The Physics Section in Symmetry

Scientific research, in the era of new technologies and globalization, is becoming a science industry, meaning it increasingly requires interdisciplinarity and transdisciplinarity to achieve its goals of scientific progress, with this also being a requirement for its application to the well-being of society.

Communication and language exchange between diverse disciplines, all with very different traditions, is an important challenge that new technologies can help with, as exemplified by algorithmic methods, such as those based on Artificial Intelligence.

Physics itself has a broad multidisciplinary character, encompassing the smallest of things—the physics of particles and elementary interactions—and more extensive subjects, such as astrophysics and cosmology, along with nonlinear statistical mechanics, quantum computing, and other fields of knowledge. Its applications address transdisciplinary and interdisciplinary aspects in very diverse fields, including in industry, in medicine, or in social relations.

In nature, symmetry is present in all fields of knowledge. Physics represents a special case, since it governs the development of models about the universe, matter, and its interactions and is directly related to the conservation laws, through Emily Noether’s theorem. In some cases, symmetries can be derived as a consequence of the physical laws themselves, but in some cases, such as Poincaré and Yang-Mills gauge invariances, it is assumed that symmetries have a fundamental character. However, this is a topic of discussion, and there are ideas about their dynamic generation character, as seen the case of random dynamics, which suggests chaos at the most fundamental level.

Symmetries can be continuous or discrete, local or global, and they can have a geometric or intrinsic character. Symmetries are of interest both for microscopic and macroscopic physics. In complex systems, scaling laws can be approximately correct and deduced from the underlying molecular dynamics using dimensional analysis arguments, provided that statistical methods are applicable.

Symmetries can be approximately accounted for in non-relativistic systems, being of particular interest in atomic and nuclear models.

Symmetry breaking is interesting in itself because it defines transitions to important phenomenological models. The fact that a symmetry is present in experimental results does not imply that it is a fundamental symmetry. On the other hand, approximate symmetries are derived, as is generally the case in macroscopic systems.

Symmetries are particularly important in particle physics models, both standard and extended, and in cosmology. The fundamental interactions of matter are explained by the standard model of particle physics and general relativity. Both theories are based on symmetry models, but they are incomplete and require new, more fundamental theories to integrate them. Grand unified models seek to explain the non-natural parameters of the standard model by introducing symmetry groups that contain those of the standard model, unifying the fundamental interactions and leading to the standard model via a mechanism of spontaneous symmetry breaking at a very high energy scale. Some of these models include supersymmetry, which relates bosons to fermions and can lead to supergravity models, which include gravity, so they are also particularly interesting.

For all these reasons, a multidisciplinary journal such as Symmetry, and more specifically, its Physics section, offers a very suitable framework for achieving the objectives of advancing knowledge and an international forum for presenting research work in this area.

The section includes the following topics: local, global, continuous, and/or spacetime symmetries; condensed matter physics and phase transitions; conservation laws and their tests; gauge theories and the standard model of particles; mathematical and theoretical physics; astrophysics, gravitation, and cosmology; spontaneous symmetry breaking and topological effects; plasma physics; conformal symmetry; dynamical symmetry breaking models; flavor symmetries; fundamental interactions; baryon and lepton number; classical and quantum field theory and their symmetries; and the scaling laws of complex systems.

It hosts international and interdisciplinary experimental and theoretical works, as well as regular articles or reviews, with no length limitations being put in place. The requirements of scientific quality and originality are guaranteed via peer review by selected expert researchers. Ethical and responsible criteria are strictly considered, avoiding plagiarism and prioritizing the quality and impact of the publications.

The journal is open access and tries, as much as possible, to ensure that publication is carried out in the shortest possible time once quality has been guaranteed via a process of revision and correction or optimization by the authors, with corrections being made in response to the reviewers following acceptance by the Editorial Board.

The Physics section contains regular articles and Special Issues on practically all lines of work in physics, catering to specific interests. Since the section’s inception in 2017, nearly 2000 articles have been published in it, with this number increasing progressively. Some of these articles have been seen by several tens of thousands of readers; the most cited articles reach nearly 200 citations, and some of them have special relevance, according to the editors.

As recent examples of such articles, we cite [1,2,3,4,5,6,7,8,9,10,11,12,13].

In the following paragraphs, we comment on the main goals and results of these contributions.

In the first paper, Recent Advances in Inflation, the authors provide a very comprehensive review of the latest trends in the inflationary dynamics of the universe for consistent modified gravity models. This paper describes current extensions of general relativity and includes generalizations of string-corrected modified gravity models, identifying the scalar field, a candidate for dark matter, as the invisible axion. The bibliography is exhaustive, including two notable reviews [14,15] and a pioneering work [16] on a unified description of inflation with dark energy, carried out by one of the authors of the paper. Their studies provide the appropriate tools for the production of inflationary cosmologies compatible with the Planck results [17].

In the second paper, From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, the authors review the alternative to general relativity, MOND (Modified Newtonian dynamics) theory, and its implications. They include a hybrid approach with light sterile neutrinos to address the existing cluster-scale problems of MOND, as well as an analysis of the standard cosmological model ΛCDM and predictions based on astronomical and large-scale evidence. Their considerations range from kiloparsec scales to the scale of the local super void. They also perform an analysis of the Hubble tension, comparing MOND with results derived from general relativity. Their studies are based, in principle, on Milgromian dynamics [18], and they also present comparisons with other modified gravity models [19]. They also include an extensive bibliography.

In the third paper, Revisiting a Negative Cosmological Constant from Low-Redshift Data, the authors explore new simplified dark energy scenarios inspired by string theory [20,21,22,23,24]. They analyze the consistency of the model against observations from the Planck collaboration [17] and the SHOES program [25], such as baryon acoustic oscillation and redshift in IA supernovae. Their conclusion is that the standard model ΛCDM is better than the negative cosmological constant model. More realistic string models are expected to be used in the future if tensions persist.

In the fourth paper, Cosmoparticle Physics of Dark Universe, the author presents an interdisciplinary study encompassing particle physics beyond the standard model and the cosmology of the dark universe. Specifically, primordial black holes, baryon asymmetry in antimatter stars, and multicharged constituents of nuclear interacting atoms of composite dark matter are analyzed. Previous studies are cited, including [26,27,28].

In the fifth paper, Entropy Bounds: New Insights, the authors review and introduce new ideas about entropy bounds with implications for cosmology and their relation to the holographic principle, in which the degrees of freedom of a spatial region reside on the surface, contrary to ordinary quantum field theory. They review the basic concepts of entropy bounds, introduced by themselves and by Bousso [29,30,31]. They also demonstrate the statistical nature of the origin of entropy bounds.

In the sixth paper, Machine Learning for Conservative-to-Primitive in Relativistic Hydrodynamics, the authors discuss the use of machine learning techniques in relativistic hydrodynamics [32] to address difficult problems such as precision gravitational wave signals in binary neutron stars [33]. Artificial neural networks are trained to replace the interpolations of an equation of state or directly to replace the conservative-to-primitive map. In both cases, accuracy is maintained, and more than an order of magnitude is gained compared to standard methods.

In the seventh paper, Lie Symmetries, Closed-Form Solutions, and Various Dynamical Profiles of Solitons for the Variable Coefficient (2+1)-Dimensional KP Equations, the authors present a study predicated on finding solutions for nonlinear wave models applicable in different physical contexts. They use the Lie symmetry technique and apply it to an extension of the Kadomtsev–Petviashvili (KP) equations with time-dependent variable coefficients, obtaining analytical solutions, including ones in the shape of distinct complex wave structures of solitons, dark and bright soliton shapes, double W-shaped soliton shapes, multi-peakon shapes, curved-shaped multi-wave solitons, and novel solitary wave solitons. The exact solutions generated are novel to the literature, and other works [34,35,36,37] related to similar research directions are cited.

In the eighth paper, Computational Analysis of MHD Nonlinear Radiation Casson Hybrid Nanofluid Flow at Vertical Stretching, the authors find solutions via the use of numerical techniques and Lie symmetry, a system of differential equations corresponding to the magnetic hydrodynamic flow of a Casson hybrid nanofluid [38] in a vertical stretching sheet. They obtain results on several aspects, such as skin friction, Nusselt number, and temperature and velocity distributions.

In the ninth paper, Quo Vadis Nonlinear Optics? An Alternative and Simple Approach to Third Rank Tensors in Semiconductors, the authors discuss the relationship between nonlinear optics and material symmetry. A theoretical analysis based on classical light–matter interaction phenomenology was conducted using the so-called simplified bond hyperpolarizability (SBHM) model [39] and compared with group theory analysis. The simplification involves improvements in the analysis of the contribution of second harmonic generation (SHG) and is analyzed for perovskite using existing experimental results [40], leaving the method ready for future studies of semiconductors with complicated structures, nanoscale surface characterization, and real-time surface deposition monitoring.

In the tenth paper, Experimental Review of ΛΛ¯ Production, the authors perform an experimental review of several past experiments with different beams (proton–antiproton in LEAR-PS185, electron–positron in CLEO-c, BESIII, and BABar) for strangeness production. Their study focuses on the ΛΛ¯ production cross-section near the threshold, which is sensitive to the prediction of perturbative QCD. The results are not conclusive, and future experiments are required, such as the PANDA proton–antiproton experiment [41], or future electron–positron experiments [42,43].

In the eleventh article, A Critical Review of Works Pertinent to the Einstein–Bohr Debate and Bell’s Theorem, the author reviews the classical Einstein–Bohr debates and the Einstein–Podolsky–Rosen (EPR) and Bohm (EPRB) virtual experiments and their implementation in real present-day experiments. His conclusion, based on the existing literature, is that the Bell and Clauser–Horne–Shimony–Holt (CHSH) theorems have a weak relationship with quantum theory and real EPRB experiments; therefore, they cannot be used to physically test quantum entanglement, or vice versa, to prove these theorems. This is because the proofs are based on statistical sampling with finite populations but do not hold for a time continuum. He also discusses Vorob’ev’s theorem [44] and how it actually includes the Bell–CHSH inequalities.

In the twelfth paper, Studies of Deformed Halo Structures of ³⁹Na and ⁴²Mg, the authors theoretically study deformed halo structures of drip-line nuclei ³⁹Na and ⁴²Mg. This study addresses the solution of the Skyrme–Hartree–Fock–Bogoliubov (Skyrme-HFB) equation [45,46], within deformed coordinate spaces, suitable for weakly bound deformed cores with continuum effects and deformed halo structures. It is found that ³⁹Na and ⁴²Mg are very weakly bound with well-prolated deformed cores, but their surface halo structures depend on the pairing interaction choices. It is shown that ³⁹Na and ⁴²Mg are good candidates for two-neutron deformed halo cores.

In the thirteenth article, The Golden Ratio in Nature: A Tour across Length Scales, the authors carry out a mathematical review of the golden ratio, which is common in very diverse fields and in phenomena of different length scales, from the galactic to the atomic. Its presence in various natural phenomena is then reviewed, the tendency of which suggests that it is a fundamental constant of nature [47,48].