DSpace Community:http://hdl.handle.net/2440/123532016-08-29T23:29:29Z2016-08-29T23:29:29ZTransition of ρ →πγ in lattice QCDOwen, B.J.Kamleh, W.Leinweber, D.B.Mahbub, M.S.Menadue, B.J.http://hdl.handle.net/2440/1007872016-08-29T03:12:33Z2015-01-01T00:00:00ZTitle: Transition of ρ →πγ in lattice QCD
Author: Owen, B.J.; Kamleh, W.; Leinweber, D.B.; Mahbub, M.S.; Menadue, B.J.
Abstract: With the ongoing experimental interest in exploring the excited hadron spectrum, evaluations of the matrix elements describing the formation and decay of such states via radiative processes provide us with an important connection between theory and experiment. In particular, determinations obtained via the lattice allow for a direct comparison of QCD expectation with experimental observation. Here we present the first light-quark determination of the ρ → πγ transition form factor from lattice QCD using dynamical quarks. Using the PACS-CS 2 þ 1 flavor QCD ensembles we are able to obtain results across a range of masses, to the near physical value of mπ ¼ 156 MeV. An important aspect of our approach is the use of variational methods to isolate the desired QCD eigenstate. For low-lying states, such techniques facilitate the removal of excited state contributions. In principle, the method enables one to consider arbitrary eigenstates. We find our results are in accord with the nonrelativistic quark model for heavy masses. In moving towards the light-quark regime we observe an interesting quark mass dependence, contrary to the quark model expectation. Comparison of our light-quark result with experimental determinations highlights a significant discrepancy suggesting that disconnected sea-quark loop contributions may play a significant role in fully describing this process.
Description: Published 25 August 20152015-01-01T00:00:00ZΔI=1/2 rule for kaon decays derived from QCD infrared fixed pointCrewther, R.J.Tunstall, L.C.http://hdl.handle.net/2440/1007862016-08-29T03:11:42Z2015-01-01T00:00:00ZTitle: ΔI=1/2 rule for kaon decays derived from QCD infrared fixed point
Author: Crewther, R.J.; Tunstall, L.C.
Abstract: This article gives details of our proposal to replace ordinary chiral SUð3ÞL × SUð3ÞR perturbation theory χPT3 by three-flavor chiral-scale perturbation theory χPTσ. In χPTσ, amplitudes are expanded at low energies and small u; d; s quark masses about an infrared fixed point αIR of three-flavor QCD. At αIR, the quark condensate h¯qqivac ≠ 0 induces nine Nambu-Goldstone bosons: π; K; η, and a 0þþ QCD dilaton σ. Physically, σ appears as the f0ð500Þ resonance, a pole at a complex mass with real part ≲mK. The ΔI ¼ 1=2 rule for nonleptonic K decays is then a consequence of χPTσ, with a KSσ coupling fixed by data for γγ → ππ and KS → γγ. We estimate RIR ≈ 5 for the nonperturbative Drell-Yan ratio R ¼ σðeþe− → hadronsÞ=σðeþe− → μþμ−Þ at αIR and show that, in the many-color limit, σ=f0 becomes a narrow q¯q state with planar-gluon corrections. Rules for the order of terms in χPTσ loop expansions are derived in Appendix A and extended in Appendix B to include inverse-power Li-Pagels singularities due to external operators. This relates to an observation that, for γγ channels, partial conservation of the dilatation current is not equivalent to σ-pole dominance.
Description: Published 17 February 20152015-01-01T00:00:00ZA method for estimating the height of a mesospheric density level using meteor radarYounger, J.P.Reid, I.M.Vincent, R.A.Murphy, D.J.http://hdl.handle.net/2440/1007022016-08-24T23:49:46Z2015-01-01T00:00:00ZTitle: A method for estimating the height of a mesospheric density level using meteor radar
Author: Younger, J.P.; Reid, I.M.; Vincent, R.A.; Murphy, D.J.
Abstract: A new technique for determining the height of a constant density surface at altitudes of 78–85 km is presented. The first results are derived from a decade of observations by a meteor radar located at Davis Station in Antarctica and are compared with observations from the Microwave Limb Sounder instrument aboard the Aura satellite. The density of the neutral atmosphere in the mesosphere/lower thermosphere region around 70–110 km is an essential parameter for interpreting airglow-derived atmospheric temperatures, planning atmospheric entry maneuvers of returning spacecraft, and understanding the response of climate to different stimuli. This region is not well characterized, however, due to inaccessibility combined with a lack of consistent strong atmospheric radar scattering mechanisms. Recent advances in the analysis of detection records from high-performance meteor radars provide new opportunities to obtain atmospheric density estimates at high time resolutions in the MLT region using the durations and heights of faint radar echoes from meteor trails. Previous studies have indicated that the expected increase in underdense meteor radar echo decay times with decreasing altitude is reversed in the lower part of the meteor ablation region due to the neutralization of meteor plasma. The height at which the gradient of meteor echo decay times reverses is found to occur at a fixed atmospheric density. Thus, the gradient reversal height of meteor radar diffusion coefficient profiles can be used to infer the height of a constant density level, enabling the observation of mesospheric density variations using meteor radar.2015-01-01T00:00:00ZParity-expanded variational analysis for nonzero momentumStokes, F.M.Kamleh, W.Leinweber, D.B.Mahbub, M.S.Menadue, B.J.Owen, B.J.http://hdl.handle.net/2440/1006992016-08-24T23:47:41Z2015-01-01T00:00:00ZTitle: Parity-expanded variational analysis for nonzero momentum
Author: Stokes, F.M.; Kamleh, W.; Leinweber, D.B.; Mahbub, M.S.; Menadue, B.J.; Owen, B.J.
Abstract: In recent years, the use of variational analysis techniques in lattice QCD has been demonstrated to be successful in the investigation of the rest-mass spectrum of many hadrons. However, due to parity mixing, more care must be taken for investigations of boosted states to ensure that the projected correlation functions provided by the variational analysis correspond to the same states at zero momentum. In this paper we present the parity-expanded variational analysis (PEVA) technique, a novel method for ensuring the successful and consistent isolation of boosted baryons through a parity expansion of the operator basis used to construct the correlation matrix.2015-01-01T00:00:00Z