Split-off band, longitudinal mass, and transverse mass in silicon

[ehrenfest]

Homework Statement

This question refers to Kittel's solid-state physics book.

I am confused the split-off band, the longitudinal mass, and the transverse mass that Kittel starts talking about on page 202 in the section about Silicon and Germanium.
Can explain what these terms mean? Thanks.

Homework Equations

The Attempt at a Solution

 

[genneth]

At a guess (I don't have the book), longitudinal mass is the effective mass of longitudinal waves and similarly for transverse mass.