10,308 research outputs found
Nucleon Form Factors of the Isovector Axial-Vector Current: Situation of Experiments and Theory
The theoretical and experimental status of the isovector axial-vector current
form factors G_A(q^2) and G_P(q^2) of the nucleon is reviewed. We also describe
a new calculation of these form factors in manifestly Lorentz-invariant chiral
perturbation theory (ChPT) with the inclusion of axial-vector mesons as
explicit degrees of freedom.Comment: 5 pages, 3 figures. Talk given by M. R. Schindler at the
International Workshop "From Parity Violation to Hadronic Structure and
more...", Milos, Greece, May 16-20, 200
Infrared regularization of baryon chiral perturbation theory reformulated
We formulate the infrared regularization of Becher and Leutwyler in a form
analogous to our recently proposed extended on-mass-shell renormalization. In
our formulation, IR regularization can be applied straightforwardly to
multi-loop diagrams with an arbitrary number of particles with arbitrary
masses.Comment: 10 pages, ReVTEX 4, no figure
TFD Extension of Open String Field Theory
We study the application of the rules of Thermo Field Dynamics (TFD) to the
covariant formulation of Open String Field Theory (OSFT). We extend the states
space and fields according to the duplication rules of TFD and construct the
corresponding classical action. The result is interpreted as a theory whose
fields would encode the statistical information of open strings.
The physical spectrum of the free theory is studied through the cohomology of
the extended BRST charge, and, as a result, we get new fields in the spectrum
emerging by virtue of the quantum entanglement and, noticeably, it presents
degrees of freedom that could be identified as those of closed strings. We also
show, however, that their appearing in the action is directly related to the
choice of the inner product in the extended algebra, so that different sectors
of fields could be eliminated from the theory by choosing that product
conveniently.
Finally, we study the extension of the three-vertex interaction and provide a
simple prescription for it whose results at tree-level agree with those of the
conventional theory.Comment: 25 pages, no figures. File format, typos, Abstract and references
modified. New subsection and concluding comments were added. To appear in
Phys. Rev.
Axial, induced pseudoscalar, and pion-nucleon form factors in manifestly Lorentz-invariant chiral perturbation theory
We calculate the nucleon form factors G_A and G_P of the isovector
axial-vector current and the pion-nucleon form factor G_piN in manifestly
Lorentz-invariant baryon chiral perturbation theory up to and including order
O(p^4). In addition to the standard treatment including the nucleon and pions,
we also consider the axial-vector meson a_1 as an explicit degree of freedom.
This is achieved by using the reformulated infrared renormalization scheme. We
find that the inclusion of the axial-vector meson effectively results in one
additional low-energy coupling constant that we determine by a fit to the data
for G_A. The inclusion of the axial-vector meson results in an improved
description of the experimental data for G_A, while the contribution to G_P is
small.Comment: 21 pages, 9 figures, REVTeX
Improving the ultraviolet behavior in baryon chiral perturbation theory
We introduce a new formulation of baryon chiral perturbation theory which
improves the ultraviolet behavior of propagators and can be interpreted as a
smooth cutoff regularization scheme. It is equivalent to the standard approach,
preserves all symmetries and therefore satisfies the Ward identities. Our
formulation is equally well defined in the vacuum, one- and few-nucleon sectors
of the theory. The equations (Bethe-Salpeter, Lippmann-Schwinger, etc.) for the
scattering amplitudes of the few-nucleon sector are free of divergences in the
new approach. Unlike the usual cutoff regularization, our 'cutoffs' are
parameters of the Lagrangian and do not have to be removed.Comment: 19 pages, 3 figures, REVTeX 4; version to be published in Phys. Rev.
D, additional section on issues of renormalization in few-body sector
include
Chiral expansion of the nucleon mass to order q^6
We present the results of a complete two-loop calculation at order q^6 of the
nucleon mass in manifestly Lorentz-invariant chiral perturbation theory. The
renormalization is performed using the reformulated infrared renormalization,
which allows for the treatment of two-loop integrals while preserving all
relevant symmetries, in particular chiral symmetry.Comment: 6 pages, 2 figures, REVTeX
Polydimethylsiloxane based microfluidic diode
In this paper, we present a novel elastomer-based microfluidic device for rectifying flow. The device is analogous to an electronic diode in function since it allows flow in one direction and stops flow in the opposing direction. The device is planar, in-line and can be replica molded via standard soft lithography techniques. The fabrication process is outlined in detail and follows a simple procedure that requires only photolithography and one replica molding step. Several geometries of devices are presented along with their flow versus pressure characteristics. A brief discussion of the device behavior is presented along with possible uses for the device
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