In this thesis, a new model for the internal structure of baryons, the Cloudy Bag Model (CBM), is presented. The baryons are assumed to be made of quarks permanently confined in a static spherical cavity called the "Bag", and of a cloud of pions which couple to the quarks at the bag surface in a way which restores chiral symmetry. When the CBM Lagrangian density is projected on the space of colourless baryons, a Hamiltonian theory of baryons coupled to pions is obtained. The model describes successfully the P₃₃ resonance in pion-nucleon scattering, the magnetic moments of the baryon octet and the charge radii of the nucleon. All these results agree rather well with experiment when the only true free parameter of the theory, the bag radius, is chosen anywhere in the range 0.8 to 1.1 fermi. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Ph. D.)--Ohio State University, 1981. / Includes bibliographical references. Available online via OhioLINK's ETD Center

No description available.

Dans le modèle de formation hiérarchique des structures, les amas de galaxies se forment et grandissent par l'accrétion de groupes plus petits ou de galaxies isolées. Dans ce scenario, comprendre comment les galaxies accrétées interagissent avec cet environnement très dense est une étape importante pour comprendre le schéma global de l'évolution des galaxies et de la formation des structures. En effet, pendant leur chute au coeur de l'amas, les galaxies sont sujettes à diverses interactions avec l'amas hôte, au niveau de leur composante baryonique aussi bien que matière noire, et ces interactions vont modifier les propriétés de la galaxie. Au niveau de la matière noire, les simulations numériques suggèrent que la friction dynamique fait plonger les galaxies vers le centre de l'amas, et que les forces de marée exercées par l'hôte peuvent arracher une partie de la matière de la galaxie, et même détruire celle-ci. Ce processus, au cours duquel une partie de la matière noire de la galaxie est arrachée, est appelé stripping. La détection du stripping de matière noire contient d'importantes informations sur l'évolution des groupes et des amas. Le travail principal de cette thèse se concentre sur l'étude des galaxies dans les amas, et en particulier sur l'étude du stripping des galaxies par les forces de marées des amas. Les profils de densité des halos sont mesurés à l’aide de l’effet de lentille gravitationnelle faible, en utilisant les catalogues de formes de galaxies des relevés CFHTLenS, CFHT Stripe 82 et DES-SV, alliés au catalogue d’amas redMaPPer. / Galaxy clusters are large structures in the Universe, composed of tens or hundreds of galaxies bound by gravity. In the hierarchical formation model, they are formed and grow by accretion of smaller groups or isolated galaxies. In this scenario, understanding how these accreted galaxies interact with the very dense cluster environnement is an important step towards explaining the global picture of galaxy evolution and structure formation. Indeed, during infall, galaxies are subject to numerous interactions with the host cluster, both at the level of the baryonic and dark matter component, and these interactions influence the properties of the infalling galaxy. At the level of dark matter, numerical simulations suggest that dynamical friction sinks galaxies towards the center of clusters, and tidal forces of the host can strip part of the satellite's matter away, and even disrupt it. The detection of this stripping contains important informations on the evolution of groups and clusters: what quantity of dark matter is associated to the cluster galaxies as a function of the distance to the centre of the cluster ? How does this depend on the redshift and dynamical state of the cluster ? Does stripping depend on the morphological type of cluster galaxies ? The main work of this thesis is focused on studying galaxies in clusters, in particular tidal stripping of their dark matter haloes. The dark matter halo profiles are measured with weak gravitational lensing, using galaxy shape catalogues from the CFHTLenS, CFHT Stripe 82 and DES-SV surveys, combined with the redMaPPer cluster catalogue.

No description available.

In this thesis the effect of antisymmetrization in diquark models of baryons composed of light (u and d) quarks is investigated. The diquark in this study is considered alternately as a pointlike and as a composite particle. The wave functions for both diquark and diquark-quark systems have been determined in a non-relativistic approximation by using the radial Schrodinger equation and a range ofcentral potentials. The ground state masses ofthe diquarkquark system have been calculated in three distinct ways: (1) The ground state energy eigenvalues and the wave functions for thediquark and diquarkquark, each being treated as a two-body system, have been calculated by using the generalized Runge-Kutta and search methods. (2) The expectation values for the potential energy and kinetic energy have been calculated by using the wave functions derived in (1) for the two-body system without antisymmetrization. These results have been checked by applying the virial theorem in parallel calculations. (3) The potential and kinetic energy expectation values have also been determined by taking antisymmetrization into account via operator kernels namely, norm, potential and kinetic energy which have been derived by using the non-local Generator Coordinate Method (GCM). The expectation values of these operator kernels have been calculated with respect to the wave functions produced in (1). For the purpose of performing the integrations the wave functions , expanded in terms of cubic splines, and Gaussian quadrature have been employed. Lastly the diquark and diquark-quark ground state masses were calculated for each approach, (1) - (3), and compared with (a) each other, (b) the results for a two-body system, (c) the results for a full three-body treatment and, (d) the average mass of N- b:. . The form factors and root mean square radii ofthe baryon for the four central potentials have been calculated with antisymmetrization for each approach (1) - (3) and compared with (a) each other, (b) the results for the baryon without antisymmetrization (c) the results for the baryon with antisymmetrization including the meson cloud (d) the experimental data. The trends found are striking and it can be concluded that there is a strong dynamical effect due to the presence of antisymmetrization in diquark models of baryons. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

Baryons are considered in the Nonrelativistic Quark Model (NQM) to be bound states of three valence quarks. Each quark has two possible spin eigenstates in the restframe of the baryon whose spin is fully carried by quarks. The baryon wavefunctions are connected through SU(6) symmetry rotations. For a long time, the measured magnetic moments of the baryons appeared to be in agreement with the NQM predictions. However, recent experiments which are examining the spin structure of the baryons show the failure of several NQM predictions. The so-called 'spin crisis' arose from the interpretation of the EMC deep inelastic scattering measurement of ∫ g^p₁ that the quark spins in the proton appeared to sum up to (almost) zero. In this thesis it will be demonstrated that the spin problem is not a phenomenon restricted to quasi-massless current quarks in the high energy limit. Symmetry arguments are used to examine the baryon magnetic moments and reveal that we can observe massive but pointhke constituent quarks, with a characteristic mass ratio m_u = m_d ≃ ²andfrasl;₃m_s. Surprisingly they do not contribute much to the baryon spin either. This analysis is free of the ambiguity arising from the UA(1} gluon anomaly which makes it impossible to calculate precisely the spin sum of the current quarks. One important finding in our analysis is the observation that the effects of SU(6) breaking hyperfine spin-spin interactions (which cause well-known splittings in the baryon masses) can be seen in the environment dependence of the constituent quark masses. The effective mass of a quark cannot be independent of its surrounding energy since the mass of the baryon is distributed amongst its constituents. Consistent with the hypothesis that different quark masses do not impose SU(3) breaking on the baryon wavefunctions is the observation of induced 'second class' form factors. The way in which SU(3) breaking alters the ^g_Aandfrasl;_{g_V} ratios in semileptonic hyperon decays will be discussed and strong evidence for a new value of F/D is given, which is close to its SU(6) value. This value is derived independently from the baryon β-decays <strong>and</strong> from their magnetic moments. Dynamical models are discussed which might explain the observed polarised strangeness 'inside' the proton, and the almost vanishing quark spin sum.

In this thesis we study aspects of the cosmological electroweak phase transition which are relevant to the possibility of baryogenesis at this epoch. We focus on two issues: first, requiring that the observed baryon number be of electroweak origin places strong constraints on electroweak physics, and second, baryogenesis at the electroweak scale may be driven by an asymmetry generated at the GUT scale. We use the effective potential at finite temperature as a means of analyzing phase transitions associated with spontaneous symmetry breaking. We develop the theory with two basic examples: the scalar and Abelian Higgs models. Infrared divergences near the phase transition make the one-loop description unreliable, and indeed invalidate conventional perturbation theory. Borrowing a method from studies of QCD at high temperatures, we demonstrate that the summation of ring diagrams cures the leading infrared divergences and achieves a more reliable perturbative expansion. We then apply this formalism to the minimal Standard Model, following previous work, and confirm weak first-order behavior at the phase transition. We show that requiring the baryon number not be erased by sphaleron processes after the phase transition places a stringent bound on the Higgs mass, which is incompatible with experiment. This cosmological bound, however, may be relaxed by extending the scalar sector of the Standard Model. We consider the two simplest such extensions, the addition of a gauge singlet and of a second doublet. We demonstrate that ring-improvement in the singlet extension alters previous arguments at the one-loop level and yields a more restrictive bound on the Higgs mass. While ring-improvement in the two-doublet model, in principle, also reduces the Higgs mass bound found earlier at one loop, the multitude of new couplings in this model does not permit a definitive statement. We then investigate a mechanism for generating the observed baryon asymmetry (n_B/S~ 10-¹⁰) at the electroweak phase transition from a pre-existing leptonic asymmetry (L_T/s~ 10-⁵) produced at the GUT scale. This mechanism works by charge transport in a strongly first-order phase transition and avoids the need for large CP-violation at the electroweak scale.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 177-181). Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. Description based on print version record. Includes bibliographical references.