8,146 research outputs found

    Radiative corrections for few-nucleon systems

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    We use a combination of effective field theory and the renormalization group to determine the impact of radiative corrections on the nucleon-nucleon potential. In order to do so, we present a modified version of pionless effective field theory inspired by earlier work in nonrelativistic quantum electrodynamics. The renormalization group analysis of corrections in the deuteron indicate that radiative corrections generate 12%1-2\% of the binding energy. This work serves as an important starting point for the study of radiative corrections in few-body systems relevant for precision tests of the Standard Model.Comment: 5 pages, 3 figure

    Implications of Large-NcN_c QCD for the NN Interaction

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    We present a method for ordering two-nucleon interactions based upon their scaling with the number of QCD colors, NcN_c, in the limit that NcN_c becomes large. Available data in the two-nucleon sector shows general agreement with this ordering, indicating that the method may be useful in other contexts where data is less readily available. However, several caveats and potential pitfalls can make the large-NcN_c ordering fragile and/or vulnerable to misinterpretation. We discuss the application of the large-NcN_c analysis to two- and three-nucleon interactions, including those originating from weak and beyond-the-standard-model interactions, as well as two-nucleon external currents. Finally, we discuss some open questions in the field.Comment: 23 pages, 1 figure, submitted to Ann. Rev. Nucl. Part. Sc

    Markov equivalence for ancestral graphs

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    Ancestral graphs can encode conditional independence relations that arise in directed acyclic graph (DAG) models with latent and selection variables. However, for any ancestral graph, there may be several other graphs to which it is Markov equivalent. We state and prove conditions under which two maximal ancestral graphs are Markov equivalent to each other, thereby extending analogous results for DAGs given by other authors. These conditions lead to an algorithm for determining Markov equivalence that runs in time that is polynomial in the number of vertices in the graph.Comment: Published in at http://dx.doi.org/10.1214/08-AOS626 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

    Worldline Monte Carlo method for few body nuclear physics

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    In this work we introduce a worldline based fermion Monte Carlo algorithm for studying few body quantum mechanics of self-interacting fermions in the Hamiltonian lattice formulation. Our motivation to construct the method comes from our interest in studying renormalization of chiral nuclear effective field theory with lattice regularization. In particular we wish to apply our method to compute the lattice spacing dependence of local lattice interactions as we take the continuum limit of the lattice theory. Our algorithm can compute matrix elements of the operator exp(βH)\exp(-\beta H) where HH is the lattice Hamiltonian and β\beta is a free real parameter. These elements help us compute deep bound states that are well separated from scattering states even at values of β\beta which are not very large. Computing these bound state energies accurately can help us study renormalization of the lattice theory. In addition to developing the algorithm, in this work we also introduce a finite volume renormalization scheme for the lattice Hamiltonian of the leading pionless effective field theory and show how it would work in the one and two body sectors.Comment: 23 pages, 8 figures, 17 table

    Basic mathematical programming applications to weed control in forestry

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    Many studies document herbicide performance for Heed and hardwood control in forestry. Few studies, hoHever, attemp t to develop optima l application strategies. Stand-level optindzation is presently limited due to lack of groHth and yield information. Forest-level optimization is possible, however, and has great potential to aid in planning forestry weed control prog rams

    Revisiting the helium isotope-shift puzzle with improved uncertainties from nuclear structure corrections

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    Measurements of the difference between the squared charge radii of the helion (3^3He nucleus) and the α\alpha-particle (4^4He nucleus) have been characterized by longstanding tensions, recently spotlighted in the 3.6 σ\sigma discrepancy of the extractions from ordinary atoms versus those from muonic atoms. Here, we present a novel analysis of uncertainties in nuclear structure corrections that must be supplied by theory to enable the extraction of the difference in radii from spectroscopic experiments. We use modern Bayesian inference techniques to quantify uncertainties stemming from the truncation of the chiral effective field theory expansion of the nuclear force for both muonic and ordinary atoms. With the new nuclear structure input, the helium isotope-shift puzzle cannot be explained, rather it is reinforced to a 4 σ\sigma discrepancy.Comment: 5 pages, 3 figures, 2 table
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