Research in Theoretical Hadronic Physics and Related Topics

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We propose to investigate a n mber of topics,including:Hard Pion Electroproduction. We will calculate high transverse momentum semi-exclusivepion electroproduction,considering especially the higher twist process where the pions are pro-duced directly and appear kinematically isolated,but including leading twist (where the pionsare produced by parton fragmentation and appear as part of a jet)and estimates of soft pro-cesses.The direct and leading twist processes allow data to yield information about the quarkand gluon distributions in the target.Two particular new items are to do electroproductionrather than photoproduction and to include initial state parton transverse momentum.An ap-plication is to see if the higher twist process are relevant to data from HERMES,and possiblyHall B data from Je .erson Lab,where there is considerable interest in the result.Dipions and the Polarization of Gluons. HERMES has measured dipions photoproducedwith polarized photons o .polarized targets,which has given the .rst determination of the po-larization of gluons in the proton.The published result depends heavily upon the theoreticalanalysis,in turn heavily based on program packages that are tuned to higher energies.Wepropose what we believe is a necessary independent calculation the contributions of the vari-ous processes (photon-gluon fusion,QCD Compton,and vector meson dominance (VMD)),inparticular to see the sensitivity of the results to di .ering fragmentation models,initial statetransverse momentum,and di .ering estimates of the VMD contribution.The Deuteron Form Factor. The only perturbative QCD calculation of the asymptoticdeuteron form factor lies well below the data,but strikingly omits the short range wave functionsthat provide for hidden color states.We have recently developed ways to manipulate 6-quarkcluster wave functions that model these components.We propose to calculate the asymptoticform factor with wave functions including a hidden color component,to see the e .ect of thehidden color components upon the magnitude of the result.Bringing Perturbative QCD to Lower Momentum Transfers. We will study formal andapplied aspects of relations between the Breit and light-front helicity amplitudes,next-to-leadingpower corrections to the high momentum transfer behavior of those amplitudes,and applicationof discrete symmetries to light-front amplitudes.The formal results can allow s,for example,to.nd constraints that approximations to the subdominant helicity amplitudes must obey (whichare not always realized in the literature).More positively,we can se the formal results to guideinvestigation of how non-leading powers can be parameterized and see,again for example,howand where the N .(1232)transition may approach the perturbative QCD results.Phenomenology of Noncommutative Field Theory. Following up on an earlier researchpath,we would like to complete the set of Feynman rules for the Lorentz conserving noncom-mutative .eld theory and .nd the signatures of noncommutative spacetime for a selection ofprocesses in addition to fAfA elastic scattering.Also we would like to consider ways to do Lorentzconserving noncommutative .eld theory with operator algebras in addition to the contractedSnyder algebra we have worked out so far.NSF Review Criteria. Intellectual merit of the proposed activity:Most of the activity is atthe forefront of modern hadronic physics,and the rest is at the forefront of the phenomenologyof an interesting direction in particle physics.The projects will lead to many publicationsin the leading refereed journals.Broader impacts of the proposed activity:The projects willhelp bridge the gap between hadronic theory and observed phenomena,and lead to greaterunderstanding of the mechanisms of hadronic reactions.They will also train new students,including undergraduates.The PI has had two successful women Ph.D.students,and thepresent project may extend opportunities for women entering the .eld.The PI is regularly atthe Je .erson Laboratory and bridging the gap between university and national lab as well asbetween data and theory.