6th Edoardo Amaldi Meeting

Matthew Benacquista, Montana State University-Billings benacquista-at-msubillings.edu
The 6th Edoardo Amaldi Conference on Gravitational Waves was held at Bankoku Shinryoukan in Okinawa, Japan on June 19th to 24th. It was attended by approximately 200 participants. The maturity of the field of gravitational wave detection was reflected in the two sessions devoted to current detectors, three sessions on data analysis, and two sessions on research and development for advanced detectors. In addition to an overview session, there were also one session devoted to gravitational wave sources and one to LISA.

The reports on the status of current detectors stressed the approach to design sensitivity for the interferometers, remarkable improvements in duty cycle and bandwidth for the bar detectors, and the impending science run for the spherical resonant detector miniGrail.

TAMA reported the accumulation of over 3000 hours of data and the beginning of automated, crewless runs in late 2003. The increase in sensitivity has been up to four orders of magnitude at some frequencies in the sensitivity band and the detector is approaching design sensitivity. This has given TAMA sufficient sensitivity to observe the entire galaxy. The planned installation of the seismic attenuation system will offer improved sensitivity for the next planned science run in early 2006. LIGO reported that all three interferometers are within roughly a factor of 2 of design sensitivity and that the installation of a preisolator system for the Livingston interferometer has significantly reduced the impact of the local anthropogenic seismic disturbances. Virgo has been commissioning since November, 2003 and now, after a reduction in noise of $10^4$ in one year, it is less than 2 orders of magnitude above design sensitivity at frequencies around 200 Hz and higher. Although the low fequency sensitivity is still several orders of magnitude above design sensitivity, continued noise hunting is expected to bring this level down as well. GEO continues in its role as both detector and prototype as its sensitivity has improved to within an order of magnitude of design in narrowband tuning at 1 kHz.

ALLEGRO has achieved a 95% duty cycle since May, 2004. It has run with 3 rotations during S4 of LIGO to search for a stochastic signal. Otherwise, it was run in parallel with the European bars as part of IGEC-2. Hardware improvements are planned for ALLEGRO in the near future. AURIGA reports a resolution of a problem of spurious peaks that had plagued it in early 2004. It has now achieved design sensitivity and a 95% duty cycle since May, 2005. They report remarkably stable, Gaussian noise over its broad 100 Hz bandwidth. The Nautilus/Explorer bars have now been running in coincidence since March, 2004 with an 85% duty cycle and a strain sensitivity of $\sim 3.5 \times 10^{-19}$ near 920 Hz. Finally, miniGRAIL anticipates the first science run in early 2006 after improvements in the sphere and the transducer.

The data analysis sessions yielded a variety of talks covering ongoing analysis on current data, as well as proposed analysis schemes for current and future data. Of particular interest from the talks on ongoing analysis was the results from Explorer/Nautilus `03 science run which has ruled out the suggestion of an excess of coincidences in the `01 science run. Although still too large to be of astrophysical interest, the upper limits on continuous wave strain amplitudes of $h
\sim 6 \times 10^{-23}$ from LIGO are approaching an order of magnitude above astrophysically reasonable values. The reports on binary coalescence rates from LIGO are still far too large, but the scientific reach of more than 20 Mpc from S4 is beginning to become interesting. Improvements in the search for stochastic backgrounds with LIGO/ALLEGRO have also begun to approach limits achieved by big bang nucleosynthesis. A number of talks focused on progress in the development of joint data analysis projects between detectors. This is of significant interest as it heralds the development of a worldwide network of detectors. In particular, the outline of a new agreement for IGEC-2 is expected to produce significant improvements in performance of a search for events. Finally, an implementation of maximum entropy techniques was presented that may have implications for improved angular resolution of both ground-based and space-based interferometers.

The sessions on advanced detectors included summaries of the plans and progress for improving existing detectors as well as designs for completely new detectors. For most of the existing interferometers, the anticipated improvements are expected to come from better seismic control at low frequencies, higher power lasers at high frequencies, and lower thermal noise in the mid-band. Advanced LIGO is now planning for installation at LLO in 2010 with commissioning runs expected to begin in 2012. Improved Virgo is still in the creative stage but is studying similar solutions to improve the sensitivity. Progress is reported on LCGT which will achieve its improved sensitivity by going underground and going cryogenic. They have begun testing mirrors for thermal noise in cryogenic conditions, and have measured significantly improved seismic noise at the planned site. The first underground cryogenic interferometer, CLIO, reports that construction is ongoing with the completion of the vacuum system and significant parts of the cryogenic systems.

Overall plans for improving the existing bar detectors have focused on increasing sensitivity by going to lower temperature, and increasing bandwidth by improving transducers and amplifiers. Most reports focused on new transducer technology and double SQUID amplifiers. Progress is being made on the Brazilian spherical detector. Work is ongoing with the DUAL detector, which anticipates achieving a wide bandwidth by nesting two bars with different resonant frequencies. Progress is reported on the development of transducers for this arrangement.

Research and development in advanced detectors has covered a number of areas for improving sensitivity. Work on squeezed light has continued with a goal of beating the quantum limit. Improvements in high power lasers were reported, along with the necessary work on improved thermal noise properties and coatings for mirrors. Alternate beam shapes (flat top profiles) have also been investigated.

The session devoted to LISA was more devoted to LISA Pathfinder, the upcoming technology demonstrator with a planned launch in 2009. The planning and design of LTP is almost completed and testing indicates that it approaches or exceeds the requirements. Construction is now underway. The ongoing design and testing of the LISA gravitational reference systems at Trento using their torsion pendulum is also approaching the LTP requirements and the capabilities of the pendulum are now limiting further testing. In addition to LISA, there were talks about possible designs for the gravitational reference system of the proposed LISA follow-on mission (BBO). An update on DECIGO, the proposed Japanese deciHertz detector, reports progress and a possible launch date of 2022. Details of the model dependence of the probable Galactic white dwarf binary background were presented as well as a discussion of testing the non-linear aspects of gravity with LISA.

The session on sources included an overview of expected sources for ground-based detectors, focusing mainly on compact object inspirals. Of particular note was a seven-fold increase in the expected event rate for neutron star inspirals based upon the observation of J0737-3039. Additional work on numerical simulation of waveforms using Whisky was reported. This will be of value to both ground-based and space-based interferometers. A detailed study of a simulation of the white dwarf binary population that included mass transfering systems was presented as a background signal for LISA. Finally, at the high frequency end of the spectrum, the potential for Low-Mass X-ray Binaries to excite f-modes may provide gravitational wave signals at high frequencies.

This was an exciting meeting as several detectors are now operating and producing data, while at the same time work is progressing toward the implementation of second generation detectors. Meanwhile, a number of collaborative efforts are underway that promise to usher in the era of a world-wide network for the detection of gravitational radiation. The next Amaldi meeting, to be held in Sydney, should be equally exciting as much of the progress reported here will be producing results in two years.


Jorge Pullin 2005-10-05