title: Double domain structure of the pair contact process with diffusion.
abstract: We investigate the domain structure of the pair contact process with diffusion (PCPD). PCPD is a stochastic reaction-diffusion model which evolves by the competition of two binary reactions, 2A-->3A and 2A-->0 . In addition, each particle diffuses isotropically, which leads to the bidirectional coupling between solitary particles and pairs. The spreading domain formed from localized activities in vacuum consists of two regions: The coupled region of size R{p} where pairs and solitary particles coexist and the uncoupled region of size R{U} where only solitary particles exist, respectively. The size of the whole domain R is given as R=R{p}+R{U} . At criticality, R{p} and R{U} scale as R{p} approximately t(1/Z{p}) and R{U} approximately t(1/Z{U}) with Z{U}>Z{p}. We estimate Z{p}=1.61(1) and Z{U}=1.768(8) . Hence the correction to the scaling of R,Q=R{U}/R{p} slowly decays extremely, which makes it practically impossible to identify the asymptotic scaling behavior of R. The double domain structure is another reason for the extremely slow approach to the asymptotic scaling regime of PCPD.
authors.affiliation: Department of Physics and Research Institute of Basic Sciences, Kyung Hee University, Seoul 130-701, Korea.
authors.forename: Sungchul
authors.initials: S
authors.lastname: Kwon
authors.forename: Yup
authors.initials: Y
authors.lastname: Kim