It is generally argued that if the wave-function in the de Broglie-Bohm theory is a physical field, it must be a field in configuration space. Nevertheless, it is possible to interpret the wave-function as a multi-field in three-dimensional space. This approach hasn't received the attention yet it really deserves. The aim of this paper is threefold: first, we show that the wave-function is naturally and straightforwardly construed as a multi-field; second, we show why this interpretation is superior to other interpretations discussed in the literature; third, we clarify common misconceptions.

In the recent literature, it has been shown that the wave function in the de Broglie-Bohm theory can be regarded as a new kind of field, i.e., a "multi-field", in three-dimensional space. In this paper, I argue that the natural framework for the multi-field is the original secondorder Bohm's theory. In this context, it is possible: i) to construe the multi-field as a real scalar field; ii) to explain the physical interaction between the multi-field and the Bohmian particles; and iii) to clarify the status of the energy-momentum conservation and the dynamics of the theory. Contents

This paper aims to clarify some conceptual aspects of decoherence that seem largely overlooked in the recent literature. In particular, I want to stress that decoherence theory, in the standard framework, is rather silent with respect to the description of (sub)systems and associated dynamics. Also, the selection of position basis for classical objects is more problematic than usually thought: while, on the one hand, decoherence offers a pragmatic-oriented solution to this problem, on the other hand, this can hardly be seen as a genuine ontological explanation of why the classical world is positionbased. This is not to say that decoherence is not useful to the foundations of quantum mechanics; on the contrary, it is a formidable weapon, as it accounts for a realistic description of quantum systems. That powerful description, however, becomes manifest when decoherence theory itself is interpreted in a realist framework of quantum mechanics.then the interaction eventually leads to the system-environment entangled state: 3' G(HFHB) I is the characteristic decoherence time of the model. As a result, the S-subsystem reduced density matrix is progressively diagonalized at a quadratic exponential rate. After very short time, 𝜌 7 will become (approximately) diagonal, and only relative components that describe well-defined states will "survive" the dynamical process (for example: only a well-defined alive cat and a well-defined dead cat): 53 Technical note: the coefficients of the entangled state superposition will generally be different from those of the initial S state superposition. However, this difference will not be relevant for the present discussion. 4 Strictly speaking, this is a density operator, while the density matrix is the density operator expressed in a particular basis (generally in the position basis). However, as this difference will not be relevant, I will just use the term density matrix in both cases. 5 The term 𝜀 in the off-diagonal components of the matrix stands for "negligible quantity": as the diagonalization process is mathematically described by a decreasing (quadratic) exponential, it will reach the zero value only asymptotically.

I argue that a particle ontology naturally emerges from the basic dynamical equations of non-relativistic quantum mechanics, when the quantum continuity equation is realistically interpreted. This was recognized by J.J. Sakurai in his famous textbook "Modern Quantum Mechanics", and then dismissed on the basis of the Heisenberg position-momentum uncertainty principle. In this paper, I show that the reasons of this rejection are based on a misunderstanding of the physical import of the uncertainty principle. As a consequence, a particle ontology can be derived from the quantum formalism without the need of additional ad hoc assumptions, and therefore it cannot be regarded as "extra-structure".

Article published in the special issue edited by A. Drezet: Pilot-wave and beyond: Louis de Broglie and David Bohm's quest for a quantum ontology, Foundations of Physics.The paper explains why the de Broglie-Bohm theory reduces to Newtonian mechanics in the macroscopic classical limit. The quantum-to-classical transition is based on three steps: (i) interaction with the environment produces effectively factorized states, leading to the formation of effective wave functions and hence decoherence; (ii) the effective wave functions selected by the environment-the pointer states of decoherence theory-will be well-localized wave packets, typically Gaussian states; (iii) the quantum potential of a Gaussian state becomes negligible under standard classicality conditions; therefore, the effective wave function will move according to Newtonian mechanics in the correct classical limit. As a result, a Bohmian system in interaction with the environment will be described by an effective Gaussian state and-when the system is macroscopic-it will move according to Newtonian mechanics.