Appearance of branched motifs in the spectra of $B{C}_N$ type Polychronakos spin chains

As is well known, energy levels appearing in the highly degenerate spectra of the $A_{N-1}$ type of Haldane-Shastry and Polychronakos spin chains can be classified through the motifs, which are characterized by some sequences of the binary digits like 0' and 1’. In a similar way, at present we classify all energy levels appearing in the spectra of the $B{C}_N$ type of Polychronakos spin chains with Hamiltonians containing supersymmetric analogue of polarized spin reversal operators. To this end, we show that the $B{C}_N$ type of multivariate super Rogers-Szeg"o (SRS) polynomials, which at a certain limit reduce to the partition functions of the later type of Polychronakos spin chains, satisfy some recursion relation involving a $q$-deformation of the elementary supersymmetric polynomials. Subsequently, we use a Jacobi-Trudi like formula to define the corresponding $q$-deformed super Schur polynomials and derive a novel expression for the $B{C}_N$ type of multivariate SRS polynomials as suitable linear combinations of the $q$-deformed super Schur polynomials. Such an expression for SRS polynomials leads to a complete classification of all energy levels appearing in the spectra of the $B{C}_N$ type of Polychronakos spin chains through the `branched’ motifs, which are characterized by some sequences of integers of the form $({\delta }_1,{\delta }_2,\mathrm{.}\mathrm{.}\mathrm{.},{\delta }_{N-1}\mathrm{\mid }l)$, where ${\delta }_i\in \{0,1\}$ and $l\in \{0,1,\mathrm{.}\mathrm{.}\mathrm{.},N\}$. Finally, we derive an extended boson-fermion duality relation among the restricted super Schur polynomials and show that the partition functions of the $B{C}_N$ type of Polychronakos spin chains also exhibit similar type of duality relation.