Showing papers by "Jeffrey Pennington published in 2007"

Bäcklund transformations, D-branes and fluxes in minimal type 0 strings

Abstract: We study the type 0A string theory in the (2, 4k) superconformal minimal model backgrounds, focusing on the fully non-perturbative string equations which define the partition function of the model. The equations admit a parameter, Γ, which in the spacetime interpretation controls the number of background D-branes, or R–R flux units, depending upon which weak coupling regime is taken. We study the properties of the string equations (often focusing on the (2, 4) model in particular) and their physical solutions. The solutions are the potential for an associated Schrodinger problem whose wavefunction is that of an extended D-brane probe. We perform a numerical study of the spectrum of this system for varying Γ and establish that when Γ is a positive integer the equations' solutions have special properties consistent with the spacetime interpretation. We also show that a natural solution-generating transformation (that changes Γ by an integer) is the Backlund transformation of the KdV hierarchy specialized to (scale invariant) solitons at the zero velocity. Our results suggest that the localized D-branes of the minimal string theories are directly related to the solitons of the KdV hierarchy.

Charge and current neutralization of an ion beam pulse by background plasma in the presence of applied magnetic field

Abstract: Plasma can be used as a convenient medium for manipulating intense charged particle beams, e.g., for ballistic focusing and steering, because the plasma can effectively reduce the self-space charge potential and self-magnetic field of the beam pulse. We previously developed a reduced analytical model of beam charge and current neutralization for an ion beam pulse propagating in a cold background plasma. The reduced-fluid description provides an important benchmark for numerical codes and yields useful scaling relations for different beam and plasma parameters. This model has been extended to include the additional effects of an applied solenoidal magnetic field. Simulations show that the self-magnetic field structure of the ion beam pulse propagating through background plasma can be complex and non-stationary. The linear system of Maxwell's equations for the self-electromagnetic fields can be solved analytically in Fourier space. For a strong enough applied magnetic field, poles emerge in Fourier space. These poles are an indication that whistler and low-hybrid waves can be excited by the beam pulse.