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This paper has been withdrawn by the authors. We have discovered an error in the evaluation of the diagram, which invalidates our conclusion.
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This paper has been withdrawn by the authors. We have discovered an error in the evaluation of the diagram, which invalidates our conclusion.
We study $bar qq$-hybrid mixing for the light vector mesons and $bar qq$-glueball mixing for the light scalar mesons in Monte-Carlo based QCD Laplace sum rules. By calculating the two-point correlation function of a vector $bar qgamma_mu q$ (scalar $bar q q$) current and a hybrid (glueball) current we are able to estimate the mass and the decay constants of the corresponding mixed physical state that couples to both currents. Our results do not support strong quark/gluonic mixing for either the $1^{--}$ or the $0^{++}$ states.
Gaussian QCD sum-rules are ideally suited to the study of mixed states of gluonium (glueballs) and quark ($qbar q$) mesons because of their capability to resolve widely-separated states of comparable strength. The analysis of the Gaussian QCD sum-rules (GSRs) for all possible two-point correlation functions of gluonic and non-strange ($I=0$) quark scalar ($J^{PC}=0^{++}$) currents is discussed. For the non-diagonal sum-rule of gluonic and $qbar q$ currents we show that perturbative and gluon condensate contributions are chirally suppressed compared to non-perturbative effects of the quark condensate, mixed condensate, and instantons, implying that the mixing of quark mesons and gluonium is of non-perturbative origin. The independent predictions of the masses and relative coupling strengths from the non-diagonal and the two diagonal GSRs are remarkably consistent with a scenario of two states with masses of approximately 1 GeV and 1.4 GeV that couple to significant mixtures of quark and gluonic currents. The mixing is nearly maximal with the heavier mixed state having a slightly larger coupling to gluonic currents than the lighter state.
We use QCD sum rules to test the nature of the recently observed mesons Y(4260), Y(4350) and Y(4660), assumed to be exotic four-quark $(cbar{c}qbar{q})$ or $(cbar{c}sbar{s})$ states with $J^{PC}=1^{--}$. We work at leading order in $alpha_s$, consider the contributions of higher dimension condensates and keep terms which are linear in the strange quark mass $m_s$. We find for the $(cbar{c}sbar{s})$ state a mass $m_Y=(4.65pm 0.10)$ GeV which is compatible with the experimental candidate Y(4660), while for the $(cbar{c}qbar{q})$ state we find a mass $m_Y=(4.49pm 0.11)$ GeV, which is higger than the mass of the experimental candidate Y(4350). With the tetraquark structure we are working we can not explain the Y(4260) as a tetraquark state. We also consider molecular $D_{s0}bar{D}_s^*$ and $D_{0}bar{D}^*$ states. For the $D_{s0}bar{D}_s^*$ molecular state we get $m_{D_{s0}bar{D}_s^*}=(4.42pm 0.10)$ GeV which is consistent, considering the errors, with the mass of the meson Y(4350) and for the $D_{0}bar{D}^*$ molecular state we get $m_{D_{0}bar{D}^*}=(4.27pm 0.10)$ GeV in excelent agreement with the mass of the meson Y(4260).
We use QCD sum rules to study the possible existence of $QQ-bar{u}bar{d}$ mesons, assumed to be a state with $J^{P}=1^{+}$. For definiteness, we work with a current with an axial heavy diquark and a scalar light antidiquark, at leading order in $alpha_s$. We consider the contributions of condensates up to dimension eight. For the $b$-quark, we predict $M_{T_{bb}}= (10.2pm 0.3) {rm GeV}$, which is below the $bar{B}bar{B}^*$ threshold. For the $c$-quark, we predict $M_{T_{cc}}= (4.0pm 0.2) {rm GeV}$, in agreement with quark model predictions.
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