Today the LIGO-Virgo-KAGRA (LVK) Collaboration begins a new observing run with upgraded instruments, new and even more accurate signal models, and more advanced data analysis methods. The LVK collaboration consists of scientists across the globe who use a network of observatories—LIGO in the United States, Virgo in Europe, and KAGRA in Japan—to search for gravitational waves, or ripples in space-time, generated by colliding black holes and other extreme cosmic events.

This observing run, known as O4, promises to take gravitational-wave astronomy to the next level. O4 will begin on May 24th and last 20 months, including up to two months of commissioning breaks. It will be the most sensitive search yet for gravitational waves. LIGO will resume operations May 24th, while Virgo will join later in the year. KAGRA will join for one month, beginning May 24th, rejoining later in the run after some upgrades. 

“Thanks to the work of more than a thousand people around the world over the last few years, we’ll get our deepest glimpse of the gravitational-wave Universe yet,” said Jess McIver, the Deputy Spokesperson for the LIGO Scientific Collaboration (LSC). “A greater reach means we will learn more about black holes and neutron stars and increases the chances we find something new. We’re very excited to see what’s out there.”

The Virgo detector will continue commissioning activities in order to increase its sensitivity before joining O4 later this year. "Over the past few months we have identified various noise sources and have made good progress in sensitivity, but it is not yet at its design goal" declared recently elected Virgo spokesperson Gianluca Gemme. "We are convinced that achieving the best detector sensitivity is the best way to maximize its discovery potential.”

KAGRA is now running with the sensitivity planned for the beginning of O4. Jun'ichi Yokoyama, the chair of KAGRA Scientific Congress, says, "KAGRA is the first 2.5th generation detector in the world which started 20 years after LIGO.  We will join O4 for one month and resume commissioning to further improve the sensitivity toward our first detection". 

With the detectors’ increased sensitivity O4 will observe a larger fraction of the universe than previous observing runs. The LIGO detectors will begin O4 approximately 30% more sensitive than before. This increased sensitivity will result in a higher  rate  of observed gravitational-wave signals, resulting in a detection of a merger every 2 or 3 days. Additionally, the increased sensitivity will increase the ability to extract more physical information (including unique astrophysical and cosmological information) from the data. This increased signal fidelity will improve scientists’ ability to test Einstein’s theory of general relativity and infer the true population of dead stars in the local Universe.  

The first gravitational-wave signals were detected in 2015. Two years later, LIGO and Virgo detected a merger of two neutron stars, which caused an explosion called a kilonova, subsequently observed by dozens of telescopes around the world. So far, the global network has detected more than 80 black hole mergers, two probable neutron star mergers and a few events that were most likely black holes merging with neutron stars. During O4, researchers expect to observe even more energetic cosmic events and gain new insights into the nature of the universe.

As in previous observing runs, alerts about gravitational-wave detection candidates will be distributed publicly during O4. Information about how to receive and interpret public alerts is available at https://wiki.gw-astronomy.org/OpenLVEM.

Gravitational-wave observatories

LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,500 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at http://ligo.org/partners.php.

The Virgo Collaboration is currently composed of approximately 850 members from 143 institutions in 15 different (mainly European) countries. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and the National Institute for Subatomic Physics (Nikhef) in the Netherlands. A list of the Virgo Collaboration groups can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at https://www.virgo-gw.eu.

KAGRA is the laser interferometer with 3 km arm-length in Kamioka, Gifu, Japan. The host institute is Institute for Cosmic Ray Research (ICRR), the University of Tokyo, and the project is co-hosted by National Astronomical Observatory of Japan (NAOJ) and High Energy Accelerator Research Organization (KEK). KAGRA collaboration is composed of over 480 members from 115 institutes in 17 countries/regions. KAGRA's information for general is at the website https://gwcenter.icrr.u-tokyo.ac.jp/en/. Resources for researchers are accessible from http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA.

An International team of astronomers led by researcher Toni Santana-Ros, from the University of Alicante and the Institute of Cosmos Sciences of the University of Barcelona and member of the Institut d'Estudis Espacials de Catalunya, has confirmed the existence of the second Earth Trojan asteroid known to date, the 2020 XL₅, after a decade of search. The results of the study have been published today, February 1, in the journal Nature Communications.

All celestial objects that roam around our solar system feel the gravitational influence of all the other massive bodies that build it, including the Sun and the planets. If we consider only the Earth-Sun system, Newton’s laws of gravity state that there are five points where all the forces that act upon an object located at that point cancel each other out. These regions are called Lagrangian points, and they are areas of great stability. Earth Trojan asteroids are small bodies that orbit around the L₄ or L₅ Lagrangian points of the Sun-Earth system.

These results confirm that 2020 XL₅ is the second transient Earth Trojan asteroid known to date, and everything indicates it will remain Trojan —that is, it will be located at the Lagrangian point— for four thousand years, thus it is qualified as transient. The researchers have provided an estimation of the object bulk size (around one kilometer in diameter, larger than the Earth Trojan asteroid known to date, the 2010 TK₇, which was 0.3 kilometres in diameter), and have made a study of the impulse a rocket needs to reach the asteroid from Earth.

Although Trojan asteroids have been known to exist for decades in other planets such as Venus, Mars, Jupiter, Uranus and Neptune, it was not until 2011 that the first Earth Trojan asteroid was found. The astronomers have described many observational strategies for the detection of new Earth Trojans. “There have been many previous attempts to find Earth Trojans, including in situ surveys such as the search within the L₄ region, carried out by the NASA OSIRIS-Rex spacecraft, or the search within the L₅ region, conducted by the JAXA Hayabusa-2 mission”, notes Toni Santana-Ros, author of the publication. He adds that “all the dedicated efforts had so far failed to discover any new member of this population”. 

The low success in these searches can be explained by the geometry of an object orbiting the Earth-Sun L₄ or L₅ as seen from our planet. These objects are usually observable close to the sun. The observation time window between the asteroid rising above the horizon and sunrise is, therefore, very small. Therefore, astronomers point their telescopes very low on the sky where the visibility conditions are at their worst and with the handicap of the imminent sunlight saturating the background light of the images just a few minutes in the observation.

To solve this problem, the team carried out a search of 4-meter telescopes that would be able to observe under such conditions, and they finally obtained the data from the 4.3m Lowel Discovery telescope (Arizona, United States), and the 4.1m SOAR telescope, operated by the National Science Foundation NOIRLab (Cerro Pachón, Chile).

The discovery of the Earth Trojan asteroids is very significant because these can hold a pristine record on the early conditions in the formation of the Solar System, since the primitive trojans might have been co-orbiting the planets during their formation, and they add restrictions to the dynamic evolution of the Solar System. In addition, Earth Trojans are the ideal candidates for potential space missions in the future.

Since the L₄ Lagrangian point shares the same orbit as the Earth, it takes a low change in velocity to be reached. This implies that a spacecraft would need a low energy budget to remain in its shared orbit with the Earth, keeping a fixed distance to it. “Earth Trojans could become ideal bases for an advanced exploration of the Solar System; they could even become a source of resources”, concludes Santana-Ros. 

The discovery of more trojans will enhance our knowledge of the dynamics of these unknown objects and will provide a better understanding of the mechanics that allow them to be transient.

Reference article:

Santana-Ros, T.; Micheli, M.; Faggioli, L.;  Cennamo, R.; Devogèle, M.;  Alvarez-Candal, A.; Oszkiewicz, D.; Ramírez, O.; Liu. P. Y.; Benavidez, P. G.; Campo Bagatín, A.; Christensen, E. J.; Wainscoat, R. J.; Weryk, R.; Fraga, L.; Briceño, C.; Conversi, L. “Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL₅”, Nature Communications, February  2022. DOI: 10.1038/s41467-022-27988-4.

The 17th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2021) was held online from August 26th to September 3rd. In this conference, about one thousand physicists from around the world presented the latest results on cosmological hot topics such as dark matter and dark energy, gravitational waves and neutrino physics among others.

ICCUB’s cosmologist Licia Verde talked about all of these results in an interview with the scientific news agency of the Spanish Foundation for Science and Technology, Agencia Sinc.

In this interview, Dr Verde painted a general picture of the state of the current research in the areas in which cosmologists are mainly focused on presently, with special attention to topics such as the tension in the Hubble constant from the observations of CMB and the data from the Plank Collaboration, the dark matter search experiments to directly detect WIMPs (weakly interactive massive particles), the experiments to study neutrinos and their fundamental properties, the insights on dark energy that will ensue from the data collected by the Dark Energy Spectroscopic Instrument (DESI) and the limit on the number of visible universes imposed by the data of the Wilkinson Microwave Anisotropy Probe (WMAP). 

She then moved on to speculate about the future challenges that cosmologists will face in the following years like detecting the gravitational waves produced during inflation, but she mentions that she does not foresee that discovery happening anytime soon.

We are thrilled to see what surprises this next decade will bring in cosmology and the areas interconnected with it.

On June 30th, the European Strategy Forum on Research Infrastructures (ESFRI) decided to include the Einstein Telescope (ET) in the 2021 upgrade of its roadmap. This confirms the relevance of this major international project for a next generation gravitational waves observatory for the future of research infrastructures in Europe and gravitational wave research at global level.

The Research Infrastructure Consortium Coordinators, Antonio Zoccoli of INFN and Stan Bentvelsen of Nikhef, are extremely excited about this result.

"We are very pleased for this important result: the ESFRI approval acknowledges the value of our project and strengthens ET at the European level", says Zoccoli. "We will work synergistically for its development, confident that it is strategic to foster our knowledge of the universe, technological innovation and social growth."

“ESFRI status is a major step toward the realisation of this European project, - says Bentvelsen - scientifically the Einstein Telescope is undisputed, and with the ESFRI status there is indispensable recognized support for its quality and impact. We are looking ahead to further develop the plans together with all countries involved.”

The Italian government submitted the proposal on September 9th, 2020 supported by the Netherlands, Belgium, Poland and Spain.

“The preparation of the proposal has been a two year large effort involving several research institutions and universities, now composing the Einstein Telescope consortium, belonging to ten European countries and having real interdisciplinary competences”, says Michele Punturo, Coordinator of the ET-ESFRI proposal preparation.

Since then, several of the people involved were invited to present the plans, to deepen specific aspects of the project and answer questions of the ESFRI evaluation committee. Among them was Marica Branchesi, member of the ET-ESFRI proposal preparation team: “We have worked hard to develop the science case of ET. Each simulation showed us the enormous capabilities of ET observing the Universe. ET will revolutionize our knowledge in fundamental physics, astrophysics, and cosmology”, says Branchesi.

The Einstein Telescope was identified after a long and accurate process of evaluation and selection. During the ESFRI Assembly meeting, delegates officially decided to include the Einstein Telescope in the Roadmap. This official European approval now brings the project into a new phase. The scientific Institutions involved from ten countries (Belgium, Germany, Hungary, Italy, Norway, Spain, Switzerland, Poland, The Netherlands and the UK) will now have to intensify their research and development work on the Einstein Telescope and gravitational waves. It will also speed up the ongoing subsurface studies for the characterization and evaluation of the candidate sites that could host the underground infrastructure.

The Spanish involvement in the Einstein Telescope

“This is a great success for the GW community in Spain as a whole”- says Mario Martinez, member of the Einstein Telescope Steering Committee that prepared the ESFRI candidature.

An effort was put in place back on early 2020 with the aim of gathering support for the Einstein Telescope among the Spanish research groups. It was a great success with up to 23 institutions expressing a strong interest in a participation in the project, including four ICTs (Singular Research Infrastructures) in Spain. Altogether, this translated into Spain formally supporting the ESFRI candidature. Now ET is a recognized infrastructure in the 2021 ESFRI roadmap.

The interest of Spain on Gravitational Waves (GW) Physics with ground-based experiments has increased enormously during the last decade. Spanish scientists have contributed to the studies determining the physics potential of ET and are now part of the working groups designing the experiment. A number of Spanish institutions already signed a memorandum of understanding for contributing to the construction of the experiment including:

the Consejo Superior de Investigaciones Científicas (CSIC),

the Institut de Ciències de l'Espai (ICE) de Barcelona,

the Institut de Física d’Altes Energies (IFAE) de Barcelona,

the Instituto de Estructura de la Materia (IEM) de Madrid,

the Instituto d eFísica Teórica (IFT) de la Universidad Autónoma de Madrid,

the Institute of Cosmos Sciences of the Universitat de Barcelona (ICCUB),

the Universitat de les Illes Balears (UIB),

the Universitat de València (UV)

With the ESFRI recognition one can foresee the growth of the ET community and a fast and energetic involvement of the Spanish institutions in the design and construction of the experiment. In addition to a top physics program, that will change our view and understanding of the universe, the ET project offers great opportunities in terms of technological developments and industrial returns.

A new window to the universe

The Einstein Telescope is a future underground observatory for gravitational waves. The instrument will be much more sensitive than existing gravitational-wave detectors. Therefore, the observatory will enable scientists to peek into the ‘dark ages’ of the universe for the first time. Gravitational waves were detected for the first time in 2015 and offer a new way of studying the universe. Until their first detection, scientists could only study the universe by looking at light or radiation, but with gravitational waves they can observe vibrations of spacetime itself. Although the existence of gravitational waves was already predicted by Albert Einstein a hundred years ago, he did not expect it was possible to ever detect them. Yet with the mind-blowing technological developments of the last century, scientists and engineers have managed to reach the sensitivity and precision that is needed to observe them. This opened a new era in the study of the universe, the era of gravitational wave and multimessenger astronomy, and led to a Nobel prize in 2017. The Einstein Telescope will lead to many more unimaginable discoveries in the future in this new field of research.

About ESFRI and the ESFRI Roadmap

ESFRI, the European Strategy Forum on Research Infrastructures, is a strategic instrument to develop the scientific integration of Europe and to strengthen its international outreach. The mission of ESFRI is to support a coherent and strategy-led approach to policy making on research infrastructures in Europe, and to facilitate multilateral initiatives leading to the better use and development of research infrastructures, at EU and international level. ESFRI's delegates are nominated by the Research Ministers of the Member and Associate Countries and include a representative of the Commission.

The ESFRI Roadmap identifies the most promising European scientific structures on the basis of an in-depth evaluation and selection procedure, and includes the ESFRI Projects, i.e. new research infrastructures under construction, and the ESFRI Landmarks, i.e. research infrastructures already implemented with success. All previous updates of the ESFRI Roadmap have proved to be very influential and have provided strategic guidance for investment by member states and associated countries, even beyond the scope of research infrastructures.

Six spanish groups have contributed to the study and analysis of the gravitational waves detected by LIGO-Virgo, in areas that range from the theoretical models of the astorphysical sources and data analysis to the improvement of the sensitivity of the detectors for present and future observation periods. Two groups, in the University of the Balearic Islands (UIB) and the Instituto Galego de Física de Altas Enerxías (IGFAE) of the University of Santiago de Compostela (USC), are part of the LIGO Scientific Collaboration while the University of Valencia, the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), the The Institute for High Energy Physics of Barcelona (IFAE) and the Institute for Theoretical Physics of the Autonomous University of Madrid-CSIC are members of Virgo.

On the 5th of January, 2020, the Advanced LIGO detector in Livingston, Louisiana in the US, and the Advanced Virgo detector in Italy, observed a gravitational wave produced by the last few decaying orbits, before the merging, of a NSBH pair; just ten days later a second gravitational-wave signal from the inspiral and merger of a similar binary system, was observed, this time by both Advanced LIGO detectors and the Virgo detector. These two events, nicknamed GW200105 and GW200115 (from the dates of their detection), represent the first observations of gravitational waves generated by a mix of neutron stars and black holes. Two past gravitational signals (GW190814 and GW190426) have been considered NSBH candidates, but without a sufficient level of confidence.

“Double neutron star systems were first observed in the Milky Way in 1974 by monitoring pulses of radio waves emitted by the neutron stars, known as radio pulsars. “Astronomers have spent decades searching for radio pulsars orbiting black holes, but have found none in the Milky Way up to now,” says Astrid Lamberts, CNRS researcher of the Virgo collaboration at Artemis and Lagrange laboratories, in Nice “ Black hole and neutron star pairs were indeed for astronomers the ‘missing binary’. With this new discovery, we can finally begin to understand how many of these systems exist, how often they merge, and why we have not yet seen examples in the Milky Way.”

The gravitational signals detected in January encode valuable information about the physical features of the systems, such as the mass and distance of the two NSBH pairs, as well as about the physical mechanisms that have generated them and bring them to collapse. The signal analysis has shown that the black hole and neutron star that created GW200105 are, respectively, about 8.9 times and 1.9 times the mass of our Sun (Mo) and their merger happened around 900 million years ago, hundreds of millions of years before the first dinosaurs appeared on Earth. For the GW200115 event, the Virgo and LIGO scientists estimate the two compact objects had masses around 5.7 Mo (BH) and 1.5 Mo (NS) and that they merged almost 1 billion years ago.


The estimated heavier mass in both cases fits within the range predicted for black holes by stellar evolution models. The lighter mass is also consistent with neutron stars and these results indicate that both detected systems are NSBH pairs, even if they have different confidence levels. In this regard, although the statistical significance of GW200105 is not very high, the ‘shape’ of the signal as well as the parameters inferred from the analyses, lead the researchers to believe in its astrophysical origin.

“A large amount of work and computational resources has been dedicated to this parameter estimation. Indeed a crucial issue in the analysis of the data recorded by gravitational-wave detectors is to disentangle the useful information, which always comes mixed with the noise”, said Giancarlo Cella, INFN researcher and Virgo data analysis coordinator. “We need to obtain our best estimates for the properties of the sources and at the same time we want to know what is the probability that the identified signal might be just a random fluctuation”

An additional proof of the detection of a mixed neutron star black-hole system would have been the detection of electromagnetic radiation along with the gravitational waves. In fact, if the masses of the two compact objects are roughly comparable, the neutron star, while approaching the black hole, is subjected to such powerful tidal forces that it is broken up. In this case, in addition to gravitational emissions, one could also observe spectacular flares of electromagnetic radiation, due to the disintegration of the stellar matter around the black hole: a mechanism similar to that which leads to the formation of accretion disks around giant black holes at the center of galaxies. This probably did not occur for either GW200105 or GW200115, because in both cases the mass of the black hole was too large, so once the separation between the two objects has been sufficiently reduced, the black hole has, so to speak, swallowed its companion in one bite.

“We got the evidence that our sensitivity is now above the threshold needed for detecting systems of this kind”, claimed Cella, “and we expect that we will do this routinely in the next runs.”

Drawing a new cosmic landscape

“The fact that we have now detected the three types of binaries will help us to develop theories that explain the properties of all of them consistently”, added Astrid Lamberts “In fact, this discovery allows us to deepen our knowledge of the most extreme phenomena in the Universe, helping us understand better which mechanisms may have generated them.”

The result announced today, alongside the dozens of detections made by Virgo and LIGO to date, allow us, for the first time, a close observation of some of the most violent and rare phenomena in the Universe and to draw an unprecedented picture of the crowded and chaotic regions that are one of the possible nursery environments of these events. Furthermore, the detailed information we have started to collect about the physics of the black hole and star mergers, gives us the chance to test the fundamental laws of physics at extreme conditions, which obviously we will never be able to reproduce on Earth.

“The discovery announced today is one more gem in the treasure of the 3rd LIGO-Virgo observing run”, stated Giovanni Losurdo, Virgo spokesperson and INFN researcher. “LIGO and Virgo keep unveiling catastrophic collisions, which have never been observed before, shedding light on a truly new cosmic landscape. We are now upgrading the detectors with the aim of looking much farther into the depth of the cosmos, searching for new gems, seeking a deeper understanding of the universe we live in.”



IN DEPTH CONTENTS

How does a black hole and neutron star pair form and merge? (see Infographics)

The current astrophysical models roughly consider two main theoretical scenarios for the formation of NSBH pairs. One, called “isolated binary evolution”, starts with two stars orbiting around one another, which, at the end of their life, become, after supernova explosions, a still-bound-together black hole and neutron star. The other possibility is that the neutron star and black hole form from separate stars in unrelated supernova explosions, and only afterwards find one another. This, called “dynamical interaction”, can be triggered by different physical mechanisms in dense stellar environments, such as globular clusters, young clusters or even the accretion disks of active galactic nuclei.

Based on these different theoretical scenarios it is possible to make predictions, for example, about the orientations of the black hole and neutron star rotations with respect to the orbital motions (i.e. their so called “spins”) or, more generally, about how many NSBH pairs merge in the Universe within a given time period (a quantity called the “merger rate”). Thanks to the detections announced today, for the first time, these predictions can be compared with the data of the two observed NSBH pairs, and we can start discriminating between the different astrophysical models.

For instance, considering that only these two NSBH events have been detected during all of the LIGO and VIRGO observing runs, it turns out that between 5 and 15 such systems merge per year within a distance of one billion light years from Earth. This rate appears to be especially consistent with both the isolated binary evolution and the dynamical interaction in young star clusters or in active galactic nuclei; however this estimated rate, as well as the measured spin values of GW200105 and GW200115, do not allow to single out just one specific formation scenario.

Multimedia materials:

https://bit.ly/3ja75hB

Gravitational-wave observatories:

The Virgo Collaboration is currently composed of approximately 700 members from 126 institutions in 15 different (mainly European) countries. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and Nikhef in the Netherlands. A list of the Virgo Collaboration groups can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at http://www.virgo-gw.eu

LIGO is funded by the National Science Foundation (NSF) and operated by Caltech and MIT, which conceived of LIGO and led the project. Financial support for the Advanced LIGO project was led by the NSF, with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. Approximately 1,300 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.

The KAGRA laser interferometer, with 3-kilometer-long arms, is located in Kamioka, Gifu, Japan. The host institute is the Institute of Cosmic Ray Researches (ICRR) at the University of Tokyo, and the project is co-hosted by National Astronomical Observatory in Japan (NAOJ) and High Energy Accelerator Research Organization (KEK). KAGRA completed its construction in 2019, and later joined the international gravitational-wave network of LIGO and Virgo. The actual data taking was started in February 2020 during the final stage of the run called "O3b." KAGRA Scientific Congress is composed of over 470 members from 115 institutes in 14 countries/regions. The list of researchers is available from http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA/KSC/Researchers. KAGRA information is at the website https://gwcenter.icrr.u-tokyo.ac.jp/en/.

It will also strengthen the European Leadership on Space Astrometry, as it was pointed out by the Committee: «Such a mission will capitalize on the expertise developed since the Hipparcos mission at the end of the 1980s and continued with the current enormous success of Gaia, both of which demonstrate the undisputed and long-standing European leadership in the area. »

The final selection of missions is a very long process and, in some cases, technological studies are needed (as would be the case for astrometry in the NIR, which needs development of specific devices). Now is the time to embark in such a process, make the mission visible, start organizing the community, look for the technological studies, etc.
We are now at the beginning of a new and exciting time and we can only hope that the proposed astrometry mission will become a reality.

More information at the the following website and link

Report of the Senior committee at Report.

Atomic nuclei make up more than 99% of the visible matter in the universe. Understanding the physics of these nuclei is therefore fundamental to understanding the world around us. Particularly important questions are: How does the complex structure of a nucleus arise from the dynamics of quarks and gluons, fundamental objects of the Standard Model which, together with gravity, is our current description of Nature? How do nuclei interact with each other and with other particles of the Standard Model? How can new physics beyond the Standard Model be discovered using nuclear isotopes as targets? The calculations proposed in this project will address parts of these broad questions and further elucidate the nuclear realm. In particular, the project will lead to the ground-state spectrum and matrix elements of s-shell nuclei. The final goal is to extract nuclear and hypernuclear forces relevant for determinations of the nuclear equation of state that governs neutron star structure and merger dynamics, and to constrain the theoretical understanding of dark matter scattering from nuclei in terrestrial detectors, representing a significant step forward in showing how nuclei emerge from the intricacies of Standard Model dynamics.

The team that will conduct the research has strong expertise in nuclear and particle physics, numerical algorithms, large-scale calculations and effective field theories, and is composed by our researchers Assumpta Parreño and Marc Illa, Zohreh Davoudi from the University of Maryland, William Detmold and Phiala Shanahan from the Massachusetts Institute of Technology, and Michael Wagman from Fermi National Accelerator Laboratory. They all are members of the Nuclear Physics with Lattice Quantum Chromodynamics Collaboration, NPLQCD, an ongoing international effort dedicated to provide a quantitative bridge between nuclear physics and the underlying theory of fundamental forces using Lattice QCD.

About Assumpta Parreño:

Assumpta Parreño is a nuclear physicist, vice dean of our Institute and a professor of the Faculty of Physics of the University of Barcelona. Prof. Parreño is member of the research group in hadronic, atomic and nuclear physics at the Institute of Cosmos Sciences. The group studies the basic properties of atomic nuclei and the interactions involving hadrons and nuclei. Prof. Parreño's research interests also include the description of weak interaction processes responsible for the decay of hypernuclei, exotic nuclei composed of neutrons, protons and their strange extensions, hyperons.

About 22nd PRACE Project Access Call:

The 22nd PRACE Project Access Call received 61 eligible proposals, of which 43 were awarded, a total of 1.92 billion core hours. These projects are led by principal investigators from 14 different countries, with 13% female leadership. Seven scientific fields are represented among the awarded proposals: 6 proposals are linked to the fields of Biochemistry, Bioinformatics and Life Sciences; 21 to Chemical Sciences and Materials; 3 to Earth System Sciences; 3 to Engineering; 8 to Fundamental Constituents of Matter; 1 to Mathematics and Computer Sciences, and 1 to Universe Sciences.

New observations carried out with the European Southern Observatory’s Very Large Telescope (ESO’s VLT) indicate that the rogue comet 2I/Borisov, which is the second and most recently detected interstellar visitor to our Solar System, is one of the most pristine comets ever observed. Astronomers suspect that the most likely thing to have happened is for the comet to never passed close to a star, making it an unaltered relic of the cloud of gas and dust where it was created.

2I/Borisov was discovered by amateur astronomer Gennady Borisov in August 2019 and weeks later it was confirmed to have come from beyond the Solar. A new study published in Nature Communications, the team, in which Toni Santana-Ros, astronomer at the Institute of Cosmos Sciences and the University of Alicante, took part, notes that the comet would have never passed close to a star before getting closer to the Sun when it was discovered.

Researchers found that 2I/Borisov has polarimetric properties different than other comets in the Solar System, except for Hale-Bopp, visible in the late nineties. Both comets are the most pristine ones observed to date. This means they have a similar composition to the gas and dust cloud in which they were created, like the rest of the Solar System about 4.5 billion years ago.

When analysing the polarization together with the color of the comet to get more clues on its composition, the team concluded that 2I/Borisov is even more pristine than Hale-Bopp. This means it has unaltered remains frmo the gas and dust cloud in which it was created.

The fact that both comets are similar suggests that the environment in which 2I/Borisov originated is not that different in composition from the environment of the early Solary System. According to Antoni Santana-Ros (ICCUB-UA), “since this is the first interstellar comet to be observed, it is unique. We do not know the frequency these objects cross our Solar System, and therefore, we may be talking about a unique situation of observing such an object. Therefore –he adds–, it is very important to analyse all the observations of this body, which take us to study in detail its composition and mainly the amount of space erosion it has received over the course of its history”.

Although 2I/Borisov was the first rogue comet to fly by the Sun, the first interstellar object to be seen passing by our Solar System was ‘Oumuamua’ –firstly classified as a comet and then reclassified as an asteroid, since it lacked a coma.

Notes

[1] Polarimetry is a technique to measure the polarisation of light. Light becomes polarised, for example, when it goes through certain filters, like the lenses of polarised sunglasses or cometary material. By studying the properties of sunlight polarised by a comet’s dust, researchers can gain insights into the physics and chemistry of comets.

More information

This research highlighted in this release was presented in the paper “Unusual polarimetric properties for interstellar comet 2I/Borisov” to appear in Nature Communications (doi: 10.1038/s41467-021-22000-x).

The team who conducted the study is composed of S. Bagnulo (Armagh Observatory & Planetarium, UK [Armagh]), A. Cellino (INAF – Osservatorio Astrofisico di Torino, Italy), L. Kolokolova (Department of Astronomy, University of Maryland, US), R. Neži? (Armagh; Mullard Space Science Laboratory, University College London, UK; Centre for Planetary Science, University College London/Birkbeck, UK), T. Santana-Ros (Departamento de Fisica, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Spain; Institut de Ciencies del Cosmos, Universitat de Barcelona, Spain), G. Borisov (Armagh; Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, Bulgaria), A. A. Christou (Armagh), Ph. Bendjoya (Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France), and M. Devogele (Arecibo Observatory, University of Central Florida, US).

Links

• Research papers:
• Bagnulo et. al, Nature Communications
• Photos of the VLT
• Photos of the ALMA

The LHCb results strengthen hints of a violation of lepton flavour universality

Today the LHCb experiment at CERN announced new results which, if confirmed, would suggest hints of a violation of the Standard Model of particle physics. The results focus on the potential violation of lepton flavour universality and were announced at the Moriond conference on electroweak interactions and unified theories, as well as at a seminar held online at CERN, the European Organization for Nuclear Research.

The measurement made by the LHCb (Large Hadron Collider beauty) collaboration, compares two types of decays of beauty quarks. The first decay involves the electron and the second the muon, another elementary particle similar to the electron but approximately 200 times heavier. The electron and the muon, together with a third particle called the tau, are types of leptons and the difference between them is referred to as “flavours”. The Standard Model of particle physics predicts that decays involving different flavours of leptons, such as the one in the LHCb study, should occur with the same probability, a feature known as lepton flavour universality that is usually measured by the ratio between the decay probabilities. In the Standard Model of particle physics, the ratio should be very close to one.

The new result indicates hints of a deviation from one: the statistical significance of the result is 3.1 standard deviations, which implies a probability of around 0.1% that the data is compatible with the Standard Model predictions. “If a violation of lepton flavour universality were to be confirmed, it would require a new physical process, such as the existence of new fundamental particles or interactions,” says LHCb spokesperson Professor Chris Parkes from the University of Manchester and CERN. “More studies on related processes are under way using the existing LHCb data. We will be excited to see if they strengthen the intriguing hints in the current results.”

The deviation presented today is consistent with a pattern of anomalies measured in similar processes by LHCb and other experiments worldwide over the past decade. The new results determine the ratio between the decay probabilities with greater precision than previous measurements and use all the data collected by the LHCb detector so far for the first time.

The LHCb experiment is one of the four large experiments at the Large Hadron Collider at CERN, situated underground on the Franco-Swiss border near Geneva. The experiment is designed to study decays of particles containing a beauty quark, a fundamental particle that has roughly four times the mass of the proton. The results presented today focus on lepton flavour universality, but the LHCb experiment also studies matter-antimatter differences.

Looking towards the future, the LHCb experiment is well placed to clarify the potential existence of new physics effects hinted at in the decays presented today. The LHCb experiment is expected to start collecting new data next year following an upgrade to the detector.

Additional material:

Photo of the LHCb experiment : http://cds.cern.ch/record/2302374?ln=fr#24

Caption: “The LHCb experiment is one of the four large experiments at the Large Hadron Collider at CERN, situated underground on the Franco-Swiss border near Geneva.”

VNR : https://videos.cern.ch/record/2758757

LHCb paper : https://arxiv.org/abs/2103.11769

LHCb article : https://lhcb-public.web.cern.ch/Welcome.html#RK2021