During the last years, IFAE scientists spent significant periods at EGO, and participated in commissioning campaigns as well as in dedicated noise hunting activities related to magnetic injections. In particular, the study, via magnetic field injection campaigns, of potential couplings of interferometer elements with magnetics fields is crucial to determine the sensitivity of the experiment to the presence of Schumann fields. Variations of the Earth magnetic fields potentially affecting the interferometer network as a whole would introduce long-distance correlations in the background noise across interferometers, invalidating the search for stochastic gravitational wave signals in the data. Most recently, IFAE has contributed in a major way to the reconstruction and calibration of the Virgo data, in the framework of the O4 commissioning efforts. M. Seglar (JdC fellow) is a recognized expert on the field. The GW signal reconstruction code has evolved significantly during the years of the commissioning of O4 to include the signal recycling mirror, online noise suppression, and to increase its flexibility to adjust the optical response of the interferometer in real time. The new methods developed for O4 have shown in addition high robustness against glitches, compared to O3. IFAE members (M. Seglar, D. Lacroze) spent significant time at EGO to further improve Virgo’s sensitivity before the experiment resumed data taking in March 2024.
The IFAE team in Virgo has invaluable support from the PIC computing center. In 2019, PIC was fully integrated in the LIGO-Virgo computing grid, providing opportunistic resources to the experiments. In 2019-2023, PIC contributed 2% to the total LIGO-Virgo CPU accounting and about 10% of the GPU accounting.
In the last years, as part of the SLC responsibility in Virgo and ET, members of the IFAE team, in collaboration with LIGO-Caltech and Virgo-EGO scientists, developed simulations of the light propagation in the interferometers. As part of the work required for the design of the new large instrumented baffles, detailed simulations took place to optimize the sensor layout in the baffle in view of the light illuminating the baffle and the baffle performance as a tool for pre-alignment and for monitoring the performance of the main mirrors and their evolution with time. The results are published in A. Macquet et al., Class. Quantum Grav. 40, 077001 (2023).
IFAE is playing a central role in the determination of key parameters in the design of the ET infrastructure. In particular, the dimensions of the vacuum tube in ET are directly conditioned by the control of the stray light inside the optical cavities. Similarly, optical requirements related to stay light dictate the layout of hundreds of baffles inside the pipes, tube maximum vibrations and the quality of coatings applied to the mirror and baffle surfaces. Detailed calculations and simulations were carried out and the results are published in M. Andrés-Carcasona, et al., Phys. Rev. D 108, 102001 (2023). Figure 3 presents some of the results.
The group put in place a strong program with three main pillars: the search and study of compact binary coalescence events with emphasis on fundamental physics related to tests of General Relativity and dark matter (DM) searches, with and without the use of deep learning techniques; the use of GW for cosmological tests; and the search for stochastic GW signals as probes of the early universe. A strong experiment–theory collaboration within IFAE has been established for this purpose. Most recently, the program has been extended towards the search for continuous GW signals. Altogether, this has translated into several publications often with IFAE students as first authors in top journals of the field. Some examples are provided in the figures below in the case of cosmological tests using GWs (Figure 4) and searches for primordial black holes using deep learning algorithms (Figure 5).
The members of the group have been very visible in international conferences and workshops, including the most important conferences in the field. As an indicator, the group in 2021-2023 gave on average more than 20 contributions to conferences and workshops for both hardware and analysis per year.
IFAE already plays a unique role in the ground-based GW projects in Europe, being the only Spanish institution that has already developed novel hardware for the current detectors, and being well placed in the R&D initiatives, initial design studies, and in the top-level governing bodies of the ET project.
IFAE coordinates the stray light control efforts in Virgo and ET. The Virgo experiment at EGO was initially initiated as a joint effort by INFN and CNRS and now includes NIKHEF in the EGO consortium. IFAE has been recently invited to participate as an observer in EGO’s council. Other governance positions inside the Virgo include participation in top level committees like the Virgo Steering committee, the joint EGO-Virgo Committee, the Virgo Organization committee, the LKV MoU committee, or the LVK climate change committee. Nowadays, ET is a collaboration formed by about 1500 members from 200 institutions involving all the key players in Europe. Since 2022, Mario Martínez acts as coordinator for the Horizon-CSA INFRA-DEV ET-PP project, a pan-European 3.5 M€ project (12 M€ project total value) for the ET preparatory phase. Mario Martínez is a member of the ET Directorate and E. Coccia is the chair of the ET collaboration board.