Tidal dynamics and stellar disruption in charged Kalb-Ramond black holes in nonlinear electrodynamics

TL;DR

This work analyzes tidal forces, geodesic deviation, and Roche limits in the KR-ModMax black-hole spacetime, where Lorentz-violating parameter $l$ and nonlinear electrodynamics parameter $\gamma$ modify strong-field dynamics. By deriving the tidal tensor components and their dependence on $l$, $\gamma$, and the electric charge $Q$, the authors identify a tidal transition region in the canonical sector and show that the nonlinear ModMax contribution dampens angular tides while the LV parameter reshapes the effective geometry. The Roche limit analysis reveals that $l$ shifts the horizon–tidal-radius relationship, causing neutron-star tidal disruption to occur inside the horizon for supermassive black holes but outside for Sun-like stars, with $\gamma$ effects becoming relevant only at ultramassive scales ($\sim10^8 M_{\odot}$). Overall, the KR-ModMax framework provides a controlled setting to test Lorentz violation and nonlinear electrodynamics through tidal phenomena and tidal-disruption events, especially in intermediate-mass regimes where observable signatures may arise.

Abstract

We investigate tidal forces, geodesic deviation, and tidal disruption in the black hole spacetime described by the Kalb-Ramond-ModMax solution, where electromagnetic nonlinearity is governed by the parameter $γ$ and Lorentz symmetry violation by the parameter $l$. In the canonical sector ($α=1$), the radial tidal force exhibits a transition marked by a sign inversion between the horizons $r_{-}$ and $r_+$, signaling internal regimes of radial compression analogous to those of charged black holes; the parameter $l$ controls the strength and location of this transition, while $γ$ regulates the nonlinear electromagnetic contribution. The angular tidal force is predominantly compressive, $l$ shaping the effective geometry, and $γ$ acting as a damping factor. In the phantom sector ($α=-1$), tidal forces and geodesic deviation diverge, indicating a tidal instability, with $l$ and $γ$ affecting only the magnitude of the response. We further show that $l$ shifts the relation between the horizon radius $r_+$ and the tidal disruption radius $r_{\rm Roche}$, thereby modifying the critical (Hills) mass defined by $r_{\rm Roche}=r_+$. Tidal disruption of neutron stars occurs inside the horizon for supermassive black holes, whereas Sun-like stars are disrupted outside the horizon, with $γ$ becoming relevant only for ultramassive black holes with masses $\sim 10^{8}M_{\odot}$. Our results demonstrate that Kalb-Ramon-ModMax effects are largely suppressed for supermassive black holes, but may be relevant for intermediate-mass systems and observable tidal disruption events, offering an indirect probe of Lorentz violation and nonlinear electrodynamics in the strong-field regime.

Figures (7)

• Figure 1: (a) Radial tidal forces with $Q=0.6$, $\gamma=0.5$ and different $l$. (b) Radial tidal forces with $l=1.24\times 10^{-1}$ for different $\gamma$ and $Q=0.6$. Here we have not used the negative values of $l$ because within the range obtained in Duan:2023gng its effect is very small, and its effects are not evident.
• Figure 2: (a) Angular tidal forces with $Q=0.6$ and different $l$. (b) Angular tidal forces with $l=1.24\times 10^{-1}$ for different $\gamma$ and $Q=0.6$. Note that we did not used negative values of $l$ because their effects can be neglected within the range obtained in Duan:2023gng.
• Figure 3: (a) Intersection of the Roche radius (solid curves) for a neutron star profile with the event horizon (dashed curves) for different values of $l$ as a function of the BH mass. (b) Profile of the Roche radius for a neutron star for fixed $l$ and different values of $\gamma$ with $Q=0.3$. Note that we did not used negative values of $l$ because their effects can be neglected within the range obtained in Duan:2023gng.
• Figure 4: (a) Intersection of the Roche radius (solid curves) for a solar-type profile with the event horizon (dashed curves) for different values of $l$ as a function of the BH mass. (b) Profile of the Roche radius for a solar-type star for fixed $l$ and different values of $\gamma$ with $Q=0.3$. Note that we did not used negative values of $l$ because their effects can be neglected within the range obtained in Duan:2023gng.
• Figure 5: In (a) we have plotted the radial component of the geodesic deviation for different values of $l$ with fixed $Q$ and $\gamma$. In (b) we have plotted radial geodesic deviation for different values of $\gamma$ and fixed $l$ with $Q=0.6$. Both of them for condition $\mathcal{CI}$.