Quasi-Hermitian formulation of quantum mechanics using two conjugate Schrödinger equations

Abstract: In an amended version of non-Hermitian interaction picture we propose to work with the states $\psi(t)$ in a dyadic representation. The control of evolution via two conjugate Schr\"{o}diner equations then renders the usual necessity of the construction of the time-dependent inner-product-metric operator $\Theta(t)$ redundant. The primary information about dynamics is assumed carried by a non-Hamiltonian observable (say, $R(t)$). A specific realization of phase transitions is then rendered possible via the Kato's exceptional-point (EP) degeneracy of the eigenvalues of $R(t)$ at the EP time $t=t^{(EP)}$. For illustration a cosmological model is proposed mimicking the unitary-evolution birth of the Universe from an initial quantum Big Bang singularity.