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A Quantum Quasi-Harmonic Nonlinear Oscillator with an Isotonic Term

The properties of a nonlinear oscillator with an additional term $k_g/x^2$, characterizing the isotonic oscillator, are studied. The nonlinearity affects to both the kinetic term and the potential and combines two nonlinearities associated to two parameters, $κ$ and $k_g$, in such a way that for $κ=0$ all the characteristics of of the standard isotonic system are recovered. The first part is devoted to the classical system and the second part to the quantum system. This is a problem of quantization of a system with position-dependent mass of the form $m(x)=1/(1 - κ x^2)$, with a $κ$-dependent non-polynomial rational potential and with an additional isotonic term. The Schrödinger equation is exactly solved and the $(κ,k_g)$-dependent wave functions and bound state energies are explicitly obtained for both $κ<0$ and $κ>0$.