Probing quantum criticality near the BTZ black hole horizon: Insights from coupled fermion-antifermion pairs

In this study, we analytically examine the behavior of a fermion-antifermion pair near the horizon of a static BTZ black hole using a fully covariant two-body Dirac equation with a position-dependent mass. This formulation leads to a set of four first-order equations that can be reduced to a second-order wave equation, enabling the analysis of gravitational effects on quantum interactions. Two mass modifications are considered: (i) $m\to m-a\mathrm{/}r$, representing an attractive Coulomb interaction, and (ii) $m\to m-a\mathrm{/}r+br$, corresponding to a Cornell potential. For case (i), an exact analytical solution is obtained, while for case (ii), conditionally exact solutions involving biconfluent Heun functions are derived. For the lowest mode ($n=0$), the results indicate that real oscillations without energy loss occur when $a>0.25$ in scenario (i) and $a>0.75$ in scenario (ii), suggesting stable oscillatory behavior. When $a<0.25$ in scenario (i) or $a<0.75$ in scenario (ii), the state exhibits decay, indicating instability below these critical thresholds. At $a=0.25$ (scenario (i)) and $a=0.75$ (scenario (ii)), the system reaches a state where its evolution ceases over time. These findings provide insights into the stability conditions of fermion-antifermion pairs near the black hole horizon and may have relevance for determining critical coupling strengths in systems such as holographic superconductors. Furthermore, this work adopts an effective semi-classical quantum gravity approach, offering a practical framework for incorporating gravitational effects.