Recent zbMATH articles in MSC 85https://zbmath.org/atom/cc/852021-11-25T18:46:10.358925ZWerkzeugMeasuring the worldhttps://zbmath.org/1472.010072021-11-25T18:46:10.358925Z"Lühning, Felix"https://zbmath.org/authors/?q=ai:luhning.felixThe article, written in German, is a very readable, popular, and simultaneously historically accurate account of the history of measuring the Earth (determination of the shape, calculation of geographical length and width, \dots). It contains little explicit mathematics, but makes clear how and why it was used since ancient times until today to obtain more and more accurate geodesic data. Old measuring instruments and their usage, as well as problems and solutions pertaining to accurate measurement of time, are also clearly described, and the article is written in an informal, very enjoyable style. It is an excellent introduction into the topic, containing also much lesser known information on the history of mathematical geography and astronomy. Consequently, it clearly demonstrates, in the author's own words, that ``without stars no determination of time, without stars no measurement of the Earth, without measurement of Earth no measures of length, and consequently no measures of volume and mass''.Strong Feller property of the magnetohydrodynamics system forced by space-time white noisehttps://zbmath.org/1472.353892021-11-25T18:46:10.358925Z"Yamazaki, Kazuo"https://zbmath.org/authors/?q=ai:yamazaki.kazuoDimension compactification -- a possible explanation for superclusters and for empirical evidence usually interpreted as dark matterhttps://zbmath.org/1472.620972021-11-25T18:46:10.358925Z"Kreinovich, Vladik"https://zbmath.org/authors/?q=ai:kreinovich.vladik-yaSummary: According to modern quantum physics, at the microlevel, the dimension of space-time is \(\ge 11\); we only observe 4 dimensions because the others are compactified: the size along each of the other dimensions is much smaller than the macroscale. There is no universally accepted explanation of why exactly 4 dimensions remain at the microscopic level. A natural suggestion is: maybe there is no fundamental reason why exactly 4 dimensions should remain, maybe when we go to even larger scales, some of the 4 dimensions will be compactified as well? In this paper, we explore the consequences of the compactification suggestion, and we show that -- on the qualitative level -- these consequences have actually been already observed: as superclusters and as evidence that is usually interpreted as justifying dark matter. Thus, we get a new possible explanation of both superclusters and dark matter evidence -- via dimension compactification.
For the entire collection see [Zbl 1467.62007].The orbital evolution of resonant chains of exoplanets incorporating circularisation produced by tidal interaction with the central star with application to the HD 158259 and EPIC 245950175 systemshttps://zbmath.org/1472.700512021-11-25T18:46:10.358925Z"Papaloizou, J. C. B."https://zbmath.org/authors/?q=ai:papaloizou.john-c-bSummary: We study orbital evolution of multi-planet systems that form a resonant chain, with nearest neighbours close to first order commensurabilities, incorporating orbital circularisation produced by tidal interaction with the central star. We develop a semi-analytic model applicable when the relative proximities to commensurability, though small, are large compared to \(\epsilon^{2/3},\) with \(\epsilon\) being a measure of the characteristic planet to central star mass ratio. This enables determination of forced eccentricities as well as which resonant angles enter libration. When there are no active linked three body Laplace resonances, the rate of evolution of the semi-major axes may also be determined. We perform numerical simulations of the HD 158259 and EPIC 245950175 systems finding that the semi-analytic approach works well in the former case but not so well in the latter case on account of the effects of three active three body Laplace resonances which persist during the evolution. For both systems we estimate that if the tidal parameter, \(Q'\), significantly exceeds 1000, tidal effects are unlikely to have influenced period ratios significantly since formation. On the other hand if \(Q' < \sim 100\) tidal effects may have produced significant changes including the formation of three body Laplace resonances in the case of the EPIC 245950175 system.Magnetic reconnection in partially ionized plasmashttps://zbmath.org/1472.780032021-11-25T18:46:10.358925Z"Ni, Lei"https://zbmath.org/authors/?q=ai:ni.lei"Ji, Hantao"https://zbmath.org/authors/?q=ai:ji.hantao"Murphy, Nicholas A."https://zbmath.org/authors/?q=ai:murphy.nicholas-a"Jara-Almonte, Jonathan"https://zbmath.org/authors/?q=ai:jara-almonte.jonathanSummary: Magnetic reconnection has been intensively studied in fully ionized plasmas. However, plasmas are often partially ionized in astrophysical environments. The interactions between the neutral particles and ionized plasmas might strongly affect the reconnection mechanisms. We review magnetic reconnection in partially ionized plasmas in different environments from theoretical, numerical, observational and experimental points of view. We focus on mechanisms which make magnetic reconnection fast enough to compare with observations, especially on the reconnection events in the low solar atmosphere. The heating mechanisms and the related observational evidence of the reconnection process in the partially ionized low solar atmosphere are also discussed. We describe magnetic reconnection in weakly ionized astrophysical environments, including the interstellar medium and protostellar discs. We present recent achievements about fast reconnection in laboratory experiments for partially ionized plasmas.The landscape of QCD axion modelshttps://zbmath.org/1472.812702021-11-25T18:46:10.358925Z"Di Luzio, Luca"https://zbmath.org/authors/?q=ai:di-luzio.luca"Giannotti, Maurizio"https://zbmath.org/authors/?q=ai:giannotti.maurizio"Nardi, Enrico"https://zbmath.org/authors/?q=ai:nardi.enrico"Visinelli, Luca"https://zbmath.org/authors/?q=ai:visinelli.lucaSummary: We review the landscape of QCD axion models. Theoretical constructions that extend the window for the axion mass and couplings beyond conventional regions are highlighted and classified. Bounds from cosmology, astrophysics and experimental searches are reexamined and updated.The Renaissance of general relativity in context: a historiographical reviewhttps://zbmath.org/1472.830032021-11-25T18:46:10.358925Z"Blum, Alexander S."https://zbmath.org/authors/?q=ai:blum.alexander-s"Lalli, Roberto"https://zbmath.org/authors/?q=ai:lalli.roberto"Renn, Jürgen"https://zbmath.org/authors/?q=ai:renn.jurgen-rennSummary: In the past years, a complex historical debate has emerged on the causes, origins, and manifestations of the process dubbed as the renaissance of Einstein's theory of gravitation. After a thirty-year period of stagnation of the theory, known as its low-water-mark phase, the renaissance marks the post-World War II return of general relativity to the mainstream of physics. As an introduction to The Renaissance of General Relativity in Context, we discuss the various historical hypotheses that have been advanced and put them in dialogue with the chapters published in the volume. In discussing these studies, we argue that our previous interpretation of the renaissance process (as resulting from the interplay of social and epistemic factors) has been substantially confirmed. In addition, these studies enable our interpretation of the renaissance of general relativity to be redefined as a two-step process. A first phase of theoretical renaissance, driven by social transformations, occurred between the mid-1950s and the early 1960s and transformed the general theory of relativity into a bona fide physical theory. The second phase of this process, which we call the astrophysical turn, was an experiment-driven shift toward relativistic astrophysics and physical cosmology and was strongly related to discoveries in the astrophysical domain in the 1960s.
For the entire collection see [Zbl 1460.83002].The socio-epistemic networks of general relativity, 1925--1970https://zbmath.org/1472.830052021-11-25T18:46:10.358925Z"Lalli, Roberto"https://zbmath.org/authors/?q=ai:lalli.roberto"Howey, Riaz"https://zbmath.org/authors/?q=ai:howey.riaz"Wintergrün, Dirk"https://zbmath.org/authors/?q=ai:wintergrun.dirkSummary: We report the results of our analysis of the development of general relativity between 1925 and 1970 based on the conceptual and methodological framework of socio-epistemic networks comprised of three different layers: social, semiotic, and semantic. Our computational approach is used to uncover the mechanism of the passage between the low-water-mark phase of general relativity -- roughly from the mid-1920s to the mid-1950s -- and the so-called renaissance of the theory after the mid-1950s. Based on this multilayer analysis, we provide substantial empirical evidence that between the second half of the 1950s and the early 1960s there was an evident shift in all three layers. Our analysis disproves common explanations of the renaissance process. It shows that this phenomenon was not a consequence of astrophysical discoveries in the 1960s, nor was it a simple by-product of socio-economic transformations in the physics landscape after World War II. We argue instead that the renaissance has to be understood as a two-phase process both at the social and at the epistemic level. The first occurred between the second half of the 1950s and the early 1960s, when a growing community of physicists redirected their interest toward physical problems in general relativity, while the previous period was characterized by a dispersion of research agendas aimed at substituting the theory with a different and more general one. We call this first phase the theoretical renaissance general relativity. The second phase, which we call the astrophysical turn, was instead an experiment-driven process that started with the discovery of quasars and was characterized by the emergence of relativistic astrophysics and physical cosmology as well as the early phases of gravitational-wave astronomy.
For the entire collection see [Zbl 1460.83002].Topological stars, black holes and generalized charged Weyl solutionshttps://zbmath.org/1472.830212021-11-25T18:46:10.358925Z"Bah, Ibrahima"https://zbmath.org/authors/?q=ai:bah.ibrahima"Heidmann, Pierre"https://zbmath.org/authors/?q=ai:heidmann.pierreSummary: We construct smooth static bubble solutions, denoted as topological stars, in five-dimensional Einstein-Maxwell theories which are asymptotic to \(\mathbb{R}^{1,3} \times S^1\). The bubbles are supported by allowing electromagnetic fluxes to wrap smooth topological cycles. The solutions live in the same regime as non-extremal static charged black strings, that reduce to black holes in four dimensions. We generalize to multi-body configurations on a line by constructing closed-form generalized charged Weyl solutions in the same theory. Generic solutions consist of topological stars and black strings stacked on a line, that are wrapped by electromagnetic fluxes. We embed the solutions in type IIB String Theory on \(S^1 \times T^4\). In this framework, the charged Weyl solutions provide a novel class in String Theory of multiple charged objects in the non-supersymmetric and non-extremal black hole regime.Dark matter as dark dwarfs and other macroscopic objects: multiverse relics?https://zbmath.org/1472.830442021-11-25T18:46:10.358925Z"Gross, Christian"https://zbmath.org/authors/?q=ai:gross.christian"Landini, Giacomo"https://zbmath.org/authors/?q=ai:landini.giacomo"Strumia, Alessandro"https://zbmath.org/authors/?q=ai:strumia.alessandro"Teresi, Daniele"https://zbmath.org/authors/?q=ai:teresi.danieleSummary: First order phase transitions can leave relic pockets of false vacua and their particles, that manifest as macroscopic Dark Matter. We compute one predictive model: a gauge theory with a dark quark relic heavier than the confinement scale. During the first order phase transition to confinement, dark quarks remain in the false vacuum and get compressed, forming Fermi balls that can undergo gravitational collapse to stable dark dwarfs (bound states analogous to white dwarfs) near the Chandrasekhar limit, or primordial black holes.Hidden dark matter from Starobinsky inflationhttps://zbmath.org/1472.830452021-11-25T18:46:10.358925Z"Li, Qiang"https://zbmath.org/authors/?q=ai:li.qiang.3|li.qiang.1|li.qiang.2|li.qiang.4"Moroi, Takeo"https://zbmath.org/authors/?q=ai:moroi.takeo"Nakayama, Kazunori"https://zbmath.org/authors/?q=ai:nakayama.kazunori"Yin, Wen"https://zbmath.org/authors/?q=ai:yin.wenSummary: The Starobinsky inflation model [\textit{S. Gottlöber} et al., Int. J. Mod. Phys. D 1, No. 2, 257--279 (1992; Zbl 0935.83520)] is one of the simplest inflation models that is consistent with the cosmic microwave background observations. In order to explain dark matter of the universe, we consider a minimal extension of the Starobinsky inflation model with introducing the dark sector which communicates with the visible sector only via the gravitational interaction. In Starobinsky inflation model, a sizable amount of dark-sector particle may be produced by the inflaton decay. Thus, a scalar, a fermion or a vector boson in the dark sector may become dark matter. We pay particular attention to the case with dark non-abelian gauge interaction to make a dark glueball a dark matter candidate. In the minimal setup, we show that it is difficult to explain the observed dark matter abundance without conflicting observational constraints on the coldness and the self-interaction of dark matter. We propose scenarios in which the dark glueball, as well as other dark-sector particles, from the inflaton decay become viable dark matter candidates. We also discuss possibilities to test such scenarios.Correction to: ``Testing creation cold dark matter cosmology with the radiation temperature-redshift relation''https://zbmath.org/1472.831112021-11-25T18:46:10.358925Z"Baranov, Iuri P. R."https://zbmath.org/authors/?q=ai:baranov.iuri-p-r"Jesus, José F."https://zbmath.org/authors/?q=ai:jesus.jose-f"Lima, José A. S."https://zbmath.org/authors/?q=ai:lima.jose-a-sA typo in Equation 2 of the authors' article [ibid. 51, No. 2, Paper No. 33, 13 p. (2019; Zbl 1414.83102)] is corrected.Low-scale seesaw from neutrino condensationhttps://zbmath.org/1472.831152021-11-25T18:46:10.358925Z"Dib, Claudio"https://zbmath.org/authors/?q=ai:dib.claudio-o"Kovalenko, Sergey"https://zbmath.org/authors/?q=ai:kovalenko.sergey"Schmidt, Ivan"https://zbmath.org/authors/?q=ai:schmidt.ivan"Smetana, Adam"https://zbmath.org/authors/?q=ai:smetana.adamSummary: Knowledge of the mechanism of neutrino mass generation would help understand a lot more about Lepton Number Violation (LNV), the cosmological evolution of the Universe, or the evolution of astronomical objects. Here we propose a verifiable and viable extension of the Standard model for neutrino mass generation, with a low-scale seesaw mechanism via LNV condensation in the sector of sterile neutrinos. To prove the concept, we analyze a simplified model of just a single family of elementary particles and check it against a set of phenomenological constraints coming from electroweak symmetry breaking, neutrino masses, leptogenesis and dark matter. The model predicts (i) TeV scale quasi-degenerate heavy sterile neutrinos, suitable for leptogenesis with resonant enhancement of the \textit{CP} asymmetry, (ii) a set of additional heavy Higgs bosons whose existence can be challenged at the LHC, (iii) an additional light and sterile Higgs scalar which is a candidate for decaying warm dark matter, and (iv) a majoron. Since the model is based on simple and robust principles of dynamical mass generation, its parameters are very restricted, but remarkably it is still within current phenomenological limits.Cosmology of linear Higgs-sigma models with conformal invariancehttps://zbmath.org/1472.831172021-11-25T18:46:10.358925Z"Lee, Hyun Min"https://zbmath.org/authors/?q=ai:lee.hyun-min"Menkara, Adriana G."https://zbmath.org/authors/?q=ai:menkara.adriana-gSummary: We consider general linear Higgs-sigma models as ultra-violet completions of the Higgs inflation. We introduce general higher curvature terms beyond Einstein gravity and recast them into a class of linear Higgs-sigma models in the scalar-dual formulation where conformal symmetry is manifest. Integrating out the sigma field in this class of linear sigma models, we obtain the same Higgs inflation Lagrangian of non-linear sigma model type in the effective theory. We show that the successful inflation for sigma field singles out the sigma-field potential derived from the \(R^2\) term and the tracker solution for dark energy at late times can be realized for the \(R^{p+1}\) term with \(-1 < p < 0\). We also discuss the implications of Higgs-sigma interactions for the inflation and the vacuum stability in the Standard Model.Stationary scalar hairy configurations supported by Neumann compact starshttps://zbmath.org/1472.850012021-11-25T18:46:10.358925Z"Peng, Yan"https://zbmath.org/authors/?q=ai:peng.yanSummary: We study stationary scalar field hairy configurations supported by asymptotically flat horizonless compact stars. At the star surface, we impose Neumann boundary conditions for the scalar field. With analytical methods, we obtain bounds on the frequency of scalar fields. For certain discrete frequency satisfying the bounds, we numerically get solutions of scalar hairy stars. We also disclose effects of model parameters on the discrete frequency of scalar fields.Non-standard magnetohydrodynamics equations and their implications in sunspotshttps://zbmath.org/1472.850022021-11-25T18:46:10.358925Z"El-Nabulsi, Rami Ahmad"https://zbmath.org/authors/?q=ai:el-nabulsi.rami-ahmadSummary: In this work, we study the physics of plasma waves and magnetohydrodynamic (MHD) equilibrium of sunspots based on the concept of non-standard Lagrangians which play an important role in several branches of science. We derived the modified fluid equations from the Maxwell-Vlasov equation using the moment conventional procedure. Several new interaction terms between physical quantities arise in the non-standard MHD (NS-MHD) equations that give rise to additional features in plasma MHD. A number of fundamental problems in plasma physics are discussed including the non-relativistic dynamics of inviscid fluid subject to the gravitational field, linear waves in plasma MHD and MHD equilibrium of sunspots. For the case of magnetoacoustic wave, it was observed that the NS-MHD equations modify the dispersion relation and its corresponding velocity depends on the sign (positive or negative) of the free parameters introduced in the theory. The non-standard Alfvén velocity is greater than the standard Alfvén velocity for the negative sign and smaller for the positive sign. Besides, in the MHD equilibrium of sunspots, non-standard MHD extends the conventional problem by adding several constraints that lead to an emergence of very low temperature inside the magnetic flux tube comparable to what is observed in low-temperature superconductors. Additional consequences are discussed accordingly.The magnetorotational instability prefers three dimensionshttps://zbmath.org/1472.850032021-11-25T18:46:10.358925Z"Oishi, Jeffrey S."https://zbmath.org/authors/?q=ai:oishi.jeffrey-s"Vasil, Geoffrey M."https://zbmath.org/authors/?q=ai:vasil.geoffrey-m"Baxter, Morgan"https://zbmath.org/authors/?q=ai:baxter.morgan"Swan, Andrew"https://zbmath.org/authors/?q=ai:swan.andrew-w"Burns, Keaton J."https://zbmath.org/authors/?q=ai:burns.keaton-j"Lecoanet, Daniel"https://zbmath.org/authors/?q=ai:lecoanet.daniel"Brown, Benjamin P."https://zbmath.org/authors/?q=ai:brown.benjamin-pSummary: The magnetorotational instability (MRI) occurs when a weak magnetic field destabilizes a rotating, electrically conducting fluid with inwardly increasing angular velocity. The MRI is essential to astrophysical disc theory where the shear is typically Keplerian. Internal shear layers in stars may also be MRI-unstable, and they take a wide range of profiles, including near-critical. We show that the fastest growing modes of an ideal magnetofluid are three-dimensional provided the shear rate, \(S\), is near the two-dimensional onset value, \(S_{}c\). For a Keplerian shear, three-dimensional modes are unstable above \(S \approx 0.10\, S_c\), and dominate the two-dimensional modes until \(S \approx 2.05\, S_c\). These three-dimensional modes dominate for shear profiles relevant to stars and at magnetic Prandtl numbers relevant to liquid-metal laboratory experiments. Significant numbers of rapidly growing three-dimensional modes remainy well past \(2.05\,S_c\). These finding are significant in three ways. First, weakly nonlinear theory suggests that the MRI saturates by pushing the shear rate to its critical value. This can happen for systems, such as stars and laboratory experiments, that can rearrange their angular velocity profiles. Second, the non-normal character and large transient growth of MRI modes should be important whenever three-dimensionality exists. Finally, three-dimensional growth suggests direct dynamo action driven from the linear instability.Cosmology from Newton-Chern-Simons gravityhttps://zbmath.org/1472.850042021-11-25T18:46:10.358925Z"Lepe, S."https://zbmath.org/authors/?q=ai:lepe.samuel"Rubio, G."https://zbmath.org/authors/?q=ai:rubio.gregorio|rubio.gerardo|rubio.gustavo|rubio.gonzalo|rubio.guillermo-j"Salgado, P."https://zbmath.org/authors/?q=ai:salgado.paulo|salgado.patricio|salgado.pablo|salgado.pilarSummary: We study a five-dimensional non-relativistic gravity theory whose action is composed of a gravitational sector and a sector of matter where the gravitational sector is given by the so called Newton-Chern-Simons gravity and where the matter sector is described by a perfect fluid. At time to do cosmology, the obtained field equations shows a close analogy with the projectable version of the Hořava-Lifshitz theory in \((3+1)\)-dimensions. Solutions and their asymptotic limits are found. In particular a phantom solution with a future singularity reminiscent of a Litlle Big Rip future singularity is obtained.Acoustic and inertial modes in planetary-like rotating ellipsoidshttps://zbmath.org/1472.860202021-11-25T18:46:10.358925Z"Vidal, Jérémie"https://zbmath.org/authors/?q=ai:vidal.jeremie"Cébron, David"https://zbmath.org/authors/?q=ai:cebron.davidSummary: The bounded oscillations of rotating fluid-filled ellipsoids can provide physical insight into the flow dynamics of deformed planetary interiors. The inertial modes, sustained by the Coriolis force, are ubiquitous in rapidly rotating fluids and
\textit{S. Vantieghem} [Proc. R. Soc. Lond., Ser. A, Math. Phys. Eng. Sci. 470, No. 2168, Article ID 20140093, 22 p. (2014; Zbl 1371.76157)]
pioneered a method to compute them in incompressible fluid ellipsoids. Yet, taking density (and pressure) variations into account is required for accurate planetary applications, which has hitherto been largely overlooked in ellipsoidal models. To go beyond the incompressible theory, we present a Galerkin method in rigid coreless ellipsoids, based on a global polynomial description. We apply the method to investigate the normal modes of fully compressible, rotating and diffusionless fluids. We consider an idealized model, which fairly reproduces the density variations in the Earth's liquid core and Jupiter-like gaseous planets. We successfully benchmark the results against standard finite-element computations. Notably, we find that the quasi-geostrophic inertial modes can be significantly modified by compressibility, even in moderately compressible interiors. Finally, we discuss the use of the normal modes to build reduced dynamical models of planetary flows.