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Integrable hydrodynamic equations for initial chiral currents and infinite hydrodynamic chains from WZNW model and string model of WZNW type with $SU(2),$ $SO(3),$ $SP(2),$ $SU(\infty)$, $SO(\infty)$, $SP(\infty)$ constant torsions

The WZNW and string models are considered in the terms of the initial and invariant chiral currents assuming that the internal and external torsions coincide (anticoincide) and they are the structure constants of the $SU(n),SO(n),$ $SP(n)$ Lie algebras. These models are the auxiliary problems in order to construct integrable equations of hydrodynamic type. It was shown that the WZNW and string models in terms of invariant chiral currents are integrable for the constant torsion associated with the structure constants of the $SU(2),$ $SO(3),$ $SP(2)$ and $SU(3)$ algebras only. The equation of motion for the density of the first Casimir operator was obtained in the form of the inviscid Burgers equation. The solution of this equation is presented through the Lambert function. Also, a new equation of motion for the initial chiral current was found. The integrable infinite hydrodynamic chains obtained from the WZNW and string models are given in terms of invariant chiral currents with the $SU(2)$, $SO(3)$, $SP(2)$ and with $SU(\infty)$, $SO(\infty)$, $SP(\infty)$ constant torsions. Also, the equations of motion for the density of any Casimir operator and new infinite dimensional equations of hydrodynamic type for the initial chiral currents through the symmetric structure constant of $SU(\infty)$, $SO(\infty),$ $SP(\infty)$ algebras are obtained.