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Register a new userExotic $1^{--}$ States in QCD Sum Rules
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Using the QCD sum rules we test if the charmonium-like structure Y(4260), observed in the $J/psipipi$ invariant mass spectrum, can be described with a $J/psi f_0(980)$ molecular current with $J^{PC}=1^{--}$. We consider the contributions of condensates up to dimension six and we work at leading order in $alpha_s$. We keep terms which are linear in the strange quark mass $m_s$. The mass obtained for such state is $m_{Y}=(4.67pm 0.09)$ GeV, when the vector and scalar mesons are in color singlet configurations. We conclude that the proposed current can better describe the Y(4660) state that could be interpreted as a $Psi(2S) f_0(980)$ molecular state. We also use different $J^{PC}=1^{--}$ currents to study the recently observed $Y_b(10890)$ state. Our findings indicate that the $Y_b(10890)$ can be well described by a scalar-vector tetraquark current.
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In the past years there has been a revival of hadron spectroscopy. Many interesting new hadron states were discovered experimentally, some of which do not fit easily into the quark model. This situation motivated a vigorous theoretical activity. This is a rapidly evolving field with enormous amount of new experimental information. In the present report we include and discuss data which were released very recently. The present review is the first one written from the perspective of QCD sum rules (QCDSR), where we present the main steps of concrete calculations and compare the results with other approaches and with experimental data.
In the past decade, due to the experimental observation of many charmonium-like states, there has been a revival of hadron spectroscopy. In particular, the experimental observation of charged charmonium-like, $Z_c$ states, and bottomonium-like, $Z_b$ states, represents a challenge since they can not be accommodated within the naive quark model. These charged states are good candidates of either tetraquark or molecular states and their observation motivated a vigorous theoretical activity. This is a rapidly evolving field with enormous amount of new experimental information. In this work, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. The present review is written from the perspective of the QCD sum rules approach, where we present the main steps of concrete calculations and compare the results with other approaches and with experimental data.
We calculate the form factors and the coupling constant in the $D^{*}D rho $ vertex in the framework of QCD sum rules. We evaluate the three point correlation functions of the vertex considering both $ D $ and $ rho $ mesons off--shell. The form factors obtained are very different but give the same coupling constant: $g_{D^{*}D rho} = 4.1 pm 0.1$ GeV$^{-1}$.
Finite energy QCD sum rules involving nucleon current correlators are used to determine several QCD and hadronic parameters in the presence of an external, uniform, large magnetic field. The continuum hadronic threshold $s_0$, nucleon mass $m_N$, current-nucleon coupling $lambda_N$, transverse velocity $v_perp$, the spin polarization condensate $langlebar qsigma_{12} qrangle$, and the magnetic susceptibility of the quark condensate $chi_q$, are obtained for the case of protons and neutrons. Due to the magnetic field, and charge asymmetry of light quarks up and down, all the obtained quantities evolve differently with the magnetic field, for each nucleon or quark flavor. With this approach it is possible to obtain the evolution of the above parameters up to a magnetic field strength $eB < 1.4$ GeV$^2$.
One of the advantages of the finite energy sum rules is the fact that every operator in the operator product expansion series can be selected individually by the use of an appropriate kernel function which removes other operator poles. This characteristic is maintained by QCD systems in the presence of external homogeneous magnetic field, providing interesting information about the magnetic evolution of QCD and hadronic parameters. In this work finite energy sum rules are applied on QCD in the light quark sector, combining axial and pseudoscalar channels in the presence of an external homogeneous magnetic field, obtaining the magnetic evolution of the light quark masses, pion mass, the pion decay constant, the gluon condensate and the continuum hadronic threshold.
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