The familiar trace identity associated with the scale transformation e?‘￥e??? a?’ e?‘￥a€2e??? = e?‘’-e??? e?‘￥e??? on the Lagrangian density for a noninteracting massive real scalar field in 2 + 1 dimensions is shown to be violated on a single plate on which the Dirichlet boundary condition e??? (e?‘?, e?‘￥1, e?‘￥2 = -e?‘?) = 0 is imposed. It is however respected in: (i) 1 + 1 dimensions in both free space and on a single plate on which the Dirichlet boundary condition e???(e?‘?, e?‘￥1 = -e?‘?) = 0 holds and (ii) in 2 + 1 dimensions in free space, i.e. the unconstrained configuration. On the plate where e???(e?‘?, e?‘￥1, e?‘￥2 = -e?‘?) = 0, the modified trace identity is shown to be anomalous with a numerical coe?±cient for the anomalous term equal to the canonical scale dimension, viz.$dfrac{1}{2}$.The technique of Bordag et al [Ann. Phys. (N.Y.), 165, 162 (1985)] is used to incorporate the said boundary condition into the generating functional for the connected Green's functions.
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