Holographic RG flows and Janus solutions from matter-coupled N=4 gauged supergravity

We study an $SO(2)\times SO(2)\times SO(2)\times SO(2)$ truncation of four-dimensional $N=4$ gauged supergravity coupled to six vector multiplets with $SO(4)\times SO(4)$ gauge group and find a new class of holographic RG flows and supersymmetric Janus solutions. In this truncation, there is a unique $N=4$ supersymmetric $AdS_4$ vacuum dual to an $N=4$ SCFT in three dimensions. In the presence of the axion, the RG flows generally preserve $N=2$ supersymmetry while the supersymmetry is enhanced to $N=4$ for vanishing axion. We find solutions interpolating between the $AdS_4$ vacuum and singular geometries with different residual symmetries. We also show that all the singularities are physically acceptable within the framework of four-dimensional gauged supergravity. Accordingly, the solutions are holographically dual to RG flows from the $N=4$ SCFT to a number of non-conformal phases in the IR. We also find $N=4$ and $N=2$ Janus solutions with $SO(4)\times SO(4)$ and $SO(2)\times SO(2)\times SO(3)\times SO(2)$ symmetries, respectively. The former is obtained from a truncation of all scalars from vector multiplets and can be regarded as a solution of pure $N=4$ gauged supergravity. On the other hand, the latter is a genuine solution of the full matter-coupled theory. These solutions describe conformal interfaces in the $N=4$ SCFT with $N=(4,0)$ and $N=(2,0)$ supersymmetries.