Environmental Imprints of Dark Matter and Accretion Disks on Eccentric EMRIs around Kerr Black Holes
Extreme-mass-ratio inspirals (EMRIs), systems in which a stellar-mass compact object spirals into a supermassive black hole ($M_1$), are prime targets for the space-based gravitational-wave interferometers and are acutely sensitive to their astrophysical environment. We quantify the joint imprint of a dark matter (DM) spike and an accretion disk on the waveforms of eccentric, equatorial Kerr EMRIs, integrating four modular effects---DM dynamical friction, DM self-gravity, Newtonian accretion-disk torques, and disk self-gravity---into a fifth post-Newtonian (5PN) augmented analytic kludge (AAK) waveform model, and assess their measurability via a Fisher-matrix analysis. The DM dynamical-friction dephasing peaks at $M_1\sim 10^6\,M_\odot$, reaching $\sim 10^2$--$10^3\,\mathrm{rad}$; there the DM spike slope is measurable to sub-percent precision and both DM channels are unambiguously detectable, while omitting DM biases the intrinsic parameters significantly. At $M_1\gtrsim 10^8\,M_\odot$ the DM and disk self-gravity channels dominate their dissipative counterparts. The disk parameters remain degenerate across the explored parameter space, since the supersonic regime dominates the inspiral and the subsonic-to-supersonic transition only mildly weakens this degeneracy without lifting it; a combined DM$+$disk analysis further reveals a cross-sector degeneracy between the DM slope and the disk parameters. This physical degeneracy, reflected in the near-singular Fisher matrix, implies that independently measuring the disk parameters requires a relativistic torque model or an electromagnetic counterpart.