Exotic Kind Research Articles

Transverse Traveling-Wave and Standing-Wave Ray-Wave Geometric Beams

Ray-wave geometric beam is an exotic kind of structured light with ray-wave duality and coupled diverse degrees of freedom (DoFs), which has attracted intense attention due to its potential applications in theories and applications. This work offers a new insight that the traditional ray-wave geometric beams can be seen as the transverse standing-wave (SW) beams, and can be decomposed into the superposition of transverse traveling-wave (TW) beams. We construct a generalized model for transverse TW and SW ray-wave geometric beams in the wave picture. In experiment, we exploit a digital hologram system with more flexible tunable DoFs to generate the transverse TW and SW beams, inspiring the exploration for the spatial wave structure of more complex structured light.

Traversable wormholes in the traceless f(R,T) gravity

Wormholes are tunnels connecting different regions in spacetime. They were obtained originally as a solution for Einstein’s General Theory of Relativity and according to this theory they need to be filled by an exotic kind of anisotropic matter. In the present sense, by “exotic matter” we mean matter that does not satisfy the energy conditions. In this paper, we propose the modeling of traversable wormholes (i.e. wormholes that can be safely crossed) within an alternative gravity theory that proposes an extra material (rather than geometrical) term in its gravitational action, namely the traceless [Formula: see text] theory of gravitation, with [Formula: see text] and [Formula: see text] being, respectively, the Ricci scalar and trace of the energy–momentum tensor. Our solutions are obtained from well-known particular cases of the wormhole metric potentials, namely redshift and shape functions. In possession of the solutions for the wormhole material content, we also apply the energy conditions to them. The features of those are carefully discussed.

Phantom evolving wormhole solutions in scalar-tensor theories

Wormholes are considered as one of the most interesting hypothetical objects whose existence is also predicted by Einstein’s relativity. It is generally argued that the theoretical construction of such objects demands an exotic kind of anisotropic matter (a matter which is not compatible with the energy constraints). The existence of such matter is regarded as a primary condition for the existence of such geometries. The present manuscript examines the existence of wormhole structures in f(R, ϕ) gravity by taking hyperbolic shape function with constant and logarithmic redshift functions into account. For this purpose, we check the validity of energy condition bounds in both cases graphically. It is found that the wormhole geometries can be constructed for both constant and logarithmic redshift functions when anisotropic phantom fluid characterized by the EoS ωr=pr/ρ<−1 is taken. Further, we discuss the background features of such objects.

Cosmic acceleration from topological considerations II: fiber bundles

In this work we study an alternative topological model for explaining the observed acceleration of space-time, we answer the question of whether this acceleration could be a consequence of the topology of the universe. For doing that, we propose that the whole universe is composed of a four-dimensional (4D) base space, which represents space-time, endowed with a fiber forming a principal fiber bundle. We analyze this hypothesis for a homogeneous and isotropic 4D space-time and show that the effect of the fiber onto the base space is that the space-time accelerates depending on the group of the fiber, even in an oscillatory way, resembling the behavior of the universe according to recent observations. We conclude that there is the possibility of the accelerating behavior of the universe being due to its whole topology instead of an exotic kind of matter.

Regular Bouncing Solutions, Energy Conditions, and the Brans—Dicke Theory

In general, to avoid a singularity in cosmological models involves the introduction of exotic kind of matter fields, for example, a scalar field with negative energy density. In order to have a bouncing solution in classical General Relativity, violation of the energy conditions is required. In this work, we discuss a case of the bouncing solution in the Brans-Dicke theory with radiative fluid that obeys the energy conditions, and with no ghosts.

Luminosity determination for the proton-deutron reactions using quasi-free reactions with WASA-at-COSY facility

The scientific aim of our research is experimental confirmation of the existence of mesic-nucleus: a new exotic kind of nuclear matter consisting of nucleons and mesons. In this report we present the method of luminosity determination for experiment performed atWASA-at-COSY detector dedicated to search for 3He-η bound state. This method is based on analysis of quasi-free $pd \to ppn_{{\rm{spec}}} $ reaction.

Phantom fluid supporting traversable wormholes in alternative gravity with extra material terms

Wormholes are tunnels connecting different regions in spacetime. They were obtained originally as a solution for Einstein’s General Relativity theory and according to this theory, they need to be filled by an exotic kind of anisotropic matter. In the present sense, by “exotic matter”, we mean matter that does not satisfy the energy conditions. In this paper, we propose the modeling of wormholes within an alternative gravity theory that proposes an extra material (rather than geometrical) term in its gravitational action. Our solutions are obtained from well-known particular cases of the wormhole metric potentials, named redshift and shape functions, and yield the wormholes to be filled by a phantom fluid, that is, a fluid with equation of state parameter [Formula: see text]. In possession of the solutions for the wormhole material content, we also apply the energy conditions to them. The features of those are carefully discussed.

Emergent pseudospin-1 Maxwell fermions with a threefold degeneracy in optical lattices

The discovery of relativistic spin-1/2 fermions such as Dirac and Weyl fermions in condensed-matter or artificial systems opens a new era in modern physics. An interesting but rarely explored question is whether other relativistic spinal excitations could be realized with artificial systems. Here, we construct twoand three-dimensional tight-binding models realizable with cold fermionic atoms in optical lattices, where the low energy excitations are effectively described by the spin-1 Maxwell equations in the Hamiltonian form. These relativistic (linear dispersion) excitations with unconventional integer pseudospin, beyond the Dirac-Weyl-Majorana fermions, are an exotic kind of fermions named asMaxwell fermions.We demonstrate that the systems have rich topological features. For instance, the threefold degenerate points called Maxwell points may have quantized Berry phases and anomalous quantum Hall effects with spin-momentum locking may appear in topological Maxwell insulators in the two-dimensional lattices. In three dimensions,Maxwell points may have nontrivial monopole charges of \pm2 with two Fermi arcs connecting them, and the merging of the Maxwell points leads to topological phase transitions. Finally, we propose realistic schemes for realizing the model Hamiltonians and detecting the topological properties of the emergent Maxwell quasiparticles in optical lattices.

Low-energy behavior of strongly interacting bosons on a flat-band lattice above the critical filling factor

Bosons interacting repulsively on a lattice with a flat lowest band energy dispersion may, at sufficiently small filling factors, enter into a Wigner-crystal-like phase. This phase is a consequence of the dispersionless nature of the system, which in turn implies the occurrence of single-particle localized eigenstates. We investigate one of these systems---the sawtooth lattice---filled with strongly repulsive bosons at filling factors infinitesimally above the critical point where the crystal phase is no longer the ground state. We find, in the hard-core limit, that the crystal retains its structure in all but one of its cells, where it is broken. The broken cell corresponds to an exotic kind of repulsively bound state, which becomes delocalized. We investigate the excitation spectrum of the system analytically and find that the bound state behaves as a single particle hopping on an effective lattice with reduced periodicity, and is therefore gapless. Thus, the addition of a single particle to a flat-band system at critical filling is found to be enough to make kinetic behavior manifest.

Integrability vs supersymmetry: Poisson structures of the pohlmeyer reduction

We construct recursively an infinite number of Poisson structures for the su- persymmetric integrable hierarchy governing the Pohlmeyer reduction of superstring sigma models on the target spaces AdS n × S n , n = 2,3,5. These Poisson structures are all non-local and not relativistic except one, which is the canonical Poisson structure of the semi-symmetric space sine-Gordon model (SSSSG). We verify that the superposition of the first three Poisson structures corresponds to the canonical Poisson structure of the reduced sigma model. Using the recursion relations we construct commuting charges on the reduced sigma model out of those of the SSSSG model and in the process we explain the integrable origin of the Zukhovsky map and the twisted inner product used in the sigma model side. Then, we compute the complete Poisson superalgebra for the conserved Drinfeld-Sokolov supercharges associated to an exotic kind of extended non-local rigid 2d supersymmetry recently introduced in the SSSSG context. The superalgebra has a kink central charge which turns out to be a generalization to the SSSSG models of the well-known central extensions of the N = 1 sine-Gordon and N = 2 complex sine-Gordon model Poisson superalgebras computed from 2d superspace. The computation is done in two different ways concluding the proof of the existence of 2d supersymmetry in the reduced sigma model phase space under the boost invariant SSSSG Poisson structure.

A unified theory of quantum holonomies

A periodic change of slow environmental parameters of a quantum system induces quantum holonomy. The phase holonomy is a well-known example. Another is a more exotic kind that exhibits eigenvalue and eigenspace holonomies. We introduce a theoretical formulation that describes the phase and eigenspace holonomies on an equal footing. The key concept of the theory is a gauge connection for an ordered basis, which is conceptually distinct from Mead–Truhlar–Berry’s connection and its Wilczek–Zee extension. A gauge invariant treatment of eigenspace holonomy based on Fujikawa’s formalism is developed. Example of adiabatic quantum holonomy, including the exotic kind with spectral degeneracy, are shown.

Elementary model of sprite igniting electric fields

Sprites are a recently discovered exotic kind of lightning above thunderstorms. An analytic model of sprite igniting electric fields is developed to describe the essence of sprite physics. The proposed model uses typical parameters of particularly intense positive lightning discharges inside thunderclouds which cause the sprites. The sensitivity of the results with respect to the natural variability of the model parameters is discussed.

The surprising magnetic topology of Sco: fossil remnant or dynamo output?

We report the discovery of a medium-strength (~0.5 kG) magnetic field on the young, massive star ? Sco (B0.2V), which becomes the third-hottest magnetic star known. Circularly polarized Zeeman signatures are clearly detected in observations collected mostly with the ESPaDOnS spectropolarimeter, recently installed on the 3.6-m Canada-France-Hawaii Telescope; temporal variability is also clearly established in the polarimetry, and can be unambiguously attributed to rotational modulation with a period close to 41 d. Archival ultraviolet (UV) spectra confirm that this modulation repeats over time-scales of decades, and refine the rotation period to 41.033 +/- 0.002 d. Despite the slow rotation rate of ? Sco, we none the less succeed in reconstructing the large-scale structure of its magnetic topology. We find that the magnetic structure is unusually complex for a hot star, with significant power in spherical-harmonic modes of degree up to 5. The surface topology is dominated by a potential field, although a moderate toroidal component is probably present. We fail to detect intrinsic temporal variability of the magnetic structure over the 1.5-yr period of our spectropolarimetric observations (in agreement with the stable temporal variations of the UV spectra), and infer that any differential surface rotation must be very small. The topology of the extended magnetic field that we derive from the photospheric magnetic maps is also more complex than a global dipole, and features in particular a significantly warped torus of closed magnetic loops encircling the star (tilted at about 90° to the rotation axis), with additional, smaller, networks of closed-field lines. This topology appears to be consistent with the exceptional X-ray properties of ? Sco and also provides a natural explanation of the variability observed in wind-formed UV lines. Although we cannot completely rule out the possibility that the field is produced through dynamo processes of an exotic kind, we conclude that its magnetic field is most probably a fossil remnant from the star formation stage. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. E-mail: donati@ast.obs-mip.fr (J-FD); idh@star.ucl.ac.uk (IDH); mmj@st-andrews.ac.uk (MMJ); petit@ast.obs-mip.fr (PP); claude.catala@obspm.fr (CC); jlandstr@uwo.ca (JDL); jean-claude.bouret@oamp.fr (J-CB); evelyne.alecian@obspm.fr (EA); jrb3@st-andrews.ac.uk (JRB); forveill@cfht.hawaii.edu (TF); fpaletou@ast.obs-mip.fr (FP); manset@cfht.hawaii.edu (NM)

An exotic kind of cosmic material: graphite-containing xenoliths from the Krymka (LL3.1) chondrite

Seven graphite-containing xenoliths were found in the Krymka (LL3.1) chondrite. The xenoliths have the following chemical and mineralogical characteristics which distinguish them from the Krymka host: (1) low totals in bulk chemical analyses obtained by electron microprobe; (2) high bulk Fe abundances; (3) a uniform recrystallized, chondrule-free texture; (4) the presence of euhedral graphite and carbon-rich material; (5) higher quantities of troilite and metal; (6) a relatively homogeneous composition of silicates; (7) a distinctive composition of metal, chromite and phosphate; (8) isotopically heavy C in graphite compared to both bulk Krymka and graphite in other ordinary chondrites. The xenoliths are mineralogically similar, but not identical, to the Krymka carbonaceous clast K1, which bears graphite microcrystals, organic compounds and mysterite. They resemble carbonaceous chondrites, both chemically and isotopically. The mineralogical, chemical and isotopic data for the graphite-containing fragments suggest that this material represents metamorphosed varieties of a previously unknown type of unequilibrated carbonaceous matter. Most likely, the graphite has a metamorphic origin and was crystallized from C-containing precursor materials through the following transformation sequence: organic compounds → C-rich material → graphite.

From Past to Present and Future: The Regenerative Spirit of the Abiku

This article investigates the representation of the famous West African abiku phenomenon in three works by three Nigerian writers, namely, J. P. Clark-Bekederemo's poem (1965), Wole Soyinka's poem also entitled (1967) and Ben Okri's novel The Famished Road (1991). The article offers a socio-political reading of the abiku (the myth of a child dies to be reborn) as handled by the three writers and based on a traditional West African world view. The article investigates how the abiku motif has attracted many writers are engaged in various agendas of cultural nationalism and identity formation, and how a close reading of their work points to their aesthetic and ideological concerns. ********** Our country is an abiku country. Like the spirit child, it keeps coming and going. One day it will decide to remain. It will become strong. --Okri, Infinite Riches Modern African literature, written in European languages, is characterized as being a literature that is extremely culture-specific as it relies heavily on local cultures, on African cosmology, and on oral tradition. This cultural specificity, in most cases, projects a political intention that is hard to disregard in any attempted interpretation of a literary text. On the other hand, these two characteristics of African literature have for the past fifty years or so created a kind of literature that is not quite accessible to the Western reader who, first of all, is not well versed in African local cultures and, second, is unable to perceive the political intentions of African writers. Ultimately modern African literature has come to be regarded as an exotic kind of writing but not really serious literature. The Nigerian writer, Ben Okri, sarcastically comments on the way the West perceives African literature: '[t]hey say, 'oh dear, I'm reading an African novel. Ooh dear it's bound to be a bit strange--there are bound to be rituals and things' (Taylor 34). What the West fails to understand, in fact, is that culture specificity in this case is part of the national agenda of many African writers are keen on promoting an exclusively African literary identity despite their awareness of the problematic and implications of writing in a foreign language as in the case of writers like Chinua Achebe, Gabriel Okara, Aye Kei Armah, among others. Indeed, Anthony Appiah explains that African intellectuals are always seeking to develop their cultures in directions that will give them a role and that, unlike the European writer, the African writer asks not who am I? but who are we? (76). Thus, the resort of African writers to their oral tradition is not simply an act of anthropological retrieval of a culture that has been intentionally confiscated by the colonizer, as Western criticism is fond of pointing out (see Cooper's discussion on this point 51-60). On the contrary, it is more of a socio-political agenda. For even though the anthropological project may have been true at a very early stage of African literature (especially West African literature) at the hands of some writers like D. O. Fagunwa and Amos Tutuola's literary production of folkloric material during the 1940s and 1950s, yet the intentions of such writers have attempted to document African folk culture remain to a great extent debatable. In fact, it could be argued that such anthropological projects had their own socio-political agenda since the historical documentation of folkloric material has indeed contributed to the process of building up the African collective memory, which the colonial power had tried earnestly to eradicate. The Abiku Phenomenon This article will investigate the use of the African oral tradition to promote the socio-political agenda of African writers by focusing on the famous West African abiku phenomenon and its representation in three literary texts by three Nigerian writers namely, J. P. Clark-Bekederemo's poem (1965), Wole Soyinka's poem also entitled (1967) and Ben Okri's novel The Famished Road (1991), where the protagonist is an abiku child (see the two poems in the appendix at the end of this article). …

Self Organizing Maps, Vector Quantization, and Fractal Image Coding

This paper reviews the properties of a popular kind of neural network, called self organizing maps, then discusses their relevance for the field of lossy image coding. In particular, vector quantization (VQ) and fractal (block based) coding are studied from a common point of view, emphasizing their relationships. The latter is an exotic kind of (non-causal) predictive-VQ; clustering algorithms, directly useful in the VQ field, can be exploited to reduce its computational complexity.