  We study the masses of the low-lying charm and bottom mesons within the
framework of heavy- hadron chiral perturbation theory (HHChPT). We work to
third order in the chiral expansion, where meson loops contribute. In contrast
to previous approaches, we use physical meson masses in evaluating these loops.
This ensures that their imaginary parts are consistent with the observed widths
of the D-mesons. The lowest odd- and even-parity, strange and nonstrange charm
mesons provide enough constraints to determine only certain linear combinations
of the low-energy constants (LECs) in the effective Lagrangian. We comment on
how lattice QCD could provide further information to disentangle these
constants. Then we use the results from the charm sector to predict the
spectrum of odd- and even-parity of the bottom mesons. The predicted masses
from our theory are in good agreement with experimentally measured masses for
the case of the odd-parity sector. For the even-parity sector, the B-meson
states have not yet been observed; thus, our results provide useful information
for experimentalists investigating such states. The near degeneracy of
nonstrange and strange scalar B mesons is confirmed in our predictions using
HHChPT. We show why previous approaches of using HHChPT in studying the mass
degeneracy in the scalar states of charm and bottom meson sectors gave
unsatisfactory results.
