27,394 research outputs found
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
-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
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