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We carry out three dimensional smoothed particle hydrodynamics simulations tostudy the role of gravitational and drag forces on the concentration of largedust grains (St > 1) in the spiral arms of gravitationally unstableprotoplanetary discs, and the resulting implications for planet formation. Wefind that both drag and gravity play an important role in the evolution oflarge dust grains. If we include both, grains that would otherwise be partiallydecoupled will become well coupled and trace the spirals. For the dust grainsmost influenced by drag (with Stokes numbers near unity), the dust disc quicklybecomes gravitationally unstable and rapidly forms clumps with masses between0.15 - 6 Earth masses. A large fraction of clumps are below the threshold whererunaway gas accretion can occur. However, if dust self-gravity is neglected,the dust is unable to form clumps, despite still becoming trapped in the gasspirals. When large dust grains are unable to feel either gas gravity or drag,the dust is unable to trace the gas spirals. Hence, full physics is needed toproperly simulate dust in gravitationally unstable discs.  Dust trapping of large grains in spiral arms of discs stable to gasfragmentation could explain planet formation in very young discs by apopulation of planetesimals formed due to the combined roles of drag andgravity in the earliest stages of a disc's evolution. Furthermore, ithighlights that gravitationally unstable discs are not just important forforming gas giants quickly, it can also rapidly form Earth mass bodies.

The Role of Drag and Gravity on Dust Concentration in a Gravitationally Unstable Disc