Michael Crescimanno

Parafermions from coset models

Conformally invariant coset models in two dimensions can be described by the gauged Wess-Zumino-Witten lagrangian. We present a semi-classical treatment of these theories in a unitary gauge. In particular, we give an explicit construction of the conserved parafermion fields in the case of an abelian gauge group, and also show that the Poisson brackets between these field close in a simple fashion. We make use of these results to find a free field realization of this Poisson structure.

Large N phases of chiral QCD2

Abstract A matrix model is constructed which describes a chiral version of the large NU (N) gauge theory on a two-dimensional sphere of area A . This theory has three separate phases. The large area phase describes the associated chiral string theory. An exact expression for the free energy in the large area phase is used to derive a remarkably simple formula for the number of topologically inequivalent covering maps of a sphere with fixed branch points and degree n .

Parafermions from non-abelian coset models☆

Abstract We generalize an earlier work on conformal coset models to the case of a non-abelian factor group. Starting with the gauged Wess-Zumino-Witten lagrangian, we derive the associated parafermion fields and deduce their Poisson brackets. We then present an explicit classical realization of these fields in terms of path ordered exponentials of free currents that satisfy an affine Lie algebra. This construction can be viewed as a non-abelian generalization of the standard free field representation of parafermions. Finally, we extended the classical construction to the full quantum mechanical case.

Out-of-plane scattering from vertically asymmetric photonic crystal slab waveguides with in-plane disorder

We characterize optical wave propagation along line defects in two-dimensional arrays of air-holes in free-standing silicon slabs. The fabricated waveguides contain random variations in orientation of the photonic lattice elements which perturb the in-plane translational symmetry. The vertical slab symmetry is also broken by a tilt of the etched sidewalls. We discuss how these lattice imperfections affect out-of-plane scattering losses and introduce a mechanism for high-Q cavity excitation related to polarization mixing.

Co-extruded mechanically tunable multilayer elastomer laser

We have fabricated and studied mechanically tunable elastomer dye lasers constructed in large area sheets by a single-step layer-multiplying co-extrusion process. The laser films consist of a central dye-doped (Rhodamine-6G) elastomer layer between two 128-layer distributed Bragg reflector (DBR) films comprised of alternating elastomer layers with different refractive indices. The central gain layer is formed by folding the coextruded DBR film to enclose a dye-doped skin layer. By mechanically stretching the elastomer laser film from 0% to 19%, a tunable miniature laser source was obtained with ~50 nm continuous tunability from red to green. Optically pumped by a frequency-doubled Nd:YAG laser, the elastomer laser showed a lasing threshold of 0.9 mJ/cm2 at 600 nm.

Geometry and duality of a non-Abelian coset model

We compute the metrics of the and , characterize their geometry and explore the “duality” k1=k2 of the target space. In particular limits of the ratio k1/k2 the latter coset becomes where k is either k1 or k2. This analysis is a starting point for investigating some properties of three-dimensional stringy gravity.

Lineshape asymmetry for joint coherent population trapping and three-photon N resonances

We show that a characteristic two-photon lineshape asymmetry arises in coherent population trapping (CPT) and three-photon (N) resonances, because both resonances are simultaneously induced by modulation sidebands in the interrogating laser light. The N resonance is a three-photon resonance in which a two-photon Raman excitation is combined with a resonant optical pumping field. This joint CPT and N resonance can be the dominant source of lineshape distortion, with direct relevance for the operation of miniaturized atomic frequency standards. We present the results of both an experimental study and theoretical treatment of the asymmetry of the joint CPT and N resonance under conditions typical to the operation of an N resonance clock.

Evaluation of the free energy of two-dimensional Yang-Mills theory

The free energy in the weak-coupling phase of two-dimensional Yang-Mills theory on a sphere for SO({ital N}) and Sp({ital N}) is evaluated in the 1/{ital N} expansion using the techniques of Gross and Matytsin. Many features of Yang-Mills theory are universal among different gauge groups in the large {ital N} limit, but significant differences arise in subleading order in 1/{ital N}. {copyright} {ital 1996 The American Physical Society.}

Coherent Perfect Rotation

Two classes of conservative, linear, optical rotary effects (optical activity and Faraday rotation) are distinguished by their behavior under time reversal. In analogy with coherent perfect absorption, where counterpropagating light fields are controllably converted into other degrees of freedom, we show that only time-odd (Faraday) rotation is capable of coherent perfect rotation in a linear and conservative medium, by which we mean the complete transfer of counterpropagating coherent light fields into their orthogonal polarization. This highlights the necessity of time reversal odd processes (not just absorption) and coherence in perfect mode conversion and may inform device design.

Analytical estimate of the critical velocity for vortex pair creation in trapped Bose condensates

We use a Thomas-Fermi approximation that includes the leading kinetic terms due to fluid motion to estimate analytically the critical velocity for the formation of vortex pairs in harmonically trapped Bose-Einstein condensates. We find rough agreement between this analytical estimate and recent experiments on trapped sodium gas condensates.