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Nuclear Theory·nucl-th

Tuesday·February 27, 2018

8 papers—5 primary·3 cross-listed

All8Primary5Cross-lists3
  1. 06

    Gauge Invariant Noether's Theorem in Yang-Mills Theory

    Gouranga C Nayak🇺🇸

    The gauge invariant definition of the spin dependent gluon distribution function from first principle is necessary to study the proton spin crisis at high energy colliders. In this paper we derive the gauge invariant Noether's theorem in Yang-Mills theory by using combined Lorentz transformation plus local non-abelian gauge transformation. We find that the definition of the gauge invariant spin (or orbital) angular momentum of the Yang-Mills field does not exist in Yang-Mills theory although the definition of the gauge invariant spin (or orbital) angular momentum of the quark exists. We show that the gauge invariant definition of the spin angular momentum of the Yang-Mills field in the literature is not correct because of the non-vanishing boundary surface term in Yang-Mills theory. We also find that the Belinfante-Rosenfeld tensor in Yang-Mills theory is not required to obtain the symmetric and gauge invariant energy-momentum tensor of the quark and the Yang-Mills field.

    ↳ hep-phnucl-th12 citations
  2. 07

    The QCD axion beyond the classical level: A lattice study

    Y. Nakamura🇯🇵 · G. Schierholz🇩🇪

    The axion is a hypothetical elementary particle postulated by the Peccei-Quinn theory to resolve the strong CP problem in QCD. If axions exist and have low mass, they are a candidate for dark matter as well. So far our knowledge of the properties of the QCD axion rests on semi-classical arguments and effective theory. In this work we perform, for the first time, a fully dynamical investigation of the Peccei-Quinn theory, focussing on the axion mass, by simulating the theory on the lattice. The results of the simulation are found to be in conflict with present axion phenomenology.

    ↳ hep-lathep-phhep-thnucl-th3 citations
  3. 08

    Different manifestations of S-matrix poles

    D. F. Ramírez Jiménez🇨🇴 · N. G. Kelkar🇨🇴

    Making use of the analytical properties of the -matrix and a theorem of Mittag-Leffler, model independent non-relativistic expressions for cross sections in single channel elastic scattering, scattering phase shifts and survival probabilities of resonances are derived. Provided certain conditions are satisfied by the poles, the residues can also be estimated analytically. Considerations of the low energy behaviour of the -matrix and cross sections reveal additional conditions on the residues of the poles appearing in the Mittag-Leffler expansions. The exact expressions for the resonant cross section and phase shift are shown to reduce to the commonly used Breit-Wigner formula plus corrections. The latter is shown to approach the exact result with the example of a meson and a baryon resonance. Finally, a comparison of the exact expressions with some realistic examples is presented. The calculations of survival probabilities in particular reveal the reason behind the non-observability of non-exponential decay.

    ↳ hep-phnucl-thquant-phAnnals Phys.(2018)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE