Search

In this article, we study mass-critical stochastic nonlinear Schrödinger equations with a multiplicative noise in 3D with a slight time decay (⁠|$\langle t \rangle ^{-\epsilon }$| for |$\epsilon>0$| arbitrarily small). We prove associated global space-time bounds and the scattering behavior. [ABSTRACT FROM AUTHOR]

Conformal Carter–Penrose diagrams are used for the visualization of hyperboloidal slices, which are smooth spacelike slices reaching null infinity. The focus is on the Schwarzschild black hole geometry in spherical symmetry, whose Penrose diagrams are introduced in a pedagogical way. The stationary regime involves time-independent slices. In this case, different options are given for integrating the height function—the main ingredient for constructing hyperboloidal foliations. The dynamical regime considers slices changing in time, which are evolved together with the spacetime using the eikonal equation. It includes the relaxation of hyperboloidal Schwarzschild trumpet slices and the collapse of a massless scalar field into a black hole, for which Penrose diagrams are presented. [ABSTRACT FROM AUTHOR]

In this paper, we introduce and characterize a pseudo-generalized Ricci-recurrent spacetimes and produce an example to verify the existence of such a spacetime. Then we demonstrate that a conformally flat generalized Ricci-recurrent spacetime with certain condition is a pseudo quasi-Einstein spacetime. Besides, it is proved that a pseudo-generalized Ricci-recurrent generalized Robertson–Walker spacetime represents a perfect fluid spacetime. Lastly, we study the impact of this spacetime under f (ℛ , T 2) and f (ℛ ∗) gravity scenario and deduce several energy conditions. [ABSTRACT FROM AUTHOR]

In this work, using a different theoretical approach, we study a homogeneous and isotropic cosmological spacetime filled with a perfect fluid. Using the framework of Brans–Dicke (BD) and Gauss–Bonnet (GB) theories and including a scalar potential, we obtain the analytical solution of the field equations and find the field functions and the relevant expansion parameter of the spacetime. We assume that the BD and GB media can interact with each other, and hence that there is an energy transfer between these two components. Using this approach, we assume that the BD scalar field is related to intrinsic properties of the GB medium. We introduced a power-law scalar field ϕ (t) = ϕ 0 t p and found the appropriate dynamical functions for the different powers p. We found that the expansion rate of spacetime also behaves as a power-law, and the accelerating expansion is always satisfied for this model. We also analyze the stability for physically acceptable critical points for a given scale factor. [ABSTRACT FROM AUTHOR]

Spatial topology endows topological solitons, such as skyrmions and hopfions, with fascinating dynamics. However, the temporal dimension has so far provided a passive stage on which topological solitons evolve. Here we construct spacetime magnetic hopfions: magnetic textures in two spatial dimensions that when excited by a time-periodic drive develop spacetime topology. We uncover two complementary construction routes using skyrmions by braiding their center of mass position and by controlling their internal low-energy excitations. Spacetime magnetic hopfions can be realized in nanopatterned grids to braid skyrmions and in frustrated magnets under an applied AC electric field. Their topological invariant, the spacetime Hopf index, can be tuned by the applied electric field as demonstrated by our collective coordinate modeling and micromagnetic simulations. The principles we have introduced to actively control spacetime topology are not limited to magnetic solitons, opening avenues to explore spacetime topology of general order parameters and fields. Topological solitons are localized structures whose stability emerges from the topology of their spatial structure, hence they are usually independent of the temporal dimension. The authors construct topological magnetic solitons in space-time from periodically driven magnetic structures that can be externally controlled. [ABSTRACT FROM AUTHOR]

We present an overview of both older and recent developments concerning scale separation in string theory. We focus on parametric scale separation obtained at the classical level in flux compactifications down to AdS vacua. We review the scenarios that have been proposed to achieve a hierarchy of scales between spacetime and the internal space, built from a low-dimensional perspective. We then discuss how they have been understood to arise from proper higher-dimensional descriptions. Eventually, limitations of these constructions as well as Swampland and holographic arguments addressing the question of scale separation in string theory are discussed. The purpose of the review is to draw an accurate picture of the state of the art of the subject at the moment. [ABSTRACT FROM AUTHOR]

The following article studies the travel narratives of contemporary writers Flávia Péret (Brazil), Introções para montar mapas, ciudades e quebra-cabeças (2021) and Fernanda Trías (Uruguay), La ciudad invencible (2014), both of which depict a stay in the city of Buenos Aires as a precarious displacement. In their texts, the writers construct a heterogeneous temporality plotted in the journeys of their protagonists for whom inhabiting a strange territory implies testing their traveling conditions as foreign Latin American women. The writing progresses by registering the political effects of this crossing in the continuities of a violence that links past and present in the Cono Sur to the extent that this space-time is marked by poverty and abandonment together with forms of politics that broaden the frameworks of cultural legibility for the recognition of loss. Their writings on displacement manage to capture in the city of Buenos Aires a zone of contact between the consequences of the 2001's economic crisis that marks lives of dispossession, particularly those of immigrant workers, while at the same time pointing to the emergence of instances that make possible a public mourning of the lives eliminated by the State terrorism of the 1970s. [ABSTRACT FROM AUTHOR]

We define a new gauge independent quasi-local mass and energy, and show its relation to the Brown–York Hamilton–Jacobi analysis. A quasi-local proof of the positivity, based on spacetime harmonic functions, is given for admissible closed spacelike 2-surfaces which enclose an initial data set satisfying the dominant energy condition. Like the Wang-Yau mass, the new definition relies on isometric embeddings into Minkowski space, although our notion of admissibility is different from that of Wang and Yau. Rigidity is also established, in that vanishing energy implies that the 2-surface arises from an embedding into Minkowski space, and conversely the mass vanishes for any such surface. Furthermore, we show convergence to the ADM mass at spatial infinity, and provide the equation associated with optimal isometric embedding. [ABSTRACT FROM AUTHOR]

Zika, a viral disease transmitted to humans by Aedes mosquitoes, emerged in the Americas in 2015, causing large-scale epidemics. Colombia alone reported over 72,000 Zika cases between 2015 and 2016. Using national surveillance data from 1121 municipalities over 70 weeks, we identified sociodemographic and environmental factors associated with Zika's emergence, re-emergence, persistence, and transmission intensity in Colombia. We fitted a zero-state Markov-switching model under the Bayesian framework, assuming Zika switched between periods of presence and absence according to spatially and temporally varying probabilities of emergence/re-emergence (from absence to presence) and persistence (from presence to presence). These probabilities were assumed to follow a series of mixed multiple logistic regressions. When Zika was present, assuming that the cases follow a negative binomial distribution, we estimated the transmission intensity rate. Our results indicate that Zika emerged/re-emerged sooner and that transmission was intensified in municipalities that were more densely populated, at lower altitudes and/or with less vegetation cover. Warmer temperatures and less weekly-accumulated rain were also associated with Zika emergence. Zika cases persisted for longer in more densely populated areas with more cases reported in the previous week. Overall, population density, elevation, and temperature were identified as the main contributors to the first Zika epidemic in Colombia. We also estimated the probability of Zika presence by municipality and week, and the results suggest that the disease circulated undetected by the surveillance system on many occasions. Our results offer insights into priority areas for public health interventions against emerging and re-emerging Aedes-borne diseases. [ABSTRACT FROM AUTHOR]

We investigate the turnaround radius of the Reissner–Nordström deSitter Spacetime and how the turnaround radius changes if a test particle carries charge. We also consider the Martínez–Troncoso–Zanelli (MTZ) solution of conformally coupled gravity and investigate how the turnaround radius changes for a scalar test charge. In both scalar and electric interaction cases we find that the Turnaround Radius depends on the particle's energy. [ABSTRACT FROM AUTHOR]

The process of the gravitational collapse might lead not only to a black hole but also to naked singularity formation. In this paper, we consider the generalized Vaidya spacetime with polytropic and generalized polytropic equations of state. We solve the Einstein and Einstein–Maxwell equations to obtain the explicit form of a mass function. We consider the limiting cases of solutions and find out, that generalized Vaidya spacetime might behave like Vaidya–de Sitter and Bonnor–Vaidya–de sitter solutions. Moreover, we explicitly show, that the part of solution, which depends on the polytropic index, is similar to cosmological fields surrounding both Vaidya and Bonnor–Vaidya black holes. The process of the gravitational collapse has been then considered. We have found out that the conditions of the naked singularity formation don't depend on the polytropic index. [ABSTRACT FROM AUTHOR]

We propose an ansatz for encoding the physics of nonlocal spacetime defects in the Green's functions for a scalar field theory defined on a causal set. This allows us to numerically study the effects of nonlocal spacetime defects on the discrete Feynman propagator of the theory defined on the causal set in 1+1 dimensions, and to compare to the defect-free limit. The latter approaches the expected continuum result, on average, when the number of points becomes large. When defects are present, two points with the same invariant spacetime interval can have different propagation amplitudes, depending on whether the propagation is between two ordinary spacetime points, two defects, or a defect and an ordinary point. We show that a coarse-grained description that is only sensitive to the average effect of the defects can be interpreted as a defect-induced mass and wave-function renormalization of the scalar theory. [ABSTRACT FROM AUTHOR]

A complete canonical formulation of general covariance makes it possible to construct new modified theories of gravity that are not of higher-curvature form, as shown here in a spherically symmetric setting. The usual uniqueness theorems are evaded by using a crucial and novel ingredient, allowing for fundamental fields of gravity distinct from an emergent space-time metric that provides a geometrical structure to all solutions. As specific examples, there are new expansion-shear couplings in cosmological models, a form of modified Newtonian dynamics can appear in a space-time covariant theory without introducing extra fields, and related effects help to make effective models of canonical quantum gravity fully consistent with general covariance. [ABSTRACT FROM AUTHOR]

The human brain is a complex system, whose activity exhibits flexible and continuous reorganization across space and time. The decomposition of whole-brain recordings into harmonic modes has revealed a repertoire of gradient-like activity patterns associated with distinct brain functions. However, the way these activity patterns are expressed over time with their changes in various brain states remains unclear. Here, we investigate healthy participants taking the serotonergic psychedelic N,N -dimethyltryptamine (DMT) with the Harmonic Decomposition of Spacetime (HADES) framework that can characterize how different harmonic modes defined in space are expressed over time. HADES demonstrates significant decreases in contributions across most low-frequency harmonic modes in the DMT-induced brain state. When normalizing the contributions by condition (DMT and non-DMT), we detect a decrease specifically in the second functional harmonic, which represents the uni- to transmodal functional hierarchy of the brain, supporting the leading hypothesis that functional hierarchy is changed in psychedelics. Moreover, HADES' dynamic spacetime measures of fractional occupancy, life time and latent space provide a precise description of the significant changes of the spacetime hierarchical organization of brain activity in the psychedelic state. [ABSTRACT FROM AUTHOR]

We determine the conjugacy classes of the Poincaré group ISO+(n, 1) and apply this to classify the stationary trajectories of Minkowski spacetimes in terms of timelike Killing vectors. Stationary trajectories are the orbits of timelike Killing vectors and, equivalently, the solutions to Frenet–Serret equations with constant curvature coefficients. We extend the 3 + 1 Minkowski spacetime Frenet–Serret equations due to Letaw to Minkowski spacetimes of arbitrary dimension. We present the explicit families of stationary trajectories in 4 + 1 Minkowski spacetime. [ABSTRACT FROM AUTHOR]

We are interested in the semilinear wave equations evolving in the expanding spacetimes with Friedmann–Lemaître–Robertson–Walker (FLRW) metric. By the weighted energy estimate, we show that when the nonlinearity depends on the time derivative of the unknown, the equation admits a global smooth solution if the spacetime is undergoing accelerated expansion. While the solution will blowup in the sense of some averaged quantity if the expanding rate is not fast enough. When the nonlinearity depends on the space derivatives of the unknown or the unknown itself, we can show that the solution will blowup in finite time even though the expanding rate is fast enough (accelerated expansion). Our results show that the semilinear wave equations in FLRW spacetimes have different properties from the famous Glassey and Strauss conjectures in flat or asymptotically flat spacetimes. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive space-time algorithm based on domain decomposition for the large-scale simulation of a recently developed thermodynamically consistent reservoir problem. In the approach, the bound constraints are represented by means of a minimum-type complementarity function to enforce the positivity of the reservoir model, and a space-time mixed finite element method is applied for the parallel-in-time monolithic discretization. In particular, we propose a time-adaptive strategy using the improved backward differencing formula of second order, to take full advantage of the high degree of space-time parallelism. Moreover, the complicated dynamics with higher nonlinearity of space-time discretization require some innovative nonlinear and linear solution strategies. Therefore, we present a class of modified semismooth Newton algorithms to enhance the convergence rate of nonlinear iterations. Multilevel space-time restricted additive Schwarz algorithms, whose subdomains cover both space and time variables, are also studied for domain decomposition-based preconditioning. Numerical experiments demonstrate the robustness and parallel scalability of the proposed adaptive space-time algorithm on a supercomputer with tens of thousands of processor cores. [ABSTRACT FROM AUTHOR]

This paper extends the definition of the complexity factor for a charged self‐gravitating structure in the background of f(R,T)$f(\mathbf {R},\mathbf {T})$ gravity. For this purpose, the modified Einstein‐Maxwell field equations and the mass function in terms of interior charge are calculated corresponding to a static sphere. The Reissner‐Nordström exterior spacetime and match it with the spherical interior at the hypersurface to determine the junction conditions are adopted then. The curvature tensor is also decomposed orthogonally, resulting in several scalar functions. Only YTF$\mathbf {Y}_{TF}$ encompasses all the required parameters and fulfills the proposed criteria to be the complexity factor for the considered setup is noticed. Moreover, some constraints to minimize the degrees of freedom in the field equations are chosen. To achieve this, complexity‐free constraint with four additional conditions depending on the matter sector that lead to different models is employed. The stability of the developed models is also analyzed in the presence and absence of charge through the standard model R+2ξ3T$\mathbf {R}+2\xi _3\mathbf {T}$ by varying the values of the model parameter ξ3$\xi _3$. The presence of charge in compact models corresponding to Pr=0$\mathrm{P}_r=0$, a polytropic and a linear equation of state make them stable for specific values of ξ3$\xi _3$ is concluded. This paper extends the definition of the complexity factor for a charged self‐gravitating structure in the background of f (R, T) gravity. For this purpose, the modified Einstein‐Maxwell field equations and the mass function in terms of interior charge are calculated corresponding to a static sphere. The Reissner‐Nordström exterior spacetime and match it with the spherical interior at the hypersurface to determine the junction conditions are adopted then. The curvature tensor is also decomposed orthogonally, resulting in several scalar functions. Only YTF encompasses all the required parameters and fulfills the proposed criteria to be the complexity factor for the considered setup is noticed. Moreover, some constraints to minimize the degrees of freedom in the field equations are chosen. To achieve this, complexity‐free constraint with four additional conditions depending on the matter sector that lead to different models is employed. The stability of the developed models is also analyzed in the presence and absence of charge through the standard model R + 2ξ3T by varying the values of the model parameter ξ3. The presence of charge in compact models corresponding to Pr = 0, a polytropic and a linear equation of state make them stable for specific values of ξ3 is concluded. [ABSTRACT FROM AUTHOR]

In general, a perfect fluid spacetime is not a generalized Robertson–Walker spacetime and the converse is also not true. In this paper, it is shown that if a perfect fluid spacetime satisfies the critical point equation, then either the spacetime becomes a generalized Robertson–Walker spacetime and represents dark era or the vorticity of the fluid vanishes as well as the spacetime is expansion free. Besides, we prove that if a generalized Robertson–Walker spacetime with constant scalar curvature satisfies the critical point equation, then the spacetime becomes a perfect fluid spacetime. Next, the existence of critical point equation is established by a non-trivial example. Finally, we discuss the critical point equation in f (r) -gravity. For the model f (r) = r − α (1 − e − r α ) (α = constant and r is the scalar curvature of the spacetime), various energy conditions in terms of the scalar curvature are examined and state that the Universe is in an accelerating phase and satisfies the weak, null, dominant, and strong energy conditions. [ABSTRACT FROM AUTHOR]

In this study, the energy–momentum localization problem is addressed within the framework of rainbow gravity. Considering the black string black hole, one of the cylindrical black hole models, energy–momentum distributions are obtained for Einstein, Bergmann–Thomson, and Landau–Liftshitz prescriptions in rainbow gravity. All prescriptions' energy densities are non-zero and depend on the rainbow functions, while the momentum distributions are zero. It has been observed that space-time energy does not depend on the energy of the test particle for some particular choices of rainbow functions. The results obtained for all special cases are given in a table. [ABSTRACT FROM AUTHOR]

In this paper, we explore the existence of wormholes in the context of f (R , T) gravity. The f (R , T) theory is a curvature-matter coupled modified gravity that depends on an arbitrary function of the Ricci scalar R and the trace of the stress-energy tensor T. In this work, we adopt two different choices for the matter Lagrangian density ( ℒ m = and ℒ m = p r ) and investigate the impact of each one on wormhole structure. By adequately specifying the redshift function and the shape function, we found a variety of exact wormhole solutions in the theory. Our finding indicates that for both classes of wormholes, the energy density is always positive throughout the spacetime, while the radial pressure is negative. This means exotic matter is necessary for the existence of wormholes in f (R , T) gravity. [ABSTRACT FROM AUTHOR]

Here, we studied Bianchi type-III string cosmological models generated using a cloud of strings with particles connected to them in the framework of Lyra geometry considering five-dimensional spacetime. We assume that the shear scalar and scalar expansion are proportional to obtain the exact solutions of the survival field equations here. Secondly, we adopt the assumption considering the Reddy string condition. From the different cases obtained here, the first case gives the Bianchi type-III string cosmology in Lyra geometry in five-dimensional spacetime, and the second case gives the five-dimensional vacuum model in general relativity. The various parameters of the model universe, which are very important for the description of the Universe, are obtained, and their properties are studied and compared with the recent observational findings. The model universe obtained here starts with the Big Bang, and as time progresses, both particle density and energy density decrease with the expansion of our Universe. [ABSTRACT FROM AUTHOR]

This article is devoted to the study of Kaluza-Klein space-time filled with cosmic string and attractive massive scalar field in the presence of minimally interacting dark energy in general relativity. Some physically significant conditions have been utilized to obtain a deterministic solution of the field equations. The behavior of cosmological parameters such as volume, scalar field, deceleration parameter, equation of state (EoS) parameter, statefinder parameter, Om diagnostic are discussed. It is also worth noting that the conclusions of the cosmological parameter are consistent with modern observational data. [ABSTRACT FROM AUTHOR]

The C*-algebraic construction of QFT by Buchholz and one of us relies on the causal structure of space-time and a classical Lagrangian. In one of our previous papers, we have introduced additional structure into this construction, namely an action of symmetries, which is related to fixing renormalization conditions. This action characterizes anomalies and satisfies a cocycle condition which is summarized in the unitary anomalous Master Ward identity. Here (using perturbation theory) we show how this cocycle condition is related to the Wess–Zumino consistency relation and the consistency relation for the anomaly in the BV formalism, where the latter follows from the generalized Jacobi identity for the associated L ∞ -algebra. In addition, we give a proof that perturbative agreement (i.e., independence of a perturbative QFT on the splitting of the Lagrangian into free and interacting parts) can be achieved by finite renormalizations. [ABSTRACT FROM AUTHOR]

We compare a relativistic and a nonrelativistic version of Ostrogradsky's method for higher-time derivative theories extended to scalar field theories and consider as an alternative a multi-field variant. We apply the schemes to space–time rotated modified Korteweg–de Vries systems and, exploiting their integrability, to Hamiltonian systems built from space–time rotated inverse Legendre transformed higher-order charges of these systems. We derive the equal-time Poisson bracket structures of these theories, establish the integrability of the latter theories by means of the Painlevé test and construct exact analytical period benign solutions in terms of Jacobi elliptic functions to the classical equations of motion. The classical energies of these partially complex solutions are real when they respect a certain modified CPT-symmetry and complex when this symmetry is broken. The higher-order Cauchy and initial-boundary value problem are addressed analytically and numerically. Finally, we provide the explicit quantization of the simplest mKdV system, exhibiting the usual conundrum of having the choice between having to deal with either a theory that includes non-normalizable states or spectra that are unbounded from below. In our non-Hermitian system, the choice is dictated by the correct sign in the decay width. [ABSTRACT FROM AUTHOR]

The purpose of this note is to show why and how the fractional operators required for formalizing dynamic issues in complex environment, mobilize among the most advanced mathematical concepts : topos, site, spectrum, sheaf, ringed spaces, p-adic numbers, etc. In the context of physical exchanges in spaces crumpled by long range interaction (hyperbolic geometries), geodesics no longer respond to Noether invariance principles but to memory effects and to the categorical limits imposed by some requirements for completion. This completion is in fine based upon algebra-topology coupling. This coupling may be expressed through the zeta function which, as a bridge, ensures the formal closure of the representation and implicitly the space-time characteristics. The analysis points out the existence of a particular case corresponding to the Riemann hypothesis (and Martin’s axiom). Above approach involves a relationship between quantum mechanics and 2D self-similarity. In non integer cases, time is discretized and an arrow of time naturally emerges from the analysis. The note relates this arrow to anti entropic properties of dissipative complex systems. [ABSTRACT FROM AUTHOR]

Research examining migrant homemaking is multi-disciplinary and well-developed, providing evidence that 'home' exists in multiple places. However, only a small component of this work examines the role of the senses. This paper draws on research conducted between 2015 and 2019 in Glasgow, a city in Scotland, UK, with migrant, refugee and asylum-seeking women that used photo elicitation interviews, to bridge the gap between scholarship on migrant homemaking and the senses. The paper empirically demonstrates how the senses allow migrants to cultivate the embodied experience of physically being elsewhere by drawing on sensory memories, practices, and material cultures, specifically engaging taste and smell. The paper analyses the experience of four participants who described this sensation, and addresses the impact of the security of migrant status and financial resources in sensory homemaking. The concluding discussion proposes the concept of 'sensory space-time compression' as a novel way of understanding the sensory experiences of home in the context of migration. [ABSTRACT FROM AUTHOR]

The study of dynamic singularity formation in spacetime, focusing on scalar field collapse models, is analyzed. We revisit key findings regarding open spatial topologies, concentrating on minimal conditions necessary for singularity and apparent horizon formation. Moreover, we examine the stability of initial data in the dynamical system governed by Einstein's equations, considering variations in parameters that influence naked singularity formation. We illustrate how these results apply to a family of scalar field models, concluding with a discussion on the concept of genericity in singularity studies. [ABSTRACT FROM AUTHOR]

We explore an idea put forward many years ago by Zeldovich and Novikov concerning the existence of compact objects endowed with arbitrarily small mass. The energy density of such objects, which we call "ghost stars", is negative in some regions of the fluid distribution, producing a vanishing total mass. Thus, the interior is matched on the boundary surface to Minkowski space–time. Some exact analytical solutions are exhibited and their properties are analyzed. Observational data that could confirm or dismiss the existence of this kind of stellar object are discussed. [ABSTRACT FROM AUTHOR]

An explanation of the nature of dark energy has been treated in extra dimensions within the scheme of string theory. One of the most successful models is inspired by the Dvali–Gabadadze–Porrati (DGP) model, in which the universe is a 4-dimensional brane embedded in a 5-dimensional Minkowski spacetime. In this landscape, the study of the evolution of the normal branch has led us to different kinds of dark energy, where the most simple case is the cosmological constant Λ. Moreover, other viable cosmological solutions are related to agegraphic dark energy, which allows a late cosmic acceleration within an interacting mechanism. To explore the viability of these solutions and possible gravitational leakage, in this paper, we present constraints on such models using recent standard sirens forecasting in addition to local observables such as Pantheon (SNIa), H (z) measurements, baryonic acoustic oscillations (BAO). Our results show that the value associated with the species of quantum fields n in these models is strongly restricted for supernovae observations to n = 2 0 , and for GW standard sirens mock data prefers a value of n = 1. [ABSTRACT FROM AUTHOR]

Neutrinos from the cosmos have proven to be ideal for probing the nature of space-time. Previous studies on high-energy events of IceCube suggested that some of these events might be gamma-ray burst neutrinos, with their speeds varying linearly with their energy, implying also the coexistence of subluminal and superluminal propagation. However, a recent reanalysis of the data, incorporating revised directional information, reveals stronger signals that neutrinos are actually being slowed down compared to previous suggestion of neutrino speed variation. Thus, it is worth discussing its implications for the brane/string inspired framework of space-time foam, which has been used to explain previous observations. We revisit effects on neutrino propagation from specific foam models within the framework, indicating that the implied violation of Lorentz invariance could necessarily cause the neutrino to decelerate. We therefore argue that this sort of model is in agreement with the updated phenomenological indication just mentioned. An extended analysis of the revised IceCube data will further test these observations and stringy quantum gravity. [ABSTRACT FROM AUTHOR]

This study introduces a deep neural network approach that utilizes radial basis functions (RBFs) to solve forward and inverse problems in the process of diffusion. The input layer incorporates multiquadric (MQ) RBFs, symbolizing the radial distance between the boundary points on the spacetime boundary and the source points positioned outside the spacetime boundary. The output layer is the initial and boundary data given by analytical solutions of the diffusion equation. Utilizing the concept of the spacetime coordinates, the approximations for forward and backward diffusion problems involve assigning initial data on the bottom or top spacetime boundaries, respectively. As the need for discretization of the governing equation is eliminated, our straightforward approach uses only the provided boundary data and MQ RBFs. To validate the proposed method, various diffusion scenarios, including forward, backward, and inverse problems with noise, are examined. Results indicate that the method can achieve high-precision numerical solutions for solving diffusion problems. Notably, only 1/4 of the initial and boundary conditions are known, yet the method still yields precise results. [ABSTRACT FROM AUTHOR]

The magnitude of life on Earth and human limitations hinder the understanding of even the most basic aspects of biodiversity, such as the identity of species inhabiting the Earth, the so‐called Linnean shortfall. Evaluating patterns in species description dates and their relationship with macroecological variables can help guide where taxonomic efforts should be focused. Therefore, we aim to assess the Linnean shortfall in the knowledge of New World coralsnake biodiversity. We modelled species description dates and estimated that approximately one‐third of the coralsnake diversity remains unknown. The undescribed species are evolutionarily closely related to the already described species. Moreover, recently described species in the group have more restricted geographic ranges and tend to be small‐bodied. The western Amazon and the dry diagonal (i.e. Caatinga, Cerrado, and Chaco) are the areas with the oldest description dates. However, assemblages in these areas have the largest average geographic distances to the type locality of their species, suggesting that little taxonomic effort has been dedicated intrinsically to these regions. We suggest that allocating taxonomic efforts to the dry diagonal and the use of integrative taxonomic techniques for better species delimitation are imperative to fill the Linnean shortfall for the New World coralsnakes. [ABSTRACT FROM AUTHOR]

In the last two decades, there has been significant progress in the understanding of ergodic properties of white-forced dissipative PDEs. The previous studies mostly focus on equations posed on bounded domains since they rely on different compactness properties and the discreteness of the spectrum of the Laplacian. In the present paper, we consider the damped complex Ginzburg--Landau equation on the real line driven by a white-in-time noise. Under the assumption that the noise is sufficiently nondegenerate, we establish the uniqueness of stationary measure and exponential mixing in the dual-Lipschitz metric. The proof is based on coupling techniques combined with a generalization of Foiaş--Prodi estimate to the case of the real line and special space-time weighted estimates, which help to handle the behavior of solutions at infinity. [ABSTRACT FROM AUTHOR]

This work develops two temporal second‐order alternating direction implicit (ADI) numerical schemes for solving multidimensional parabolic‐type integrodifferential equations with multi‐term weakly singular Abel kernels. For the two‐dimensional (2D) case, applying the Crank–Nicolson method and product integration rule to discretizations of temporal derivative and integral terms, respectively, and the spatial discretization is proposed using a compact difference formulation combined with the ADI algorithm; for the three‐dimensional case, the method of temporal discretization is the same as the 2D case, and then we employ the standard finite difference in space to construct a fully discrete ADI finite difference scheme. The ADI technique is used to reduce the calculation cost of the high‐dimensional problem. Besides, the stability and convergence of two ADI schemes are rigorously proved by the energy argument, in which the first scheme converges to the order τ2+h14+h24$$ {\tau}^2+{h}_1^4+{h}_2^4 $$, where τ$$ \tau $$, h1$$ {h}_1 $$, and h2$$ {h}_2 $$ denote the time‐space step sizes, respectively, and the second scheme converges to the space‐time second‐order accuracy. Finally, the numerical results verify the correctness of the theoretical analysis and show that the method of this article is competitive with the existing research work. [ABSTRACT FROM AUTHOR]

This article is an interview with Carlos Walter Porto-Gonçalves, a geographer and activist, discussing his upbringing in Rio de Janeiro and his work with indigenous families and fishermen. Porto-Gonçalves emphasizes the importance of geobiography and the connection between people, places, and ideas. He reflects on his political activism and the concept of dignity as the foundation for all struggles for life. Porto-Gonçalves invites readers to explore his methodology and shares his utopian political vision. The text also discusses the author's experiences working with a community affected by sugarcane plantations and their commitment to defending marginalized groups and the environment. It explores the role of theory in research and the importance of respecting diverse forms of knowledge. The text emphasizes the significance of dignity in social movements and the rejection of oppression. Porto-Gonçalves expresses a desire for a society based on friendship and communal values. The text acknowledges the limitations of language and emphasizes the importance of experiencing situations. [Extracted from the article]

We use the semiclassical approach to solve the Klein–Gordon and Dirac equations in the presence of a time-varying electric field. Our objective is to calculate the density of particle creation in a cosmological anisotropic Bianchi- I space–time. We demonstrate that when the electric interaction is proportional to the Ricci scalar of curved space–time, the distribution of particles subjected to the electric field transforms into a thermal state. [ABSTRACT FROM AUTHOR]

Space‐time adaptive processor (STAP) has been widely used for global navigation satellite system (GNSS) anti‐jamming receiver due to its good anti‐jamming performance. When direction of satellite is unknown, STAP can be implemented based on power inversion (PI) criterion. However, existing space‐time PI algorithm will introduce tens to hundreds of degrees biases into carrier phase, and sometimes will even cause cycle slips, which will reduce the success rate of ambiguity resolution, ultimately deteriorating positioning accuracy. A distortion‐less carrier phase tracking space‐time PI algorithm is proposed. The main novelty is that the proposed algorithm keeps the coefficients of the temporal taps as real values by imposing constraints on the weights of the antenna array. Several experiments are implemented to verify the effectiveness of the proposed algorithm. For comparison, the results of PI algorithm and minimum variance distortion‐less response (MVDR) algorithm are shown. Results show that when the number, style, and direction of interferences and the direction of GNSS signal vary, different degrees of biases are introduced into carrier phases for the PI and the MVDR algorithm. However, no bias is introduced into the proposed algorithm. As a result, the effectiveness of the proposed algorithm is verified. [ABSTRACT FROM AUTHOR]

The focus of this paper is to analyze the trends and locations of accidents in the Greater Melbourne Area (GMA) during a 15-year period (2006–2020). The places where accidents were most prevalent were discovered and the reasons which are contributing to the high accident rates in those areas are determined. Analyzing the patterns over time and variations in the frequency of accidents helped to identify areas that have improved or deteriorated in terms of road safety. A Tweedie model was developed to examine the intricate interaction between the accident frequency and its potential contributing factors such as socio-demographics, road transport infrastructure, and built environment. Ultimately, a clustering analysis was performed to elucidate the dispersion of road accident risk ratings among different local government areas (LGAs), offering useful insights into road safety initiatives and prioritization. • The study linked built environment to accidents with Twidee and Space-time Cube. • Accidents down overall (20 yrs), but hotspots move outward. • Melbourne suburbs form five risk clusters based on accident frequency. [ABSTRACT FROM AUTHOR]

The paper argues for the renewed relevance of time geography in tourism in light of the use of mobile technologies and ubiquitous connectivity. The paper proposes the concept of phygitality to understand how digital technologies are used in physical space, and how the interaction between the physical and the digital reconfigures tourists' projects, paths, bundles, and constraints. The theoretical contribution builds on fifteen semi-structured interviews. The analysis shows that capability, coupling, and authority constraints are altered and mediated by digital devices. In the phygital time-space, tourists orient themselves in physical spaces, influenced by digital information; they create phygital paths and move between stations that result from the overlaying of digital information onto the physical space. Tourists' goal-oriented mobility results in phygital projects, where logics of efficiency and optimization reduce the liminality of the tourist experience. Tourists' bundles are created within and outside the physical vacation prism through digital communication. [ABSTRACT FROM AUTHOR]

We prove that a Finsler spacetime endowed with a smooth reference measure whose induced weighted Ricci curvature \mathrm {Ric}_N is bounded from below by a real number K in every timelike direction satisfies the timelike curvature-dimension condition \mathrm {TCD}_q(K,N) for all q\in (0,1). The converse and a nonpositive-dimensional version (N \le 0) of this result are also shown. Our discussion is based on the solvability of the Monge problem with respect to the q-Lorentz–Wasserstein distance as well as the characterization of q-geodesics of probability measures. One consequence of our work is the sharp timelike Brunn–Minkowski inequality in the Lorentz–Finsler case. [ABSTRACT FROM AUTHOR]

The nonlinear space–time fractional Sasa–Satsuma and Schrödinger–Hirota equations with beta derivative describe optical soliton, photonics, plasmas, neutral scalar masons, and long-surface gravitational waves in the real world. Through the fractional wave transform, the models are converted into a single wave variable equation. In this article, we examine a range of compatible, useful, and typical wave solutions expressed in the forms of hyperbolic, trigonometric, and rational functions uniformly through the ( Q ′ / Q , 1 / Q )-expansion approach. When specific parameter values are set, the generalized wave solutions exhibit a wide range of shapes, including asymptotic, anti-asymptotic, dark-optical, breather, lump-periodic, kink, kink-bell-shaped, homoclinic-breather, bright, dark, and periodic solitons that resemble periodic breathing patterns. We also investigate the effect of the fractional parameter δ into the wave profile, revealing a clear correlation between changes in the fractional order derivative δ and variation in the soliton's shape. The results underscore the use of this approach for the exploration of diverse nonlinear fractional systems within the context of beta derivatives. Varying the fractional-order δ and maintaining specific fixed parameter values, we depict 3D-surface, 2D-surface, density, and contour plots to visualize some of the derived solutions. [ABSTRACT FROM AUTHOR]

In this work, we investigate coupled space–time fractional nonlinear Schrödinger equation (FNSE) arising in physics. The FNSE can be utilized to explain non-relativistic quantum mechanical phenomena. With the aid of the conformable fractional derivative (CFD) and fractional complex transform (FCT), we implement the extensive direct algebraic approach (EDAA), the behaviors of some of the generated solutions are shown as 3D-graphics for various with different fractal orders. The optical soliton solutions that are bright periodic, kink bright and kink-bright periodic are among these precise solutions. The acquired results demonstrate the simplicity, effectiveness, and capacity to produce additional kinds of exact solutions of these proposed methods, which are useful in deciphering the intricate physical interpretation of space–time FNSE. [ABSTRACT FROM AUTHOR]

The direct detection of gravitational waves offers a powerful tool to explore the nature of gravity and the structure of space-time. This paper focuses on the capabilities of space-based gravitational wave detectors in testing space-time non-commutativity. Our findings indicate that TianQin has the potential to impose constraints on the non-commutative scale at a sub-Planckian level using massive black hole binaries. Additionally, we have developed a pipeline tailored to this specific topic. [ABSTRACT FROM AUTHOR]

The weak cosmic censorship conjecture is a hypothesis about the nature of event horizons and singularities during the formation of black holes. It posits that singularities are always enveloped by the event horizons of black holes, thereby preventing naked singularities from affecting the causal structure of spacetime. In this paper, we study the effect of rotating short haired black holes on the weak cosmic censorship conjecture. Discussion of whether the event horizons of a rotating short haired black hole is disrupted by studying incident neutral test particles and scalar fields. In the context of short haired black holes, when incident neutral test particles are considered for extreme and near extreme cases, our research results indicate that neutral test particles can destroy the event horizons of short haired black holes, violating the weak cosmic censorship conjecture. In the case of scalar field incidence in short haired black holes, for extreme situations, when the incident wave modes fall within the range of 1 2 κ M + β M κ < ω m < 1 2 M κ + β M κ - 1 2 κ , the results indicate that the event horizons of rotating short haired black holes is disrupted. For near extreme cases, the presence of hair allows for the disruption of the event horizons of rotating short haired black holes, as indicated by our results. Therefore, these conclusions are intriguing and will provide new insights for us to further understand the weak cosmic censorship conjecture and explore the properties of short haired black holes. [ABSTRACT FROM AUTHOR]

In our previous work (Zhang and Shu in Eur Phys J. C 84(3):256, 2024), we have explored quantum gravity induced entanglement of masses (QGEM) in curved spacetime, observing entanglement formation between particles moving along geodesics in a Schwarzschild spacetime background. We find that long interaction time induces entanglement, even for particles with microscopic mass, addressing decoherence concerns. In this work, we build upon our previous work (Zhang and Shu 2024) by extending our investigation to a time-dependent spacetime. Specifically, we explore the entanglement induced by the mutual gravitation of massive particles in the Friedmann–Lemaître–Robertson–Walker (FLRW) universe. With the help of the phase shift and the QGEM spectrum, our proposed scheme offers a potential method for observing the formation of entanglement caused by the quantum gravity of massive particles as they propagate in the FLRW universe. Consequently, it provides insights into the field of entanglement in cosmology. [ABSTRACT FROM AUTHOR]

The study aimed to detect high-risk areas for deaths of children and adolescents 5 to 14 years of age in the state of Mato Grosso, Brazil, from 2009 to 2020. This was an exploratory ecological study with municipalities as the units of analysis. Considering mortality data from the Mortality Information System (SIM) and demographic data from the Brazilian Institute of Geography and Statistics (IBGE), the study used multivariate statistics to identify space-time clusters of excess mortality risk in this age group. From 5 to 9 years of age, two clusters with high mortality risk were detected; the most likely located in the state's southern mesoregion (RR: 1.6; LRT: 8,53). Among the 5 clusters detected in the 10-14- year age group, the main cluster was in the state's northern mesoregion (RR: 2,26; LRT: 7,84). A reduction in mortality rates was observed in the younger age group and an increase in these rates in the older group. The identification of these clusters, whose analysis merits replication in other parts of Brazil, is the initial stage in the investigation of possible factors associated with morbidity and mortality in this group, still insufficiently explored, and for planning adequate interventions. [ABSTRACT FROM AUTHOR]

In this work, we apply an a posteriori error analysis for the space-time, discontinuous in time, Galerkin scheme, which has been proposed in Antonopoulou (2020, Space-time discontinuous Galerkin methods for the |$\varepsilon $| -dependent stochastic Allen–Cahn equation with mild noise. IMA J. Num. Analysis , 40 , 2076–2105) for the |$\varepsilon $| -dependent stochastic Allen–Cahn equation with mild noise |$\dot{W}^\varepsilon $| tending to rough as |$\varepsilon \rightarrow 0$|⁠. Our results are derived under low regularity since the noise even smooth in space is assumed only one-time continuously differentiable in time, according to the minimum regularity properties of Funaki (1999, Singular limit for stochastic reaction–diffusion equation and generation of random interfaces. Acta Math. Sinica , 15 , 407–438). We prove a posteriori error estimates for the |$m$| -dimensional problem, |$m\leq 4$| for a general class of space-time finite element spaces. The a posteriori bound is growing only polynomially in |$\varepsilon ^{-1}$| if the step length |$h$| is bounded by a positive power of |$\varepsilon $|⁠. This agrees with the restriction posed so far in the a priori error analysis of continuous finite element schemes for the |$\varepsilon $| -dependent deterministic Allen–Cahn or deterministic and stochastic Cahn–Hilliard equation. As an application, we examine tensorial elements where the discrete solution is approximated by polynomial functions of separated space and time variables; the a posteriori estimates there involve dimensions, and the space, time discretization parameters. We then consider the special case of the mild noise |$\dot{W}^\varepsilon $| as defined in Weber (2010, On the short time asymptotic of the stochastic Allen–Cahn equation. Ann. Inst. Henri Poincare Probab. Stat. , 46 , 965–975) through the convolution of a Gaussian process with a proper mollifying kernel, which is then numerically constructed. Finally, we provide some useful insights for the numerical algorithm, and present for the first time some numerical experiments of the scheme for both one- and two-dimensional problems in various cases of interest, and compare with the deterministic ones. [ABSTRACT FROM AUTHOR]

The classification of emergent spinor fields according to modified bilinear covariants is scrutinized in space-times with nontrivial topology, which induce inequivalent spin structures. Extended Clifford algebras, constructed by equipping the underlying space-time with an extended bilinear form with additional terms coming from the nontrivial topology, naturally yield emergent extended algebraic spinor fields and their subsequent extended bilinear covariants, which are contrasted to the classical spinor classification. An unexpected duality between the standard and the exotic spinor field classes is therefore established, showing that a complementary fusion process among the spinor field classes sets in, when extended Clifford bundles are addressed in multiply connected space-times. [ABSTRACT FROM AUTHOR]