Eusebio's primary research is in cosmology, especially dark energy, large-scale structure and the interplay between cosmology and particle physics. He is the responsible of the Cosmology Group at CIEMAT, that particpates in several of the most advanced projects in the world, dedicated to the study of the Universe and its most unknown constituents: The dark matter and the dark energy.

The CIEMAT Group participates in the Dark Energy Survey, DES, since 2005. The DES Collaboration has built an extremely red sensitive 570 Megapixel camera (DECam) and has installed it at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo observatory in Chile. Over 5 years, a 30% of the available time on the telescope will be used to pursue a high precision multi-bandpass wide area galaxy survey, specially designed to obtain new and precise information about the nature of the dark energy. Currently, the project is in phase of data taking, and is already producing scientific results.

The CIEMAT group is one of the founders and driving groups of the Physics of the Accelerating Universe (PAU) project. PAU is a large galaxy survey being carried out by a collaboration of particle physicists, astrophysicists and cosmologists from several european institutions that started as a Consolider Ingenio 2010 project. The PAU Survey studies the existence and properties of dark energy from the observations of Red-shift Space Distortions (RSD) and Weak Lensing Magnification (MAG) from galaxy cross-correlations as main cosmological probes. In order to perform such a survey, the PAU Team has built a new and powerful instrument, PAUCam. It has been installed at the prime focus of the 4-m diameter William Herschel Telescope (WHT) in La Palma, Canary Islands (Spain), and has taken its first data, which are currently being analyzed.

Finally, the CIEMAT group particpates also in the project DESI (Dark Energy Spectroscopic Instrument). This is the largest galaxy survey to study dark energy after DES. Currentlly, it is in phase of construction of the most advanced spectrograph of the world, and of adaptation of the Mayall telescope (4m), in the Kitt Peak observatory (Arizona, USA), where the spectrograph will be installed. It is expected that the scientific data taking will begin in 2020. The CIEMAT group is responsible, together with several institutions, of the design and construction of the guiding and alignment system, which is currently being built.