74,326 research outputs found
Perceptions of research
The term 'research' is rarely questioned. It is a term whose meaning seems to be implicitly understood. Certainly there is an institutional bureaucracy which supports 'research', and academic staff are rewarded for their strength in 'research'. But what is this research? It is likely that there are multiple understandings of 'research', but unless this diversity of understanding is recognised, it is difficult to have meaningful dialogue about it
Recent results in chiral effective field theory for the NN system
I describe recent progress towards a theory of the NN force which captures
the consequences of QCD's chiral symmetry and the pattern of its breaking, and
is formulated as an expansion in a ratio of low and high mass scales,
M_{lo}/M_{hi}. This "chiral effective field theory" of the NN system is a firm
foundation for explorations of nuclear structure and reactions that are
grounded in QCD's low-energy symmetries. While calculations that use a ChiPT
expansion for the NN potential have proven very successful, they can only be
used with a narrow range of momentum-space cutoffs, which leaves the expansion
parameter for observable quantities somewhat murky. Here we seek a truly
systematic effective field theory for the NN amplitude, that is manifestly
renormalization-group invariant at each order in a demonstrably perturbative
expansion.Comment: Invited talk at the 7th International Workshop on Chiral Dynamics,
August 6-10, 2012, Jefferson Lab, Newport News, VA. To appear in the
proceedings. 12 pages, 5 figure
The nucleon-nucleon system in chiral effective theory
I discuss the conditions under which the application of chiral perturbation
theory to the NN potential gives reliable results for NN scattering phase
shifts. ChiPT also yields a convergent expansion for the deuteron charge
operator. For cutoffs < 1 GeV, this produces precise predictions for
deuterium's quadrupole and charge form factors in the range Q^2 < 0.25 GeV^2.Comment: 4 pages, 4 figures. Contribution to Proceedings of "12th
International Conference on Meson-Nucleon Physics and the Structure of the
Nucleon", Williamsburg, VA, May 31-June 4, 201
Electron-deuteron scattering in a relativistic theory of hadrons
We review a three-dimensional formalism that provides a systematic way to
include relativistic effects including relativistic kinematics, the effects of
negative-energy states, and the boosts of the two-body system in calculations
of two-body bound-states. We then explain how to construct a conserved current
within this relativistic three-dimensional approach. This general theoretical
framework is specifically applied to electron-deuteron scattering both in
impulse approximation and when the meson-exchange current is
included. The experimentally-measured quantities , , and are
calculated over the kinematic range that is probed in Jefferson Lab
experiments. The role of both negative-energy states and meson retardation
appears to be small in the region of interest.Comment: 17 pages, 4 figures, uses BoxedEPS.tex, lamuphys.sty, bibnorm.sty. To
appear in the proceedings of the Workshop on Electron-Nucleus Scattering held
at the Elba International Physics Center, June 199
Comment
With the proper role of judging so unsettled, it is hardly surprising that Americans also do not agree on what training, experience or temperament will produce the best judge
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