18,354 research outputs found
Gravitational waves from cosmic bubble collisions
Cosmic bubbles are nucleated through the quantum tunneling process. After
nucleation they would expand and undergo collisions with each other. In this
paper, we focus in particular on collisions of two equal-sized bubbles and
compute gravitational waves emitted from the collisions. First, we study the
mechanism of the collisions by means of a real scalar field and its quartic
potential. Then, using this model, we compute gravitational waves from the
collisions in a straightforward manner. In the quadrupole approximation,
time-domain gravitational waveforms are directly obtained by integrating the
energy-momentum tensors over the volume of the wave sources, where the
energy-momentum tensors are expressed in terms of the scalar field, the local
geometry and the potential. We present gravitational waveforms emitted during
(i) the initial-to-intermediate stage of strong collisions and (ii) the final
stage of weak collisions: the former is obtained numerically, in \textit{full
General Relativity} and the latter analytically, in the flat spacetime
approximation. We gain qualitative insights into the time-domain gravitational
waveforms from bubble collisions: during (i), the waveforms show the
non-linearity of the collisions, characterized by a modulating frequency and
cusp-like bumps, whereas during (ii), the waveforms exhibit the linearity of
the collisions, featured by smooth monochromatic oscillations.Comment: 17 pages, 5 figure
Properties of Microlensing Central Perturbations by Planets in Binary Stellar Systems under the Strong Finite-Source Effect
We investigate high-magnification events caused by planets in wide binary
stellar systems under the strong finite-source effect, where the planet orbits
one of the companions. From this, we find that the pattern of central
perturbations in triple lens systems commonly appears as a combination of
individual characteristic patterns of planetary and binary lens systems in a
certain range where the sizes of the caustics induced by a planet and a binary
companion are comparable, and the range changes with the mass ratio of the
planet to the planet-hosting star. Specially, we find that because of this
central perturbation pattern, the characteristic feature of high-magnification
events caused by the triple lens systems appears in the residual from the
single-lensing light curve despite the strong finite-source effect, and it is
discriminated from those of the planetary and binary lensing events and thus
can be used for the identification of the existence of both planet and binary
companion. This characteristic feature is a simultaneous appearance of two
features. First, double negative-spike and single positive-spike features
caused by the binary companion appear together in the residual, where the
double negative spike occurs at both moments when the source enters and exits
the caustic center and the single positive spike occurs at the moment just
before the source enters into or just after the source exits from the caustic
center. Second, the magnification excess before or after the single
positive-spike feature is positive due to the planet, and the positive excess
has a remarkable increasing or decreasing pattern depending on the source
trajectory.Comment: 12 pages, 3 figures, accepted for publication in Ap
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