We study the kinematics of timelike geodesic congruences in two and four dimensions in spacetime geometries representing stringy black holes. The Raychaudhuri equations for the kinematical quantities (namely, expansion, shear and rotation) characterising such geodesic flows are written down and subsequently solved analytically (in two dimensions) and numerically (in four dimensions) for specific geodesics flows. We compare between geodesic flows in dual (electric and magnetic) stringy black hole backgrounds in four dimensions, by showing the differences that arise in the corresponding evolutions of the kinematic variables. The crucial role of initial conditions and the spacetime curvature on the evolution of the kinematical variables is illustrated. Some novel general conclusions on geodesic focusing are obtained from the analytical and numerical findings. We also propose new quantifiers in terms of (a) the time (affine parameter) of approach to a singularity and (b) the location of extrema in the functional evolution of the kinematic variables, which may be used to distinguish between flows in different geometries. In summary, our quantitative findings bring out hitherto unknown features of the kinematics of geodesic flows, which, otherwise, would have remained overlooked, if we confined ourselves to only a qualitative analysis.
Null geodesic defocusing in dynamical black-hole-to-white-hole transitions
Abdus Salam Centre for Theoretical Physics, Imperial College London（阿卜杜斯·萨拉姆理论物理中心，伦敦帝国理工学院）；SISSA（的里雅斯特国际高等研究学校）；INFN, Sez. Trieste（意大利国家核物理研究所，的里雅斯特分部）；IFPU–Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；School of Mathematics and Statistics, Victoria University of Wellington（惠灵顿维多利亚大学数学与统计学院）
在这篇论文中，我们在弦论的框架下研究隐藏对称性。在这项工作中有两种隐藏的对称性研究：第一种类型是与量子场的动力学和第二种类型是与各种背景下的弦的可积性。这篇论文的目标有两个：将广义相对论中已知的隐藏对称性扩展到更高维度的弦背景和构建新的可积弦论。在第一个目标的背景下，我们研究弦背景的隐藏对称性，有和没有超对称性。对于超对称几何产生的D-膜，我们确定的背景与可解方程测地线，这可能会引起可积弦论。放松超对称性的要求，我们还研究了更高维度的带电黑洞，并确定了它们隐藏在所谓的Killing（-Yano）张量中的对称性。我们构造了任意维带电旋转黑洞的Killing（-Yano）张量的显式形式，研究了这种张量在弦对偶下的行为，并利用对隐藏对称性的分析来解释为什么在超过5维的情况下，黑环（具有非球形事件视界的黑洞）的精确解仍然是难以捉摸的.作为副产品，我们确定了AdSp x S^q背景的标准参数化与椭圆坐标在一个平坦的基础上。这项工作的第二个目标是建设新的可积弦论通过应用已知的例子连续变形。我们使用最新的发展称为（广义）的可积变形构造新的可积背景依赖于几个连续的参数和研究分析性质的这种变形。
Violations of the null convergence condition in kinematical transitions between singular and regular black holes, horizonless compact objects, and bounces
Probing nonlinear electrodynamics-sourced black holes via light and orbital mechanics
Faculdade de Ciências Naturais, Universidade Federal do Pará（帕拉联邦大学自然科学学院）；Departamento de Física, Universidade Federal da Paraíba（帕拉伊巴联邦大学物理系）；Faculdade de Física, Universidade Federal do Pará（帕拉联邦大学物理学院）；Programa de Pós-Graduação em Física, Universidade Federal do Sul e Sudeste do Pará（帕拉南部和东南部联邦大学物理学研究生项目）
