  In this work, an unquenched quark model is proposed for describing the
heavy-light mesons by taking into account the coupled-channel effects induced
by chiral dynamics. After including a relativistic correction term for the
strong transition amplitudes, both the mass spectra and decay widths of the
observed heavy-light mesons can be successfully described simultaneously in a
unified framework, several long-standing puzzles related to the small masses
and broad widths are overcome naturally. We also provide valuable guidance in
searching new heavy-light mesons by the detailed predictions of their masses,
widths, and branching ratios. The success of the unquenched quark model
presented in this work indicates it may be an important step for understanding
the hadron spectrum.
