  The SU(3) quark model encounters a great challenge in describing even-parity
mesons. Specifically, the $q\bar q$ quark model has difficulties in
understanding the light scalar mesons below 1 GeV, scalar and axial-vector
charmed mesons and $1^+$ charmonium-like state $X(3872)$. A common wisdom for
the resolution of these difficulties lies on the coupled channel effects which
will distort the quark model calculations. In this work, we focus on the near
mass degeneracy of scalar charmed mesons, $D_{s0}^*$ and $D_0^{*0}$, and its
implications. Within the framework of heavy meson chiral perturbation theory,
we show that near degeneracy can be qualitatively understood as a consequence
of self-energy effects due to strong coupled channels. Quantitatively, the
closeness of $D_{s0}^*$ and $D_0^{*0}$ masses can be implemented by adjusting
two relevant strong couplings and the renormalization scale appearing in the
loop diagram. Then this in turn implies the mass similarity of $B_{s0}^*$ and
$B_0^{*0}$ mesons. The $P_0^* P'_1$ interaction with the Goldstone boson is
crucial for understanding the phenomenon of near degeneracy. Based on heavy
quark symmetry in conjunction with corrections from QCD and $1/m_Q$ effects, we
obtain the masses of $B^*_{(s)0}$ and $B'_{(s)1}$ mesons, for example,
$M_{B_{s0}^*}= (5715\pm1)\,{\rm MeV}+\delta\Delta_S$,
$M_{B'_{s1}}=(5763\pm1)\,{\rm MeV}+\delta\Delta_S$ with $\delta\Delta_S$ being
$1/m_Q$ corrections. We find that the predicted mass difference of 48 MeV
between $B'_{s1}$ and $B_{s0}^*$ is larger than that of $20\sim 30$ MeV
inferred from the relativistic quark models, whereas the difference of 15 MeV
between the central values of $M_{B'_{s1}}$ and $M_{B'_1}$ is much smaller than
the quark model expectation of $60-100$ MeV.
