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arXiv 1403.4243astro-ph.COgr-qchep-ph
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突现宇宙学再探

Emergent Cosmology Revisited

Satadru Bag, Varun Sahni, Yuri Shtanov, Sanil Unnikrishnan

摘要:

我们利用有效势形式主义探讨了突现宇宙学的可能性。我们发现了新的涌现宇宙学模型,它满足宇宙微波背景(CMB)的约束。我们证明,在修改的重力的框架内,紧急情况下,可以出现在一个宇宙空间开放/封闭。相比之下,在广义相对论(GR)中,涌现宇宙学产生于一个空间封闭的过去永恒的爱因斯坦静态宇宙(ESU)。在GR中,ESU是不稳定的,这给突现宇宙学带来了微调问题。然而,包括膜世界模型、圈量子宇宙学(LQC)和渐近自由引力在内的修正引力模型导致了稳定的ESU。因此,在这些模型中,涌现宇宙学产生于更大类的初始条件,包括宇宙围绕ESU不动点永恒振荡的初始条件。我们证明了这样一个振荡的宇宙必然伴随着引力子的产生。对于参数空间中的一个大区域,引力子的产生是通过参数共振增强的,这使人们严重怀疑这种紧急情况是否可以是过去永恒的。

英文摘要:

We explore the possibility of emergent cosmology using the effective potential formalism. We discover new models of emergent cosmology which satisfy the constraints posed by the cosmic microwave background (CMB). We demonstrate that, within the framework of modified gravity, the emergent scenario can arise in a universe which is spatially open/closed. By contrast, in general relativity (GR) emergent cosmology arises from a spatially closed past-eternal Einstein Static Universe (ESU). In GR the ESU is unstable, which creates fine tuning problems for emergent cosmology. However, modified gravity models including Braneworld models, Loop Quantum Cosmology (LQC) and Asymptotically Free Gravity result in a stable ESU. Consequently, in these models emergent cosmology arises from a larger class of initial conditions including those in which the universe eternally oscillates about the ESU fixed point. We demonstrate that such an oscillating universe is necessarily accompanied by graviton production. For a large region in parameter space graviton production is enhanced through a parametric resonance, casting serious doubts as to whether this emergent scenario can be past-eternal.

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