  In this work we study the T, CP and CPT symmetries in the B-meson system. Our
analysis and results are addressed to the case of correlated mesons in the
B-factories.
  In the first set of theory and results we investigate the consequences of
these discrete symmetries in the B-mixing and interference between mixing and
decay. With the help of the CP-tag we compute all possible intensities and
asymmetries which concern flavour-specific and CP Golden Plate decays. Our
proposed observables are a new self-consistency check for the Standard Model,
as well as a new exploration for the traces of the discrete symmetries in the
B-system.
  In the second set of results we study CPT violation in the initial state of
the B-factories through the loss of indistinguishability of $B^0$ and $\bar
B^0$. We show that, if the consequence of Bose statistic is relaxed, then the
equal-sign dilepton events are considerably modified. We analyze the demise of
flavour tagging and we also prove that the equal-sign charge asymmetry,
$A_{sl}$, is an optimal observable where to look for this new CPT violation
effect. The detailed study of this asymmetry allows us to predict different
behaviours according to the possible values of the CPT violating parameter
$\w$. We conclude that the best observable where to find traces of this novel
kind of CPT violation is the analysis of $A_{sl}$ at small $\Dt$'s. We use
existing data on $A_{sl}$ to put the first limits on $\w$.
