56 research outputs found
There are no abnormal solutions of the BetheSalpeter equation in the static model
The four-point Green's function of static QED, where a fermion and an
antifermion are located at fixed space positions, is calculated in covariant
gauges. The bound state spectrum does not display any abnormal state
corresponding to excitations of the relative time. The equation that was
established by Mugibayashi in this model and which has abnormal solutions does
not coincide with the BetheSalpeter equation. Gauge transformation from the
Coulomb gauge also confirms the absence of abnormal solutions in the
BetheSalpeter equation.Comment: 11 pages, late
The Relativistic N-body Problem in a Separable Two-Body Basis
We use Dirac's constraint dynamics to obtain a Hamiltonian formulation of the
relativistic N-body problem in a separable two-body basis in which the
particles interact pair-wise through scalar and vector interactions. The
resultant N-body Hamiltonian is relativistically covariant. It can be easily
separated in terms of the center-of-mass and the relative motion of any
two-body subsystem. It can also be separated into an unperturbed Hamiltonian
with a residual interaction. In a system of two-body composite particles, the
solutions of the unperturbed Hamiltonian are relativistic two-body internal
states, each of which can be obtained by solving a relativistic
Schr\"odinger-like equation. The resultant two-body wave functions can be used
as basis states to evaluate reaction matrix elements in the general N-body
problem. We prove a relativistic version of the post-prior equivalence which
guarantees a unique evaluation of the reaction matrix element, independent of
the ways of separating the Hamiltonian into unperturbed and residual
interactions. Since an arbitrary reaction matrix element involves composite
particles in motion, we show explicitly how such matrix elements can be
evaluated in terms of the wave functions of the composite particles and the
relevant Lorentz transformations.Comment: 42 pages, 2 figures, in LaTe
Isospin breaking corrections to low-energy pi-K scattering
We evaluate the matrix elements for the processes pi^0 K^0 -> pi^0 K^0 and
pi^- K^+ -> pi^0 K^0 in the presence of isospin breaking terms at leading and
next-to-leading order. As a direct application the releveant combination of the
S-wave scattering lengths involved in the pion-kaon atom lifetime is
determined. We discuss the sensitivity of the results with respect to the input
parameters.Comment: 33 pages, plain latex, 2 figure
A Tale of Three Equations: Breit, Eddington-Guant, and Two-Body Dirac
G.Breit's original paper of 1929 postulates the Breit equation as a
correction to an earlier defective equation due to Eddington and Gaunt,
containing a form of interaction suggested by Heisenberg and Pauli. We observe
that manifestly covariant electromagnetic Two-Body Dirac equations previously
obtained by us in the framework of Relativistic Constraint Mechanics reproduce
the spectral results of the Breit equation but through an interaction structure
that contains that of Eddington and Gaunt. By repeating for our equation the
analysis that Breit used to demonstrate the superiority of his equation to that
of Eddington and Gaunt, we show that the historically unfamiliar interaction
structures of Two-Body Dirac equations (in Breit-like form) are just what is
needed to correct the covariant Eddington Gaunt equation without resorting to
Breit's version of retardation.Comment: 15 pages latex, published in Foundations of Physics, Vol 27, 67
(1997
Relativistic Calculation of the Meson Spectrum: a Fully Covariant Treatment Versus Standard Treatments
A large number of treatments of the meson spectrum have been tried that
consider mesons as quark - anti quark bound states. Recently, we used
relativistic quantum "constraint" mechanics to introduce a fully covariant
treatment defined by two coupled Dirac equations. For field-theoretic
interactions, this procedure functions as a "quantum mechanical transform of
Bethe-Salpeter equation". Here, we test its spectral fits against those
provided by an assortment of models: Wisconsin model, Iowa State model,
Brayshaw model, and the popular semi-relativistic treatment of Godfrey and
Isgur. We find that the fit provided by the two-body Dirac model for the entire
meson spectrum competes with the best fits to partial spectra provided by the
others and does so with the smallest number of interaction functions without
additional cutoff parameters necessary to make other approaches numerically
tractable. We discuss the distinguishing features of our model that may account
for the relative overall success of its fits. Note especially that in our
approach for QCD, the resulting pion mass and associated Goldstone behavior
depend sensitively on the preservation of relativistic couplings that are
crucial for its success when solved nonperturbatively for the analogous
two-body bound-states of QED.Comment: 75 pages, 6 figures, revised content
Non-Relativistic Pion Interactions and the Pionium Lifetime
We construct an effective Lagrangian for interacting pions with
non-relativistic energies. The coupling constants can be expressed in terms of
the different scattering lengths and slopes. When used in the calculation of
the pionium decay rate, the scattering slope contribution gives a correction of
about 8% compared with the lowest order contribution coming from the scattering
lengths alone.Comment: 8 pages, 5 figure
Public opinion on energy crops in the landscape: considerations for the expansion of renewable energy from biomass
Public attitudes were assessed towards two dedicated biomass crops – Miscanthus and Short Rotation Coppice (SRC), particularly regarding their visual impacts in the landscape. Results are based on responses to photographic and computer-generated images as the crops are still relatively scarce in the landscape. A questionnaire survey indicated little public concern about potential landscape aesthetics but more concern about attendant built infrastructure. Focus group meetings and interviews indicated support for biomass end uses that bring direct benefits to local communities. Questions arise as to how well the imagery used was able to portray the true nature of these tall, dense, perennial plants but based on the responses obtained and given the caveat that there was limited personal experience of the crops, it appears unlikely that wide-scale planting of biomass crops will give rise to substantial public concern in relation to their visual impact in the landscape
(Pi+Pi-) Atom in Chiral Perturbation Theory
Hadronic (Pi+Pi-) atom is studied in the relativistic perturbative approach
based on the Bethe-Salpeter equation. The general expression for the atom
lifetime is derived. Lowest-order corrections to the relativistic Deser-type
formula for the atom lifetime are evaluated within the Chiral Perturbation
Theory.Comment: 36 pages, LaTeX-file (revtex.sty
In Vivo Methods to Study Uptake of Nanoparticles into the Brain
Several in vivo techniques have been developed to study and measure the uptake of CNS compounds into the brain. With these techniques, various parameters can be determined after drug administration, including the blood-to-brain influx constant (Kin), the permeability-surface area (PS) product, and the brain uptake index (BUI). These techniques have been mostly used for drugs that are expected to enter the brain via transmembrane diffusion or by carrier-mediated transcytosis. Drugs that have limitations in entering the brain via such pathways have been encapsulated in nanoparticles (based on lipids or synthetic polymers) to enhance brain uptake. Nanoparticles are different from CNS compounds in size, composition and uptake mechanisms. This has led to different methods and approaches to study brain uptake in vivo. Here we discuss the techniques generally used to measure nanoparticle uptake in addition to the techniques used for CNS compounds. Techniques include visualization methods, behavioral tests, and quantitative methods
Barriers to Non-Viral Vector-Mediated Gene Delivery in the Nervous System
Efficient methods for cell line transfection are well described, but, for primary neurons, a high-yield method different from those relying on viral vectors is lacking. Viral transfection has several drawbacks, such as the complexity of vector preparation, safety concerns, and the generation of immune and inflammatory responses when used in vivo. However, one of the main problems for the use of non-viral gene vectors for neuronal transfection is their low efficiency when compared with viral vectors. Transgene expression, or siRNA delivery mediated by non-viral vectors, is the result of multiple processes related to cellular membrane crossing, intracellular traffic, and/or nuclear delivery of the genetic material cargo. This review will deal with the barriers that different nanoparticles (cationic lipids, polyethyleneimine, dendrimers and carbon nanotubes) must overcome to efficiently deliver their cargo to central nervous system cells, including internalization into the neurons, interaction with intracellular organelles such as lysosomes, and transport across the nuclear membrane of the neuron in the case of DNA transfection. Furthermore, when used in vivo, the nanoparticles should efficiently cross the blood-brain barrier to reach the target cells in the brain
- …