He has also made contributions in the area of black hole perturbation theory, loop quantum cosmology, singularities and gravitational wave science.

[1] His career choices were heavily influenced by his father,[18] Dr. Mohinder P. Khanna, a well-known theoretical particle physicist in Panjab University, India.

He trained this model on the basis of waveform data generated by point-particle black hole perturbation theory (ppBHPT), and evaluated its applicability for large-mass-ratio and comparable mass-ratio binaries finding that it was unreasonably effective.

[22][23] In his paper published in 2016, he solved the inhomogeneous Teukolsky equation, and focused linearized gravitational waves emitted from a plunge into a nearly extremal Kerr black hole.

[25] In his study regarding scientific computation, Khanna introduced a strategy to scale complex hybrid systems, and also discussed a prototype tool which was built over the theorem prover PVS.

[32] He also introduced a class of loop quantizations in terms of anisotropic models including the black hole interior, and studied the refinement process of lattice in context of dynamical changes of the volume.

[33] Khanna published a paper focused on the numerical study of Marolf-Ori singularity inside fast spinning black holes in terms of scalar field or vacuum gravitational perturbations.

[38][39] Furthermore, he studied about the stability of extreme black holes against linearized gravitational perturbations, and argued that the divergence of ψ4 is a consequence of the choice of a fixed tetrad.

[40][41] His most recent work on gravitational hair in the context of extremal black holes received significant attention in the community and popular media.