Two Homomorphisms from the affine Yangian associated with $\widehat{\mathfrak{sl}}(n)$ to the affine Yangian associated with $\widehat{\mathfrak{sl}}(n+1)$

Abstract: We construct a homomorphism from the affine Yangian $Y_{\hbar,\varepsilon+\hbar}(\widehat{\mathfrak{sl}}(n))$ to the affine Yangian $Y_{\hbar,\varepsilon}(\widehat{\mathfrak{sl}}(n+1))$ which is different from the one in arXiv:2312.09933. By using this homomorphism, we give a homomorphism from $Y_{\hbar,\varepsilon}(\widehat{\mathfrak{sl}}(n))\otimes Y_{\hbar,\varepsilon+n\hbar}(\widehat{\mathfrak{sl}}(m))$ to $Y_{\hbar,\varepsilon}(\widehat{\mathfrak{sl}}(m+n))$. As an application, we construct a homomorphism from the affine Yangian $Y_{\hbar,\varepsilon+n\hbar}(\widehat{\mathfrak{sl}}(m))$ to the centralizer algebra of the pair of affine Lie algebras $(\widehat{\mathfrak{gl}}(m+n),\widehat{\mathfrak{gl}}(n))$ and the coset vertex algebra of the pair of rectangular $W$-algebras $(\mathcal{W}^k(\mathfrak{gl}(2m+2n),(2^{m+n})),\mathcal{W}^{k+m}(\mathfrak{sl}(2n),(2^{n})))$.