arXiv subjects

Xiao Zhang

Publications and source records attributed to Xiao Zhang.

582 records · Page 33Linked to original sources

arXiv2006

On the relation between ADM and Bondi energy-momenta

When a spacetime takes Bondi radiating metric, and is vacuum and asymptotically flat at spatial infinity which ensures the positive mass theorem, we prove that the standard ADM energy-momentum is the past limit of the Bondi energy-momentum. We also derive a formula relating the ADM energy-momentum of any asymptotically flat spacelike hypersurface to the Bondi energy-momentum of any null hypersurface. The formula indicates that the Bondi mass is always less than the ADM total energy if the system has {\it news}. The assumed asymptotic flatness precludes gravitational radiation. We therefore study further the relation between the ADM total energy and the Bondi mass when gravitational radiation emits. We find that in this case the ADM total energy is no longer the past limit of the Bondi mass. They differ by certain quantity relating to the {\it news} of the system.

gr-qc↗

arXiv2006

On the relation between ADM and Bondi energy-momenta III -- perturbed radiative spatial infinity

In a vacuum spacetime equipped with the Bondi's radiating metric which is asymptotically flat at spatial infinity including gravitational radiation ({\bf Condition D}), we establish the relation between the ADM total energy-momentum and the Bondi energy-momentum for perturbed radiative spatial infinity. The perturbation is given by defining the "real" time the sum of the retarded time, the Euclidean distance and certain function $f$.

gr-qc↗

arXiv2006

The Positive Mass Theorem near null infinity

In this short paper, we review recent progress on the positive mass theorem for spacelike hypersurfaces which approach to null infinity in asymptotically flat spacetimes. We use it to prove, if the functions $c(u, θ, ψ)$, $d(u, θ, ψ)$ vanish at certain retarded time in vacuum Bondi's radiating spacetimes, then the Bondi mass is nonnegative up to that time.

math.DG↗

arXiv2006

Positivity of the Bondi mass in Bondi's radiating spacetimes

We find two conditions related to the {\it news functions} of the Bondi's radiating vacuum spacetimes. We provide a complete proof of the positivity of the Bondi mass by using Schoen-Yau's method under one condition and by using Witten's method under another condition.

math.DG↗

arXiv2000

Dirac Operator on Embedded Hypersurfaces

New extrinsic lower bounds are given for the classical Dirac operator on the boundary of a compact domain of a spin manifold. The main tool is to solve some boundary problems for the Dirac operator of the domain under boundary conditions of Atiyah-Patodi-Singer type. Spinorial techniques are used to give simple proofs of classical results for compact embedded hypersurfaces.

math.DG↗

arXiv2000

Eigenvalues of the Dirac Operator on Manifolds with Boundary

Under standard local boundary conditions or certain global APS boundary conditions, we get lower bounds for the eigenvalues of the Dirac operator on compact spin manifolds with boundary. Limiting cases are characterized by the existence of real Killing spinors and the minimality of the boundary.

math.DG↗