstration of the framework for the neutron induced fission of 235U, 238U and 239Pu was performed. Randomly perturbed sets of fission fragment data were created by GEF and fed into TALYS for simulation of the evaporation process using a Hauser-Feshbach statistical model. The impact that the perturbation of parameters in GEF has on results from TALYS were investigated for prompt particle multiplicity and energy. The results showed that a perturbation of parameter values in GEF by 3 percent has significant effects on values for fission observables produced by TALYS. The TALYS results for 235U showed an uncertainty for prompt neutron multiplicity of σn = 0.16 neutrons with an uncertainty for the neutron energy of σϵn = 0.03 MeV. The corresponding values for the uncertainty of the prompt γ-ray multiplicity were σγ = 0.10 γ-rays with an uncertainty for the γ-ray energy of σϵγ = 0.02 MeV. An investigation of how changes in the angular momentum of the fission fragments affects the evaporation process in GEF and TALYS was performed through the perturbation of the GEF parameter Jscaling. The results highlighted the need to scrutinize the handling of angular momentum in TALYS. physics nuclear physics fission neutron-induced evaporation Hauser-Feshbach GEF TALYS Total Monte Carlo TMC fysik kärnfysik neutron-inducerad Subatomic Physics Subatomär fysik
153	MAC-E-Filter characterization for PTOLEMY : a relic neutrino direct detection experiment Strid, Carl-Fabian January 2019 (has links) The cosmic neutrino background (CNB) can be composed of both active and hypothetical sterileneutrinos. At approximately one second after big bang, neutrinos decoupled from radiationand matter at a temperature of approximately one MeV. Neutrinos played an important role inthe origin and evolution of our universe and have been indirectly verified by cosmological dataon the BBN (Big Bang nucleosynthesis) of the Big Bang.It was Steven Weinberg in 1962 that first theorized on the direct detection of relic neutrinos.The signal of the relic neutrino capture on a tritium target can be observed by studying theendpoint of the electrons kinetic energy that are above the endpoint energy of the beta decayspectrum. The PTOLEMY project aims to archive direct detection of the relic neutrinobackground with a large tritium target of 100 gram, MAC-E-Filter, RF-tracking, Time of flighttracking and a cryogenic calorimetry.In this thesis the MAC-E-Filter have been simulated in two filter configurations. In the firstconfiguration, the electron were simulated five times in the filter. Two in the opposite sideof the detector, one in the middle, and two at the detector. In the second configuration theelectrons was simulated in the entrance solenoid at a fixed position of y = -0.19634954 m fromthe center of the filter and in random positions. Both multiple electrons and single electronswere simulated in the second configuration.In the single electron configuration the electron had a starting position of y = -0.19634954 mfrom the center of the filter, and an initial kinetic energy of 18.6 KeV. The first filter configurationsuccessfully accomplished to simulate the electron track, as the electron was reflectedback and forth between the entry and detector solenoid. The electric and magnetic field profilediered at the entry and detector solenoid. The second filter configuration successfully showedthat the electron will reach the end solenoid, when the filter length was 0.5 m. When the filterlength was increased to 0.7 m, then the electron was reflected in the middle of the filter. Thesimulation showed that the electron energy dropped below 1 eV from 18.6 KeV as the electronpropagated through the filter. The magnetic and electric fields decreased exponentially in thedirection of the detector solenoid. The Simulation of multiple electrons showed mixed resultsand would need more modifications in order to come to a final conclusion. particle physics astroparticle physics astrophysics PTOLEMY relic neutrinos monte carlo simulation mac-e-filter sterile neutrinos physics beyond the standard model Subatomic Physics Subatomär fysik Astronomy, Astrophysics and Cosmology Astronomi, astrofysik och kosmologi
154	Asymptotic Symmetries and Faddeev-Kulish states in QED and Gravity Gaharia, David January 2019 (has links) When calculating scattering amplitudes in gauge and gravitational theories one encounters infrared (IR) divergences associated with massless fields. These are known to be artifacts of constructing a quantum field theory starting with free fields, and the assumption that in the asymptotic limit (i.e. well before and after a scattering event) the incoming and outgoing states are non-interacting. In 1937, Bloch and Nordsieck provided a technical procedure eliminating the IR divergences in the cross-sections. However, this did not address the source of the problem: A detailed analysis reveals that, in quantum electrodynamics (QED) and in perturbative quantum gravity (PQG), the interactions cannot be ignored even in the asymptotic limit. This is due to the infinite range of the massless force-carrying bosons. By taking these asymptotic interactions into account, one can find a picture changing operator that transforms the free Fock states into asymptotically interacting Faddeev- Kulish (FK) states. These FK states are charged (massive) particles surrounded by a “cloud” of soft photons (gravitons) and will render all scattering processes infrared finite already at an S-matrix level. Recently it has been found that the FK states are closely related to asymptotic symmetries. In the case of QED the FK states are eigenstates of the large gauge transformations – U(1) transformations with a non-vanishing transformation parameter at infinity. For PQG the FK states are eigenstates of the Bondi-Metzner-Sachs (BMS) transformations – the asymptotic symmetry group of an asymptotically flat spacetime. It also appears that the FK states are related the Wilson lines in the Mandelstam quantization scheme. This would allow one to obtain the physical FK states through geometrical or symmetry arguments. We attempt to clarify this relation and present a derivation of the FK states in PQG from the gravitational Wilson line in the eikonal approximation, a result that is novel to this thesis. Faddeev-Kulish BMS Bondi-Metzner-Sachs Asymptotic Symmetries Asymptotic States Wilson Lines Infrared Divergence Bloch-Nordsieck Large Gauge Transformations Fock QED Quantum Electrodynamics Perturbative Quantum Gravity PQG U(1) Transformations Mandelstam Quantization Subatomic Physics Subatomär fysik
155	AdS/CFT correspondence and c-extremization Goranci, Roberto January 2017 (has links) In this project we review the method of using c-extremization and computing anomalies to obtain AdS/CFT theories. We start with a quick introduction to CFT's and AdS/CFT correspondence which gives us the tools to later understand the 2D N= (2,0) SCFT and its gravity duals in particular AdS_5xS^5 and AdS_7xS^4 compactified on Riemann surfaces. AdS/CFT c-extremization Super Yang-Mills Supergravity M5 membrane Conformal field theory Anomalies superconformal CFT 6d SCFT black string String theory compactification Other Physics Topics Annan fysik Subatomic Physics Subatomär fysik
156	Predictions of Effective Models in Neutrino Physics Bergström, Johannes January 2011 (has links) Experiments on neutrino oscillations have confirmed that neutrinos have small, but non-zero masses, and that the interacting neutrino states do not have definite masses, but are mixtures of such states.The seesaw models make up a group of popular models describing the small neutrino masses and the corresponding mixing.In these models, new, heavy fields are introduced and the neutrino masses are suppressed by the ratio between the electroweak scale and the large masses of the new fields. Usually, the new fields introduced have masses far above the electroweak scale, outside the reach of any foreseeable experiments, making these versions of seesaw models essentially untestable. However, there are also so-called low-scale seesaw models, where the new particles have masses above the electroweak scale, but within the reach of future experiments, such as the LHC.In quantum field theories, quantum corrections generally introduce an energy-scale dependence on all their parameters, described by the renormalization group equations. In this thesis, the energy-scale dependence of the neutrino parameters in two low-scale seesaw models, the low-scale type I and inverse seesaw models, are considered. Also, the question of whether the neutrinos are Majorana particles, \ie , their own antiparticles, has not been decided experimentally. Future experiments on neutrinoless double beta decay could confirm the Majorana nature of neutrinos. However, there could also be additional contributions to the decay, which are not directly related to neutrino masses. We have investigated the possible future bounds on the strength of such additional contributions to neutrinoless double beta decay, depending on the outcome of ongoing and planned experiments related to neutrino masses. / QC 20110812 Neutrino mass lepton mixing Majorana neutrinos effective field theory Weinberg operator seesaw models low-scale seesaw models inverse seesaw right-handed neutrinos renormalization group threshold effects neutrinoless double beta decay Subatomic Physics Subatomär fysik
157	Manufacturing methods for (U-Zr)N-fuels Hollmer, Tobias January 2011 (has links) In this work a manufacturing method for UN, ZrN and (U,Zr)N pellets was established at the nuclear fuel laboratory at KTH Stockholm/Sweden, which consists of the production of nitride powders and their sintering into pellets by spark plasma sintering. The nitride powders were produced by the hydriding-nitriding route using pure metal as starting material. This synthesis was performed in a stream of the particular reaction gas. A synthesis control and monitoring system was developed, which can follow the reactions in real time by measuring the gas flow difference before and after the reaction chamber. With the help of this system the hydriding and nitriding reactions of uranium and zirconium were studied in detail. Fine nitride powders were obtained; however, the production of zirconium nitride involved one milling step of the brittle zirconium hydride. Additionally uranium and zirconium alloys with different zirconium contents were produced and synthesized to nitride powders. It was found that also the alloys could be reduced to fine powder, but only by cyclic hydriding-dehydriding. Pellets were sintered out of uranium nitrides, zirconium nitrides, mixed nitrides and alloy nitrides. These experiments showed that relative densities of more than 90% can easily be achieved for all those powders. Pellets sintered from mechanically mixed nitride powders were found to still consist of two separate nitride phases, while nitride produced from alloy was demonstrated to be a monophasic solid solution both as powder and as sintered pellets. nuclear fuel nitride fuel uranium nitride zirconium nitride spark plasma sintering solid solution reaction kinetics hydriding nitriding denitriding uranium hydride zirconium hydride uranium zirconium alloy Subatomic Physics Subatomär fysik
158	Charged particle distributions and robustness of the neural network pixel clustering in ATLAS Sidebo, Edvin January 2016 (has links) This thesis contains a study of the robustness of the artificial neural network used in the ATLAS track reconstruction algorithm as a tool to recover tracks in dense environments. Different variations, motivated by potential discrepancies between data and simulation, are performed to the neural network’s input while monitoring the corresponding change in the output. Within reasonable variation magnitudes, the neural networks prove to be robust to most variations. In addition, a measurement of charged particle distributions is summarised. This is one of the first such measurements carried out for proton-proton colli- sions at √s = 13 TeV, limited to a phase space defined by transverse momentum pT > 100 MeV and absolute pseudorapidity \|η\| < 2.5. Tracks are corrected for de- tector inefficiencies and unfolded to particle-level. The result is compared to the prediction of different models. Overall, the EPOS and Pythia 8 A2 models show the best agreement with the data. / Spår från elektriskt laddade partiklar rekonstrueras i ATLAS genom att kombinera mätningar från de innersta subdetektorerna. I de extrema miljöer som skapas i proton-proton-kollisionerna i Large Hadron Collider vid CERN är det av yttersta vikt att algoritmen för att rekonstruera spår är högpresterande. Uppgiften är särskilt svår i partikelrika miljöer där flera partiklar färdas nära varandra, åtskilda av avstånd jämförbara med storleken på detektorns utläsningselement. Ett artificiellt neuralt nätverk används i algoritmen för att klassificera mätdata från pixeldetektorn, belägen närmast interaktionspunkten, för att lyckas identifiera spår i partikelrika miljöer som annars hade gått förlorade. I denna avhandling utreds det neurala nätverkets stabilitet. Dess känslighet studeras genom att manuellt manipulera dess indata och därefter utvärdera dess resultat. Nätverket tränas med simulerad data. Variationerna i indata är utformade för att undersöka skillnader mellan data och simulering, orsakade av osäkerheter i simuleringsmodellen eller osäkerheter i pixeldetektorns kalibrering. Av de undersökta variationerna har en osäkerhet i skalan eller utläsningströskeln för pixeldetektorns kalibrering den största effekten på nätverkets resultat. Andra variationer har en betydligt mindre påverkan. Avhandlingen presenterar också en studie av distributioner av elektriskt laddade partiklar producerade i proton-proton-kollisioner. Det är en av de första studierna av partikeldistributioner för Large Hadron Colliders andra körning med mass-centrum-energi √s = 13 TeV. Mätningen är begränsad till fasrymden definierad av en transversell rörelsemängd pT > 100 MeV, och absolut rapiditet \|η\| < 2.5. Spår av partiklar rekonstrueras och korrigeras för detektorns ineffektiviteter för att presenteras på partikelnivå. Dessa jämförs sedan med förutsägelser från olika modeller. Modellerna EPOS och Pythia 8 A2 är generellt de som bäst överensstämmer med data. Författaren har undersökt partiklar som migrerar in och ut ur fasrymden. Andelen spår associerade till partiklar som migrerat utifrån uppskattas med simulerad data, till som mest 10% nära fasrymdens gränser. Osäkerheten på denna andel uppskattas till att vara som mest 4.5%, huvudsakligen orsakad av osäkerheten på mängden material i de innersta subdetektorerna. / <p>QC 20160817</p> p p: scattering ATLAS LHC charged particle: multiplicity semiconductor detector: pixel neural network: performance track data analysis: cluster charged particle: cluster splitting CERN LHC Coll Subatomic Physics Subatomär fysik
159	Astrophysical and Collider Signatures of Extra Dimensions Melbéus, Henrik January 2010 (has links) In recent years, there has been a large interest in the subject of extra dimensions in particle physics. In particular, a number of models have been suggested which provide solutions to some of the problems with the current Standard Model of particle physics, and which could be tested in the next generation of high-energy experiments. Among the most important of these models are the large extra dimensions model by Arkani-Hamed, Dimopoulos, and Dvali, the universal extra dimensions model, and models allowing right-handed neutrinos to propagate in the extra dimensions. In this thesis, we study phenomenological aspects of these three models, or simple modifications of them. The Arkani-Hamed-Dimopoulos-Dvali model attempts to solve the gauge hierarchy problem through a volume suppression of Newton's gravitational constant, lowering the fundamental Planck scale down to the electroweak scale. However, this solution is unsatisfactory in the sense that it introduces a new scale through the radius of the extra dimensions, which is unnaturally large compared to the electroweak scale. It has been suggested that a similar model, with a hyperbolic internal space, could provide a more satisfactory solution to the problem, and we consider the hadron collider phenomenology of such a model. One of the main features of the universal extra dimensions model is the existence of a potential dark matter candidate, the lightest Kaluza-Klein particle. In the so-called minimal universal extra dimensions model, the identity of this particle is well defined, but in more general models, it could change. We consider the indirect neutrino detection signals for a number of different such dark matter candidates, in a five- as well as a six-dimensional model. Finally, right-handed neutrinos propagating in extra dimensions could provide an alternative scenario to the seesaw mechanism for generating small masses for the left-handed neutrinos. Since extra-dimensional models are non-renormalizable, the Kaluza-Klein tower is expected to be cut off at some high-energy scale. We study a model where a Majorana neutrino at this cutoff scale is responsible for the generation of the light neutrino masses, while the lower modes of the tower could possibly be observed in the Large Hadron Collider. We investigate the bounds on the model from non-unitarity effects, as well as collider signatures of the model. / QC 20110324 Extra-dimensional quantum field theories universal extra dimensions Kaluza-Klein dark matter Arkani-Hamed-Dimopoulos-Dvali model hierarchy problem neutrino mass seesaw mechanism Large Hadron Collider phenomenology Subatomic Physics Subatomär fysik
160	Exotic Decays of a Vector-liketop Partner at the LHC Skwarcan-Bidakowski, Alexander January 2019 (has links) An evaluation of how sensitive some ATLAS searches for new physics are to a new beyond standard model (BSM) vector-like quark (VLQ) and a pseudo Nambu-Goldstone boson (pNGB) scalar. This was done by simulating a signal containing these new particles and making a recast of it onto existing verified ATLAS searches for new physics at center-of-mass (CM) energy of 13 TeV (Run 2) at the Large Hadron Collider (LHC). Signals for recasting were tailored such that their final states would be appropriate in relation to each respective ATLAS search in order to use the same selection criteria as applied in the existing searches. The results are summarized in the form of significances (Z) for each masspoint of the new top-partner and S particle. Significances did not show any expectiation of excluding any masspoint in the examined mass range for the recasts at 95% CL. This suggests that a dedicated search for these particles in the considered masspoints would be required. Particle physics Vector-like quarks VLQ Composite Higgs model CHM Top-partner pseudo Nambu-Goldstone boson pNGB NGB ATLAS LHC CMS Significance Recast CheckMate CM MadGraph Pythia Delphes Detector Analysis Hierarchy Problem Exotic Decay QFT Quantum Field Theory fermions bosons Jets photons leptons 13 TeV Missing Transverse Energy momentum hypothetical selection criteria Standard model Signal background event Higgs Mechanism Simulation Confidence limit Other Physics Topics Annan fysik Accelerator Physics and Instrumentation Acceleratorfysik och instrumentering Subatomic Physics Subatomär fysik

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