论文标题
简单以外的自旋泡沫振幅的数值评估
Numerical evaluation of spin foam amplitudes beyond simplices
论文作者
论文摘要
我们介绍了具有超管组合物的顶点的4D欧几里得自旋泡沫顶点振幅的第一个数值计算。具体而言,我们计算了在长方体和粉状形状上达到峰值的相干边界数据的幅度。我们提出数值算法,以明确计算顶点振幅,并将不同情况下的结果与振幅的半古典近似值进行比较。总体而言,我们发现振幅的良好定性一致性和渐近公式与已经相当小的旋转时已经振幅的整体振幅收敛的证据,但在振荡频率和在4个简单情况下缺乏相位移位的差异。但是,由于数值迅速增长,我们无法达到足够高的旋转来证明这两种振幅的一致性。最后,这种设置使我们能够探索不均匀的顶点振幅,其中有些表示很小,而另一些表示则很大。我们发现,即使某些旋转仍然很小,也可能存在一种情况,即半古典振幅是有效的近似值。这表明量子向半古典状态(对于单个顶点振幅)的过渡很复杂。
We present the first numerical calculation of the 4D Euclidean spin foam vertex amplitude for vertices with hypercubic combinatorics. Concretely, we compute the amplitude for coherent boundary data peaked on cuboid and frustum shapes. We present the numerical algorithms to explicitly compute the vertex amplitude and compare the results in different cases to the semi-classical approximation of the amplitude. Overall we find good qualitative agreement of the amplitudes and evidence of convergence of the asymptotic formula to the full amplitude already at fairly small spins, yet also differences in the frequency of oscillations and a phase shift absent in the 4-simplex case. However, due to rapidly growing numerical costs, we cannot reach sufficiently high spins to prove agreement of both amplitudes. Lastly, this setup allows us to explore non-uniform vertex amplitudes, where some representations are small while others are large; we find indications that scenarios might exist in which the semi-classical amplitude is a valid approximation even if some spins remain small. This suggests that the transition of the quantum to the semi-classical regime (for a single vertex amplitude) is intricate.