标题： 涌现的修改引力与标量物质耦合 显示英文标题

标题： Emergent modified gravity coupled to scalar matter

摘要： 涌现的修正引力呈现了一组新的普遍协变引力理论，其中时空度规不是由一个基本场直接给出的。 与之相反，一个与修正引力动力学相容的度规是通过规范形式下时空的协变条件导出的。 本文将现有的真空模型显著扩展到标量场在球对称情况下与涌现的修正引力耦合的情况。 与之前的一些尝试不同，例如环量子引力模型，在存在修正引力-标量耦合的情况下，可以保持普遍协变性。 然而一般来说，涌现的时空度规不仅依赖于耦合理论中引力部分的相空间自由度，还依赖于标量场。 因此，物质直接且深刻地影响时空的几何结构，不仅通过应力-能量与曲率的动力学耦合，如爱因斯坦方程中所熟知的那样，而且甚至在运动方程求解之前就在动力学层面上产生影响。 本文引入了进一步的物理要求，这些要求可能被施加于修正理论以将其减少到更具体的类别，在某些情况下消除了在真空情况下可能存在的某些修正。 在最小耦合的情况下，发现真空涌现修正引力中去除经典黑洞奇点的结果在引入物质后变得不稳定，但在某些替代修正中，即使在存在物质的情况下奇点也可以被去除。 涌现的修正引力被看到提供了一大类具有二阶场方程的新标量-张量理论。 显示英文摘要

摘要： Emergent modified gravity presents a new set of generally covariant gravitational theories in which the space-time metric is not directly given by one of the fundamental fields. A metric compatible with the modified dynamics of gravity is instead derived from covariance conditions for space-time in canonical form. This paper presents a significant extension of existing vacuum models to the case of a scalar field coupled to emergent modified gravity in a spherically symmetric setting. Unlike in previous attempts for instance in models of loop quantum gravity, it is possible to maintain general covariance in the presence of modified gravity-scalar couplings. In general, however, the emergent space-time metric depends not only on the phase-space degrees of freedom of the gravitational part of the coupled theory, but also on the scalar field. Matter therefore directly and profoundly affects the geometry of space-time, not only through the well-known dynamical coupling of stress-energy to curvature as in Einstein's equation, but even on a kinematical level before equations of motion are solved. This paper introduces further physical requirements that may be imposed for a reduction of modified theories to more specific classes, in some cases eliminating certain modifications that would be possible in a vacuum situation. With minimal coupling, results about the removal of classical black-hole singularities in vacuum emergent modified gravity are found to be unstable under the inclusion of matter, but alternative modifications exist in which singularities are removed even in the presence of matter. Emergent modified gravity is seen to provide a large class of new scalar-tensor theories with second-order field equations.