The IFAE group made very significant contributions to the AdV+ upgrade program. The technology from the IMC instrumented baffle was completely validated thanks to more than five years of smooth operations. A paper with a summary of the five years experience was submitted for publication.
The process of fabrication of the new large baffles for the interferometer arms was enormous and the baffles are essentially finalised and scheduled to be installed in Virgo in June 2026. Two baffles with 120 sensors each taking data at 1kHz rate will be installed at the entrance of the towers of the input mirrors. In addition, IFAE built a full spare. IFAE also fabricated upgraded non instrumented baffles for both the entrance of the input towers and the signal recycling mirror. The latter aimed to reduce the contamination from higher-order modes present in the marginally stable cavities thus improving the whole sensitivity of the experiment. Finally, senior members of the group were deeply involved in the high level discussion on upgrade strategy. Finally IFAE maintains the top level responsibilities in the stray light control subgroup. The results have been presented in a number of conferences and led to several publications.
New updated simulations for Virgo and ET have been performed. In the case of Virgo, simulations were needed for the new location of the instrumented baffles (at the entrance of the input towers instead of suspended together with the mirrors) to ensure the new location would preserve the performance of the instrument without introducing additional noise to the experiment. In the case of ET the simulations of the stray light induced noise in the tube included significant improvements in the calculator of backscattering and diffraction sources. This knowledge has been propagated to CE and IFAE was co-author of the CE vacuum pipe key recommendation document . Results were presented in a number of conferences and led to several publications.
IFAE has contributed to the design of the baffle system based on detailed simulations and produced the first 7 baffles for their implementation in the CERN prototype. Samples with different materials (different stainless steel) and black nickel coating were produced using the knowledge from LIGO to test at CERN for their feasibility in terms of optical quality after polishing and UHV validation. IFAE has been very present in the ET-CE workshops focused on the vacuum beam pipe as promoted by CERN, ET and CE. Results were presented in a number of conferences and led to several publications.
Finally, IFAE mechanical engineers have contributed to the design of the ET-pathfinder cryoshielding hosting the cold mirrors. The shieldings at 290 K, 80 K and 40 K have been revisited and detailed thermal simulations have been made. IFAE provided all the final drawings, as well as manufacturing and assembly instructions. IFAE produced the design of the 15 K cryoshield and the mechanical design of the three cooling stages (Ne, H2 & He) + kick starter necessary to cool the mirrors to 8 K. IFAE helped with the design and plans for the liquid N2 vessel. Some parts were produced in Spanish companies. Concrete plans are now being put in place to equip the ET-pathfinder 10 m arms with a demonstrator of a pre-alignment system, based on the instrumented baffles concept and sensors suitable for 1550 nm light. First feasibility studies and simulations were already produced.
In 2025, the group made enormous progress in the physics exploitation of the LVK data in all its research lines. Since 2018, a strong program was put in place 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. Altogether, this has translated into several publications in 2025, often with IFAE GW students as first authors and performed in close collaboration with the IFAE theory division, in top journals of the field. Most notably:
IFAE continues the investigations in this area focused on search for special double peak structures in the power spectrum of the GW stochastic signal and also contributed to the central effort in the framework of the LVK physics analysis. Results have been presented in conference and lead to a short-author list publication with C. Miritescu as first author. C. Miritescu is now concluding her PhD thesis.
IFAE has played a central role in some of the LVK analysis focusing on testing GR. Special attention was put in testing environmental effects and the ringdown part of the GW waveform. Some special events were analysed in detail. Results were presented in a number of conferences and have led to a number of publications. G. Caneva defended the PhD thesis in 2025.
IFAE continued its participation in analyses related to Cosmology and the determination of the Hubble constant using GWs. In particular, emphasis has been put on the best use of dark sirens (black holes binaries) and the correlation with galaxy catalogs, including the novel idea of using HI density maps to increase the redshift coverage. In the framework of ET a collaboration with U. Geneva has been established to explore new ideas in using neutron star narrow mass spectrum to test modified Cosmology models leading to clear modifications and shifts of the observed mass spectrum as a function of redshift. Results were presented in a number of conferences and have led to a number of publications.
IFAE continued the efforts on searches for CBC events using deep learning techniques. The first studies using CNNs on 2D spectrograms and O2 data were naturally continued using O3 events. A new search for pBH in the O1-O3 data was carried out through a population analysis, using a hierarchical Bayesian approach, where a possible subdominant population of pBHs on top of an astrophysical one could be identified.The group included techniques from the search for continuous GW (CW) signals. The group included the search for continuous GW (CW) signals either from isolated spinning NS or dark matter candidates at the LVK collaboration level. For the latter search, a pipeline aiming specifically at binary pBH systems has been developed (BSD-COBI). The analyses led to several presentations in conferences and publications.
In 2025, the members of the group kept a good visibility in international conferences and workshops, including the most important conferences in the field. The group gave more than 20 contributions to conferences and workshops for both hardware and physics analysis.