480 research outputs found
More on gravitational memory
Two novel results for the gravitational memory effect are presented in this
paper. We first extend the formula for the memory effect to solutions with
arbitrary two surface boundary topology. The memory effect for the
Robinson-Trautman solution is obtained in its standard form. Then we propose a
new observational effect for the spin memory. It is a time delay of time-like
free falling observers.Comment: v3: presentation improved, discussion extended, typos corrected,
refs. added v4: typos correcte
Critical phenomena in gravitational collapse of Husain-Martinez-Nunez scalar field
We construct analytical models to study the critical phenomena in
gravitational collapse of the Husain-Martinez-Nunez massless scalar field. We
first use the cut-and-paste technique to match the conformally flat solution
( ) onto an outgoing Vaidya solution. To guarantee the continuity of the
metric and the extrinsic curvature, we prove that the two solutions must be
joined at a null hypersurface and the metric function in Vaidya spacetime must
satisfy some constraints. We find that the mass of the black hole in the
resulting spacetime takes the form , where the
critical exponent is equal to . For the case , we show
that the scalar field must be joined onto two pieces of Vaidya spacetimes to
avoid a naked singularity. We also derive the power-law mass formula with
. Compared with previous analytical models constructed from a
different scalar field with continuous self-similarity, we obtain the same
value of . However, we show that the solution with is not
self-similar. Therefore, we provide a rare example that a scalar field without
self-similarity also possesses the features of critical collapse.Comment: 14 pages, 6 figure
New electromagnetic memories and soft photon theorems
In this paper, we present a new type of electromagnetic memory. It is a
`magnetic' type, or B mode, radiation memory effect. Rather than a residual
velocity, we find a position displacement of a charged particle induced by the
B mode radiation with memory. We find two types of electromagnetic displacement
(ordinary and null). We also show that the null electromagnetic memory formulas
are nothing but a Fourier transformation of soft photon theorems.Comment: v2: interpretation improved and typos fixed, refs adde
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