Quantum to Classical Transition of Inflationary Perturbations - Continuous Spontaneous Localization as a Possible Mechanism -

Abstract: The inflationary paradigm provides a mechanism to generate the primordial perturbations needed to explain the observed large scale structures in the universe. Inflation traces back all the inhomogeneities to quantum fluctuations although the structures look classical today. Squeezing of primordial quantum fluctuations along with the mechanism of decoherence accounts for many aspects of this quantum to classical transition, although it remains a matter of debate as to whether this is sufficient to explain the issue of realization of a single outcome (i.e. the issue of macro-objectification) from a quantum ensemble given that the universe is a closed system. A similar question of emergence of classical behavior of macroscopic objects exists also for laboratory systems and apart from decoherence there have been attempts to resolve this issue through Continuous Spontaneous Localization (CSL), which is a stochastic nonlinear modification of the non-relativistic Schr\"{o}dinger equation. Recently, Martin {\it et al.} have investigated whether a CSL-like mechanism with a constant strength parameter, when the Mukhanov-Sasaki variable is taken as the "collapse-operator", can explain how the primordial quantum perturbations generated during inflation become classical. Within the scope of their assumptions they essentially come to a negative conclusion. In the present work, we generalize their analysis by allowing the CSL strength parameter to depend on physical scales so as to capture the CSL amplification mechanism. We show that such a generalization provides a mechanism for macro-objectification (i.e. classicalization) of the inflationary quantum perturbations, while also preserving scale invariance of the power spectrum and phase coherence of super-horizon perturbation modes in a particular class of these models.