Detecting extreme mass ratio inspirals with LISA using time–frequency methods

The inspirals of stellar-mass compact objects into supermassive black holes are some of the most important sources for LISA. Detection techniques based on fully coherent matched filtering have been shown to be computationally intractable. We describe an efficient and robust detection method that utilizes the time–frequency evolution of such systems. We show that a typical extreme mass ratio inspiral (EMRI) source could possibly be detected at distances of up to ~2 Gpc, which would mean ~tens of EMRI sources can be detected per year using this technique. We discuss the feasibility of using this method as a first step in a hierarchical search

Photons with sub-Planckian Energy Cannot Efficiently Probe Space-Time Foam

Extra-galactic sources of photons have been used to constrain space-time quantum fluctuations in the Universe. In these proposals, the fundamental "fuzziness" of distance caused by space-time quantum fluctuations has been directly identified with fluctuations in optical paths. Phase-front corrugations deduced from these optical-path fluctuations are then applied to light from extra-galactic point sources, and used to constrain various models of quantum gravity. However, when a photon propagates in three spatial dimensions, it does not follow a specific ray, but rather samples a finite, three-dimensional region around that ray --- thereby averaging over space-time quantum fluctuations all through that region. We use a simple, random-walk type model to demonstrate that, once the appropriate wave optics is applied, the averaging of neighboring space-time fluctuations will cause much less distortion to the phase front. In our model, the extra suppression factor due to diffraction is the wave length in units of the Planck length, which is at least $10^{29}$ for astronomical observations.Comment: This is a revised version of arXiv:gr-qc/060509

Application of graphics processing units to search pipelines for gravitational waves from coalescing binaries of compact objects

We report a novel application of a graphics processing unit (GPU) for the purpose of accelerating the search pipelines for gravitational waves from coalescing binaries of compact objects. A speed-up of 16-fold in total has been achieved with an NVIDIA GeForce 8800 Ultra GPU card compared with one core of a 2.5 GHz Intel Q9300 central processing unit (CPU). We show that substantial improvements are possible and discuss the reduction in CPU count required for the detection of inspiral sources afforded by the use of GPUs

Detection of Binary Black Hole Mergers from the Signal-to-Noise Ratio Time Series Using Deep Learning

Gravitational wave detection has opened up new avenues for exploring and understanding some of the fundamental principles of the universe. The optimal method for detecting modelled gravitational-wave events involves template-based matched filtering and doing a multi-detector search in the resulting signal-to-noise ratio time series. In recent years, advancements in machine learning and deep learning have led to a flurry of research into using these techniques to replace matched filtering searches and for efficient and robust parameter estimation. This paper presents a novel approach that utilizes deep learning techniques to detect gravitational waves from the signal-to-noise ratio time series produced from matched filtering. We do this to investigate if an efficient deep-learning model could replace the computationally expensive post-processing in current search pipelines. We present a feasibility study where we look to detect gravitational waves from binary black hole mergers in simulated stationary Gaussian noise from the LIGO detector in Hanford, Washington. We show that our model can match the performance of a single-detector matched filtering search and that the ranking statistic from the output of our model was robust over unseen noise, exhibiting promising results for practical online implementation in the future. We discuss the possible implications of this work and its future applications to gravitational-wave detection.Comment: 9 pages, 4 figure

Gravitational wave astronomy

We are entering a new era of gravitational-wave astronomy. The ground-based interferometers have reached their initial design sensitivity in the audio band. Several upper limits have been set for anticipated astrophysical sources from the science data. The advanced detectors in the US and in Europe are expected to be operational around 2015. New advanced detectors are also planned in Japan and in India. The first direct detections of gravitational waves are expected within this decade. In the meanwhile, three pulsar timing array projects are forming an international collaboration to detect gravitational waves directly in the nanoHertz range using timing data from millisecond pulsars. The first direct detection of nanoHertz gravitational waves are also expected within this decade. In this paper, we review the status of current gravitational-wave detectors, possible types of sources, observational upper limits achieved, and future prospects for direct detection of gravitational waves

Geometrical Expression for the Angular Resolution of a Network of Gravitational-Wave Detectors

We report for the first time general geometrical expressions for the angular resolution of an arbitrary network of interferometric gravitational-wave (GW) detectors when the arrival-time of a GW is unknown. We show explicitly elements that decide the angular resolution of a GW detector network. In particular, we show the dependence of the angular resolution on areas formed by projections of pairs of detectors and how they are weighted by sensitivities of individual detectors. Numerical simulations are used to demonstrate the capabilities of the current GW detector network. We confirm that the angular resolution is poor along the plane formed by current LIGO-Virgo detectors. A factor of a few to more than ten fold improvement of the angular resolution can be achieved if the proposed new GW detectors LCGT or AIGO are added to the network. We also discuss the implications of our results for the design of a GW detector network, optimal localization methods for a given network, and electromagnetic follow-up observations.Comment: 13 pages, for Phys. Rev.