Subregion spectrum form factor via pseudoentropy

We introduce a subsystem generalization of the spectral form factor via pseudo entropy, von-Neumann entropy for reduced transition matrix. consider matrix between thermofield double state and its time-evolved in two-dimensional conformal field theories, study time-dependence single interval. show that real part behaves similarly to factor; it starts from thermal initially drops minimum, then increasing, finally approaches vacuum entanglement entropy. also theory-dependence behavior by considering theories on compact space.