Generating functions of dual K-theoretic P- and Q-functions and boson-fermion correspondence

In this paper, we present a new algebraic description of Ikeda-Naruse's $K$-theoretic Schur $P$- and $Q$-functions and their dual functions in terms of neutral fermion operators. We introduce four families of ``$β$-deformed neutral-fermion operators'' depending on a parameter $β$, which reduce to the usual neutral-fermion operators when $β$ is zero. Using these operators, we introduce two families of $β$-deformed vertex operators, power sums, and boson-fermion correspondences. From commutation relations among these operators, we naturally derive the $K$-theoretic Cauchy kernel of Nakagawa-Naruse. Exploiting this fact, we show that the four $K$-theoretic functions can be realized as vacuum expectation values of certain $β$-deformed fermionic operators. This presentation also allows us to derive generating functions for the dual $K$-theoretic $P$-and $Q$-functions, as conjectured by Nakagawa-Naruse.