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arXiv 2101.06140math-phmath.CAmath.MP
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无穷维因果变分原理:极小值的存在性

Causal Variational Principles in the Infinite-Dimensional Setting: Existence of Minimizers

Christoph Langer

摘要:

我们提供了一种方法,用于构建(可能是非平凡的)措施的非局部紧波兰子空间的无限维可分Banach空间,在适当的假设下,因果变分原理的最小值在非局部紧设置。此外,对于非平凡极小,相应的欧拉-拉格朗日方程的推导。该方法是用尽的基础Banach空间的有限维子空间,并证明存在的因果变分原理限制到这些有限维子集的波兰空间在适当的假设下的拉格朗日。这就产生了一个相应的极小化序列。限制所得到的序列的波兰空间的可数许多紧凑的子集,通过考虑所得到的对角序列,我们能够构建一个正规措施的Borel代数在整个拓扑空间。对于有界值域的连续拉格朗日量,可以证明,在适当的假设下,所得到的测度在紧支集的变化下是(可能是非平凡的)极小元。在额外的假设下,我们证明了所构造的测度是有限体积变化下的极小元,并求解了相应的Euler-Lagrange方程。之后,我们将我们的结果扩展到连续拉格朗日消失熵。最后,假设所得到的测度是局部有限的,我们得到了时空的拓扑性质,并建立了与维数理论的联系。

英文摘要:

We provide a method for constructing (possibly non-trivial) measures on non-locally compact Polish subspaces of infinite-dimensional separable Banach spaces which, under suitable assumptions, are minimizers of causal variational principles in the non-locally compact setting. Moreover, for non-trivial minimizers the corresponding Euler-Lagrange equations are derived. The method is to exhaust the underlying Banach space by finite-dimensional subspaces and to prove existence of minimizers of the causal variational principle restricted to these finite-dimensional subsets of the Polish space under suitable assumptions on the Lagrangian. This gives rise to a corresponding sequence of minimizers. Restricting the resulting sequence to countably many compact subsets of the Polish space, by considering the resulting diagonal sequence we are able to construct a regular measure on the Borel algebra over the whole topological space. For continuous Lagrangians of bounded range it can be shown that, under suitable assumptions, the obtained measure is a (possibly non-trivial) minimizer under variations of compact support. Under additional assumptions, we prove that the constructed measure is a minimizer under variations of finite volume and solves the corresponding Euler-Lagrange equations. Afterwards, we extend our results to continuous Lagrangians vanishing in entropy. Finally, assuming that the obtained measure is locally finite, topological properties of spacetime are worked out and a connection to dimension theory is established.

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