  It is known that the capacity region of a two user physically degraded
discrete memoryless (DM) broadcast channel (BC) is not enlarged by feedback. An
identical result holds true for a physically degraded Gaussian BC, established
later using a variant of the Entropy Power Inequality (EPI). In this paper, we
extend the latter result to a physically degraded Gaussian Vector BC (PD-GVBC).
However, the extension is not EPI based, but employs a recent result on the
factorization of concave envelopes. While the existing concave envelope
factorization results do not hold in the presence of feedback, we show that
factorizing the corresponding directed information quantities suffice to attain
the feedback capacity region of a PD-GVBC. Our work demonstrates that
factorizing concave envelopes of directed information can handle situations
involving feedback. We further show that the capacity region of a discrete
memoryless reversely physically degraded BC is not enlarged by feedback.
