Time reversal symmetry and the structure of Cooper pair wavefunction in topological superconductor UTe2

•Magnetic group m′m′m is established for nounitary uperconducting order parameter of UTe2.•Cooper pair's wave functions for m′m′m are constructed group-theoretically.•It is obtained that Au± Cooper pair's symmetries correspond to experimental data for UTe2. Recently discovered topological superconductor UTe2 reveals unusual symmetry features, namely, chiral nonunitary triplet ESP (equal spin pairing) SOP (superconducting order parameter) with point nodes. However, the description of these symmetry features in a framework of crystal point group D2h is not sufficient. In the present work the space-group approach to the wavefunction of a Cooper pair, based on Mackey-Bradley theorem, is extended, making use of Anderson ansatz, to the pair functions in Shubnikov group symmetry and applied to UTe2. A nonunitary triplet SOP was obtained for Shubnikov group m′m′m on the basis of one-electron functions. Irreducible corepresentations of group m′m′m for triplet ESP Cooper pairs, whose nodal structure corresponds to all experimentally established symmetry features, namely point nodes, nonunitarity and chirality, of SOP of UTe2 are identified.