9,722 research outputs found
Self-duality, Helicity and Higher-loop Euler-Heisenberg Effective Actions
The Euler-Heisenberg effective action in a self-dual background is remarkably
simple at two-loop. This simplicity is due to the inter-relationship between
self-duality, helicity and supersymmetry. Applications include two-loop
helicity amplitudes, beta-functions and nonperturbative effects. The two-loop
Euler-Heisenberg effective Lagrangian for QED in a self-dual background field
is naturally expressed in terms of one-loop quantities. This mirrors similar
behavior recently found in two-loop amplitudes in N=4 SUSY Yang-Mills theory.Comment: 7 pp, latex, axodraw.sty; Based on talks given by G. Dunne at QTS3
(Cincinnati, OH, Sept. 2003) and QFEXT03 (Norman, OK, Sept. 2003
Pair creation in inhomogeneous fields from worldline instantons
We show how to do semiclassical nonperturbative computations within the
worldline approach to quantum field theory using ``worldline instantons''.
These worldline instantons are classical solutions to the Euclidean worldline
loop equations of motion, and are closed spacetime loops parametrized by the
proper-time. Specifically, we compute the imaginary part of the one loop
effective action in scalar and spinor QED using worldline instantons, for a
wide class of inhomogeneous electric field backgrounds.Comment: 10 pages, 2 figures, talk given by C.S. at X Mexican Workshop on
Particles and Fields, Morelia, Mexico, Nov. 6 - 12, 2005 (to appear in the
conference proceedings
Electron effective mass in AlGaN alloys determined by mid-infrared optical Hall effect
The effective electron mass parameter in Si-doped AlGaN is
determined to be from mid-infrared optical Hall
effect measurements. No significant anisotropy of the effective electron mass
parameter is found supporting theoretical predictions. Assuming a linear change
of the effective electron mass with the Al content in AlGaN alloys and
for GaN, an average effective electron mass of
can be extrapolated for AlN. The analysis of mid-infrared
spectroscopic ellipsometry measurements further confirms the two phonon mode
behavior of the E(TO) and one phonon mode behavior of the A(LO) phonon
mode in high-Al-content AlGaN alloys as seen in previous Raman scattering
studies
Closed-form two-loop Euler-Heisenberg Lagrangian in a self-dual background
We show that the two-loop Euler-Heisenberg effective Lagrangian for scalar
QED in a constant Euclidean self-dual background has a simple explicit closed
form expression in terms of the digamma function. This result leads to a simple
analysis of the weak- and strong-field expansions, the two-loop scalar QED beta
function, and the analytic continuation properties of the effective Lagrangian
and its imaginary part.Comment: 8 pages, late
Bernoulli Number Identities from Quantum Field Theory and Topological String Theory
We present a new method for the derivation of convolution identities for
finite sums of products of Bernoulli numbers. Our approach is motivated by the
role of these identities in quantum field theory and string theory. We first
show that the Miki identity and the Faber-Pandharipande-Zagier (FPZ) identity
are closely related, and give simple unified proofs which naturally yield a new
Bernoulli number convolution identity. We then generalize each of these three
identities into new families of convolution identities depending on a
continuous parameter. We rederive a cubic generalization of Miki's identity due
to Gessel and obtain a new similar identity generalizing the FPZ identity. The
generalization of the method to the derivation of convolution identities of
arbitrary order is outlined. We also describe an extension to identities which
relate convolutions of Euler and Bernoulli numbers.Comment: 18 pages, final version published in CNTP (title modified, note added
on relevant work that has appeared since the preprint version; otherwise
unchanged
Schwinger Pair Creation of Particles and Strings
I shortly review the worldline instanton method for calculating Schwinger
pair production rates in (i) one-loop QED (ii) multiloop QED and (iii) one-loop
open string theory.Comment: 8 pages, 3 figures, talk given at XIV Mexican School of Particles and
Fields, November 8 - 12, 2010, Morelia, Mexico, to appear in the conference
proceeding
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