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We discuss the intrinsic relations between Dirac monopole theory and Berry geometric phases. We demonstrate that the existence of Dirac strings with endpoints brings non-integrable phase factors in the parameters space. We choose one of the simplest two-mode Hamilton model to visualize Dirac string and its endpoint of a wave function, based on its eigenstates. The geometric phase variation around an arbitrary circle can be calculated explicitly according to Dirac's picture, where the well-known Berry connection and curvature can be derived directly by performing Dirac monopole theory in the parameters space. The correspondence between the endpoints of Dirac strings and the accident degenerated points of eigenvalues are clearly shown for the Hermitian systems. These results suggest that Berry phase can be seen as the non-integrable phase factor induced by Dirac strings with endpoints in the parameters space, and would motivate more studies on geometric phase by performing or extending Dirac monopole theory.

Most of previously reported dark-bright solitons admit identical width for the two components in both theoretical and experimental studies. We report dark-bright solitons can admit strikingly different widths, and derive a family of analytical solutions for them by Lagrangian variational method. The existence regimes for these solitons become much more widespread in the space of nonlinear parameters, than the ones for the previously known dark-bright solitons with identical width. Our analysis indicates that the effective quantum wells are quite different in the two components, in sharp contrast to the ones for all previously known vector solitons. Especially, the particle number of bright soliton can be used to control the generation of dark-bright solitons with varied ratios of solitons' widths. Based on the current experimental technologies, we propose an experimental scheme for observing these novel dark-bright solitons. The results suggest that abundant vector solitons with difference widths exist in multi-components coupled systems, and would inspire experiments to observe them in nonlinear optical fibers, Bose-Einstein condensates, and other nonlinear coupled systems.