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Studies of pentaquarks and of noncommutative field theory
Nazaryan, Vahagn
Nazaryan, Vahagn
Abstract
Several experiments reported seeing evidence in their data of a new particle, the strangeness +1 Theta+ pentaquark made of four quarks and an antiquark. In the first few chapters of this dissertation we study four-quark-antiquark systems within the framework of a constituent quark model. We describe the Theta+ as a member of a spin-½ pentaquark antidecuplet. For both parity-odd, and parity-even antidecuplets we derive useful decompositions of the quark model wave functions that allow for easy computation of color-flavor-spin-orbital matrix elements, and we compute mass splittings within the antidecuplet. We study parity-even antidecuplet in an effective theory with dominant flavor-spin interactions. We predict narrow strangeness -2 cascade pentaquarks at about 1900 MeV in this framework. The wave function for the positive parity Theta+ has a small overlap with the kinematically allowed final states, and naturally explains the observed narrowness of the state. In this dissertation we also study noncommutative field theories. Specifically, we study phenomenology of Lorentz-conserving noncommutative QED developed by Carlson, Carone, and Zobin. We obtain bounds on the energy scale of noncommutativity Lambda by calculating modifications to dilepton and diphoton production, and comparing our results to LEP 2 data. We find that Lambda is greater than 160 GeV at 95% C.L., and we make predictions for what may be seen in future collider experiments. We also present a way to extend the discussion of nontrivial commutators to include nonvanishing anticommutation relations among spinor coordinates theta and theta-bar in N = 1 superspace. We present a consistent algebra for the supercoordinates, and find a star-product. We give the Wess-Zumino Lagrangian within our model. It is manifestly Hermitian, with Lorentz-invariant modifications due to non (anti)commutativity.
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2004-01-01
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3158734.pdf
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Physics
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https://dx.doi.org/doi:10.21220/s2-qsd8-hc46