Physics

26 pages, 553 KiB

Open AccessReview

The Casimir Effect in Finite-Temperature and Gravitational Scenarios

by Valdir Barbosa Bezerra, Herondy Francisco Santana Mota, Augusto P. C. M. Lima, Geová Alencar and Celio Rodrigues Muniz

Physics 2024, 6(3), 1046-1071; https://doi.org/10.3390/physics6030065 - 13 Aug 2024

Viewed by 192

Abstract

In this paper, we review some recent findings related to the Casimir effect. Initially, the thermal corrections to the vacuum Casimir energy density are calculated, for a quantum scalar field, whose modes propagate in the (3+1)-dimensional Euclidean spacetime, subject to a nontrivial compact [...] Read more.

In this paper, we review some recent findings related to the Casimir effect. Initially, the thermal corrections to the vacuum Casimir energy density are calculated, for a quantum scalar field, whose modes propagate in the (3+1)-dimensional Euclidean spacetime, subject to a nontrivial compact boundary condition. Next, we analyze the Casimir effect induced by two parallel plates placed in a weak gravitational field background. Finally, we review the three-dimensional wormhole solutions sourced by the Casimir density and pressures associated with the quantum vacuum fluctuations of the Yang-Mills field. Full article

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

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11 pages, 257 KiB

Open AccessArticle

Entangled Probability Distributions for Center-of-Mass Tomography

by Ivan V. Dudinets, Margarita A. Man’ko and Vladimir I. Man’ko

Physics 2024, 6(3), 1035-1045; https://doi.org/10.3390/physics6030064 - 13 Aug 2024

Viewed by 145

Abstract

We review the formalism of center-of-mass tomograms, which allows us to describe quantum states in terms of probability distribution functions. We introduce the concept of separable and entangled probability distributions for center-of-mass tomography. We obtain the time evolution of center-of-mass tomograms of entangled [...] Read more.

We review the formalism of center-of-mass tomograms, which allows us to describe quantum states in terms of probability distribution functions. We introduce the concept of separable and entangled probability distributions for center-of-mass tomography. We obtain the time evolution of center-of-mass tomograms of entangled states of the inverted oscillator. Full article

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

3 pages, 152 KiB

Open AccessEditorial

Foreword to the Special Issue “In Honor of Professor Serge Galam for His 70th Birthday and Forty Years of Sociophysics”

by Serge Galam

Physics 2024, 6(3), 1032-1034; https://doi.org/10.3390/physics6030063 - 6 Aug 2024

Viewed by 540

Abstract

I am deeply moved and honored by this Special Issue of the journal Physics celebrating my seventieth birthday and forty years of sociophysics [...] Full article

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

19 pages, 606 KiB

Open AccessArticle

Agent Mental Models and Bayesian Rules as a Tool to Create Opinion Dynamics Models

by André C. R. Martins

Physics 2024, 6(3), 1013-1031; https://doi.org/10.3390/physics6030062 - 31 Jul 2024

Viewed by 333

Abstract

Traditional models of opinion dynamics provide a simplified approach to understanding human behavior in basic social scenarios. However, when it comes to issues such as polarization and extremism, a more nuanced understanding of human biases and cognitive tendencies are required. This paper proposes [...] Read more.

Traditional models of opinion dynamics provide a simplified approach to understanding human behavior in basic social scenarios. However, when it comes to issues such as polarization and extremism, a more nuanced understanding of human biases and cognitive tendencies are required. This paper proposes an approach to modeling opinion dynamics by integrating mental models and assumptions of individuals agents using Bayesian-inspired methods. By exploring the relationship between human rationality and Bayesian theory, this paper demonstrates the usefulness of these methods in describing how opinions evolve. The analysis here builds upon the basic idea in the Continuous Opinions and Discrete Actions (CODA) model, by applying Bayesian-inspired rules to account for key human behaviors such as confirmation bias, motivated reasoning, and human reluctance to change opinions. Through this, This paper updates rules that are compatible with known human biases. The current work sheds light on the role of human biases in shaping opinion dynamics. I hope that by making the model more realistic this might lead to more accurate predictions of real-world scenarios. 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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14 pages, 613 KiB

Open AccessArticle

3D–2D Crossover and Phase Shift of Beats of Quantum Oscillations of Interlayer Magnetoresistance in Quasi-2D Metals

by Taras I. Mogilyuk, Pavel D. Grigoriev, Vladislav D. Kochev, Ivan S. Volokhov and Ilya Y. Polishchuk

Physics 2024, 6(3), 999-1012; https://doi.org/10.3390/physics6030061 - 25 Jul 2024

Cited by 1 | Viewed by 388

Abstract

Magnetic quantum oscillations (MQOs) are traditionally applied to investigate the electronic structure of metals. In layered quasi-two-dimensional (Q2D) materials, the MQOs have several qualitative features, offering additional helpful information, provided their theoretical description is developed. Within the framework of the Kubo formula and [...] Read more.

Magnetic quantum oscillations (MQOs) are traditionally applied to investigate the electronic structure of metals. In layered quasi-two-dimensional (Q2D) materials, the MQOs have several qualitative features, offering additional helpful information, provided their theoretical description is developed. Within the framework of the Kubo formula and the self-consistent Born approximation, we reconsider the phase of the beats in the amplitude of the Shubnikov oscillations of the interlayer conductivity in Q2D metals. We show that the phase shift of the beats of the Shubnikov (conductivity) oscillations relative to the de Haas–van Alphen (magnetization) oscillations is larger than woud be expected and, under certain conditions, can reach the value of

π / 2

, as observed experimentally. We explain the phase inversion of the MQOs during the 3D–2D crossover and predict the decrease in the relative MQO amplitude of the interlayer magnetoresistance in a strong magnetic field, larger than the beat frequency. Full article

(This article belongs to the Section Applied Physics)

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9 pages, 2272 KiB

Open AccessArticle

Characterization of Below-Bandgap Absorption in Type II GaSb Quantum Dots in GaAs Solar Cells

by Juanita Saroj James, Hiromi Fujita, Peter J. Carrington, Andrew R. J. Marshall, Susan Krier and Anthony Krier

Physics 2024, 6(3), 990-998; https://doi.org/10.3390/physics6030060 - 19 Jul 2024

Viewed by 450

Abstract

An approach to derive the below-bandgap absorption in GaSb/GaAs self-assembled quantum dot devices using room-temperature external quantum efficiency measurement results is presented. Devices with five layers of delta-doped quantum dots placed in the intrinsic, n- and p-regions of a GaAs solar cell are [...] Read more.

An approach to derive the below-bandgap absorption in GaSb/GaAs self-assembled quantum dot devices using room-temperature external quantum efficiency measurement results is presented. Devices with five layers of delta-doped quantum dots placed in the intrinsic, n- and p-regions of a GaAs solar cell are studied. The importance of incorporating an extended Urbach tail absorption in analyzing the absorption strength of quantum dots and the transition states is demonstrated. The theoretically integrated absorbance via quantum dot ground states is calculated as 1.04 × 10¹⁵ cm⁻¹s⁻¹, which is in reasonable agreement with the experimentally derived value 8.1 × 10¹⁵ cm⁻¹s⁻¹. The wetting layer and quantum dot absorption contributions are separated from the tail absorption and their transition energies are calculated. Using these transition energies and the GaAs energy gap of 1.42 eV, the heavy hole confinement energies for the quantum dots (320 meV) and for the wetting layer (120 meV) are estimated. Full article

(This article belongs to the Section Applied Physics)

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26 pages, 8666 KiB

Open AccessArticle

Discovering Bohr’s Yin-Yang Diagram in Quantum Tunneling Dynamics

by Ciann-Dong Yang

Physics 2024, 6(3), 964-989; https://doi.org/10.3390/physics6030059 - 18 Jul 2024

Viewed by 702

Abstract

On 17 October 1947, Niels Bohr was made a knight of the Order of the Elephant by the King of Denmark in view of his outstanding achievements and contributions to science. Bohr designed his own coat of arms that featured a pattern of [...] Read more.

On 17 October 1947, Niels Bohr was made a knight of the Order of the Elephant by the King of Denmark in view of his outstanding achievements and contributions to science. Bohr designed his own coat of arms that featured a pattern of Yin and Yang (Tai Chi symbol) to symbolize the wave–particle complementarity. However, Bohr’s Yin-Yang diagram (YYD) was neither drawn based on the principles of quantum mechanics, nor did it originate from the traditional Taoist YYD. Scientists still have doubts about the legitimacy of using YYD as the icon of the wave–particle complementarity, because the YYD belonging to quantum mechanics itself is unknown so far. This paper reports the YYDs existing in quantum mechanics and justifies the role of YYD in the wave–particle duality by showing that any system, whether classical or quantum, has an ideal YYD as long as it satisfies Bohr’s principle of complementarity (BPC). The deviation of a deformed YYD from the ideal YYD indicates the extent to which a real system satisfies BPC. This paper constructs the quantum YYD by the complex quantum trajectory of a particle tunneling via a step barrier, which displays the continuous transition between the wave behavior and the particle behavior. It appears that the YYD designed by Bohr in his coat of arms resembles the YYD generated by tunneling motion, not only in appearance but also in the governing equation. Full article

(This article belongs to the Section Atomic Physics)

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19 pages, 324 KiB

Open AccessArticle

Dirac Theory in Noncommutative Phase Spaces

by Shi-Dong Liang

Physics 2024, 6(3), 945-963; https://doi.org/10.3390/physics6030058 - 8 Jul 2024

Viewed by 399

Abstract

Based on the position and momentum of noncommutative relations with a noncanonical map, we study the Dirac equation and analyze its parity and time reversal symmetries in a noncommutative phase space. Noncommutative parameters can be endowed with the Planck length and cosmological constant [...] Read more.

Based on the position and momentum of noncommutative relations with a noncanonical map, we study the Dirac equation and analyze its parity and time reversal symmetries in a noncommutative phase space. Noncommutative parameters can be endowed with the Planck length and cosmological constant such that the noncommutative effect can be interpreted as an effective gauge potential or a

(0, 2)

-type curvature associated with the Plank constant and cosmological constant. This provides a natural coupling between dynamics and spacetime geometry. We find that a free Dirac particle carries an intrinsic velocity and force induced by the noncommutative algebra. These properties provide a novel insight into the Zitterbewegung oscillation and the physical scenario of dark energy. Using perturbation theory, we derive the perturbed and nonrelativistic solutions of the Dirac equation. The asymmetric vacuum gaps of particles and antiparticles reveal the particle–antiparticle symmetry breaking in the noncommutative phase space, which provides a clue to understanding the physical mechanisms of particle–antiparticle asymmetry and quantum decoherence through quantum spacetime fluctuation. Full article

(This article belongs to the Section Classical Physics)

24 pages, 4910 KiB

Open AccessArticle

Relations between Shot Noise, Gain Bandwidth, and Saturation of Instabilities

by Yichao Jing, Vladimir N. Litvinenko, Jun Ma and Gang Wang

Physics 2024, 6(3), 921-944; https://doi.org/10.3390/physics6030057 - 25 Jun 2024

Viewed by 759

Abstract

There are numerous instabilities present in charged particle beams that undergo exponential growth and reach saturation. In various applications, such as free-electron lasers or micro-bunching light sources, achieving saturation is desirable. Conversely, there are applications where these instabilities are utilized as linear broad-band [...] Read more.

There are numerous instabilities present in charged particle beams that undergo exponential growth and reach saturation. In various applications, such as free-electron lasers or micro-bunching light sources, achieving saturation is desirable. Conversely, there are applications where these instabilities are utilized as linear broad-band amplifiers for signals embedded in the charged beam. In the latter scenario, the saturation of an instability induces non-linear distortions in the imprinted signal, thereby limiting the useful range of such amplifiers. Accurate evaluation of these instabilities necessitates a complete and comprehensive modeling approach that includes shot noise within the beam. Unfortunately, such modeling is not always feasible or practical. In this paper, we introduce a methodology utilizing the frequency and bandwidth of the instability as key parameters. Through this, we derive an estimation for the range of linear instability growth. Our derivation is conducted in a model-independent manner, making it applicable to a broad spectrum of instabilities. To validate our approach, we employ established and thoroughly benchmarked simulations with a free electron laser (FEL) code as well as self-consistent 3-dimensional simulation of plasma-cascade instability using code SPACE. Full article

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

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Physics, Volume 6, Issue 3 (September 2024) – 9 articles

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