Astro-quark Matter: a Challenge Facing Astroparticle Physics

More than two thousand years ago, a Chinese philosopher, Zhuang Zi, speculated that all of matter in the world are dividable. However, at almost the same time, a Greek philosopher, Demokritos (∼ 460BC to 370BC), suggested that everything is made up from elements that can not be divided any further, called atoms (i.e., in-dividable elements). Now, it is understood in modern physics that atoms are actually dividable because of the detections of electron (discovered by Thomson) and nucleus (by Rutherford), and that the dynamics in an atom is governed by quantum mechanics. In the standard model of particle physics, all of matter are composed of fundamental Fermions, 6 flavors of quarks and 6 flavors of leptons, between which elementary interactions are mediated by gauge bosons. In spite of that, each type of these fundamental particles is supposed to correspond to one of certain vibrational modes of strings (typically ∼ 10 cm) described mathematically in the string theory in order to explain the great discrepancy between the quantum theory and the general relativity. Anyway, it is well recognized that a variety of states of matter exist in different physical conditions (e.g., Fig. 1). Quark matter is composed of quarks (and possible gluons) as the dominant degrees of freedom. Quark matter could be the key to the sub-quarkian physics. If Zhuang Zi’s idea is true, we may ask naively: Could the fundamental Fermions be dividable? What