暗物质衰变的人因解释
Anthropic Explanation of the Dark Matter Abundance
摘要：
我使用Bousso因果钻石测度对暗物质丰度进行了统计预测，假设一个轴子的衰变常数f_a >> 10^{12} GeV。使用观察者形成的粗略近似，预测与观察结果吻合得很好：30%的观察者形成在比我们观察到的暗物质少的区域，而70%的观察者形成在暗物质多的区域。大的暗物质比会受到一个基本效应的不利影响：增加暗物质的数量，同时保持重子与光子的比例不变，会减少一个视界体积内的重子数量。因此，这个预测对于宇宙中观测者形成的假设是相当不敏感的，因为宇宙中的暗物质比我们自己的多得多。关键的假设是，对于接近观测值的比率，每个重子的观测者数量大致与暗物质比率无关。
英文摘要：
I use Bousso's causal diamond measure to make a statistical prediction for the dark matter abundance, assuming an axion with a large decay constant f_a >> 10^{12} GeV. Using a crude approximation for observer formation, the prediction agrees well with observation: 30% of observers form in regions with less dark matter than we observe, while 70% of observers form in regions with more dark matter. Large values of the dark matter ratio are disfavored by an elementary effect: increasing the amount of dark matter while holding fixed the baryon to photon ratio decreases the number of baryons inside one horizon volume. Thus the prediction is rather insensitive to assumptions about observer formation in universes with much more dark matter than our own. The key assumption is that the number of observers per baryon is roughly independent of the dark matter ratio for ratios near the observed value.
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