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Register a new userEffects of the disconnected flavor singlet corrections on the hyperfine splitting in charmonium
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Experimentally the charmonium hyperfine splitting is $M_{J/psi}-M_{eta_c}=117$ MeV and current lattice results are generally below this value. The difference could be due to the effects of the disconnected flavor singlet diagrams which have not been included in these calculations. Previous attempts to determine the disconnected flavor singlet corrections have led just to rough estimates in the range of $pm 20$ MeV. We present preliminary results for these corrections calculated on fine ($aapprox 0.09$ fm) Asqtad 2+1 flavor lattices provided by the MILC Collaboration.
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In calculations of the hyperfine splitting in charmonium, the contributions of the disconnected diagrams are considered small and are typically ignored. We aim to estimate nonperturbatively the size of the resulting correction, which may eventually be needed in high precision calculations of the charmonium spectrum. We study this problem in the quenched and unquenched QCD cases. On dynamical ensembles the disconnected charmonium propagators contain light modes which complicate the extraction of the signal at large distances. In the fully quenched case, where there are no such light modes, the interpretation of the signal is simplified. We present results from lattices with $aapprox 0.09$ fm and $aapprox 0.06$ fm.
In calculations of the hyperfine splitting in charmonium, the contributions of the disconnected diagrams is considered small and is typically ignored. We aim to estimate nonperturbatively the size of the resulting error, which could potentially affect the high precision calculations of the charmonium spectrum. Following our work on the effects of the disconnected diagrams in unquenched QCD presented at Lattice 2007, we study the same problem in the quenched case. On dynamical ensembles the disconnected charmonium propagators contain light modes which complicate the extraction of the signal at large distances. In the fully quenched case, where there are no such light modes, the interpretation of the signal is simplified. We present results from lattices with $aapprox 0.09$ fm and $aapprox 0.063$ fm.
Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs mo
dels). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.
We report the calculation of the flavor-singlet scalar in the SU(3) gauge theory with the degenerate twelve fermions in the fundamental representation using a HISQ-type action at a fixed $beta$. In order to reduce the large statistical error coming from the vacuum-subtracted disconnected correlator, we employ a noise reduction method and a large number of configurations. We observe that the flavor-singlet scalar is lighter than the pion in this theory from the calculations with the fermion bilinear and gluonic operators. This peculiar feature is considered to be due to the infrared conformality of this theory, and it is a promissing signal for a walking technicolor, where a light composite Higgs boson is expected to emerge by approximate conformal dynamics.
We present results for the mass of the eta-prime meson in the continuum limit for two-flavor lattice QCD, calculated on the CP-PACS computer, using a renormalization-group improved gauge action, and Sheikholeslami and Wohlerts fermion action with tadpole-improved csw. Correlation functions are measured at three values of the coupling constant beta corresponding to the lattice spacing a approx. 0.22, 0.16, 0.11 fm and for four values of the quark mass parameter kappa corresponding to mpi over mrho approx. 0.8, 0.75, 0.7 and 0.6. For each beta, kappa pair, 400-800 gauge configurations are used. The two-loop diagrams are evaluated using a noisy source method. We calculate eta-prime propagators using local sources, and find that excited state contributions are much reduced by smearing. A full analysis for the smeared propagators gives metaprime=0.960(87)+0.036-0.248 GeV, in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations.
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