The study lifts certain Sasakian manifolds to quasi-Einstein spacetimes.
problem Understanding lifts of Sasakian manifolds to quasi-Einstein spacetimes.
method Analyzing smooth Sasakian manifolds and their lifts to 4D quasi-Einstein spacetimes.
result Smooth Sasakian manifolds can be lifted to quasi-Einstein shearfree spacetimes of Petrov type II or D.
We consider axisymmetric stationary dirty black holes with regular non-extremal or extremal horizons, and compute their on-horizon Petrov types. The Petrov type (PT) in the frame of the observer crossing the horizon can be different from that formally obtained in the usual (but singular in the horizon limit) frame of a…
The paper classifies Weyl tensors in Riemannian 4-manifolds via Lorentzian deformation.
problem Classifying Weyl tensors in Riemannian 4-manifolds.
method Deforming the metric into a Lorentzian one via a nonzero vector T. result Only Petrov Types I and D can occur, and each is determined by the number of critical points of the associated Lorentzian quadratic form.
On an oriented 4-manifold, we examine the geometry that arises when the curvature operator of a Riemannian or Lorentzian metric g commutes, not with its own Hodge star operator, but rather with that of another semi-Riemannian metric h that is a suitable deformation of g. We classify the case when one of these met…
Study properties of null string congruences in complex and real pseudo-Riemannian spaces.
problem Analyze properties of null string congruences in 4D spaces.
method Investigate the geometry of null strings and their congruences in complex and real pseudo-Riemannian spaces.
result Relations between null string congruences, Petrov-Penrose types, and Ricci tensor algebraic types are established.
Study para-Kähler-Einstein metrics and their non-integrable twistor distributions.
problem Characterize para-Kähler-Einstein metrics and their associated non-integrable twistor distributions.
method Use Cartan's method of equivalence and analyze the anti-self-dual Weyl tensor.
result Establish a correspondence between the anti-self-dual Weyl tensor and the Cartan quartic of the twistor distribution.
The paper classifies and explores isoparametric hypersurfaces in pseudo-Riemannian space forms.
problem Investigating isoparametric hypersurfaces in pseudo-Riemannian space forms.
method Petrov's classification theorem and shape operator analysis.
result No isoparametric hypersurfaces of index 2 with complex principal curvatures exist.
Derives new symmetry operators for linearized gravity.
problem Symmetries of linearized gravity on vacuum backgrounds.
method Operator identities and adjoints, Teukolsky equation, separability.
result New symmetry operators of differential orders 4 and 6.
The local structure of the manifolds named in the title is described. Although curvature homogeneous, they are not, in general, locally homogeneous. Not all of them are Ricci-flat, which answers an existence question about type III Jordan-Osserman metrics, raised by Diaz-Ramos, Garcia-Rio and Vazquez-Lorenzo (2006).
The Einstein Equation on 4-dimensional Lorentzian manifolds admitting recurrent null vector fields is discussed. Several examples of a special form are constructed. The holonomy algebras, Petrov types and the Lie algebras of Killing vector fields of the obtained metrics are found.
Optical (or Robinson) structures are one generalisation of four-dimensional shearfree congruences of null geodesics to higher dimensions. They are Lorentzian analogues of complex and CR structures. In this context, we extend the Goldberg-Sachs theorem to five dimensions. To be precise, we find a new algebraic condition…
2D twistor manifolds explain Teukolsky equations for rotating black holes.
problem Understanding the geometry of Teukolsky equations for rotating black holes.
method Using 2D twistor manifolds to explain the Teukolsky equations.
result All geometric structures can be understood by considering a 2D twistor manifold.
Kähler metrics derived from Lorentzian geometry in 4D.
problem Constructing Kähler metrics from Lorentzian structures.
method Using vector fields and Lie bracket relations to define Kähler metrics.
result Kähler metrics coincide with the original manifold in many examples.
Study on mode stability of gravitational instantons of type D.
problem Proving mode stability of gravitational instantons of type D.
method Analogous to Lorentzian case, analyze Weyl curvature scalars satisfying a separable Teukolsky equation.
result Prove mode stability, showing no solutions compatible with regularity and asymptotic flatness.
The paper constructs a new Ricci-flat metric on almost abelian Lie groups.
problem Finding Lorentzian homogeneous Ricci-flat metrics on almost abelian Lie groups.
method Constructing left-invariant metrics on almost abelian Lie groups, focusing on dimensions four or higher.
result A new Ricci-flat metric that generalizes the Petrov solution to higher dimensions.
Derives new identities for linearized gravity on Kerr spacetime.
problem Linearized gravity on Kerr spacetime.
method Derives a complex symmetric 2-tensor M_ab and shows it solves linearized Einstein equations.
result Derives three additional equations for linearized gravity, not consequences of classical identities.
We study the geometric properties of holomorphic distributions of totally null m-planes on a (2m+ε)-dimensional complex Riemannian manifold (M,g), where ε∈0,1 and m≥2. In particular, given such a distribution N, say, we obtain algebraic conditions on the Weyl tensor and t…
The study characterizes and classifies specific types of manifolds using conformal and quasi-Einstein properties.
problem Characterizing and classifying manifolds with specific geometric properties.
method Analyzing warped products, contact manifolds, and semi-Riemannian manifolds.
result Characterizations and classifications of weakly conformally flat and quasi-Einstein manifolds.
It is well known that the classification of the Weyl tensor in Lorentzian manifolds of dimension four, the so called Petrov classification, was a great tool to the development of general relativity. Using the bivector approach it is shown in this article a classification for the Weyl tensor in all four-dimensional mani…
In this paper we consider the field equations for linearized gravity and other integer spin fields on the Kerr spacetime, and more generally on spacetimes of Petrov type D. We give a derivation, using the GHP formalism, of decoupled field equations for the linearized Weyl scalars for all spin weights and identify the g…
Algorithm classifies five-dimensional spacetimes, generalizing Karlhede's for four dimensions.
problem Classifying five-dimensional spacetimes for general relativity.
method Introduces an algorithm to determine spacetime equivalence using alignment classification of the Weyl tensor.
result Illustrates the algorithm with three examples and discusses its applications.
Conformally quasi-recurrent (CQR)_n pseudo-Riemannian manifolds are investigated, and several new results are obtained. It is shown that the Ricci tensor and the gradient of the fundamental vector are Weyl compatible tensors (the notion was introduced recently by the authors and applies to significative space-times), (…
Calculates volumes of knot cone-manifolds using Schläfli formula.
problem Calculating volumes of specific knot cone-manifolds.
method Schläfli formula, Hilden-Lozano-Montesinos-Amilibia instructions, Ham-Mednykh-Petrov methods, Hoste-Shanahan presentation.
result Concrete and explicit formula for volumes of C(2n,3) cone-manifolds. The Petrov classification is an important algebraic classification for the Weyl tensor valid in 4-dimensional space-times. In this thesis such classification is generalized to manifolds of arbitrary dimension and signature. This is accomplished by interpreting the Weyl tensor as a linear operator on the bundle of p-for…
We consider static spacetimes whose spatial part admits foliations with the extrinsic curvature tensor K_{ab}=0. There are two complementary cases when the gradient of the lapse function points 1) to the direction of foliation or 2) orthogonally to it. Case 1) gives generalization of metrics like Bertotti-Robinson or N…
The most recent update of financial option models is American options under stochastic volatility models with jumps in returns (SVJ) and stochastic volatility models with jumps in returns and volatility (SVCJ). To evaluate these options, mesh-based methods are applied in a number of papers but it is well-known that the…
We consider Legendrian contact structures on odd-dimensional complex analytic manifolds. We are particularly interested in integrable structures, which can be encoded by compatible complete systems of second order PDEs on a scalar function of many independent variables and considered up to point transformations. Using …
The study finds obstructions for certain Weyl curvature tensors on manifolds.
problem Can manifolds admit metrics with purely electric or magnetic Weyl tensors?
method Analyzes algebraic curvature tensors and their Pontryagin classes on scalar product spaces.
result Obstructions to the existence of metrics with PE or PM Weyl tensors in top-degree cohomology.
It is shown that a self-dual neutral Einstein four-manifold of Petrov type III, admitting a two-dimensional null parallel distribution compatible with the orientation, cannot be compact or locally homogeneous, and its maximum possible degree of mobility is 3. Diaz-Ramos, Garcia-Rio and Vazquez-Lorenzo found a general c…
The study characterizes spacetimes with quasi-constant sectional curvature and explores their properties in F(R)-gravity.
problem Characterizing spacetimes with quasi-constant sectional curvature.
method Investigation through examples, proofs, and analysis of energy conditions.
result A spacetime of quasi-constant sectional curvature can represent a Robertson Walker spacetime or a static spacetime.
An almost Robinson structure on an n-dimensional Lorentzian manifold $(\mcM,g)$, where n=2m+ε, ε∈{0,1}, is a complex m-plane distribution $\mcN$ that is totally null with respect to the complexified metric, and intersects its complex conjugate in a real null line distribution $\mcK$, say. When $\mcN$ an…
The Teukolsky connection is linked to a complex structure on Einstein spacetimes.
problem Understanding the symmetries and structures in Einstein spacetimes.
method Analyzing the Teukolsky connection and its relation to conformal and GHP covariant connections.
result The Teukolsky connection is a manifestation of a complex structure on the conformal class of the spacetime.
Researchers correct earlier work on surgeries of Gieseking's hyperbolic simplex manifold.
problem Incorrectly identified Gieseking's manifold as orbifolds, leading to a conflict with known theorems.
method Revised and completed the analysis of Dehn surgeries on Gieseking's manifold, identifying them as cone manifolds.
result Corrected the understanding of Gieseking's manifold, identifying it as cone manifolds and derived new orbifold series.
Wilson lines in gauge theories admit several path integral descriptions. The first one (due to Alekseev-Faddeev-Shatashvili) uses path integrals over coadjoint orbits. The second one (due to Diakonov-Petrov) replaces a 1-dimensional path integral with a 2-dimensional topological σ-model. We show that this σ-model i…
In this paper the Weyl tensor is used to define operators that act on the space of forms. These operators are shown to have interesting properties and are used to classify the Weyl tensor, the well known Petrov classification emerging as a special case. Particularly, in the Euclidean signature this classification turns…
Impact of projective curvature tensor in f(R,G), f(R,T) and f(R,Lm)-gravitygr-qc The study characterizes spacetime and modified gravity models using projective curvature tensor.
problem Characterizing spacetime and modified gravity models with projective curvature tensor.
method Analyzing $f\left(R,G
ight)$, $f\left(R,T
ight)$, and $f\left(R,L_{m}
ight)$-gravity models.
result Projectively flat perfect fluid spacetimes represent dark energy era and are locally isometric to Minkowski or de-Sitter spacetimes.
Develops VPINNs for solving PDEs with reduced training cost and improved accuracy.
problem Solving partial differential equations efficiently and accurately.
method Integrates variational forms of PDEs into neural network loss functions, using Legendre polynomials as test spaces.
result VPINNs outperform PINNs in terms of accuracy and speed for solving PDEs.
GPS model predicts subspace-valued functions efficiently.
problem Accurate and efficient prediction of subspace-valued functions.
method Gaussian Process Subspace regression (GPS) model, using multivariate Gaussian distributions on Euclidean space.
result GPS provides accurate, smooth predictions with uncertainty quantification.
This paper simplifies hedge ratios in financial models using pathwise algorithmic differentiation.
problem Expensive and unstable computation of hedge ratios from pathwise sensitivities.
method Develops reduced stochastic hedge ratios of the form φ_j^r = Σ_j^r ξ_j^q X_q, retaining sensitivity tensor through empirical averages.
result Two coefficient criteria are introduced to minimize pathwise residuals and satisfy moment equations.
Typilus predicts types for Python programs using neural networks.
problem Type inference in dynamically typed languages is challenging.
method Graph neural network model that predicts types by probabilistically reasoning over program structure, names, and patterns.
result Typilus can predict types for 70% of all annotatable symbols and type checks 95% of the predicted types.
LambdaNet infers TypeScript types using graph neural networks.
problem Automatic inference of TypeScript type annotations.
method Graph Neural Network for type dependency graph analysis.
result LambdaNet outperforms existing methods by 14%.
Classifies different types of Darboux transformations for multidimensional operators.
problem Classifying Darboux transformations for multidimensional operators.
method Analyzes all known types of Darboux transformations and introduces new types.
result Full classification of first-order Darboux transformations and a description of higher-order transformations.
Study shows partially-typed NER datasets can match fully-typed ones in model performance.
problem Leveraging multiple partially-typed NER datasets for training models without fully-typed annotations.
method Systematic analysis and controlled experiments comparing partially-typed and fully-typed datasets.
result Models trained with partially-typed annotations can achieve similar performance to those trained with fully-typed annotations.
New model predicts fine-grained types for high-multiplicity entities.
problem Fine-grained entity typing with high type multiplicity.
method Set-prediction approach to high-multiplicity fine-grained typing.
result Model outperforms baselines on Wikipedia-based corpus.
The generic fiber of a Lagrangian fibration on an irreducible holomorphic symplectic manifold is an abelian variety. Associate a polarization type to such Lagrangian fibrations coming from polarizations on a generic fiber. We prove that this polarization type is constant in families of Lagrangian fibrations. Further, w…
Paper introduces a new adversarial attack type that cheats classifiers with significant changes.
problem Cheating well-trained classifiers with small permutations.
method Supervised variation autoencoder and gradient-based updates to latent variables.
result The proposed attack significantly cheats classifiers with significant changes, reducing Type I error.
Constructs odd Khovanov homotopy types for links, linking them to even types.
problem Understanding and constructing odd Khovanov homotopy types for links.
method Constructs stable homotopy types X^j_o(L) for links L, with cohomology matching odd Khovanov homology.
result Odd Khovanov homotopy types carry a Z/2 action whose fixed points are related to even Khovanov homotopy types.
Study shows infinite real homotopy types for complex nilmanifolds.
problem Understanding real homotopy types of complex nilmanifolds.
method Analyzing 2n-dimensional nilmanifolds with generalized complex structures. result Infinitely many real homotopy types exist for 2n-dimensional nilmanifolds.