Study for the elementarity of composite systems

Recently, the hadronic composite states have been studied extensively in the context of the dynamically generated states. The question of ``elementarity'' has been studied by using the wave function renormalization constant $Z$ [1, 2]. The attempts have been made not only for bound states but also for resonant states [3--5]. In this talk, we show that the renormalization constant $Z$ can be zero for any composite state dynamically generated by a Weinberg-Tomozawa type interaction. We discuss the underlying mechanism of $Z=0$ for composite systems and how we should employ the renormalization constant $Z$ to understand the nature of hadrons [6]. We also discuss a special case of the zero-energy bound state. We show that the meaning of the condition $Z=0$ for a barely bound system can be different from that of finite binding energy or resonant case. \\[4pt] [1] S. Weinberg, PR130(63)776; PR137(65)B672.\\[0pt] [2] D. Lurie and A. J. Macfarlane, PR136(64)B816.\\[0pt] [3] T. Hyodo, D. Jido, and A. Hosaka, PRC85(12)015201.\\[0pt] [4] H. Nagahiro et al., PRD83(11)111504.\\[0pt] [5] H. Nagahiro and A. Hosaka, PRC88(13)055203.\\[0pt] [6] H. Nagahiro and A. Hosaka, e-print arXiv:1406.3684 [hep-ph].