629 research outputs found
Relativistic Multiple Scattering Theory and the Relativistic Impulse Approximation
It is shown that a relativistic multiple scattering theory for hadron-nucleus
scattering can be consistently formulated in four-dimensions in the context of
meson exchange. We give a multiple scattering series for the optical potential
and discuss the differences between the relativistic and non-relativistic
versions. We develop the relativistic multiple scattering series by separating
out the one boson exchange term from the rest of the Feynman series. However
this particular separation is not absolutely necessary and we discuss how to
include other terms. We then show how to make a three-dimensional reduction for
hadron-nucleus scattering calculations and we find that the relative energy
prescription used in the elastic scattering equation should be consistent with
the one used in the free two-body t-matrix involved in the optical potential.
We also discuss what assumptions are involved in making a Dirac Relativistic
Impulse Approximation (RIA).Comment: 20 pages, 9 figures, Accepted for publication in Journal of Physics
Instantaneous Bethe-Salpeter Equation: Analytic Approach for Nonvanishing Masses of the Bound-State Constituents
The instantaneous Bethe-Salpeter equation, derived from the general
Bethe-Salpeter formalism by assuming that the involved interaction kernel is
instantaneous, represents the most promising framework for the description of
hadrons as bound states of quarks from first quantum-field-theoretic
principles, that is, quantum chromodynamics. Here, by extending a previous
analysis confined to the case of bound-state constituents with vanishing
masses, we demonstrate that the instantaneous Bethe-Salpeter equation for
bound-state constituents with (definitely) nonvanishing masses may be converted
into an eigenvalue problem for an explicitly - more precisely, algebraically -
known matrix, at least, for a rather wide class of interactions between these
bound-state constituents. The advantages of the explicit knowledge of this
matrix representation are self-evident.Comment: 12 Pages, LaTeX, 1 figur
Numerical Gram-Schmidt Orthonormalization
A numerical Gram-Schmidt orthonormalization procedure is presented for constructing an orthonormal basis function set from a non-orthonormal set, when the number of basis functions is large. This method will provide a pedagogical illustration of the Gram-Schmidt procedure and can be presented in classes on numerical methods or computational physics
Instantaneous Bethe-Salpeter equation: utmost analytic approach
The Bethe-Salpeter formalism in the instantaneous approximation for the
interaction kernel entering into the Bethe-Salpeter equation represents a
reasonable framework for the description of bound states within relativistic
quantum field theory. In contrast to its further simplifications (like, for
instance, the so-called reduced Salpeter equation), it allows also the
consideration of bound states composed of "light" constituents. Every
eigenvalue equation with solutions in some linear space may be (approximately)
solved by conversion into an equivalent matrix eigenvalue problem. We
demonstrate that the matrices arising in these representations of the
instantaneous Bethe-Salpeter equation may be found, at least for a wide class
of interactions, in an entirely algebraic manner. The advantages of having the
involved matrices explicitly, i.e., not "contaminated" by errors induced by
numerical computations, at one's disposal are obvious: problems like, for
instance, questions of the stability of eigenvalues may be analyzed more
rigorously; furthermore, for small matrix sizes the eigenvalues may even be
calculated analytically.Comment: LaTeX, 23 pages, 2 figures, version to appear in Phys. Rev.
Explaining Myanmar's Regime Transition: The Periphery is Central
In 2010, Myanmar (Burma) held its first elections after 22 years of direct military rule. Few compelling explanations for this regime transition have emerged. This article critiques popular accounts and potential explanations generated by theories of authoritarian ‘regime breakdown’ and ‘regime maintenance’. It returns instead to the classical literature on military intervention and withdrawal. Military regimes, when not terminated by internal factionalism or external unrest, typically liberalise once they feel they have sufficiently addressed the crises that prompted their seizure of power. This was the case in Myanmar. The military intervened for fear that political unrest and ethnic-minority separatist insurgencies would destroy Myanmar’s always-fragile territorial integrity and sovereignty. Far from suddenly liberalising in 2010, the regime sought to create a ‘disciplined democracy’ to safeguard its preferred social and political order twice before, but was thwarted by societal opposition. Its success in 2010 stemmed from a strategy of coercive state-building and economic incorporation via ‘ceasefire capitalism’, which weakened and co-opted much of the opposition. Having altered the balance of forces in its favour, the regime felt sufficiently confident to impose its preferred settlement. However, the transition neither reflected total ‘victory’ for the military nor secured a genuine or lasting peace
On the Lorentz structure of the confinement potential
We investigate the Lorentz structure of the confinement potential through a
study of the meson spectrum using Salpeter's instantaneous approximation to the
Bethe-Salpeter equation. The equivalence between Salpeter's and a
random-phase-approximation (RPA) equation enables one to employ the same
techniques developed by Thouless, in his study of nuclear collective
excitations, to test the stability of the solutions. The stablity analysis
reveals the existence of imaginary eigenvalues for a confining potential that
transforms as a Lorentz scalar. Moreover, we argue that the instability
persists even for very large values of the constituent quark mass. In contrast,
we find no evidence of imaginary eigenvalues for a timelike vector potential
--- even for very small values of the constituent mass.Comment: 18 pages using RevTeX 3.0, with 8 figures available upon request,
FSU-SCRI-94-1
The Nystrom plus Correction Method for Solving Bound State Equations in Momentum Space
A new method is presented for solving the momentum-space Schrodinger equation
with a linear potential. The Lande-subtracted momentum space integral equation
can be transformed into a matrix equation by the Nystrom method. The method
produces only approximate eigenvalues in the cases of singular potentials such
as the linear potential. The eigenvalues generated by the Nystrom method can be
improved by calculating the numerical errors and adding the appropriate
corrections. The end results are more accurate eigenvalues than those generated
by the basis function method. The method is also shown to work for a
relativistic equation such as the Thompson equation.Comment: Revtex, 21 pages, 4 tables, to be published in Physical Review
Mass drug administration for the acceleration of malaria elimination in a region of Myanmar with artemisinin-resistant falciparum malaria: a cluster-randomised trial
Background: To contain multidrug-resistant Plasmodium falciparum, malaria elimination in the Greater Mekong subregion needs to be accelerated while current antimalarials remain effective. We evaluated the safety, effectiveness, and potential resistance selection of dihydroartemisinin–piperaquine mass drug administration (MDA) in a region with artemisinin resistance in Myanmar.
Methods: We did a cluster-randomised controlled trial in rural community clusters in Kayin (Karen) state in southeast Myanmar. Malaria prevalence was assessed using ultrasensitive quantitative PCR (uPCR) in villages that were operationally suitable for MDA (villages with community willingness, no other malaria control campaigns, and a population of 50–1200). Villages were eligible to participate if the prevalence of malaria (all species) in adults was greater than 30% or P falciparum prevalence was greater than 10% (or both). Contiguous villages were combined into clusters. Eligible clusters were paired based on P falciparum prevalence (estimates within 10%) and proximity. Community health workers provided routine malaria case management and distributed long-lasting insecticidal bed-nets (LLINs) in all clusters. Randomisation of clusters (1:1) to the MDA intervention group or control group was by public coin-flip. Group allocations were not concealed. Three MDA rounds (3 days of supervised dihydroartemisinin–piperaquine [target total dose 7 mg/kg dihydroartemisinin and 55 mg/kg piperaquine] and single low-dose primaquine [target dose 0·25 mg base per kg]) were delivered to intervention clusters. Parasitaemia prevalence was assessed at 3, 5, 10, 15, 21, 27, and 33 months. The primary outcomes were P falciparum prevalence at months 3 and 10. All clusters were included in the primary analysis. Adverse events were monitored from the first MDA dose until 1 month after the final dose, or until resolution of any adverse event occurring during follow-up. This trial is registered with ClinicalTrials.gov, NCT01872702.
Findings: Baseline uPCR malaria surveys were done in January, 2015, in 43 villages that were operationally suitable for MDA (2671 individuals). 18 villages met the eligibility criteria. Three villages in close proximity were combined into one cluster because a border between them could not be defined. This gave a total of 16 clusters in eight pairs. In the intervention clusters, MDA was delivered from March 4 to March 17, from March 30 to April 10, and from April 27 to May 10, 2015. The weighted mean absolute difference in P falciparum prevalence in the MDA group relative to the control group was −10·6% (95% CI −15·1 to −6·1; p=0·0008) at month 3 and −4·5% (−10·9 to 1·9; p=0·14) at month 10. At month 3, the weighted P falciparum prevalence was 1·4% (0·6 to 3·6; 12 of 747) in the MDA group and 10·6% (7·0 to 15·6; 56 of 485) in the control group. Corresponding prevalences at month 10 were 3·2% (1·5 to 6·8; 34 of 1013) and 5·8% (2·5 to 12·9; 33 of 515). Adverse events were reported for 151 (3·6%) of 4173 treated individuals. The most common adverse events were dizziness (n=109) and rash or itching (n=20). No treatment-related deaths occurred.
Interpretation: In this low-transmission setting, the substantial reduction in P falciparum prevalence resulting from support of community case management was accelerated by MDA. In addition to supporting community health worker case management and LLIN distribution, malaria elimination programmes should consider using MDA to reduce P falciparum prevalence rapidly in foci of higher transmission.
Funding: The Global Fund to Fight AIDS, Tuberculosis and Malaria
Bethe-Salpeter equation: 3D reductions, heavy mass limits and abnormal solutions
We show that the 3D reductions of the Bethe-Salpeter equation have the same
bound state spectrum as the original equation, with the possible exception of
some solutions for which the corresponding 3D wave function vanishes. The
abnormal solutions of the Bethe-Salpeter equation (corresponding to excitations
in the relative time-energy degree of freedom), when they exist, are recovered
in the 3D reductions via a complicated dependence of the final potential on the
total energy. We know however that the one-body (or one high mass) limit of
some 3D reductions of the exact Bethe-Salpeter equation leads to a compact 3D
equation (by a mutual cancellation of the ladder and crossed graph
contributions), which does not exhibit this kind of dependence on the total
energy anymore. We conclude that the exact Bethe-Salpeter equation has no
abnormal solution at this limit, or has only solutions for which our 3D wave
function vanishes. This is in contrast with the results of the ladder
approximation, where no such cancellation occurs. We draw the same conclusions
for the static model, which we obtain by letting the mass of the lighter
particle go also to infinity. These results support Wick's conjecture that the
abnormal solutions are a spurious consequence of the ladder approximation.Comment: 11 pages Latex, 1 figure Postscript. Submitted to Journal of Physics
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