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Physics, Volume 6, Issue 2 (June 2024) – 26 articles

Cover Story (view full-size image): The phenomenon of laser-induced breakdown in colloids of nanoparticles forms the basis for widely used methods of synthesizing and modifying nanoparticles. The effect of various physical factors has been well researched both on the processes that characterize the laser breakdown of solutions themselves and on the final properties of nanoparticles formed. However, the impact of the concentration of nanoparticles within the irradiated solution remains unclear in terms of both the characteristics of individual breakdown and the dynamics of plasma generation. Therefore, the aim of this study is to investigate the high-speed processes of plasma formation during irradiation of dysprosium nanoparticle colloids and to study how the concentration of nanoparticles and energy density of laser radiation influence these processes. View this paper
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16 pages, 331 KiB  
Article
Dressing the Lorentz Atom
by Stephen M. Barnett, James D. Cresser and Sarah Croke
Physics 2024, 6(2), 905-920; https://doi.org/10.3390/physics6020056 - 20 Jun 2024
Viewed by 808
Abstract
We investigate the effects of the electromagnetic vacuum field on a harmonically bound electron. We show that in the electric-dipole approximation the model atom couples only to an effective one-dimensional electric field. In a simplified form, in which the problem is reduced to [...] Read more.
We investigate the effects of the electromagnetic vacuum field on a harmonically bound electron. We show that in the electric-dipole approximation the model atom couples only to an effective one-dimensional electric field. In a simplified form, in which the problem is reduced to a single spatial dimension, we determine, analytically, the form of the ground state and discuss the significance of this state. Full article
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14 pages, 3805 KiB  
Review
A Brief Review of Some Recent Precision Casimir Force Measurements
by Madhav Dhital and Umar Mohideen
Physics 2024, 6(2), 891-904; https://doi.org/10.3390/physics6020055 - 13 Jun 2024
Cited by 1 | Viewed by 1177
Abstract
Here, we review recent advances in precision Casimir force measurements with both non-magnetic and magnetic materials. In addition, the measurement of the geometric dependence of the Casimir force, both lateral and normal, using uniformly corrugated surfaces is briefly presented. Finally, the measurement of [...] Read more.
Here, we review recent advances in precision Casimir force measurements with both non-magnetic and magnetic materials. In addition, the measurement of the geometric dependence of the Casimir force, both lateral and normal, using uniformly corrugated surfaces is briefly presented. Finally, the measurement of the thermal Casimir force in graphene is discussed. Full article
(This article belongs to the Special Issue 75 Years of the Casimir Effect: Advances and Prospects)
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14 pages, 1690 KiB  
Article
Present Status of Spectroscopy of the Hyperfine Structure and Repolarization of Muonic Helium Atoms at J-PARC
by Seiso Fukumura, Patrick Strasser, Mahiro Fushihara, Yu Goto, Takashi Ino, Ryoto Iwai, Sohtaro Kanda, Shiori Kawamura, Masaaki Kitaguchi, Shoichiro Nishimura, Takayuki Oku, Takuya Okudaira, Hirohiko M. Shimizu, Koichiro Shimomura, Hiroki Tada and Hiroyuki A. Torii
Physics 2024, 6(2), 877-890; https://doi.org/10.3390/physics6020054 - 12 Jun 2024
Viewed by 996
Abstract
The mass mμ of the negative muon is one of the parameters of the elementary particle Standard Model and it allows us to verify the CPT (charge–parity–time) symmetry theorem by comparing mμ value with the mass mμ+ [...] Read more.
The mass mμ of the negative muon is one of the parameters of the elementary particle Standard Model and it allows us to verify the CPT (charge–parity–time) symmetry theorem by comparing mμ value with the mass mμ+ of the positive muon. However, the experimental determination precision of mμ is 3.1ppm, which is an order of magnitude lower than the determination precision of mμ+ at 120ppb. The authors aim to determine mμ and the magnetic moment μμ with a precision of O(10ppb) through spectroscopy of the hyperfine structure (HFS) of muonic helium-4 atom (4Heμe) under high magnetic fields. He4μe is an exotic atom where one of the two electrons of the He4 atom is replaced by a negative muon. To achieve the goal, it is necessary to determine the HFS of He4μe with a precision of O(1ppb). This paper describes the determination procedure of the HFS of He4μe in weak magnetic fields reported recently, and the work towards achieving the goal of higher precision measurement. Full article
(This article belongs to the Special Issue Precision Physics and Fundamental Physical Constants (FFK 2023))
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18 pages, 599 KiB  
Article
Fake News: “No Ban, No Spread—With Sequestration”
by Serge Galam
Physics 2024, 6(2), 859-876; https://doi.org/10.3390/physics6020053 - 6 Jun 2024
Cited by 3 | Viewed by 1635
Abstract
To curb the spread of fake news, I propose an alternative to the current trend of implementing coercive measures. This approach would preserve freedom of speech while neutralizing the social impact of fake news. The proposal relies on creating an environment to naturally [...] Read more.
To curb the spread of fake news, I propose an alternative to the current trend of implementing coercive measures. This approach would preserve freedom of speech while neutralizing the social impact of fake news. The proposal relies on creating an environment to naturally sequestrate fake news within quite small networks of people. I illustrate the process using a stylized model of opinion dynamics. In particular, I explore the effect of a simultaneous activation of prejudice tie breaking and contrarian behavior, on the spread of fake news. The results show that indeed most pieces of fake news do not propagate beyond quite small groups of people and thus pose no global threat. However, some peculiar sets of parameters are found to boost fake news so that it “naturally” invades an entire community with no resistance, even if initially shared by only a handful of agents. These findings identify the modifications of the parameters required to reverse the boosting effect into a sequestration effect by an appropriate reshaping of the social geometry of the opinion dynamics landscape. Then, all fake news items become “naturally” trapped inside limited networks of people. No prohibition is required. The next significant challenge is implementing this groundbreaking scheme within social media. Full article
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14 pages, 1844 KiB  
Review
Avogadro and Planck Constants, Two Pillars of the International System of Units
by Enrico Massa
Physics 2024, 6(2), 845-858; https://doi.org/10.3390/physics6020052 - 3 Jun 2024
Viewed by 1373
Abstract
The International System of Units (SI), the current form of the metric system and the world’s most used system of units, has been continuously updated and refined since the Metre Convention of 1875 to ensure that it remains up to date with the [...] Read more.
The International System of Units (SI), the current form of the metric system and the world’s most used system of units, has been continuously updated and refined since the Metre Convention of 1875 to ensure that it remains up to date with the latest scientific and technological advances. The General Conference on Weights and Measures, at its 26th meeting in 2018, decided to adopt stipulated values of seven physical constants linked to seven measurement units (the second, meter, kilogram, ampere, kelvin, mole, and candela). This paper reviews the technologies developed, in intense and long-standing work, to determine the Avogadro and Planck constants, which are now integral to realising the kilogram. Full article
(This article belongs to the Special Issue Precision Physics and Fundamental Physical Constants (FFK 2023))
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17 pages, 3657 KiB  
Article
Swirling Capillary Instability of Rivlin–Ericksen Liquid with Heat Transfer and Axial Electric Field
by Dhananjay Yadav, Mukesh Kumar Awasthi, Ashwani Kumar and Nitesh Dutt
Physics 2024, 6(2), 828-844; https://doi.org/10.3390/physics6020051 - 3 Jun 2024
Cited by 1 | Viewed by 993
Abstract
The mutual influences of the electric field, rotation, and heat transmission find applications in controlled drug delivery systems, precise microfluidic manipulation, and advanced materials’ processing techniques due to their ability to tailor fluid behavior and surface morphology with enhanced precision and efficiency. Capillary [...] Read more.
The mutual influences of the electric field, rotation, and heat transmission find applications in controlled drug delivery systems, precise microfluidic manipulation, and advanced materials’ processing techniques due to their ability to tailor fluid behavior and surface morphology with enhanced precision and efficiency. Capillary instability has widespread relevance in various natural and industrial processes, ranging from the breakup of liquid jets and the formation of droplets in inkjet printing to the dynamics of thin liquid films and the behavior of liquid bridges in microgravity environments. This study examines the swirling impact on the instability arising from the capillary effects at the boundary of Rivlin–Ericksen and viscous liquids, influenced by an axial electric field, heat, and mass transmission. Capillary instability arises when the cohesive forces at the interface between two fluids are disrupted by perturbations, leading to the formation of characteristic patterns such as waves or droplets. The influence of gravity and fluid flow velocity is disregarded in the context of capillary instability analyses. The annular region is formed by two cylinders: one containing a viscous fluid and the other a Rivlin–Ericksen viscoelastic fluid. The Rivlin–Ericksen model is pivotal for comprehending the characteristics of viscoelastic fluids, widely utilized in industrial and biological contexts. It precisely characterizes their rheological complexities, encompassing elasticity and viscosity, critical for forecasting flow dynamics in polymer processing, food production, and drug delivery. Moreover, its applications extend to biomedical engineering, offering insights crucial for medical device design and understanding biological phenomena like blood flow. The inside cylinder remains stationary, and the outside cylinder rotates at a steady pace. A numerically analyzed quadratic growth rate is obtained from perturbed equations using potential flow theory and the Rivlin–Ericksen fluid model. The findings demonstrate enhanced stability due to the heat and mass transfer and increased stability from swirling. Notably, the heat transfer stabilizes the interface, while the density ratio and centrifuge number also impact stability. An axial electric field exhibits a dual effect, with certain permittivity and conductivity ratios causing perturbation growth decay or expansion. Full article
(This article belongs to the Section Classical Physics)
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27 pages, 776 KiB  
Article
Thermodynamics of Irreversible Processes: Fundamental Constraints, Representations, and Formulation of Boundary Conditions
by Giuseppe Procopio, Chiara Pezzotti, Davide Cocco and Massimiliano Giona
Physics 2024, 6(2), 801-827; https://doi.org/10.3390/physics6020050 - 27 May 2024
Viewed by 966
Abstract
Starting from the analysis of the lack of positivity of the Cattaneo heat equation, this work addresses the thermodynamic relevance of the positivity constraint in irreversible thermodynamics, that is at least as significant as the entropic constraints. The fulfillment of this condition in [...] Read more.
Starting from the analysis of the lack of positivity of the Cattaneo heat equation, this work addresses the thermodynamic relevance of the positivity constraint in irreversible thermodynamics, that is at least as significant as the entropic constraints. The fulfillment of this condition in hyperbolic models leads to the parametrization of the concentration fields with respect to internal variables associated with the microscopic dynamics. Using Brownian motion theory as a landmark example for deriving macroscopic transport equations from the equations of motion at the particle/molecular level, we discuss two typical problems involving hydrodynamic interactions at the microscale: surface chemical reactions at a solid interface of a diffusing reactant, and mass-balance equations in a complex viscoelastic fluid, in which the physics of the interaction leads either to overcoming the parabolic diffusion model or to considering the parametrization of the concentration with respect to the degrees of freedom associated with the relaxation dynamics of the solvent fluid. Full article
(This article belongs to the Special Issue Trends in Contemporary Thermodynamics)
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8 pages, 189 KiB  
Communication
Locality in the Schrödinger Picture of Quantum Mechanics
by Vlatko Vedral
Physics 2024, 6(2), 793-800; https://doi.org/10.3390/physics6020049 - 19 May 2024
Viewed by 941
Abstract
This paper explains how the so-called Einstein locality is to be understood in the Schrödinger picture of quantum mechanics. This notion is fully compatible with the Bell non-locality exhibited by entangled states. Contrary to the belief that quantum mechanics is incomplete, it is, [...] Read more.
This paper explains how the so-called Einstein locality is to be understood in the Schrödinger picture of quantum mechanics. This notion is fully compatible with the Bell non-locality exhibited by entangled states. Contrary to the belief that quantum mechanics is incomplete, it is, As a matter of fact, its overcompleteness, as exemplified by the different pictures of quantum physics, that points to the same underlying reality. Full article
(This article belongs to the Section Atomic Physics)
13 pages, 2464 KiB  
Article
Anisotropy Induced by Electric Charge: A Computational Analytical Approach
by Franyelit Suárez-Carreño and Luis Rosales-Romero
Physics 2024, 6(2), 780-792; https://doi.org/10.3390/physics6020048 - 16 May 2024
Viewed by 811
Abstract
This paper presents a novel class of interior solutions for anisotropic stars under the imposition of a self-similar symmetry. This means proposing exact solutions to the Einstein field equations to describe charged matter distribution with radiation flow. The Einstein–Maxwell system by employing specific [...] Read more.
This paper presents a novel class of interior solutions for anisotropic stars under the imposition of a self-similar symmetry. This means proposing exact solutions to the Einstein field equations to describe charged matter distribution with radiation flow. The Einstein–Maxwell system by employing specific choices of mass function is formulated to describe the gravitational collapse of charged, anisotropic, spherically symmetric distributions using the Schwarzschild metric. Two ordinary differential equations governing the dynamics are derived by matching a straightforward solution of the symmetry equations to the charged exterior (Reissner–Nordström–Vaidya). Models with satisfactory physical behavior are constructed by extensively exploring self-similar solutions for a set of parameters and initial conditions. Finally, the paper presents the evolution of physical variables and the collapsing radius, demonstrating the inevitable collapse of the matter distribution. Full article
(This article belongs to the Section Astronomy, Astrophysics and Planetology)
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20 pages, 1428 KiB  
Article
First- and Second-Order Forces in the Asymmetric Dynamical Casimir Effect for a Single δδ Mirror
by Matthew J. Gorban, William D. Julius, Patrick M. Brown, Jacob A. Matulevich, Ramesh Radhakrishnan and Gerald B. Cleaver
Physics 2024, 6(2), 760-779; https://doi.org/10.3390/physics6020047 - 14 May 2024
Cited by 1 | Viewed by 967
Abstract
Here, we consider an asymmetric δδ mirror undergoing time-dependent interactions with a massless scalar field in 1 + 1 dimensions. Using fluctuation-dissipation theory for a mirror in vacuum, we compute the force on a moving δδ mirror [...] Read more.
Here, we consider an asymmetric δδ mirror undergoing time-dependent interactions with a massless scalar field in 1 + 1 dimensions. Using fluctuation-dissipation theory for a mirror in vacuum, we compute the force on a moving δδ mirror with time-dependent material properties. We investigate the first-order forces arising from the two distinct fluctuation sources and calculate the linear susceptibility in each case. We then plot the resulting forces. At the second order, we also find the independent contributions to the total force as well as the force that arises from the interference phenomena between the two fluctuation sources. Full article
(This article belongs to the Special Issue 75 Years of the Casimir Effect: Advances and Prospects)
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18 pages, 526 KiB  
Article
Complex Transitions of the Bounded Confidence Model from an Odd Number of Clusters to the Next
by Guillaume Deffuant
Physics 2024, 6(2), 742-759; https://doi.org/10.3390/physics6020046 - 8 May 2024
Cited by 1 | Viewed by 1087
Abstract
The bounded confidence model assumes simple continuous opinion dynamics in which agents ignore opinions which are too far from their own. The two initial variants—Hegselmann–Krause (HK) and Deffuant–Weisbuch (DW)—of the model have attracted significant attention since the early 2000s. This paper revisits the [...] Read more.
The bounded confidence model assumes simple continuous opinion dynamics in which agents ignore opinions which are too far from their own. The two initial variants—Hegselmann–Krause (HK) and Deffuant–Weisbuch (DW)—of the model have attracted significant attention since the early 2000s. This paper revisits the version of the HK model applied to a probability distribution, earlier studied by Jan Lorenz. It shows that the bifurcation diagram depends on the parity of the size of the discretisation and that adding a small noise to the initial conditions leads to complex transitions involving several phases. Full article
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52 pages, 4729 KiB  
Article
Force Metrology with Plane Parallel Plates: Final Design Review and Outlook
by Hamid Haghmoradi, Hauke Fischer, Alessandro Bertolini, Ivica Galić, Francesco Intravaia, Mario Pitschmann, Raphael A. Schimpl and René I. P. Sedmik
Physics 2024, 6(2), 690-741; https://doi.org/10.3390/physics6020045 - 7 May 2024
Cited by 4 | Viewed by 1173
Abstract
During the past few decades, abundant evidence for physics beyond the two standard models of particle physics and cosmology was found. Yet, we are tapping in the dark regarding our understanding of the dark sector. For more than a century, open problems related [...] Read more.
During the past few decades, abundant evidence for physics beyond the two standard models of particle physics and cosmology was found. Yet, we are tapping in the dark regarding our understanding of the dark sector. For more than a century, open problems related to the nature of the vacuum remained unresolved. As well as the traditional high-energy frontier and cosmology, technological advancement provides complementary access to new physics via high-precision experiments. Among the latter, the Casimir And Non-Newtonian force EXperiment (Cannex) has successfully completed its proof-of-principle phase and is going to commence operation soon. Benefiting from its plane parallel plate geometry, both interfacial and gravity-like forces are maximized, leading to increased sensitivity. A wide range of dark sector forces, Casimir forces in and out of thermal equilibrium, and gravity can be tested. This paper describes the final experimental design, its sensitivity, and expected results. Full article
(This article belongs to the Special Issue 75 Years of the Casimir Effect: Advances and Prospects)
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16 pages, 472 KiB  
Review
Probing Relativistic Heavy-Ion Collisions via Photon Anisotropic Flow Ratios. A Brief Review
by Rupa Chatterjee and Pingal Dasgupta
Physics 2024, 6(2), 674-689; https://doi.org/10.3390/physics6020044 - 4 May 2024
Viewed by 1263
Abstract
The anisotropic flow of photons produced in relativistic nuclear collisions is known as a promising observable for studying the initial state and the subsequent evolution of the hot and dense medium formed in such collisions. The investigation of photon anisotropic flow coefficients,  [...] Read more.
The anisotropic flow of photons produced in relativistic nuclear collisions is known as a promising observable for studying the initial state and the subsequent evolution of the hot and dense medium formed in such collisions. The investigation of photon anisotropic flow coefficients, vn, has attracted high interest over the last decade, involving both theory and experiment. The thermal emission of photons and their anisotropic flow are found to be highly sensitive to the initial state of the fireball, where even slight modifications can lead to significant variations in the final state results. In contrast, the ratio of photon anisotropic flow stands out as a robust observable, exhibiting minimal sensitivity to the initial conditions. Here, we briefly review the studies of the individual elliptic and triangular flow parameters of photons as well as their ratios and how these parameters serve as valuable probes for investigating the intricacies of the initial state and addressing the challenges posed by the direct photon puzzle. Full article
(This article belongs to the Special Issue Jean Cleymans A Life for Physics)
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15 pages, 429 KiB  
Article
The Influence of Lobbies: Analyzing Group Consensus from a Physics Approach
by Ugo Merlone and Arianna Dal Forno
Physics 2024, 6(2), 659-673; https://doi.org/10.3390/physics6020043 - 1 May 2024
Cited by 2 | Viewed by 921
Abstract
In this paper, we study the influence of a small group of agents (i.e., a lobby) that is trying to spread a rumor in a population by using the known model proposed by Serge Galam. In particular, lobbies are modeled as subgroups of [...] Read more.
In this paper, we study the influence of a small group of agents (i.e., a lobby) that is trying to spread a rumor in a population by using the known model proposed by Serge Galam. In particular, lobbies are modeled as subgroups of individuals who strategically choose their seating in the social space in order to protect their opinions and influence others. We consider different social gatherings and simulate, using finite Markovian chains, opinion dynamics by comparing situations with a lobby to those without a lobby. Our results show how the lobby can influence opinion dynamics in terms of the prevailing opinion and the mean time to reach unanimity. The approach that we take overcomes some of the problems that behavioral economics and psychology have recently struggled with in terms of replicability. This approach is related to the methodological revolution that is slowly changing the dominant perspective in psychology. Full article
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14 pages, 667 KiB  
Article
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 - 24 Apr 2024
Cited by 1 | Viewed by 1115
Abstract
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  
Article
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
Cited by 1 | Viewed by 1213
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
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16 pages, 622 KiB  
Article
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
Cited by 2 | Viewed by 955
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  
Article
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
Viewed by 1142
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
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20 pages, 1593 KiB  
Article
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
Viewed by 875
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
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11 pages, 404 KiB  
Communication
Rectified Lorentz Force from Thermal Current Fluctuations
by Carsten Henkel
Physics 2024, 6(2), 568-578; https://doi.org/10.3390/physics6020037 - 9 Apr 2024
Cited by 1 | Viewed by 1198
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  
Article
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 - 9 Apr 2024
Cited by 4 | Viewed by 910
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/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  
Article
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 - 9 Apr 2024
Cited by 1 | Viewed by 975
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  
Article
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 - 8 Apr 2024
Cited by 2 | Viewed by 941
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
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19 pages, 412 KiB  
Article
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 - 2 Apr 2024
Cited by 1 | Viewed by 997
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 SiO2 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  
Article
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
Cited by 1 | Viewed by 791
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
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15 pages, 344 KiB  
Article
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
Cited by 3 | Viewed by 1030
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
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