Tuesdays 10:30 - 11:30 | Fridays 11:30 - 12:30
Showing votes from 2016-03-25 12:30 to 2016-03-29 11:30 | Next meeting is Tuesday May 5th, 10:30 am.
First discovery of the gravitational wave (GW) event, GW150914, suggests a higher merger rate of black-hole (BH) binaries. If this is true, a number of BH binaries will be observed via the second-generation GW detectors, and the statistical properties of the observed BH binaries can be scrutinized. A naive but important question to ask is whether the spatial distribution of BH binaries faithfully traces the matter inhomogeneities in the Universe or not. Although the BH binaries are thought to be formed inside the galaxies in most of the scenarios, there is no observational evidence to confirm such a hypothesis. Here, we estimate how well the second-generation GW detectors can statistically confirm the BH binaries to be a tracer of the large-scale structure by looking at the auto- and cross-correlation of BH binaries with photometric galaxies and weak lensing measurements, finding that, with a three-year observation, the $>3\sigma$ detection of non-zero signal is possible if the BH merger rate today is $\dot{n}_0\gtrsim100$ Gpc$^{-3}$yr$^{-1}$ and the clustering bias of BH binaries is $b_{\rm BH,0}\gtrsim1.5$.
We point out that the gravitational wave event GW150914 observed by the LIGO detectors can be explained by the coalescence of primordial black holes (PBHs). It is found that the expected PBH merger rate would exceed the rate estimated by the LIGO scientific collaboration and Virgo collaboration if PBHs were the dominant component of dark matter, while it can be made compatible if PBHs constitute a fraction of dark matter. Intriguingly, the abundance of PBHs required to explain the suggested lower bound on the event rate, $> 2$ events/year/${\rm Gpc}^3$, roughly coincides with the existing upper limit set by the non-detection of the CMB spectral distortion. This implies that the proposed PBH scenario may be tested in the not-too-distant future.
Given the recent direct measurement of gravitational waves (GWs) by the LIGO-VIRGO collaboration, the coupling between electromagnetic fields and GW have a special relevance since it might open new perspectives for future GW detectors and also potentially provide information on the physics of highly energetic GW sources. We explore such couplings using the field equations of electrodynamics on (pseudo) Riemann manifolds and apply it to the background of a GW, seen as a linear perturbation of Minkowski geometry. Electric and magnetic oscillations are induced that propagate as electromagnetic waves and contain information of the GW which generates them. We also show very briefly the generation of charge density fluctuations induced by GW and the implications for astrophysics.