“…Existing results mostly rely on simulation (e.g., Zaglauer and Bauer, 2008;Deelstra and Rayée, 2013;Hieber et al, 2019, and many others). The case of a regime switching interest rate where the valuation can use Fourier techniques (e.g., Fan et al, 2015;Ignatieva et al, 2016;Hieber, 2017;Cui et al, 2017) or Erlangization techniques (e.g., Deelstra and Hieber, 2023) is analytically rather tractable. For the special case of two subperiods, Persson and Aase (1997) and Miltersen and Persson (1999) derive premiums in closed-form in a generalization of the Vasicek-Black-Scholes model.…”