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arXiv 1008.0171gr-qcastro-ph.COhep-th
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度量仿射引力的动力学

The dynamics of metric-affine gravity

Vincenzo Vitagliano, Thomas P. Sotiriou, Stefano Liberati

摘要:

引力的度量-仿射理论提供了一种有趣的替代广义相对论的方法:在这种方法中,度量和仿射(不一定是对称的)联系是独立的量。此外,作用应该包括物质场的协变导数,协变导数自然地使用独立连接来定义。因此,在度量仿射理论中,也存在涉及物质和连接的直接耦合。在这种理论中的连接的作用和动力进行了探讨。我们使用功率计数来构造动作,并搜索它应该满足的最小要求,以使连接成为动态的。我们发现,对于最一般的行动包含低阶不变量的曲率和扭转的独立连接不进行任何动态。它实际上简化为一个辅助场的角色,并且可以在代数上完全消除,而有利于度规和物质场,引入关于广义相对论的额外相互作用。然而,我们也表明,包括高阶项的行动从根本上改变了这一形象,并激发新的自由度的连接,使它(或它的一部分)动态。构造构成该规则的例外的动作需要对连接进行显著的微调和/或额外的先验约束。我们还考虑f(R)作用作为一个特殊的例子,以表明它们构成了一类具有特殊性质的度量仿射理论,因此它们不能作为代表性的玩具理论来研究度量仿射引力的性质。

英文摘要:

Metric-affine theories of gravity provide an interesting alternative to General Relativity: in such an approach, the metric and the affine (not necessarily symmetric) connection are independent quantities. Furthermore, the action should include covariant derivatives of the matter fields, with the covariant derivative naturally defined using the independent connection. As a result, in metric-affine theories a direct coupling involving matter and connection is also present. The role and the dynamics of the connection in such theories is explored. We employ power counting in order to construct the action and search for the minimal requirements it should satisfy for the connection to be dynamical. We find that for the most general action containing lower order invariants of the curvature and the torsion the independent connection does not carry any dynamics. It actually reduces to the role of an auxiliary field and can be completely eliminated algebraically in favour of the metric and the matter field, introducing extra interactions with respect to general relativity. However, we also show that including higher order terms in the action radically changes this picture and excites new degrees of freedom in the connection, making it (or parts of it) dynamical. Constructing actions that constitute exceptions to this rule requires significant fine tuned and/or extra a priori constraints on the connection. We also consider f(R) actions as a particular example in order to show that they constitute a distinct class of metric-affine theories with special properties, and as such they cannot be used as representative toy theories to study the properties of metric-affine gravity.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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