The notion of a $(\varphi,\hat{G})$-module is defined by Tong Liu in 2010 to classify lattices in semi-stable representations. In this paper, we study torsion $(\varphi,\hat{G})$-modules, and torsion p-adic representations associated with them, including the case where p=2. First we prove that the category of torsion p-adic representations arising from torsion $(\varphi,\hat{G})$-modules is an abelian category. Secondly, we construct a maximal (minimal) theory for $(\varphi,\hat{G})$-modules by using the theory of \'etale $(\varphi, \hat{G})$-modules, essentially proved by Xavier Caruso, which is an analogue of Fontaine's theory of \'etale $(\varphi,\Gamma)$-modules. Non-isomorphic two maximal (minimal) objects give non-isomorphic two torsion p-adic representations.

Comment: arXiv admin note: significant text overlap with arXiv:1105.5477