19 research outputs found
Nucleon-Nucleon Effective Field Theory Without Pions
Nuclear processes involving momenta much below the mass of the pion may be
described by an effective field theory in which the pions do not appear as
explicit degrees of freedom. The effects of the pion and all other virtual
hadrons are reproduced by the coefficients of gauge-invariant local operators
involving the nucleon field. Nucleon-nucleon scattering phase shift data
constrains many of the coefficients that appear in the effective Lagrangean but
at some order in the expansion coefficients enter that must be constrained by
other observables. We compute several observables in the two-nucleon sector up
to next-to-next-to leading order in the effective field theory without pions,
or to the order at which a counterterm involving four-nucleon field operators
is encountered. Effective range theory is recovered from the effective field
theory up to the order where relativistic corrections enter or where
four-nucleon-external current local operators arise. For the deuteron magnetic
moment, quadrupole moment and the radiative capture cross
section a four-nucleon-one-photon counterterm exists at next-to-leading order.
The electric polarizability and electric charge form factor of the deuteron are
determined up to next-to-next-to-leading order, which includes the first
appearance of relativistic corrections.Comment: 27 pages, 8 figures, latex. SD-mixing, quadrupole moment modifie
TRY plant trait database â enhanced coverage and open access
Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of traitâbased plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for âplant growth formâ. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and traitâenvironmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives