# Browsing by Subject "Particles (Nuclear physics)"

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Item Background field effects on particle physics(2005) Tinsley, Todd Michael; Dicus, Duane A.Show more Investigation into the effects of magnetic fields on particle interactions is not only integral to a complete description of the physics near such fields, but it can also provide a unique probe into “new” physics by stimulating processes that are either suppressed or not allowed in the free-field case. Such processes become very relevant in astrophysical phenomena such as supernovae and neutron stars, where their evolution is highly sensitive to the rates of elementary particle interactions. Furthermore, these objects can posses enormous magnetic field strengths capable of exciting processes well beyond what would be expected in the vacuum. With these astrophysical implications in mind, this thesis presents three examples in which the presence of an electromagnetic field permits an interaction that is otherwise forbidden. These examples include: Z-boson decay into two photons and decay into two gluons, electron-positron pair production using a muon neutrino in an intense laser field, and electron-positron pair production using a neutrino in an intense homogenous magnetic field. This work will include detailed calculations representing different methods of solving problems in the presence of electromagnetic fields.Show more Item Cosmology driven by physics beyond the standard model(2007-12) Žanić, Marija, 1972-; Paban, SoniaShow more This dissertation investigates several problems inspired by the interplay of cosmology and theories beyond the Standard Model of particle physics. The first part of this work is a study of time evolution of unstable dS[subscript p] x S[superscript q] configurations with flux in theories of gravity with a cosmological constant. We find that, depending on the flux, these configurations either evolve towards newly identified stable solutions with a smaller final effective cosmological constant, or tend toward decompactication of the internal sphere. In the second part, we investigate the problem of evolution of vacuum bubbles in inhomogeneous backgrounds. It is expected that the process of inflation will signifcantly smooth out spatial inhomogeneities. However, the initial conditions for inflation are often taken in the already homogeneous and isotropic FRW form, even though it is assumed that initial homogeneity is not necessary for the onset of inflation. We determine the effects of certain inhomogeneities, introduced in the curvature of the outside spacetime, on the propagation of bubbles, and how these effects differ depending on whether the perspective taken is that of the outside observer or an observer on the bubble. The last part of the dissertation presents a model for a novel component of the energy density of the universe. The observational limits on the present energy density allow for a component that redshifts like 1/a² and can contribute significantly to the total. We show that one possible origin for such a contribution is that the universe has a toroidal topology with "wound" scalar fields around its cycles.Show more Item Darwinian evolution: the mutation of a weakly relativistic lagrangian(2004) Krause, Todd Brandon; Morrison, Philip J.Show more The work studies Darwin’s order-(v/c)2 approximation to the relativistic interaction of classical charged particles. The first part presents an in- troduction to the methods of symplectic reduction in the Newtonian two- body problem and then applies these to a two-body Darwin interaction. The momentum-dependent interaction of the Darwin system plays an important role in the ability to reduce to a system of one degree of freedom. Circular orbits are sought, and it is shown that two of the three possible orbits are prohibited by velocity conditions. The second part of the work derives a self-consistent Darwin particle theory from a Lagrangian for electromagnetic fields coupled to particles. The resulting particle Lagrangian agrees with previous results. A similar procedure is followed to obtain a Low-Darwin system, coupling the self-consistent Darwin theory to the Vlasov equation.Show more Item Probing exotic physics with pulsating white dwarfs(2007-05) Kim, Agnès, 1975-; Winget, Donald Earl, 1955-Show more Item Self-consistent dynamics of nonlinear phase space structures(2004) Eremin, Denis; Berk, H. L.Show more This thesis investigates the self-consistent dynamics of nonlinear ”hole” and ”clump” phase space structures and the nonlinear modes supported by the structures in the presence of dissipation due to the background plasma. A system consisting of a single mode driven by a weakly destabilizing distribution function in a dissipative medium close to the threshold of linear instability exhibits explosive instability. This instability results in the formation of the phase space structures and the corresponding modes. The holes and clumps were expected to persist for an appropriate collisional time scale. However, for certain initial conditions Fokker-Planck calculations for the nonlinear system abruptly break down in the course of the calculation. We find that this is because an adiabatic description of phase space structures at zero collisionality does not necessarily lead to continual adiabatic frequency sweeping. For a class of initial distribution functions criteria are found that detervii mine whether adiabatic frequency sweeping will continue indefinitely or suddenly terminate. For certain other initial distribution functions that describe the predominantly deeply trapped particles, critical points may be encountered where the adiabatic analysis fails to yield a unique solution. Except for establishing boundary conditions, the contribution of passing particles is found to be unimportant in the dynamics of the phase space structures within the framework of the adiabatic description. We derived a self-consistent dispersion relation for the perturbed eigenmodes of the system and benchmarked the result with the dispersion relation obtained earlier in Ref. [53] and demonstrated their agreement. We analyzed this dispersion relation and demonstrated that the critical points of the adiabatic theory occur exactly where linear instability is triggered. Numerical runs were performed to test both the adiabatic theory and the instability analysis of a BGK (Bernstein-Greene-Kruskal) mode for a model problem where the distribution function of passing particles has zero slope with respect to the action variable. This problem has same essential features as the problem where the slope of the passing particle distribution function is constant. In particular, linear instability of the same nature is also predicted to arise whenever adiabatic analysis predicts termination of frequency sweeping. This procedure has the virtue of enabling a precise comparison of the theory with the simulations and indeed it does so until instability sets in. The model problem was also used to demonstrate the agreement between the numerical growth rate and the growth rate predicted in the instability analysis. Then a passing particle distribution function was used that has a constant slope with respect to the action variable, and it too showed agreement with the theory for the evolution of the adiabatic phase, for where the onset of the instability was predicted to occur, and for where the persistence of the phase space structures after the instability relaxation. Both cases showed that after the instability dies away, smaller phase space structures still persist and the frequency sweeping continues at a slower rate. The numerical simulations demonstrated the additional effect that several generations of the nonlinear phase space structures are often produced. The numerical data shows that the mode amplitude is reduced when there are neighboring modes. We considered two possible mechanisms that may account for such reduction of the primary mode amplitude. In one mechanism, the particle orbits remain regular and the mode amplitude reduction is caused by the accumulation (in the case of a clump) [or depletion in the case of a hole] of the passing particle distribution of one of the modes, because it is part of the trapped particle region of the other mode. The other mechanism is the chaotic erosion of trapped particles near the separatrix.Show more Item A study of angular asymmetries in the rare decay B (right arrow) K*[lambda]⁺[lambda]⁻(2008-08) Schilling, Chris James, 1980-; Ritchie, Jack L., 1955-Show more This dissertation describes studies of the rare quark transition process b → s`+` −, in particular the B meson decay B → K∗ ` +` − where the ` +` − is either e +e − or µ +µ −. These decays are highly suppressed in the Standard Model and could be strongly affected by new physics. The angular observables describing the lepton forward-backward asymmetry and the longitudinal K∗ polarization are measured in this mode. The measurements were performed using the BABAR detector at the SLAC PEPII storage ring running at the Υ(4S) resonance. The analysis was performed on a 349 fb−1 sample corresponding to 384 million BB pairs. The data was collected over a period of six years beginning in 1999. For low dilepton invariant masses, m`` < 2.5 GeV/c2 , we measure a lepton forward backward asymmetry AFB = 0.24+0.18 −0.23 ± 0.05 and a K∗ longitudinal polarization FL = 0.35 ± 0.16 ± 0.04. For m`` > 3.2 GeV/c2 , we measure AFB = 0.76+0.52 −0.32 ± 0.07 and FL = 0.71+0.20 −0.22 ± 0.04.Show more