Yun-Kau Lau

A scientific case study of an advanced LISA mission

A brief status report of an ongoing scientific case study of the Advanced Laser Interferometer Antenna (ALIA) mission is presented. Key technology requirements and primary science objectives of the mission are covered in the study. Possible descope options for the mission and the corresponding compromise in science are also considered and compared. Our preliminary study indicates that ALIA holds promise in mapping out the mass and spin distribution of intermediate mass black holes possibly present in dense star clusters at low redshift as well as in shedding important light on the structure formation in the early Universe.

Descope of the ALIA mission

The present work reports on a feasibility study commissioned by the Chinese Academy of Sciences of China to explore various possible mission options to detect gravitational waves in space alternative to that of the eLISA/LISA mission concept. Based on the relative merits assigned to science and technological viability, a few representative mission options descoped from the ALIA mission are considered. A semi-analytic Monte Carlo simulation is carried out to understand the cosmic black hole merger histories starting from intermediate mass black holes at high redshift as well as the possible scientific merits of the mission options considered in probing the light seed black holes and their coevolution with galaxies in early Universe. The study indicates that, by choosing the armlength of the interferometer to be three million kilometers and shifting the sensitivity floor to around one-hundredth Hz, together with a very moderate improvement on the position noise budget, there are certain mission options capable of exploring light seed, intermediate mass black hole binaries at high redshift that are not readily accessible to eLISA/LISA, and yet the technological requirements seem to within reach in the next few decades for China.

Gravitational wave astronomy: the current status

In the centenary year of Einstein’s General Theory of Relativity, this paper reviews the current status of gravitational wave astronomy across a spectrum which stretches from attohertz to kilohertz frequencies. Sect. 1 of this paper reviews the historical development of gravitational wave astronomy from Einstein’s first prediction to our current understanding the spectrum. It is shown that detection of signals in the audio frequency spectrum can be expected very soon, and that a north-south pair of next generation detectors would provide large scientific benefits. Sect. 2 reviews the theory of gravitational waves and the principles of detection using laser interferometry. The state of the art Advanced LIGO detectors are then described. These detectors have a high chance of detecting the first events in the near future. Sect. 3 reviews the KAGRA detector currently under development in Japan, which will be the first laser interferometer detector to use cryogenic test masses. Sect. 4 of this paper reviews gravitational wave detection in the nanohertz frequency band using the technique of pulsar timing. Sect. 5 reviews the status of gravitational wave detection in the attohertz frequency band, detectable in the polarisation of the cosmic microwave background, and discusses the prospects for detection of primordial waves from the big bang. The techniques described in sects. 1–5 have already placed significant limits on the strength of gravitational wave sources. Sects. 6 and 7 review ambitious plans for future space based gravitational wave detectors in the millihertz frequency band. Sect. 6 presents a roadmap for development of space based gravitational wave detectors by China while sect. 7 discusses a key enabling technology for space interferometry known as time delay interferometry.

Strong causality of null infinity of stationary simple spacetime

The strong causality of null infinity in relation to geometric conditions imposed on a stationary simple spacetime is studied. Given a stationary simple spacetime whose timelike Killing vector field is future pointing, timelike everywhere, it is proved that the conformal completion of the spacetime is necessarily strongly causal and therefore the topology of the future and past null infinity of the spacetime is S2×R. This result, together with the previously established result that null infinity of a stationary simple spacetime is geodesically complete, imply that the structure of null infinity of a stationary simple spacetime resembles that of Minkowski space. Any deviation on the structure of null infinity of a simple spacetime from that of Minkowski space may then be attributed to the dynamics of the isolated self-gravitational source giving rise to the spacetime.

Generalised Error Functions from the Kerr Metric

Motivated by the effort to understand the mathematical structure underlying the Teukolsky equations in a Kerr metric background, a homogeneous integral equation related to the prolate spheroidal function is studied. From the consideration of the Fredholm determinant of the integral equation, a family of generalized error function is defined, with which the Fredholm determinant of the sinc kernel is also evaluated. An analytic solution of a special case of the fifth Painleve transcendent is then worked out explicitly.

MACROSCOPIC QUANTUM MECHANICS AND SINGLE-PHOTON MICHELSON INTERFEROMETRY

Single-photon Michelson interferometry as a probe to macroscopic quantum mechanics is considered. With dual output readout at both the bright and dark ports, it is shown that a nonlocal, linear superposition of two Schrodinger cats may be generated by the opto-mechanical coupling of a single photon with a movable macroscopic quantum mirror in one arm of the interferometer. With a balanced homodyne readout scheme, a CHSH inequality may be formulated and the violation of which serves to verify the nonlocality of the two spacelike separated Schrodinger cats. The relevance of this result in our understanding of possible wave function collapse dynamics is briefly touched upon. Macroscopic entangled state of two mirrors generated by opto-mechanical coupling and the associated CHSH inequality are also discussed.