No abstract

Onset of chaos for the holographic dual of a QQ system at finite temperature and baryon density is studied. We consider a string in the AdS Reissner-Nordstrom background near the black-hole horizon and investigate small time-dependent perturbations of the static configurations. The proximity to the horizon induces chaos, which is softened increasing the chemical potential. A background geometry including the effect of a dilaton is also examined. The Maldacena, Shenker, and Stanford bound on the Lyapunov exponents characterizing the perturbations is satisfied for finite baryon chemical potential and when the dilaton is included in the metric.

We analyze the form factors parametrizing the Bc→ J/ψ, ηc matrix elements of the operators in a generalized low-energy b → c semileptonic Hamiltonian. We consider an expansion in nonrelativistic QCD, classifying the heavy quark spin symmetry breaking terms and expressing the form factors in terms of universal functions in a selected kinematical range. Using as an input the lattice QCD results for the Bc → J/ψ matrix element of the SM operator, we obtain information on other form factors. The extrapolation to the full kinematical range is also presented.