arXiv subjects

F. Minotti

Publications and source records attributed to F. Minotti.

13 recordsLinked to original sources

arXiv2026

Beyond minimal coupling for charged scalars? Modified electrodynamics and London-penetration tests

We discuss an effective modification of the electromagnetic coupling for charged scalar condensates. The motivation is not an inconsistency of standard scalar QED, but a semiclassical tension: for scalar fields the term linear in $A_\mu$ is not itself the conserved source current of the interacting theory, while for Dirac fields the usual interaction already has the form $-A_\mu J^\mu$ with an $A_\mu$-independent conserved current. We review this distinction, clarify the effective-theory status of the alternative coupling, and state explicitly the corresponding limitations: the framework is not proposed as a UV-complete replacement of gauge theory and standard Ward identities or scattering-theory results should not be expected to survive unchanged. We then focus on the condensed-matter consequence relevant to superconductors. For bosonic charged condensates the modified framework predicts a rescaled magnetic penetration depth, $\lambda_{\rm mag}=\lambda_L/\sqrt{2}$, while leaving the qualitative structure of AC electrodynamics and the type-I/type-II classification unchanged up to parameter mapping. Finally, we compare literature values of an ``optical'' penetration depth $\lambda_{\rm opt}$, inferred from optical/THz superfluid spectral weight, with independently determined magnetic lengths $\lambda_{\rm mag}$ for Nb, Pb, YBCO, MgB$_2$ and Ba(Fe,Co)$_2$As$_2$. The present data do not constitute a proof of the modified coupling, because sample, doping and disorder systematics remain important; nevertheless, Nb, optimally doped YBCO and Ba(Fe,Co)$_2$As$_2$ show the suggestive trend $\lambda_{\rm opt}>\lambda_{\rm mag}$, whereas MgB$_2$ is consistent with the standard result $\lambda_{\rm opt}\simeq\lambda_{\rm mag}$ and Pb is not a clean test because of strong nonlocal corrections.

physics.gen-ph↗

arXiv2026

Quantum collapse, local conservation of charge, and possible experimental consequences

We investigate the possibility that idealized quantum state-reduction processes may produce a local violation of charge conservation. If this occurs, the corresponding electromagnetic fields cannot be consistently described within Maxwell electrodynamics, and a natural alternative is provided by Aharonov-Bohm electrodynamics, which reduces to Maxwell theory when local charge conservation holds, but remains compatible with non-conserved sources. Within this framework we first analyze how state reduction may generate non-conserved local currents, including statistically compensated cases and biased tunnelling configurations with persistent average current. We then study the interaction of gauge waves with fermionic and bosonic quantum systems, the latter being described by a modified Schr\"odinger equation previously proposed for boson matter. As an application, we discuss the interaction of gauge waves with superconductors and show that they can effectively shield such waves. Finally, we present experimental proposals based on inverse-biased diodes and estimate the expected detector response.

physics.gen-ph↗

arXiv2026

Fluctuations in Aharonov-Bohm Electrodynamics

We consider the application of the Fluctuation Dissipation Theorem (FDT) to the electrodynamics of Aharonov-Bohm (ABE), which differs from Maxwell's in that it allows for local non-conservation of charge. For the case of a system of non-conserved charges at thermal equilibrium we obtain the same spectral distribution of energy of the electromagnetic field as in Maxwell electrodynamics. However, the electric field contribution to that energy doubles that in Maxwell case, while the magnetic contribution is the same as in Maxwell theory, the electric excess energy is compensated by a negative contribution arising form the Aharonov-Bohm (AB) scalar field. For a conductor with local non-conservation of charge described by the $\gamma$ model, we derive the spectrum of current correlation at first order in $\gamma$, which results in a violet noise contribution added to the classical Johnson-Nyquist white noise result for the voltage fluctuations in a conductor.

physics.gen-ph↗

arXiv2026

Scalar-tensor gravity and Aharonov-Bohm electrodynamics with bosons: applications to superconductors

We study a scalar-tensor extension of gravity with two scalar fields coupled to the Aharonov-Bohm extension of electrodynamics, where the scalar mode $S\equiv\partial_\mu A^\mu$ is dynamical. In this framework the trace of the electromagnetic energy-momentum tensor is nonvanishing and the scalar $S$ induces an electro-gravitational coupling that can be enhanced by the vacuum expectation value of the second gravitational scalar. For bosonic matter described by a macroscopic wavefunction (as in superconductors), the coupling to the electromagnetic potential generates $S$ already at the semiclassical level, implying sizable junction-induced discontinuities. Including the scalar-tensor sector yields a nonlinear system for $S$ and a gravitational scalar combination $\beta$ that admits a bulk saturation solution $S_{\rm sat}^2=(\Lambda\lambda_L^2)^{-1}$ and a corresponding threshold condition for macroscopic effects. We apply these results to pulsed discharges across normal-superconducting junctions and obtain scaling relations for the onset of anomalous gravitational signals in terms of current density, pulse duration, and superconducting volume, consistent with reported threshold behavior in two independent experimental configurations for a single microscopic parameter. We also present time-dependent propagating solutions in the weak-field regime and derive a class of one-dimensional traveling exact solutions of the nonlinear vacuum Einstein equations.

physics.gen-ph↗

arXiv2025

Generalized local charge conservation in many-body quantum mechanics

In the framework of the quantum theory of many-particle systems, we study the compatibility of approximated Non-Equilibrium Green Functions (NEGFs) and of approximated solutions of the Dyson equation with a modified continuity equation of the form $\partial_t \langle \rho \rangle+(1-\gamma)\nabla\cdot \langle\mathbf{J} \rangle=0$. A continuity equation of this kind allows the e.m.\ coupling of the system in the extended Aharonov-Bohm electrodynamics, but not in Maxwell electrodynamics. Focusing on the case of molecular junctions simulated numerically with the Density Functional Theory (DFT), we further discuss the re-definition of local current density proposed by Wang et al., which also turns out to be compatible with the extended Aharonov-Bohm electrodynamics.

physics.gen-ph↗

arXiv2025

Do we need an alternative to local gauge coupling to electromagnetic fields?

The local gauge coupling through the recipe $\partial_\mu \psi \to \partial_\mu \psi + iqA_\mu \psi$, that works so well with Dirac spinors in QED and in the gauge theories of the Standard Model, has a peculiarity when applied to scalar fields: it generates in the Lagrangian a coupling term $J_\mu A^\mu$ in which $J_\mu$ does not coincide with the conserved N\"other current associated to the global gauge symmetry. This is not an inconsistency, just a feature that appears when working out the locally gauge invariant action, and which ensures that the correct conserved current is the source of the gauge field. What would happen then if we were to assume for the scalar field the same coupling $J_\mu A^\mu$ through a conserved current which holds for spinor QED and classical electrodynamics? The consequence is that one is forced in that case to renounce to the principle of local gauge symmetry and must thus consider the electromagnetic (e.m.) field to be described by electrodynamic theories compatible with that lack of invariance, like the extended electrodynamics by Aharonov-Bohm. No differences with the usual theory appear for fermion systems when strict local charge conservation applies. In particular, if we consider the non-relativistic quantum theory as the low-energy limit of the relativistic theory, we would expect no modifications of Schr\"odinger equation when applied to fermion systems. However, when scalar boson systems are considered, like Cooper pairs quasi-particles in superconductors, in the new formulation the e.m.\ fields include a source, additional to the usual conserved four-current, and, besides, the corresponding Schr\"odinger equation acquires a new term, proportional to $\mathbf{A}^2$, which can lead to observable consequences, like ... (length limit reached, see PDF)

physics.gen-ph↗

arXiv2024

A new theory of tensor-scalar gravity coupled to Aharonov-Bohm electrodynamics

Tensor-scalar theories of gravitation are commonly employed as extensions of General Relativity that allow to describe a much wider phenomenology. They are also naturally generated as low energy limit of higher-dimensional or unified theories, and the gravitational scalar components can represent quantum corrections to the Einstein theory. The coupling of the scalars to an e.m. field does not introduce any relevant new physics if the e.m. action has the usual Maxwell form, implying a vanishing trace of the e.m. energy-momentum tensor. In the case of the extended Aharonov-Bohm electrodynamics some interesting new situations are possible, which in this work are analyzed in the gravitational weak-field approximation and for a basic version of tensor-scalar gravity involving only a Brans-Dicke field plus another scalar. Since the Aharonov-Bohm theory differs from Maxwell theory only in the presence of anomalous sources with local violation of charge conservation, which is thought to be possible only at a quantum level, the resulting formal framework can be useful to model interactions between gravitation and physical systems with macroscopic quantization. The theory contains some unknown parameters, the most important being the VEV $\psi_0$ of the second gravitational scalar and the level $\gamma$ of violation of local charge conservation in the e.m. sector. An attempt is done to relate these parameters to some experimental constraints. However, there is presently much space left for uncertainty.

physics.gen-ph↗

arXiv2024

Simple circuit and experimental proposal for the detection of gauge-waves

Aharonov-Bohm electrodynamics predicts the existence of traveling waves of pure potentials, with zero electromagnetic fields, denoted as gauge waves, or g-waves for short. In general, these waves cannot be shielded by matter since their lack of electromagnetic fields prevents the material from reacting to them. However, a not-locally-conserved electric current present in the material does interact with the potentials in the wave, giving the possibility of its detection. In [F.M., G.M., Eur.Phys.J. C 83, 1086 (2023)] the basic theoretical description of a detecting circuit was presented, based on a phenomenological theory of materials that can sustain not-locally-conserved electric currents. In the present work we discuss how that circuit can be built in practice, and used for the effective detection of g-waves.

physics.class-ph↗

arXiv2023

Gauge waves generation and detection in Aharonov-Bohm electrodynamics

The extended Aharonov-Bohm electrodynamics has a simple formal structure and allows to couple the e.m. field also to currents which are not locally conserved, like those resulting from certain non-local effective quantum models of condensed matter. As it often happens in physics and mathematics when one tries to extend the validity of some equations or operations, new perspectives emerge in comparison to Maxwell theory, and some ''exotic'' phenomena are predicted. For the Aharonov-Bohm theory the main new feature is that the potentials $A^\mu$ become univocally defined and can be measured with probes in which the ''extra-current'' $I=\partial_\mu j^\mu$ is not zero at some points. As a consequence, it is possible in principle to detect pure gauge-waves with $\mathbf{E}=\mathbf{B}=0$, which would be regarded as non-physical in the Maxwell gauge-invariant theory with local current conservation. We discuss in detail the theoretical aspects of this phenomenon and propose an experimental realization of the detectors. A full treatment of wave propagation in anomalous media with extra-currents and of energy-momentum balance issues is also given.

physics.gen-ph↗

arXiv2023

Aharonov-Bohm electrodynamics in material media: a scalar e.m. field cannot cause dissipation in a medium

In the extension of Maxwell equations based on the Aharonov-Bohm Lagrangian the e.m. field has an additional degree of freedom, namely a scalar field generated by charge and currents that are not locally conserved. We analyze the propagation of this scalar field through two different media (a pure dielectric and an ohmic conductor) in a range of frequencies such that the properties of the media are independent from the frequency. We find that an e.m. scalar wave cannot propagate in a material medium. If a scalar wave in vacuum impinges on a material medium it is reflected, at most exciting in the medium a pure "potential" wave (which we also call a "gauge" wave) propagating at $c$, the speed of light in vacuum, with a vector potential whose Fourier amplitude is related to that of the scalar potential by $\omega \mathbf{A}_{0}=\mathbf{k}\phi _{0}$, where $\omega^{2}=c^{2}\left\vert \mathbf{k}\right\vert^{2}$.

physics.class-ph↗

arXiv2021

Quantum uncertainty and energy flux in extended electrodynamics

In quantum theory, for a system with macroscopic wavefunction, the charge density and current density are represented by non-commuting operators. It follows that the anomaly $I=\partial_t \rho + \nabla \cdot \mathbf{j}$, being essentially a linear combination of these two operators in the frequency-momentum domain, does not admit eigenstates and has a minimum uncertainty fixed by the Heisenberg relation $\Delta N \Delta \phi \simeq 1$ which involves the occupation number and the phase of the wavefunction. We give an estimate of the minimum uncertainty in the case of a tunnel Josephson junction made of Nb. Due to this violation of the local conservation of charge, for the evaluation of the e.m. field generated by the system it is necessary to use the extended Aharonov-Bohm electrodynamics. After recalling its field equations, we compute in general form the energy-momentum tensor and the radiation power flux generated by a localized oscillating source. The physical requirements that the total flux be positive, negative or zero yield some conditions on the dipole moment of the anomaly $I$.

physics.gen-ph↗

arXiv2021

Are current discontinuities in molecular devices experimentally observable?

An ongoing debate in the first-principles description of conduction in molecular devices concerns the correct definition of current in the presence of non-local potentials. If the physical current density ${\bf j}=(-ie\hbar/2m)(\Psi^* \nabla \Psi- \Psi \nabla \Psi^*)$ is not locally conserved but can be re-adjusted by a non-local term, which current should be regarded as real? We prove that the extended Maxwell equations by Aharonov-Bohm give the e.m.\ field generated by such currents without any ambiguity. For an oscillating dipole we show that the radiated electrical field has a longitudinal component proportional to $ \omega \hat{P}$, where $\hat{P}$ is the anomalous moment $\int \hat{I}(\mathbf{x})\mathbf{x} d^3x$ and $\hat{I}$ is the space-dependent part of the anomaly $I=\partial_t \rho+\nabla \cdot \mathbf{j}$. In the case of a stationary current in a molecular device, a failure of local current conservation causes a "missing field" effect that can be experimentally observable, especially if its entity depends on the total current.

physics.gen-ph↗

arXiv2020

An application of a solar-type dynamo model for Epsilon Eridani

During the last decade, the relation between activity cycle periods with stellar parameters has received special attention. The construction of reliable registries of activity reveals that solar type stars exhibit activity cycles with periods from few years to decades and, in same cases, long and short activity cycles coexist suggesting that two dynamos could operate in these stars. In particular, Epsilon Eridani is an active young K2V star (0.8 Gyr), which exhibits a short and long-term chromospheric cycles of near 3 and 13-yr periods. Additionally, between 1985 and 1992, the star went through a broad activity minimum, similar to the solar Maunder Minimum-state. Motivated by these results, we found in Epsilon Eridani a great opportunity to test the dynamo theory. Based on the model developed in Sraibman & Minotti (2019), in this work we built a non linear axisymmetric dynamo for Epsilon Eridani. The time series of the simulated magnetic field components near the surface integrated in all the stellar disc exhibits both the long and short-activity cycles with periods similar to the ones detected from observations and also time intervals of low activity which could be associated to the broad Minimun. The short activity cycle associated to the magnetic reversal could be explained by the differential rotation, while the long cycle is associated to the meridional mass flows induced by the Lorentz force. In this way, we show that a single non-linear dynamo model derived from first principles with accurate stellar parameters could reproduce coexisting activity cycles.

astro-ph.SR↗