arXiv subjects

S. Lo Franco

Publications and source records attributed to S. Lo Franco.

4 recordsLinked to original sources

arXiv2026

Quantum Big Bounce in Wheeler-DeWitt scattering theory: Ekpyrotic and LQC-like transitions

We present a rigorous description of the quantum dynamics of the closed isotropic Universe in the presence of an ekpyrotic-like scalar field, expressed in terms of relativistic quantum scatterings. Working in a covariant approach to the minisuperspace, we demonstrate the quantum equivalence between parametrizations in terms of the logarithmic scale factor and the volume variable. The analogy between the Wheeler-DeWitt equation and the Klein-Gordon equation, together with a proper definition of asymptotic states, allows us to construct a relativistic quantum-mechanical scattering framework. We describe the bouncing transitions a collapsing Universe undergoes when interacting with a Dirac delta potential, which represents the limit of an infinitely steep ekpyrotic potential. Two different transition channels can be distinguished depending on whether the relational time flow is preserved or not. We show that bouncing transitions cannot be neglected for highly delocalized states in coordinate space.

gr-qc↗

arXiv2026

Big-Bounce in Quantum f(R)-Cosmology: Polymer Dynamics with Internal Time

We construct the Hamiltonian formulation of the isotropic Universe in a generic metric f(R)-theory in the Jordan frame. We canonically quantize the Universe volume via a polymer formulation, and we adopt the scalar field naturally arising from this scenario as a physical clock. Being within the limit of cut-off values of the space volume, we are legitimized to neglect, at first approximation level, the self-interacting potential term associated with the scalar field. We first study the semi-classical polymer dynamics, outlining the emergence of a bouncing cosmology, both in the internal as well as in the synchronous time. In this latter time variable, we are also able to compare the obtained picture with that of a standard polymer Big-Bounce. We see that in the studied case, the collapsing and expanding branches are no longer symmetric with respect to the minimum volume configuration. Then, we fully quantize the system dynamics in the momentum representation, constructing a suitable dynamical Hilbert space and setting up the dynamics of localized wave packets. The mean value dynamics, both for the momentum and volume spaces, is characterized by a bouncing dynamics as described via the internal time, which closely resembles that one obtained in Loop Quantum Cosmology and Polymerization, respectively.

gr-qc↗

arXiv2025

Is the BKL map an intrinsic feature of the Quantum Mixmaster Universe?

We study the quantum Mixmaster dynamics by constructing the corresponding Wheeler-DeWitt equation as a relativistic quantum theory in a pseudo-Riemannian Mini-superspace. The transition amplitude from a Kasner regime to the next one is built via the standard S-matrix of a relativistic scattering, and mediated by a single wall potential. We provide a coherent and convincing representation of the original Misner's idea that quasi-classical states can survive arbitrarily close to the cosmological singularity. By constructing a complete set of states, we demonstrate that the quasi-classical BKL map is preserved by the resulting transition amplitude to a new state when their mean total momentum is high enough (exactly coinciding with Misner's high occupation numbers). This scheme is naturally iterated to the initial singularity without appreciable shape changes. We also clarify the role played by the state localization, and, in particular, we outline that when the incoming state is spread, the possibility of violating the Kasner map is no longer negligible. Thus, Kasner-like wave packets can approach the initial singularity.

gr-qc↗

arXiv2024

Quantum Big-Bounce as a phenomenology of RQM in the Mini-superspace

We investigate the emergence of a quantum Big-Bounce in the context of an isotropic Universe, filled by a self-interacting scalar field, which plays the role of a physical clock. The bouncing cosmology is the result of a scattering process, driven by the scalar field potential, which presence breaks down the frequency separation of the Wheeler-DeWitt equation, treated in strict analogy to a relativistic quantum system. Differently from previous analyses, we consider a really perturbative self-interaction potential, affecting the dynamics in a finite range of the time labeled by the scalar clock (and in particular we remove the divergent character previously allowed). The main result of the present analysis is that, when the Relativistic Quantum Mechanics formalism is properly implemented in the Mini-superspace analogy, the probability amplitude for the bounce is, both in the standard and polymerized case, characterized by a maximum in correspondence of the quasi-classical condition of a Universe minimum volume.

gr-qc↗