JIUNN-WEI CHENCHANG-TSE HSIEH2022-06-302022-06-30201115507998https://www.scopus.com/inward/record.uri?eid=2-s2.0-79960761408&doi=10.1103%2fPhysRevD.83.115006&partnerID=40&md5=b23dc5d00fe7a548f88b8fe49dd033f3https://scholars.lib.ntu.edu.tw/handle/123456789/614636The rich phenomena of the shear viscosity (η) to entropy density (s) ratio, η/s, in weakly coupled N-component scalar field theories are studied. η/s can have a "double dip" behavior due to resonances and the phase transition. If an explicit Goldstone mass term is added, then η/s can either decrease monotonically in temperature or, as seen in many other systems, reach a minimum at the phase transition. We also show how to go beyond the original variational approach to make the Boltzmann equation computation of η systematic. © 2011 American Physical Society.journal article10.1103/PhysRevD.83.1150062-s2.0-79960761408