Composite Strings in (2+1)-Dimensional Anisotropic Weakly-Coupled Yang-Mills Theory

The small-scale structure of a string connecting a pair of static sources is explored for the weakly-coupled anisotropic SU(2) Yang-Mills theory in (2+1) dimensions. A crucial ingredient in the formulation of the string Hamiltonian is the phenomenon of color smearing of the string constituents. The quark-anti-quark potential is determined. We close with some discussion of the standard, fully Lorentz-invariant Yang-Mills theory.Comment: Some minor errors corrected, references slightly reorganized, version to appear in Phys. Rev.

Confinement in (2+1)-Dimensional Gauge Theories at Weak Coupling

In axial gauge, the (2+1)-dimensional SU($N$) Yang-Mills theory is equivalent to a set of (1+1)-dimensional integrable models with a non-local coupling between charge densities. This fact makes it possible to determine the static potential between charges at weak coupling in an anisotropic version of the theory, and understand features of the spectrum.Comment: Four pages, Based on a talk given at ``Quark Confinement and the Hadron Spectrum 7", Ponta Delgada, Sao Miguel, Azores, Portugal, Sept. 2-7, 200

Flory theory revisited

The Flory theory for a single polymer chain is derived as the lowest order of a cumulant expansion. In this approach, the full original Flory free energy (including the logarithmic term), is recovered. %This term does not change the wandering exponent $\nu$ but turns out to %be responsible for the crossover from Brownian $(d>4)$ to swollen $$ %regime. The prefactors of the elastic and repulsive energy are calculated from the microscopic parameters. The method can be applied to other types of monomer-monomer interactions, and the case of a single chain in a bad solvent is discussed . The method is easily generalized to many chain systems (polymers in solutions), yielding the usual crossovers with chain concentration. Finally, this method is suitable for a systematic expansion around the Flory theory. The corrections to Flory theory consist of extensive terms (proportional to the number $N$ of monomers) and powers of $N^{2-\nu d}$ . These last terms diverge in the thermodynamic limit, but less rapidly than the usual Fixman expansion in $N^{2- d/2}$.Comment: Email contact: [email protected]

Electric response of DNA hairpins to magnetic fields

We study the electric properties of single-stranded DNA molecules with hairpin-like shapes in the presence of a magnetic flux. It is shown that the current amplitude can be modulated by the applied field. The details of the electric response strongly depend on the twist angles. The current exhibits periodicity for geometries where the flux through the plaquettes of the ladder can be cancelled pairwise (commensurate twist). Further twisting the geometry and changing its length causes complex aperiodic oscillations. We also study persistent currents: They reduce to simple harmonic oscillations if the system is commensurate, otherwise deviations occur due to the existence of closed paths leading to a washboard shape.Comment: 11 pages, 4 figure