Exact models of pure radiation in R^2 gravity for spatially homogeneous Shapovalov spacetimes type II

基于Shapovalov II型波时空和引力二次理论的Bianchi III宇宙中引力波的精确模型

An exact model of a gravitational wave in the Bianchi III universe based on Shapovalov II wave spacetime and the quadratic theory of gravity

基于Shapovalov II型波时空和引力二次理论，构造了Bianchi III宇宙中原初引力波的精确模型，求得了场方程精确解、纯辐射特性、标量场函数显式形式及光线传播轨迹。

Rotating and spatially twisting Locally Rotationally Symmetric Spacetimes in f(R)-Gravity: a No-Go theorem

Recently, in a series of papers, we established the existence and found a general solution for the simultaneously rotating and twisting locally rotationally symmetric spacetimes in general relativity, which can model inhomogeneous and dynamic astrophysical bodies. However, these spacetimes necessarily require imperfect fluids with entropy flux. Therefore, in this paper, we investigate the existence of these spacetimes in generic f(R)-gravity models, where the entropy flux is generated purely by higher order curvature effects, while the standard matter still remains a perfect fluid. However, we…

Spatially Overlapped Partners in Quantum Field Theory

In quantum field theory particles are physically defined as what Unruh-DeWitt particle detectors observe. By detecting a particle mode $A$, a reduced density operator for a quantum state of $A$ is constructed. Even if the entire quantum state of the quantum field is pure, the state of $A$ is not pure but mixed due to entanglement between other subsystems. The partner mode $B$ of the field is defined as a purification partner of $A$ such that the $AB$ system in a pure state. We show that, without any fine-tuning of the particle detector design of $A$, the weighting function of partner $B$ has s…

探索 Einstein-Dirac 宇宙学框架内的弱测量

Exploring Weak measurements within the Einstein-Dirac Cosmological framework

本文在 Einstein-Dirac 宇宙学中结合双态形式体系与弱测量，推导能量-动量张量、自旋分量和纯态的弱值，并将宇宙加速膨胀解释为后选择结果。

Spatially homogeneous Lifshitz black holes in five dimensional higher derivative gravity

We consider spatially homogeneous Lifshitz black hole solutions in five dimensional higher derivative gravity theories, which can be possible near horizon geometries of some systems that are interesting in the framework of gauge/gravity duality. We show the solutions belonging to the nine Bianchi classes in the pure R^2 gravity. We find that these black holes have zero entropy at non-zero temperatures and this property is the same as the case of BTZ black holes in new massive gravity at the critical point. In the most general quadratic curvature gravity theories, we find new solutions in Bianc…

Spatially Homogeneous String Cosmologies

We determine the most general form of the antisymmetric $H$-field tensor derived from a purely time-dependent potential that is admitted by all possible spatially homogeneous cosmological models in 3+1-dimensional low-energy bosonic string theory. The maximum number of components of the $H$ field that are left arbitrary is found for each homogeneous cosmology defined by the Bianchi group classification. The relative generality of these string cosmologies is found by counting the number of independent pieces of Cauchy data needed to specify the general solution of Einstein's equations. The hier…