What is "t" in this equation?
Yes, the dead-time body diode conduction losses are another part of the bottom FET losses. They can be approximated as:
Ploss,body diode = 2 * Vf,body * Imax * Tdead * Fsw.
The "t" in the above equation was placed there by mistake. A correct version of the equation can be found in the LTC7872 data sheet. The LTC7872 is a 4-phase version of the LTC7871. This equation is inserted below.
I think the P_BOT may be incomplete. It doesn't calculate the power loss due to the body diode during the dead time.