arXiv subjects

Onyx Gautam

Publications and source records attributed to Onyx Gautam.

3 recordsLinked to original sources

arXiv2026

Semilinear wave equations on the Witten bubble spacetime

We initiate the study of nonlinear wave equations on the Witten bubble spacetime (also known as the "bubble of nothing"), which is an $\mathrm{SO}(3,1)\times \mathrm{U}(1)$-symmetric solution to the Einstein vacuum equations in $(4 + 1)$ dimensions. This spacetime was introduced by Witten to model the semiclassical instability of the Kaluza--Klein spacetime $\mathbf{R}^{3+1}\times S^1$ (which is classically stable by work of Huneau--Stingo--Wyatt (arXiv:2307.15267)). We prove a small-data global existence result without symmetry assumptions and an improved decay result for $\mathrm{U}(1)$-symmetric solutions to a class of semilinear equations satisfying a version of the null condition. Key to the proof are novel estimates for the linear wave equation, which has been studied in the physics literature by Bhawal and Viveshwara and in the mathematics literature by Bachelot (arXiv:1601.03682).

gr-qc↗

arXiv2026

Late-time tails for linear waves on radially symmetric stationary spacetimes of two space dimensions

We show that the leading-order term in the late-time asymptotics of solutions to the linear wave equation on radially symmetric stationary perturbations of $(2 + 1)$-dimensional Minkowski space is proportional to $u^{-1/2}v^{-1/2}$ (which solves the wave equation on Minkowski space), where $u$ and $v$ are double null coordinates. Our proof adapts the physical space techniques in the work of Gajic (arXiv:2203.15838) on the wave equation with an inverse-square potential on the Schwarzschild spacetime. In particular, we extend the $r^p$-weighted energy estimates of Dafermos--Rodnianski (arXiv:0910.4957) to two space dimensions.

math.AP↗

arXiv2024

Late-time tails and mass inflation for the spherically symmetric Einstein-Maxwell-scalar field system

We establish a decay result in the black hole exterior region of spherically symmetric solutions to the Einstein-Maxwell-scalar field system arising from compactly supported admissible data. Our result allows for large initial data, and it is the first decay statement for higher order derivatives of the scalar field. Solutions to this model generically develop a singularity in the black hole interior. Indeed, Luk--Oh (arxiv:1702.05715, arxiv:1702.05716) identify a generic class of initial data that produces $C^2$-future-inextendible solutions. However, they leave open the question of mass inflation: does the Hawking mass become identically infinite at the Cauchy horizon? By work of Luk--Oh--Shlapentokh-Rothman (arxiv:2201.12294), our decay result implies mass inflation for sufficiently regular solutions in the generic class considered by Luk--Oh (arxiv:1702.05715, arxiv:1702.05716). Together with the methods and results of Luk--Oh (arXiv:2404.02220), our estimates imply a late-time tails result for the scalar field. This result provides another proof of generic mass inflation, through a result of Dafermos (arXiv:arch-ive/0307013). Another application of our late-time tails result, due to Van de Moortel, is the global construction of two-ended black holes that contain null and spacelike singularities.

gr-qc↗