Explosive hypervelocity drag accelerator

Accelerator for launching hypervelocity projectile by drag force of jet produced by gaseous explosive product

2D Yang-Mills Theory as a Matrix String Theory

Quantization of two-dimensional Yang-Mills theory on a torus in the gauge where the field strength is diagonal leads to twisted sectors that are completely analogous to the ones that originate long string states in Matrix String Theory. If these sectors are taken into account the partition function is different from the standard one found in the literature and the invariance of the theory under modular transformations of the torus appears to hold in a stronger sense. The twisted sectors are in one-to-one correspondence with the coverings of the torus without branch points, so they define by themselves a string theory. A possible duality between this string theory and the Gross-Taylor string is discussed, and the problems that one encounters in generalizing this approach to interacting strings are pointed out. This talk is based on a previous paper by the same authors, but it contains some new results and a better interpretation of the results already obtained.Comment: 11 pages, LaTeX, 2 figures included with epsf. Talk presented at the 2nd Conference on Quantum aspects of Gauge Theories, Supersymmetry and Unification, Corfu, Greece, 21-26 September 199

Scalable reconstruction of density matrices

Recent contributions in the field of quantum state tomography have shown that, despite the exponential growth of Hilbert space with the number of subsystems, tomography of one-dimensional quantum systems may still be performed efficiently by tailored reconstruction schemes. Here, we discuss a scalable method to reconstruct mixed states that are well approximated by matrix product operators. The reconstruction scheme only requires local information about the state, giving rise to a reconstruction technique that is scalable in the system size. It is based on a constructive proof that generic matrix product operators are fully determined by their local reductions. We discuss applications of this scheme for simulated data and experimental data obtained in an ion trap experiment.Comment: 9 pages, 5 figures, replaced with published versio

Non-Douglas-Kazakov phase transition of two-dimensional generalized Yang-Mills theories

In two-dimensional Yang-Mills and generalized Yang-Mills theories for large gauge groups, there is a dominant representation determining the thermodynamic limit of the system. This representation is characterized by a density the value of which should everywhere be between zero and one. This density itself is determined through a saddle-point analysis. For some values of the parameter space, this density exceeds one in some places. So one should modify it to obtain an acceptable density. This leads to the well-known Douglas-Kazakov phase transition. In generalized Yang-Mills theories, there are also regions in the parameter space where somewhere this density becomes negative. Here too, one should modify the density so that it remains nonnegative. This leads to another phase transition, different from the Douglas-Kazakov one. Here the general structure of this phase transition is studied, and it is shown that the order of this transition is typically three. Using carefully-chosen parameters, however, it is possible to construct models with phase-transition orders not equal to three. A class of these non-typical models are also studied.Comment: 11 pages, accepted for publication in Eur. Phys. J.

Momentum Analyticity and Finiteness of the 1-Loop Superstring Amplitude

The Type II Superstring amplitude to 1-loop order is given by an integral of $\vartheta$-functions over the moduli space of tori, which diverges for real momenta. We construct the analytic continuation which renders this amplitude well defined and finite, and we find the expected poles and cuts in the complex momentum plane.Comment: 10pp, /UCLA/93/TEP/

Magneto-optical imaging of voltage-controlled magnetization reorientation

We study the validity and limitations of a macrospin model to describe the voltage-controlled manipulation of ferromagnetic magnetization in nickel thin film/piezoelectric actuator hybrid structures. To this end, we correlate simultaneously measured spatially resolved magneto-optical Kerr effect imaging and integral magnetotransport measurements at room temperature. Our results show that a macrospin approach is adequate to model the magnetoresistance as a function of the voltage applied to the hybrid, except for a narrow region around the coercive field - where the magnetization reorientation evolves via domain effects. Thus, on length scales much larger than the typical magnetic domain size, the voltage control of magnetization is well reproduced by a simple Stoner-Wohlfarth type macrospin model

Construction of nonlocal light-cone operators with definite twist

A systematic procedure is introduced to uniquely decompose nonlocal LC-operators into harmonic operators of well defined geometric twist. The method will be demonstrated for (pseudo)scalar, (axial) vector and skew tensor bilocal quark light-ray operatorsComment: 4 pages, AMSTeX, Contribution to 7th Int. Workshop on Deep Inelastic Scatterin and QCD, Zeuthen, April 1999 change of formulas 25 and 2

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(N) and Sp(N) is evaluated in the 1/N expansion using the techniques of Gross and Matytsin. Many features of Yang-Mills theory are universal among different gauge groups in the large N limit, but significant differences arise in subleading order in 1/N.Comment: 10 pages; no figures; LaTe