I study the Fock representations for a Dirac field given by the the different choices of creation and annihilation variables. This is done in the context of a perturbed flat cosmology that, in addition, is minimally coupled to fermionic perturbations. In our description, I use a canonical formulation for the entire system, formed by the underlying cosmological spacetime and all its perturbations. I start with the family of vacua that allows a unitarily implementable quantum evolution that is employed in hybrid quantum cosmology. Then, its restriction to that lead to some finite ultraviolet backreaction in the quantum Hamiltonian constraint and to a fermionic Hamiltonian operator that is properly defined in the span of the n-particle/antiparticle states, in the context of hybrid quantum cosmology. The ultimate step comes with a completely diagonal quan- tum evolution, achieved by restricting our choice to an almost complete extent. I compare these results with the ones given by the so-called adiabatic scheme which was originally developed in the context of quantum field theory in fixed cosmological backgrounds, I find that all adiabatic states belong to the unitary equivalence class of Fock representations that allow a unitarily implementable quantum evolution. In particular, this unitarity of the dynamics ensures that the vacua defined with adiabatic initial conditions at different times are unitar- ily equivalent. Finally, all adiabatic orders other than zero allow the definition of annihilation and creation operators for the Dirac field with appropriate ultraviolet properties.
Proton-range verification is an important challenge in proton radiotherapy. Many methods have been proposed to reduce the uncertainty in the localization of the deposited dose with these treatments. The radio-induced thermoacoustic effect (i.e. the conversion of some of the deposited energy in a tissue into acoustic waves) can be used to measure the penetration depth of the proton beams in real-time. This method has significant advantages compared to other alternatives, as it requires a low-cost and small equipment, but it is challenging due to the intrinsic low signal-to-noise ratio (SNR) of the measured data and the complex propagation of the acoustic waves in heterogeneous media. In this work, we present several algorithms and regularization methods for protoacoustic image reconstruction, and evaluated which one is able to provide better image quality with very noisy data. We used simulated data of the deposited dose of a proton beam in a water tank, converted into an initial pressure-wave using the dose-acoustic equation, and then propagated the acoustic wave in the medium using the software k-Wave. We finally added zero-mean Gaussian noise to the resulting signal recorded by a transducer placed in the beam direction. Our results indicate that even with noisy data, both the gradient-descent and a adapted version of the MLEM algorithm, commonly used in other medical imaging techniques such as Positron Emission Tomography, can be used to successfully reconstruct the dose distribution. These promising results have to be validated with real data acquired in a proton-beam facility.
Chair: Sergio Pastor
We revisit Brans-Dicke type cosmologies. In the last years, this alternative has grown in popularity, because of the possibility it may explain cosmological data better than the current ΛCDM paradigm. Besides, as a difference from other scalar-tensor theories, we can assign a clear role to the variation of the scalar field through the cosmic history: a change in the effective Gravitational constant which, despite small, can affect the structure formation and reduce the H0 tension. In addition, if one tries to encapsulate the slow evolution of the BD-field in terms of the current GR paradigm (in which G remains constant), the effective theory that emerges is a variant of the ΛCDM framework in which ρΛ acquires a time-evolving component and plays the role of an effective dynamical vacuum energy density. The effective model, therefore, is not exactly the traditional ΛCDM but, when confronted with cosmological data, it has additional features that let it to be a possible good candidate for the new model of gravity that governs our cosmos
Chair: Sergio Pastor
Muography is emerging as an effective Non-Destructive Testing technique in the last years. Due to the high penetration power of cosmic muons and its natural and inexpensive origin, several companies are considering to apply it to the preventive maintenance of industrial equipment such as pipes and cauldrons. This contribution reviews the construction of a fully operative gas-based muon detector system and the development of algorithms including state-of-the-art machine learning techniques applied to the measurement of the degradation of the inner walls of an insulated pipe.
Chair: Sergio Pastor