6,613 research outputs found
Balanced filters for the analysis of Al, Si, K, Ca, Fe, and Ni
Balanced filters evaluated for performance in X-ray fluorescence analysis of lunar and planetary surface material
Complex Saddles in Two-dimensional Gauge Theory
We study numerically the saddle point structure of two-dimensional (2D)
lattice gauge theory, represented by the Gross-Witten-Wadia unitary matrix
model. The saddle points are in general complex-valued, even though the
original integration variables and action are real. We confirm the
trans-series/instanton gas structure in the weak-coupling phase, and identify a
new complex-saddle interpretation of non-perturbative effects in the
strong-coupling phase. In both phases, eigenvalue tunneling refers to
eigenvalues moving off the real interval, into the complex plane, and the
weak-to-strong coupling phase transition is driven by saddle condensation.Comment: 4+4 pages RevTeX, 9 figures; v2: version published in PR
Landau Levels in the noncommutative
We formulate the Landau problem in the context of the noncommutative analog
of a surface of constant negative curvature, that is surface, and
obtain the spectrum and contrast the same with the Landau levels one finds in
the case of the commutative space.Comment: 19 pages, Latex, references and clarifications added including 2
figure
Chiral symmetry restoration in (2+1)-dimensional with a Maxwell-Chern-Simons term at finite temperature
We study the role played by a Chern-Simons contribution to the action in the
formulation of a two-dimensional Heisenberg model of quantum spin
systems with a strictly fixed site occupation at finite temperature. We show
how this contribution affects the screening of the potential which acts between
spinons and contributes to the restoration of chiral symmetry in the spinon
sector. The constant which characterizes the Chern-Simons term can be related
to the critical temperature above which the dynamical mass goes to zero.Comment: 8 pages, 4 figure
Coordinate noncommutativity in strong non-uniform magnetic fields
Noncommuting spatial coordinates are studied in the context of a charged
particle moving in a strong non-uniform magnetic field. We derive a relation
involving the commutators of the coordinates, which generalizes the one
realized in a strong constant magnetic field. As an application, we discuss the
noncommutativity in the magnetic field present in a magnetic mirror.Comment: 4 page
Casimir Effects in Renormalizable Quantum Field Theories
We review the framework we and our collaborators have developed for the study
of one-loop quantum corrections to extended field configurations in
renormalizable quantum field theories. We work in the continuum, transforming
the standard Casimir sum over modes into a sum over bound states and an
integral over scattering states weighted by the density of states. We express
the density of states in terms of phase shifts, allowing us to extract
divergences by identifying Born approximations to the phase shifts with low
order Feynman diagrams. Once isolated in Feynman diagrams, the divergences are
canceled against standard counterterms. Thus regulated, the Casimir sum is
highly convergent and amenable to numerical computation. Our methods have
numerous applications to the theory of solitons, membranes, and quantum field
theories in strong external fields or subject to boundary conditions.Comment: 27 pp., 11 EPS figures, LaTeX using ijmpa1.sty; email correspondence
to R.L. Jaffe ; based on talks presented by the authors at
the 5th workshop `QFTEX', Leipzig, September 200
Numerical Investigation of Monopole Chains
We present numerical results for chains of SU(2) BPS monopoles constructed
from Nahm data. The long chain limit reveals an asymmetric behavior transverse
to the periodic direction, with the asymmetry becoming more pronounced at
shorter separations. This analysis is motivated by a search for semiclassical
finite temperature instantons in the 3D SU(2) Georgi-Glashow model, but it
appears that in the periodic limit the instanton chains either have
logarithmically divergent action or wash themselves out.Comment: 14 pages, 6 figures; v2 minor changes, published versio
The Negative Dimensional Oscillator at Finite Temperature
We study the thermal behavior of the negative dimensional harmonic oscillator
of Dunne and Halliday that at zero temperature, due to a hidden BRST symmetry
of the classical harmonic oscillator, is shown to be equivalent to the
Grassmann oscillator of Finkelstein and Villasante. At finite temperature we
verify that although being described by Grassmann numbers the thermal behavior
of the negative dimensional oscillator is quite different from a Fermi system.Comment: 8 pages, IF/UFRJ/93/0
Schwinger Pair Production at Finite Temperature in Scalar QED
In scalar QED we study the Schwinger pair production from an initial ensemble
of charged bosons when an electric field is turned on for a finite period
together with or without a constant magnetic field. The scalar QED Hamiltonian
depends on time through the electric field, which causes the initial ensemble
of bosons to evolve out of equilibrium. Using the Liouville-von Neumann method
for the density operator and quantum states for each momentum mode, we
calculate the Schwinger pair-production rate at finite temperature, which is
the pair-production rate from the vacuum times a thermal factor of the
Bose-Einstein distribution.Comment: RevTex 10 pages, no figure; replaced by the version accepted in Phys.
Rev. D; references correcte
On the QED Effective Action in Time Dependent Electric Backgrounds
We apply the resolvent technique to the computation of the QED effective
action in time dependent electric field backgrounds. The effective action has
both real and imaginary parts, and the imaginary part is related to the pair
production probability in such a background. The resolvent technique has been
applied previously to spatially inhomogeneous magnetic backgrounds, for which
the effective action is real. We explain how dispersion relations connect these
two cases, the magnetic case which is essentially perturbative in nature, and
the electric case where the imaginary part is nonperturbative. Finally, we use
a uniform semiclassical approximation to find an expression for very general
time dependence for the background field. This expression is remarkably similar
in form to Schwinger's classic result for the constant electric background.Comment: 27 pages, no figures; reference adde
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