arXiv subjects

Roberto Onofrio

Publications and source records attributed to Roberto Onofrio.

At least 19 recordsLinked to original sources

arXiv2026

Maximization of nuclear fusion reactivity via optimal energy distributions

We investigate the optimization of nuclear fusion reactivity relative to the choice of energy probability distribution. A single Maxwell-Boltzmann (MB) distribution is found to be optimal in the region where reactivity is a concave function of the average available kinetic energy, specifically near the reactivity peak. Conversely, in regions where the reactivity curve is convex, optimization is achieved through a bimodal MB distribution. We then discuss our results in the context of three classes of generalized energy distributions (superstatistics), which are modeled as a continuum of MB distributions. As expected, in all cases examined, the reactivity gains provided by superstatistics are bounded by the proposed optimal distribution. Finally, we apply these findings to deuterium-deuterium and deuterium-tritium fusion processes using empirical parametrizations of their respective cross sections. For both reactions, employing optimal bimodal MB distributions at low average energies-of particular interest for magnetically confined plasmas-yields a reactivity enhancement of approximately a factor of 2.

physics.plasm-ph↗

arXiv2026

Generation of non-Maxwell-Boltzmann energy distributions during thermalization of interacting baths

We report on numerical experiments of thermalization between two reservoirs in which interspecies interactions are mediated via a Hamiltonian with a Gaussian dependence upon the distance between the particles. By using relatively high statistics, we are able to study deviations from the initially imprinted Maxwell-Boltzmann energy distributions as a function of the range and strength of the interaction, as well as the parameters of the two baths such as masses, trapping frequencies, that strongly affect the spatial overlap of the two species. At large interaction strengths and for any range, deviations are attributable to the sudden conversion of latent interaction energy into kinetic energy of the particles. In addition, long range interactions generate deviations even for interaction strengths in the weak regime, and non-uniform confinement introduces a further source of deviation from the Maxwell-Boltzmann energy distribution. This latter results in transient two temperature Maxwell-Boltzmann distributions suggestive of an inverse cascading route from inter-particle dynamics to thermalization. In the weakly-interacting regime, a simple expression for the equilibrium temperature is also obtained and discussed. These findings may be of relevance in the dynamics of exothermic chemical reactions, in the physics of ultracold atomic mixtures, and in self-sustained burning plasmas.

physics.plasm-ph↗

arXiv2026

Dynamics of thermalization in classical three-dimensional many-body systems: Non-Maxwellian distributions and the role of anisotropic trapping

The physics of interacting baths is of interest in a variety of contexts, ranging from ultracold atoms to ionized gases. While many features can already be captured in a one-dimensional model, others are specific to the situation of two or three-dimensional systems. In this paper, we focus on three-dimensional features of a model for thermalization between two baths that we have explored in earlier publications. In contrast to the one-dimensional situation we show that, en route to thermalization, deviations from the Maxwell-Boltzmann energy distributions more akin to $κ$-distributions are observed. In three dimensions, these can be seen in changes at the peak of the distribution, which is precluded by the expected monotonic behavior of the energy distributions in one dimension. Furthermore, we consider thermalization for anisotropic trapping and explore its role in the onset of anomalous scaling with respect to the particle number. These results may be pertinent to the understanding of the interplay between turbulent behavior and nonlinearities for a variety of many-body classical systems.

physics.plasm-ph↗

arXiv2025

Testing the weak equivalence principle for nonclassical matter with torsion balances

We propose tests of the weak equivalence principle (WEP) using a torsion balance, in which superposition of energy eigenstates are created in a controllable way for the test masses. After general considerations on the significance of tests of the WEP using quantum states and the need for considering inertial and gravitational masses as operators, we develop a model to derive the matrix elements of the free-fall operator, showing that the variance of the acceleration operator, in addition to its mean, enables estimation of violations of the WEP due to quantum coherence in a way that is robust with respect to shot-to-shot fluctuations. Building on this analysis, we demonstrate how the validity of the WEP may be tested in a torsion balance setup, by accessing the mean and variance of a torque operator we introduce and quantize. Due to the long acquisition times of the signal as compared to the timescale on which coherent superposition states may survive, we further propose a dynamical setting, where the torsion balance is subject to a time-dependent gravitational field, and measurements of angular acceleration encode possible violations of the WEP.

quant-ph↗

arXiv2024

Enhancement of fusion reactivities using non-Maxwellian energy distributions

We discuss conditions for the enhancement of fusion reactivities arising from different choices of energy distribution functions for the reactants. The key element for potential gains in fusion reactivity is identified in the functional dependence of the tunnellng coefficient upon the energy, ensuring the existence of a finite range of temperatures for which reactivity of fusion processes is boosted with respect to the Maxwellian case. This is shown, using a convenient parameterization of the tunneling coefficient dependence upon the energy, analytically in the simplified case of a bimodal Maxwell-Boltzmann distribution, and numerically for kappa-distributions. We then consider tunneling potentials progressively better approximating fusion processes, and evaluate in each case the average reactivity in the case of kappa-distributions.

physics.plasm-ph↗

arXiv2024

State dependence of tunneling processes and thermonuclear fusion

We discuss the sensitivity of tunneling processes to the initial preparation of the quantum state. We compare the case of Gaussian wave packets of different positional variances using a generalised Woods-Saxon potential for which analytical expressions of the tunneling coefficients are available. Using realistic parameters for barrier potentials we find that the usual plane wave approximation underestimates fusion reactivities by an order of magnitude in a range of temperatures of practical relevance for controlled energy production.

quant-ph↗

arXiv2024

Bounds to strong gravity from electron-positron annihilations near threshold

We discuss bounds to strong gravity arising from annihilation of electron and positrons and the corresponding enhancement of the cross section for the production of massive particles. Two complementary examples are discussed, the case of the $e^+e^- \to W^+ W^-$ processes, with maximum mass and short lifetime for the particle pairs in the final state, and the case of electron positron annihilation into heavier charged lepton pairs, $e^+ e^- \to μ^+ μ^-$ and $e^+ e^- \to τ^+ τ^-$. These bounds may be improved by the next generation of electron-positron colliders, and are complementary to bounds arising from direct graviton searches.

hep-ph↗

arXiv2022

Relationship between nonlinearities and thermalization in classical open systems: The role of the interaction range

We discuss results on the dynamics of thermalization for a model with Gaussian interactions between two classical many-body systems trapped in external harmonic potentials. Previous work showed an approximate, power-law scaling of the interaction energy with the number of particles, with particular focus on the dependence of the anomalous exponent on the interaction strength. Here we explore the role of the interaction range in determining anomalous exponents, showing that it is a more relevant parameter to differentiate distinct regimes of responses of the system. More specifically, on varying the interaction range from its largest values while keeping the interaction strength constant, we observe a crossover from an integrable system, approximating the Caldeira-Leggett interaction term in the long range limit, to an intermediate interaction range in which the system manifests anomalous scaling, and finally to a regime of local interactions in which anomalous scaling disappears. A Fourier analysis of the interaction energy shows that nonlinearities give rise to an effective bath with a broad band of frequencies, even when starting with only two distinct trapping frequencies, yielding efficient thermalization in the intermediate regime of interaction range. We provide qualitative arguments, based on an analogous Fourier analysis of the standard map, supporting the view that anomalous scaling and features of the Fourier spectrum may be used as proxies to identify the role of chaotic dynamics. Our work, that encompasses models developed in different contexts and unifies them in a common framework, may be relevant to the general understanding of the role of nonlinearities in a variety of many-body classical systems, ranging from plasmas to trapped atoms and ions.

cond-mat.stat-mech↗

arXiv2021

Bounds on charged-lepton flavor violations via resonant scattering

We explore the possibility of probing flavor violations in the charged-lepton sector by means of high-luminosity lepton-photon and electron-muon collisions, by inverting initial and final states in a variety of decay channels presently used to bound such violations. In particular, we analyse the resonant lepton, $γ\, \ell \to \ell^{\prime}$, and neutral-meson, $e^- μ^+ \to ϕ,η,π^0\!$, scattering channels, whose cross sections are critically dependent on the colliding-beams energy spread, being particularly demanding in the case of leptonic processes. For these processes, we compute upper bounds to the cross-section corresponding to present limits on the inverse decay channel rates. In order to circumvent the beam energy spread limitations we extend the analysis to processes in which a photon accompanies the resonance in the final state, compensating the off-shellness effects by radiative return. These processes might be studied at future facilities with moderate energies, in case lepton-photon and electron-muon collisions with sufficiently high luminosity will be available.

hep-ph↗

arXiv2020

Non-Maxwellian rate coefficients for electron and ion collisions in Rydberg plasmas: implications for excitation and ionization

Scattering phenomena between charged particles and highly excited Rydberg atoms are of critical importance in many processes in plasma physics and astrophysics. While a Maxwell-Boltzmann (MB) energy distribution for the charged particles is often assumed for calculations of collisional rate coefficients, in this contribution we relax this assumption and use two different energy distributions, a bimodal MB distribution and a $κ$-distribution. Both variants share a high-energy tails occurring with higher probability than the corresponding MB distribution. The high energy tail may significantly affect rate coefficients for various processes. We focus the analysis to specific situations by showing the dependence of the rate coefficients on the principal quantum number of hydrogen atoms in n-changing collisions with electrons in the excitation and ionization channels and in a temperature range relevant to the divertor region of a tokamak device. We finally discuss the implications for diagnostics of laboratory plasmas.

physics.plasm-ph↗

arXiv2020

Black hole production at lepton colliders

Production of black holes has been discussed in a variety of extensions of the Standard Model, and related bounds have been established from data taken at the Large Hadron Collider. We show that, if the Higgs particle has a fully gravitational content via the equivalence principle, enhanced cross-sections of black holes at colliders should be expected within the Standard Model itself. The case of black hole production by precision measurements at electron colliders is discussed. The Coulomb repulsion strongly suppresses the related cross-section with respect to the one based on the hoop conjecture, making the possible production of black holes still unfeasible with current beam technology. At the same time, this suggests the reanalysis of the bounds, based on the hoop conjecture, already determined in hadronic collisions for extra-dimensional models.

hep-ph↗

arXiv2019

Concepts for a deuterium-deuterium fusion reactor

We revisit the assumption that reactors based on deuterium-deuterium (D-D) fusion processes have to be necessarily developed after the successful completion of experiments and demonstrations for deuterium-tritium (D-T) fusion reactors. Two possible mechanisms for enhancing the reactivity are discussed. Hard tails in the energy distribution of the nuclei, through the so-called kappa-distribution, allow to boost the number of energetic nuclei available for fusion reactions. At higher temperatures than usually considered in D-T plasmas, vacuum polarization effects from real $e^+e^-$ and $μ^+μ^-$ pairs may provide further speed-up due to their contribution to screening of the Coulomb barrier. Furthermore, the energy collection system can benefit from the absence of the lithium blanket, both in simplicity and compactness. The usual thermal cycle can be bypassed with comparable efficiency levels using hadronic calorimetry and third-generation photovoltaic cells, possibly allowing to extend the use of fusion reactors to broader contexts, most notably maritime transport.

physics.plasm-ph↗

arXiv2019

Scaling laws for harmonically trapped two-species mixtures at thermal equilibrium

We discuss the scaling of the interaction energy with particle numbers for a harmonically trapped two-species mixture at thermal equilibrium experiencing interactions of arbitrary strength and range. In the limit of long-range interactions and weak coupling, we recover known results for the integrable Caldeira-Leggett model in the classical limit. In the case of short-range interactions and for a balanced mixture, numerical simulations show scaling laws with exponents that depend on the interaction strength, its attractive or repulsive nature, and the dimensionality of the system. Simple analytic considerations based on equilibrium statistical mechanics and small interspecies coupling quantitatively recover the numerical results. The dependence of the scaling on interaction strength helps to identify a threshold between two distinct regimes. Our thermalization model covers both local and extended interactions allowing for interpolation between different systems such as fully ionized gases and neutral atoms, as well as parameters describing integrable and chaotic dynamics.

cond-mat.stat-mech↗

arXiv2017

A proposal for a quantitative indicator of original research output

The use of quantitative indicators of scientific productivity seems now quite widespread for assessing researchers and research institutions. There is a general perception, however, that these indicators are not necessarily representative of the originality of the research carried out, being primarily indicative of a more or less prolific scientific activity and of the size of the targeted scientific subcommunity. We first discuss some of the drawbacks of the broadly adopted $h$-index and of the fact that it represents, in an average sense, an indicator derivable from the total number of citations. Then we propose an indicator which, although not immune from biases, seems more in line with the general expectations for quantifying what is typically considered original work. Qualitative arguments on how different indicators may shape the future of science are finally discussed.

physics.soc-ph↗

arXiv2017

Cooling and thermometry of atomic Fermi gases

We review the status of cooling techniques aimed at achieving the deepest quantum degeneracy for atomic Fermi gases. We first discuss some physical motivations, providing a quantitative assessment of the need for deep quantum degeneracy in relevant physics cases, such as the search for unconventional superfluid states. Attention is then focused on the most widespread technique to reach deep quantum degeneracy for Fermi systems, sympathetic cooling of Bose-Fermi mixtures, organizing the discussion according to the specific species involved. Various proposals to circumvent some of the limitations on achieving the deepest Fermi degeneracy, and their experimental realizations, are then reviewed. Finally, we discuss the extension of these techniques to optical lattices and the implementation of precision thermometry crucial to the understanding of the phase diagram of classical and quantum phase transitions in Fermi gases.

cond-mat.quant-gas↗

arXiv2017

Simulating sympathetic cooling of atomic mixtures in nonlinear traps

We discuss the dynamics of sympathetic cooling of atomic mixtures in realistic, nonlinear trapping potentials using a microscopic effective model developed earlier for harmonic traps. We contrast the effectiveness of different atomic traps, such as Ioffe-Pritchard magnetic traps and optical dipole traps, and the role their intrinsic nonlinearity plays in speeding up or slowing down thermalization between the two atomic species. This discussion includes cases of configurations with lower effective dimensionality. From a more theoretical standpoint, our results provide the first exploration of a generalized Caldeira-Leggett model with nonlinearities both in the trapping potential as well as in the interspecies interactions, and no limitations on their coupling strength.

cond-mat.quant-gas↗

arXiv2017

Universal and anomalous behavior in the thermalization of strongly interacting harmonically trapped gas mixtures

We report on the dynamics of thermalization by extending a generalization of the Caldeira-Leggett model, developed in the context of cold atomic gases confined in a harmonic trap, to higher dimensions. Universal characteristics en route to thermalization which appear to be independent of dimensionality are highlighted, which additionally suggest a scaling analogous to turbulent mixing in fluid dynamics. We then focus on features dependent on dimensionality, with particular regard to the role of angular momentum of the two atomic clouds, having in mind the goal of efficient thermalization between the two species. Finally, by considering asymmetry in species numbers, we find that nonlinear inter-species interactions provide a mode locking mechanism between the majority and minority species, relevant to recent experiments involving Fermi-Bose mixtures in the normal phase.

cond-mat.stat-mech↗

arXiv2016

All-optical cooling of Fermi gases via Pauli inhibition of spontaneous emission

A technique is proposed to cool Fermi gases to the regime of quantum degeneracy based on the expected inhibition of spontaneous emission due to the Pauli principle. The reduction of the linewidth for spontaneous emission originates a corresponding reduction of the Doppler temperature, which under specific conditions may give rise to a runaway process through which fermions are progressively cooled. The approach requires a combination of a magneto-optical trap as a cooling system and an optical dipole trap to enhance quantum degeneracy. This results in expected Fermi degeneracy factors $T/T_F$ comparable to the lowest values recently achieved, with potential for a direct implementation in optical lattices. The experimental demonstration of this technique should also indirectly provide a macroscopic manifestation of the Pauli exclusion principle at the atomic physics level.

cond-mat.quant-gas↗