Casimir energy in the gauge/gravity description of Bjorken flow?

In the AdS/CFT description of four-dimensional QCD matter undergoing Bjorken expansion, does the holographic energy-momentum tensor contain a Casimir-type contribution that should not be attributed to thermal matter? When the bulk isometry ansatz that yielded such a Casimir term for $(1+1)$-dimensional boundary matter is generalized to a four-dimensional boundary, we show that a Casimir term does not arise, owing to singularities in the five-dimensional bulk solution. The geometric reasons are traced to a difference between the isometries of ${\mathrm{AdS}}_3$ and ${\mathrm{AdS}}_{d+1}$ for $d\ge 3$.