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Register a new userConfigurational entropy of heavy-quark QCD exotica: engendering the next generation
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The mass spectroscopy of exotic meson states is scrutinized in the AdS/QCD paradigm. The differential configurational entropy is then used to study, derive, and analyze the mass spectrum of excited exotic vector meson resonances, whose configurational stability is also addressed. For it, the hadronic molecule, the hadrocharmonium, and the hybrid description of heavy-quark exotic mesonic states are employed to more precisely match experimental data in the Particle Data Group and also to predict the next generations of heavy-quark QCD exotica in the $Z_c$, $Y$, $pi_1$, and $Z_b$ exotic meson families.
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The meson family of $eta$ pseudoscalars is studied in the context of the AdS/QCD correspondence and the differential configurational entropy (DCE). For it, two forms of configurational-entropic Regge-like trajectories are engendered, relating the $eta$ mesonic states excitation number to both their experimental mass spectrum in the Particle Data Group (PDG) and the DCE as well. Hence, the mass spectrum of $eta$ pseudoscalar mesonic states, beyond the already detected states $eta(550)$, $eta(958)$, $eta(1295)$, $eta(1405)$, $eta(1475)$, $eta(1760)$, $eta(2225)$, and $eta(2320)$, is derived for any excitation number. The three first ulterior members of this family are then analyzed and also compared to existing candidates in PDG.
We compute the imaginary part of the heavy quark contribution to the photon polarization tensor, i.e. the quarkonium spectral function in the vector channel, at next-to-leading order in thermal QCD. Matching our result, which is valid sufficiently far away from the two-quark threshold, with a previously determined resummed expression, which is valid close to the threshold, we obtain a phenomenological estimate for the spectral function valid for all non-zero energies. In particular, the new expression allows to fix the overall normalization of the previous resummed one. Our result may be helpful for lattice reconstructions of the spectral function (near the continuum limit), which necessitate its high energy behaviour as input, and can in principle also be compared with the dilepton production rate measured in heavy ion collision experiments. In an appendix analogous results are given for the scalar channel.
We briefly report the modern status of heavy quark sum rules (HQSR) based on stability criteria by emphasizing the recent progresses for determining the QCD parameters (alpha_s, m_{c,b} and gluon condensates)where their correlations have been taken into account. The results: alpha_s(M_Z)=0.1181(16)(3), m_c(m_c)=1286(16) MeV, m_b(m_b)=4202(7) MeV,<alpha_s G^2> = (6.49+-0.35)10^-2 GeV^4, < g^3 G^3 >= (8.2+-1.0) GeV^2 <alpha_s G^2> and the ones from recent light quark sum rules are summarized in Table 2. One can notice that the SVZ value of <alpha_s G^2> has been underestimated by a factor 1.6, <g^3 G^3> is much bigger than the instanton model estimate, while the four-quark condensate which mixes under renormalization is incompatible with the vacuum saturation which is phenomenologically violated by a factor (2~4). The uses of HQSR for molecules and tetraquarks states are commented.
We present the first calculation of the next-to-next-to-leading order threshold soft function for top quark pair production at hadron colliders, with full velocity dependence of the massive top quarks. Our results are fully analytic, and can be entirely written in terms of generalized polylogarithms. The scale-dependence of our result coincides with the well-known two-loop anomalous dimension matrix including the three-parton correlations, which at the two-loop order only appear when more than one massive partons are involved in the scattering process. In the boosted limit, our result exhibits the expected factorization property of mass logarithms, which leads to a consistent extraction of the soft fragmentation function. The next-to-next-to-leading order soft function obtained in this paper is an important ingredient for threshold resummation at the next-to-next-to-next-to-leading logarithmic accuracy.
In response to the growing need for theoretical tools that can be used in QCD to describe and understand the dynamics of gluons in hadrons in the Minkowski space-time, the renormalization group procedure for effective particles (RGPEP) is shown in the simplest available context of heavy quarkonia to exhibit a welcome degree of universality in the first approximation it yields once one assumes that beyond perturbation theory gluons obtain effective mass. Namely, in the second-order terms, the Coulomb potential with Breit-Fermi spin couplings in the effective quark-antiquark component of a heavy quarkonium, is corrected in one-flavor QCD by a spin-independent harmonic oscillator term that does not depend on the assumed effective gluon mass or the choice of the RGPEP generator. The new generator we use here is much simpler than the ones used before and has the advantage of being suitable for studies of the effective gluon dynamics at higher orders than the second and beyond the perturbative expansion.
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