A prime geodesic theorem for SL4

A prime geodesic theorem is derived for rank-one geodesics in quotients of SL4. This has applications in class number asymptotics for quartic fields. For these applications it is necessary to prove a more general statement than in the literature: several regularity conditions have to be abandoned. As a consequence, the analytical difficulties multiply. The final result is obtained by a sandwiching argument from infinitely many independent asymptotics.