657 research outputs found
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
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
Quantum electrodynamics for vector mesons
Quantum electrodynamics for mesons is considered. It is shown that, at
tree level, the value of the gyromagnetic ratio of the is fixed to 2
in a self-consistent effective quantum field theory. Further, the mixing
parameter of the photon and the neutral vector meson is equal to the ratio of
electromagnetic and strong couplings, leading to the mass difference
at tree order.Comment: 4 pages, 2 figures, REVTeX 4, accepted for publication in PR
Two-nucleon problem in semi-relativistic baryon chiral perturbation theory
We consider a symmetry-preserving approach to the nucleon-nucleon scattering
problem in the framework of the higher-derivative formulation of baryon chiral
perturbation theory. Within this framework the leading-order amplitude is
calculated by solving renormalizable equations and corrections are taken into
account perturbatively.Comment: 3 pages, talk given at 20th European Conference on Few-Body Problems
in Physics (EFB 20), Pisa, Italy, 10-14 Sep 200
Signed double Roman domination on cubic graphs
The signed double Roman domination problem is a combinatorial optimization
problem on a graph asking to assign a label from to each
vertex feasibly, such that the total sum of assigned labels is minimized. Here
feasibility is given whenever (i) vertices labeled have at least one
neighbor with label in ; (ii) each vertex labeled has one
-labeled neighbor or at least two -labeled neighbors; and (iii) the sum
of labels over the closed neighborhood of any vertex is positive. The
cumulative weight of an optimal labeling is called signed double Roman
domination number (SDRDN). In this work, we first consider the problem on
general cubic graphs of order for which we present a sharp
lower bound for the SDRDN by means of the discharging method. Moreover, we
derive a new best upper bound. Observing that we are often able to minimize the
SDRDN over the class of cubic graphs of a fixed order, we then study in this
context generalized Petersen graphs for independent interest, for which we
propose a constraint programming guided proof. We then use these insights to
determine the SDRDNs of subcubic grid graphs, among other results
Universality of the rho-meson coupling in effective field theory
It is shown that both the universal coupling of the rho-meson and the
Kawarabayashi-Suzuki-Riadzuddin-Fayyazuddin expression for the magnitude of its
coupling constant follow from the requirement that chiral perturbation theory
of pions, nucleons, and rho-mesons is a consistent effective field theory. The
prerequisite of the derivation is that all ultraviolet divergences can be
absorbed in the redefinition of fields and the available parameters of the most
general effective Lagrangian.Comment: 4 pages, 2 figures, REVTeX 4, accepted for publication in PR
Infrared renormalization of two-loop integrals and the chiral expansion of the nucleon mass
We describe details of the renormalization of two-loop integrals relevant to
the calculation of the nucleon mass in the framework of manifestly
Lorentz-invariant chiral perturbation theory using infrared renormalization. It
is shown that the renormalization can be performed while preserving all
relevant symmetries, in particular chiral symmetry, and that renormalized
diagrams respect the standard power counting rules. As an application we
calculate the chiral expansion of the nucleon mass to order O(q^6).Comment: Version accepted for publication in Nucl. Phys. A, missing one-loop
diagram added, minor changes in notation, discussion of results improve
Methods of sputum processing for cell counts, immunocytochemistry and in situ hybridisation.
Since the first attempts to use standardised methods for sampling induced airways sputum, two methods for processing the expectorate have evolved. The first involves selecting all viscid or denser portions from the expectorated sample with the aid of an inverted microscope. This method has been extensively evaluated and reported in detail. The second approach involves processing the entire expectorate, comprising sputum plus variable amounts of saliva. Recent modifications to this method include collecting saliva and sputum separately in order to reduce salivary contamination. Both methods have advantages and disadvantages.
The advantages of using selected sputum are: squamous cell contamination is v5%, making cell counting easier and quicker to perform, the total cell count (TCC) can be expressed per gram of lower airway secretions, and concentrations of chemicals in the fluid phase are unaffected by the confounding influence of saliva, and can be accurately corrected for dilution. The disadvantage is that selection takes a few minutes longer to perform and requires an inverted microscope. The advantage of using the entire expectorate is that the technique is quicker to perform, but there are some disadvantages that require consideration. The expectorate contains a variable mixture of sputum plus saliva which maydilute the sputum and confound its analysis. The reproducibility of cell counts has been reported to be lower if squamous cell contamination represents w20% of all recovered cells. There is conflicting data as to whether or not differential cell counts (DCCs) differ between the two methods. One study reported a higher percentage of eosinophils in sputum processed by the selection method compared to the entire expectorate but this has not been confirmed in other studies. Although, both the selected sputum and the entire expectorate methods have the same ability to distinguish asthmatics or bronchitics from healthy subjects, they are not interchangeable, and, once a technique has been adopted for a given study, it should always be applied
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