Bosonic crystalline symmetry protected topological phases beyond the group cohomology proposal

It is demonstrated by explicit construction that three-dimensional bosonic crystalline symmetry protected topological (cSPT) phases are classified by H-phi(5) (G; Z) circle plus H-phi(1) (G; Z) for all 230 space groups G, where H-phi(n) (G; Z) denotes the nth twisted group cohomology of G with Z coefficients, and phi indicates that g is an element of G acts nontrivially on coefficients by sending them to their inverses if g reverses space-time orientation and acts trivially otherwise. The previously known summand H-phi(5) (G; Z) corresponds only to crystalline phases built without the E-8 state or its multiples on 2-cells of space. It is the crystalline analog of the group cohomology proposal for classifying bosonic symmetry protected topological (SPT) phases, which takes the form H-phi(d+2) (G; Z) congruent to H-phi(d+1) (g; U(1)) for finite internal symmetry groups in d spatial dimensions. The new summand H-phi(1) (G; Z) classifies possible configurations of E-8 states on 2-cells that can be used to build crystalline phases beyond the group cohomology proposal. The completeness of our classification and the physical meaning of H-phi(1) (G; Z) are established through a combination of dimensional reduction, surface topological order, and explicit cellular construction. The value of H-phi(1) (G; Z) can be easily read off from the international symbol for G. Our classification agrees with the prediction of the generalized cohomology hypothesis, which concerns the general structure of the classification of SPT phases, and therefore provides strong evidence for the validity of the said hypothesis in the realm of crystalline symmetries.