Coexistence of Compressive and Rarefactive Nonlinear Dust-acoustic Waves in Non-thermal Complex (Dusty) Plasma Under Gravity and Microgravity Conditions

Abstract

This study presents a comprehensive theoretical investigation of nonlinear dust-acoustic (DA) wave dynamics in a nonthermal complex plasma environment, with a particular focus on the effects of gravity and microgravity. By employing Sagdeev pseudo-potential analysis and considering both constant and variable dust charge scenarios, we demonstrate the fundamental role of external fields and suprathermal electron populations in modulating wave structures. Under microgravity, the plasma supports the coexistence of both compressive and rarefactive DA solitons due to a symmetric double-well potential profile, with charge variability significantly enhancing soliton amplitude, especially for rarefactive modes. In contrast, gravity breaks this symmetry, suppresses compressive solitons, and induces spatial asymmetry and oscillatory electric field structures due to gravito-electrostatic coupling and dust stratification. Furthermore, we establish a physical equivalence between increasing nonthermal electron effects (via the non-thermal parameter \(\alpha\)) and reducing dust grain mass, both of which enhance the charge-to-mass ratio and deepen electrostatic confinement. This equivalence, however, is shown to hold only under microgravity. Analytical scaling relations and numerical simulations reveal that microgravity enables a charge-driven regime, while gravity imposes density-dominated dynamics. These findings provide new insights into the behavior of nonlinear structures in dusty plasmas and offer relevant interpretations for plasma conditions in both space and laboratory settings such in parabolic flight experiments.