Speaker
Description
Quench is an abrupt change in a system's parameters. In the quantum context, it can be viewed as a perturbation of the initial state of a quantum field theory relative to a known density matrix, such as that for the vacuum state or a finite-temperature state. Within the framework of the inflationary model of the early universe, a quantum quench can be used to study the system's evolution following a sudden transition during inflation, whose characteristic timescale is much shorter than that of all other processes. As an example, we consider a scalar quantum field theory in de Sitter space to model inflation, examining the expanding Poincaré patch and global de Sitter separately; the latter is characterized by an initial contracting phase. In this setting, we investigate and compare the evolution of the two-point correlator following two types of global quench: first, through an explicit, abrupt change of the scalar field's mass $M\rightarrow m$, and second, via a strong perturbation of the equilibrium density matrix $\widehat{\rho}_0$ by the action of a quench operator $\widehat{Q}$ as $\widehat{\rho} = \widehat{Q}^{\dagger}\widehat{\rho}_0 \widehat{Q}$. The first approach is well-studied in the literature for flat space-time, with several works also existing in a cosmological context. For the second case, the problem of determining the evolution is solved for a specific class of states known as Calabrese-Cardy states. We describe a new class of states where the operator $\widehat{Q}$ inserts, at a specific time $t_0$, an operator polynomial in the scalar field operator $\widehat{\phi}$ into the system's Hamiltonian. We explain how to find the evolution of correlators for such operators using the non-equilibrium Keldysh functional integral formalism. Furthermore, using the simplest example of inserting a quadratic operator, we compare the results for different types of quantum quenches in de Sitter space.
