Physics

14 pages, 667 KiB

Open AccessArticle

Hierarchically Coupled Ornstein–Uhlenbeck Processes for Transient Anomalous Diffusion

by Jingyang Wang and Nikolaos K. Voulgarakis

Physics 2024, 6(2), 645-658; https://doi.org/10.3390/physics6020042 (registering DOI) - 24 Apr 2024

Viewed by 215

The nonlinear dependence of the mean-squared displacement (MSD) on time is a common characteristic of particle transport in complex environments. Frequently, this anomalous behavior only occurs transiently before the particle reaches a terminal Fickian diffusion. This study shows that a system of hierarchically [...] Read more.

The nonlinear dependence of the mean-squared displacement (MSD) on time is a common characteristic of particle transport in complex environments. Frequently, this anomalous behavior only occurs transiently before the particle reaches a terminal Fickian diffusion. This study shows that a system of hierarchically coupled Ornstein–Uhlenbeck equations is able to describe both transient subdiffusion and transient superdiffusion dynamics, as well as their sequential combinations. To validate the model, five distinct experimental, molecular dynamics simulation, and theoretical studies are successfully described by the model. The comparison includes the transport of particles in random optical fields, supercooled liquids, bedrock, soft colloidal suspensions, and phonons in solids. The model’s broad applicability makes it a convenient tool for interpreting the MSD profiles of particles exhibiting transient anomalous diffusion. Full article

(This article belongs to the Section Statistical Physics and Nonlinear Phenomena)

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16 pages, 1731 KiB

Open AccessArticle

Statistical Mechanics of Social Hierarchies: A Mathematical Model for the Evolution of Human Societal Structures

by Nestor Caticha, Rafael S. Calsaverini and Renato Vicente

Physics 2024, 6(2), 629-644; https://doi.org/10.3390/physics6020041 - 19 Apr 2024

Viewed by 332

Abstract

Social structure may have changed from hierarchical to egalitarian and back along the evolutionary line of humans. Within the tradition of sociophysics, we construct a mathematical model of a society of agents subject to competing cognitive and social navigation constraints and predict, using [...] Read more.

Social structure may have changed from hierarchical to egalitarian and back along the evolutionary line of humans. Within the tradition of sociophysics, we construct a mathematical model of a society of agents subject to competing cognitive and social navigation constraints and predict, using statistical mechanics methods, that its degree of hierarchy decreases with encephalization and increases with group size, hence suggesting human societies were driven from hierarchical to egalitarian structures by the encephalization during the last few million years and back to hierarchical due to fast demographic changes during the Neolithic. In addition, applied to a different problem, the theory leads to the following predictions for modern pre-literary humans: (i) an intermediate hierarchy degree in mild climates. In harsher climates, societies will be (ii) more egalitarian if organized in small groups (of less than 100 persons) but (iii) more hierarchical if in larger (of more than 1000 persons) groups. The predicted bifurcation, characteristic of a phase transition, is also seen in the empirical cross-cultural record (248 cultures in the Ethnographic Atlas). Full article

(This article belongs to the Special Issue In Honor of Professor Serge Galam for His 70th Birthday and Forty Years of Sociophysics)

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16 pages, 622 KiB

Open AccessArticle

Casimir Energy in (2 + 1)-Dimensional Field Theories

by Manuel Asorey, Claudio Iuliano and Fernando Ezquerro

Physics 2024, 6(2), 613-628; https://doi.org/10.3390/physics6020040 - 17 Apr 2024

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Abstract

We explore the dependence of vacuum energy on the boundary conditions for massive scalar fields in (2 + 1)-dimensional spacetimes. We consider the simplest geometrical setup given by a two-dimensional space bounded by two homogeneous parallel wires in order to compare it with [...] Read more.

We explore the dependence of vacuum energy on the boundary conditions for massive scalar fields in (2 + 1)-dimensional spacetimes. We consider the simplest geometrical setup given by a two-dimensional space bounded by two homogeneous parallel wires in order to compare it with the non-perturbative behaviour of the Casimir energy for non-Abelian gauge theories in (2 + 1) dimensions. Our results show the existence of two types of boundary conditions which give rise to two different asymptotic exponential decay regimes of the Casimir energy at large distances. The two families are distinguished by the feature that the boundary conditions involve or not interrelations between the behaviour of the fields at the two boundaries. Non-perturbative numerical simulations and analytical arguments show such an exponential decay for Dirichlet boundary conditions of SU(2) gauge theories. The verification that this behaviour is modified for other types of boundary conditions requires further numerical work. Subdominant corrections in the low-temperature regime are very relevant for numerical simulations, and they are also analysed in this paper. Full article

(This article belongs to the Special Issue 75 Years of the Casimir Effect: Advances and Prospects)

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14 pages, 2315 KiB

Open AccessArticle

Critical Temperature and Critical Current Enhancement in Arrays of Josephson Junctions: A Ginzburg–Landau Perspective

by Elena Tomei, Riccardo Bizzi, Vittorio Merlo, Francesco Romeo, Gaetano Salina and Matteo Cirillo

Physics 2024, 6(2), 599-612; https://doi.org/10.3390/physics6020039 - 15 Apr 2024

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Abstract

The present investigation explores the spatial distribution of Cooper pair density in graph-shaped arrays of Josephson junctions using a Ginzburg–Landau approach. We specifically investigate double-comb structures and compare their properties with linear arrays as reference systems. Our findings reveal that the peculiar connectivity [...] Read more.

The present investigation explores the spatial distribution of Cooper pair density in graph-shaped arrays of Josephson junctions using a Ginzburg–Landau approach. We specifically investigate double-comb structures and compare their properties with linear arrays as reference systems. Our findings reveal that the peculiar connectivity of the double-comb structure leads to spatial gradients in the order parameter, which can be readily detected through measurements of Josephson critical currents. We present experimental results which indicate the specific dependence of the order parameter on the branches of the graphs and are evidence of the theoretical predictions. Full article

(This article belongs to the Special Issue Matter-Radiation Interactions—In Memory of Professor Francesco Saverio Persico)

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20 pages, 1593 KiB

Open AccessArticle

Ultrafast Resonant Photon Emission from a Molecule Driven by a Strong Coherent Field in Terms of Complex Spectral Analysis

by Maito Katayama, Satoshi Tanaka and Kazuki Kanki

Physics 2024, 6(2), 579-598; https://doi.org/10.3390/physics6020038 - 11 Apr 2024

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Abstract

In this study, we investigate the time–frequency-resolved resonant photon emission from a molecular vibrational oscillator driven by a monochromatic coherent external field. Using the complex spectral analysis of the Liouvillian, which integrates irreversible dissipative phenomena into quantum theory, we elucidate the fundamental processes [...] Read more.

In this study, we investigate the time–frequency-resolved resonant photon emission from a molecular vibrational oscillator driven by a monochromatic coherent external field. Using the complex spectral analysis of the Liouvillian, which integrates irreversible dissipative phenomena into quantum theory, we elucidate the fundamental processes of photon emission. Indeed, our analytical approach successfully decomposes the emission spectrum into two intrinsic contributions: one from a resonance eigenmode and another from continuous eigenmodes. These components are responsible for incoherent luminescence and coherent scattering photon emission processes, respectively. Our results show that while spontaneous emission dominates in the early stages of the emission process, coherent scattering gradually becomes more pronounced with time. Furthermore, destructive quantum interference between the two components plays a key role in determining the overall shape of the emission spectrum. Full article

(This article belongs to the Special Issue Matter-Radiation Interactions—In Memory of Professor Francesco Saverio Persico)

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11 pages, 404 KiB

Open AccessCommunication

Rectified Lorentz Force from Thermal Current Fluctuations

by Carsten Henkel

Physics 2024, 6(2), 568-578; https://doi.org/10.3390/physics6020037 - 09 Apr 2024

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Abstract

In a conducting medium held at finite temperature, free carriers perform Brownian motion and generate fluctuating electromagnetic fields. In this paper, an averaged Lorentz force density is computed that turns out to be nonzero in a thin subsurface layer, pointing towards the surface, [...] Read more.

In a conducting medium held at finite temperature, free carriers perform Brownian motion and generate fluctuating electromagnetic fields. In this paper, an averaged Lorentz force density is computed that turns out to be nonzero in a thin subsurface layer, pointing towards the surface, while it vanishes in the bulk. This is an elementary example of rectified fluctuations, similar to the Casimir force or radiative heat transport. The results obtained also provide an experimental way to distinguish between the Drude and so-called plasma models. Full article

(This article belongs to the Special Issue 75 Years of the Casimir Effect: Advances and Prospects)

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24 pages, 431 KiB

Open AccessArticle

Casimir Forces in CFT with Defects and Boundaries

by Philippe Brax and Sylvain Fichet

Physics 2024, 6(2), 544-567; https://doi.org/10.3390/physics6020036 - 09 Apr 2024

Cited by 1 | Viewed by 234

Abstract

We investigate the quantum forces occurring between the defects and/or boundaries of a conformal field theory (CFT). We propose to model imperfect defects and boundaries as localized relevant double-trace operators that deform the CFT. Our focus is on pointlike and codimension-one planar defects. [...] Read more.

We investigate the quantum forces occurring between the defects and/or boundaries of a conformal field theory (CFT). We propose to model imperfect defects and boundaries as localized relevant double-trace operators that deform the CFT. Our focus is on pointlike and codimension-one planar defects. In the case of two parallel membranes, we point out that the CFT 2-point function tends to get confined and develops a tower of resonances with a constant decay rate when the operator dimension approaches the free field dimension. Using a functional formalism, we compute the quantum forces induced by the CFT between a variety of configurations of pointlike defects, infinite plates and membranes. Consistency arguments imply that these quantum forces are attractive at any distance. Forces of the Casimir–Polder type appear in the UV (ultraviolet), while forces of the Casimir type appear in the IR (infrared), in which case the CFT gets repelled from the defects. Most of the forces behave as a non-integer power of the separation, controlled by the dimension of the double-trace deformation. In the Casimir regime of the membrane–membrane configuration, the quantum pressure behaves universally as

1 / ℓ^{d}

; however, information about the double-trace nature of the defects still remains encoded in the strength of the pressure. Full article

(This article belongs to the Special Issue 75 Years of the Casimir Effect: Advances and Prospects)

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15 pages, 4318 KiB

Open AccessArticle

Nanosecond-Laser-Induced Breakdown of Aqueous Colloidal Solutions of Dysprosium Nanoparticles: The Influence of Nanoparticle Concentration on the Breakdown Plasma and the Intensity of Physical and Chemical Processes

by Ilya V. Baimler, Alexey S. Baryshev, Anastasiya O. Dikovskaya, Viktor K. Chevokin, Oleg V. Uvarov, Maxim E. Astashev, Sergey V. Gudkov and Aleksander V. Simakin

Physics 2024, 6(2), 529-543; https://doi.org/10.3390/physics6020035 - 09 Apr 2024

Viewed by 248

Abstract

This paper studies the dynamics of the development of laser breakdown plasma in aqueous colloids of dysprosium nanoparticles by analyzing the time patterns of plasma images obtained using a high-speed streak camera. In addition, the distribution of plasma flashes in space and their [...] Read more.

This paper studies the dynamics of the development of laser breakdown plasma in aqueous colloids of dysprosium nanoparticles by analyzing the time patterns of plasma images obtained using a high-speed streak camera. In addition, the distribution of plasma flashes in space and their luminosity were studied, and the amplitude of acoustic signals and the rate of generation of new chemical products were studied depending on the concentration of dysprosium nanoparticles in the colloid. Laser breakdown was initiated by pulsed radiation from a nanosecond Nd:YAG laser. It is shown that the size of the plasma flash, the speed of motion of the plasma–liquid interface, and the lifetime of the plasma flash decrease with an increasing concentration of nanoparticles in the colloid. In this case, the time delay between the beginning of the laser pulse and the moment the plasma flash reaches its maximum intensity increases with increasing concentrations of nanoparticles. Varying the laser fluence in the range from 67 J/cm² to 134 J/cm² does not lead to noticeable changes in these parameters, due to the transition of the breakdown plasma to the critical regime. For dysprosium nanoparticles during laser breakdown of colloids, a decrease in the yield of hydrogen peroxide and an increase in the rate of formation of hydroxyl radicals per water molecule, characteristic of nanoparticles of rare earth metals, are observed, which may be due to the participation of nanoparticles and hydrogen peroxide in reactions similar to the Fenton and Haber–Weiss reactions. Full article

(This article belongs to the Section Applied Physics)

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14 pages, 443 KiB

Open AccessArticle

Aging in Some Opinion Formation Models: A Comparative Study

by Jaume Llabrés, Sara Oliver-Bonafoux, Celia Anteneodo and Raúl Toral

Physics 2024, 6(2), 515-528; https://doi.org/10.3390/physics6020034 - 08 Apr 2024

Cited by 1 | Viewed by 248

Abstract

Changes of mind can become less likely the longer an agent has adopted a given opinion state. This resilience or inertia to change has been called “aging”. We perform a comparative study of the effects of aging on the critical behavior of two [...] Read more.

Changes of mind can become less likely the longer an agent has adopted a given opinion state. This resilience or inertia to change has been called “aging”. We perform a comparative study of the effects of aging on the critical behavior of two standard opinion models with pairwise interactions. One of them is the voter model, which is a two-state model with a dynamic that proceeds via social contagion; another is the so-called kinetic exchange model, which allows a third (neutral) state, and its formed opinion depends on the previous opinions of both interacting agents. Furthermore, in the noisy version of both models, random opinion changes are also allowed, regardless of the interactions. Due to aging, the probability of changing diminishes with the age, and to take this into account, we consider algebraic and exponential kernels. We investigate the situation where aging acts only on pairwise interactions. Analytical predictions for the critical curves of the order parameters are obtained for the opinion dynamics on a complete graph, in good agreement with agent-based simulations. For both models considered, the consensus is optimized via an intermediate value of the parameter that rules the rate of decrease of the aging factor. Full article

(This article belongs to the Special Issue In Honor of Professor Serge Galam for His 70th Birthday and Forty Years of Sociophysics)

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19 pages, 412 KiB

Open AccessArticle

Casimir Interaction of Chern–Simons Layers on Substrates via Vacuum Stress Tensor

by Valery N. Marachevsky and Arseny A. Sidelnikov

Physics 2024, 6(2), 496-514; https://doi.org/10.3390/physics6020033 - 02 Apr 2024

Viewed by 408

Abstract

We develop a Green’s functions scattering method for systems with Chern–Simons plane boundary layers on dielectric half-spaces. The Casimir pressure is derived by evaluation of the stress tensor in a vacuum slit between two half-spaces. The sign of the Casimir pressure on a [...] Read more.

We develop a Green’s functions scattering method for systems with Chern–Simons plane boundary layers on dielectric half-spaces. The Casimir pressure is derived by evaluation of the stress tensor in a vacuum slit between two half-spaces. The sign of the Casimir pressure on a Chern–Simons plane layer separated by a vacuum slit from the Chern–Simons layer at the boundary of a dielectric half-space is analyzed for intrinsic

Si

and

{SiO}_{2}

glass substrates. Full article

(This article belongs to the Special Issue 75 Years of the Casimir Effect: Advances and Prospects)

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13 pages, 553 KiB

Open AccessArticle

Adiabatically Manipulated Systems Interacting with Spin Baths beyond the Rotating Wave Approximation

by Benedetto Militello and Anna Napoli

Physics 2024, 6(2), 483-495; https://doi.org/10.3390/physics6020032 - 28 Mar 2024

Viewed by 321

Abstract

The Stimulated Raman Adiabatic Passage (STIRAP) on a three-state system interacting with a spin bath is considered, focusing on the efficiency of the population transfer. Our analysis is based on the perturbation treatment of the interaction term evaluated beyond the Rotating Wave Approximation, [...] Read more.

The Stimulated Raman Adiabatic Passage (STIRAP) on a three-state system interacting with a spin bath is considered, focusing on the efficiency of the population transfer. Our analysis is based on the perturbation treatment of the interaction term evaluated beyond the Rotating Wave Approximation, thus focusing on the limit of weak system–bath coupling. The analytical expression of the correction to the efficiency and the consequent numerical analysis show that, in most of the cases, the effects of the environment are negligible, confirming the robustness of the population transfer. Full article

(This article belongs to the Special Issue Matter-Radiation Interactions—In Memory of Professor Francesco Saverio Persico)

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15 pages, 344 KiB

Open AccessArticle

A Theory of Best Choice Selection through Objective Arguments Grounded in Linear Response Theory Concepts

by Marcel Ausloos, Giulia Rotundo and Roy Cerqueti

Physics 2024, 6(2), 468-482; https://doi.org/10.3390/physics6020031 - 27 Mar 2024

Viewed by 423

Abstract

In this study, we propose how to use objective arguments grounded in statistical mechanics concepts in order to obtain a single number, obtained after aggregation, which would allow for the ranking of “agents”, “opinions”, etc., all defined in a very broad sense. We [...] Read more.

In this study, we propose how to use objective arguments grounded in statistical mechanics concepts in order to obtain a single number, obtained after aggregation, which would allow for the ranking of “agents”, “opinions”, etc., all defined in a very broad sense. We aim toward any process which should a priori demand or lead to some consensus in order to attain the presumably best choice among many possibilities. In order to specify the framework, we discuss previous attempts, recalling trivial means of scores—weighted or not—Condorcet paradox, TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), etc. We demonstrate, through geometrical arguments on a toy example and with four criteria, that the pre-selected order of criteria in previous attempts makes a difference in the final result. However, it might be unjustified. Thus, we base our “best choice theory” on the linear response theory in statistical physics: we indicate that one should be calculating correlations functions between all possible choice evaluations, thereby avoiding an arbitrarily ordered set of criteria. We justify the point through an example with six possible criteria. Applications in many fields are suggested. Furthermore, two toy models, serving as practical examples and illustrative arguments are discussed. Full article

(This article belongs to the Special Issue In Honor of Professor Serge Galam for His 70th Birthday and Forty Years of Sociophysics)

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Physics, Volume 6, Issue 2 (June 2024) – 12 articles

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