(Press-News.org)
Understanding the structure of hadrons, such as protons and neutrons, is currently one of the most important goals for researchers studying nuclear and particle physics. Hadrons consist of quarks and gluons, together called partons. The behavior of partons inside hadrons is described by mathematical tools called parton distribution functions (PDFs), which tell us the probability of finding partons carrying a fraction x of the hadron's total momentum. Until recently, PDFs were mainly determined by fitting data obtained from decades of high-energy experiments, a process known as phenomenological modeling. Recently, the interest in calculating PDFs from first principal calculations has gained considerable momentum.
Partons interact via the strong force, one of the four fundamental forces of nature, which is governed by quantum chromodynamics (QCD), known to be notoriously difficult to solve. Lattice QCD is a computational approach that makes QCD tractable, by simulating spacetime into a finite grid or lattice. Even with lattice QCD, calculating PDFs from first principles remains challenging. PDFs are naturally defined using light-cone coordinates, which represent all possible paths where light can travel in space-time. In these coordinates, time always moves forward. In contrast, lattice QCD works in Euclidean spacetime, where time behaves like a fourth spatial dimension. This makes it difficult to directly calculate PDFs.
To circumvent this problem, researchers have developed alternative methods. One such method is short-distance expansion (SDE), in which PDFs are calculated by analyzing parton correlations over very short Euclidean distances using standard QCD. A more recent and powerful method called Large-Momentum Effective Theory (LaMET), allows calculation of PDFs over a broad x-range. While these two methods are equivalent at infinite momentum, they have major differences at finite momentum, where actual calculations are performed.
Now, in a recent study, Distinguished University Professor Xiangdong Ji from the University of Maryland, College Park, USA, who first pioneered LaMET, presented a detailed comparison of LaMET and SDE. “Both LaMET and SDE are widely studied approaches for calculating PDFs and have their strengths in different aspects,” explains Prof. Ji. “In this study, I discuss how these approaches contrast and how they complement each other to give us a more complete understanding of partons.” The study was published in Volume 8 of the journal Research on May 28, 2025.
In LaMET, approximations of PDFs are calculated using lattice QCD at a large but finite hadron momentum. These approximations can be largely corrected through a process called matching, which produces increasingly accurate representations of true light cone PDFs as momentum increases. This method allows the precise study of local x-dependence of PDFs over a broad x-range. However, LaMET becomes less reliable at very small and very large x values, requiring extremely large momentum, which makes computations inaccessible at present.
This is where SDE can help. It provides global constraints on PDFs. Prof. Ji suggests that SDE can be used to bridge the gaps in LaMET analyses. Particularly, LaMET can be used to calculate PDFs for the middle x-region and the global constraints obtained from SDE, together with theoretical and phenomenological modeling, can be used for end limits of very small and very large x.
He demonstrated this approach by calculating the valence PDFs of pions. The results were successfully validated using high-precision data from the Argonne National Laboratory (ANL)/Brookhaven National Laboratory (BNL) collaboration. The LaMET calculations generated reasonable predictions in the x-range of 0.1 to 0.7. Beyond this range, LaMET's reliability decreased, while phenomenological modeling using global SDE constraints improved predictions, especially for large-x.
“This approach will prove beneficial for generating state-of-the-art lattice QCD PDFs,” says Prof. Ji. “These can be used to make predictions for high-energy particle collisions at facilities like the Large Hadron Collider, potentially leading to the discovery of new particles and deepening our understanding of partons, and by extension, hadrons.”
Overall, this study marks a significant step forward in using lattice QCD for calculating PDFs and uncovering new insights into parton physics in hadrons.
About the University of Maryland, College Park, USA
Founded in 1856, University of Maryland, College Park is the flagship institution of the state of Maryland. It is the largest university in Maryland and the Washington metropolitan area. brings together world-class scientists and scholars in an unbeatable location near the nation's capital to discover and innovate. Its proximity to Washington, D.C. has resulted in many partnerships with the federal government of the USA. It fosters a culture of environmental sustainability, social innovation and leadership, through teaching, research, service and campus operations. The university strives to provide exceptional opportunities to learn, innovate, and serve the public good.
About Research by Science Partner Journal
Launched in 2018, Research is the first journal in the Science Partner Journal (SPJ) program. Research is published by the American Association for the Advancement of Science (AAAS) in association with Science and Technology Review Publishing House. Research publishes fundamental research in the life and physical sciences as well as important findings or issues in engineering and applied science. The journal publishes original research articles, reviews, perspectives, and editorials. IF=10.7, Citescore=13.3.
Sources: https://doi.org/10.34133/research.0695
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Primates, birds, and elephants are all known to make tools, but examples of tool use among marine animals are much more limited. Reporting in the Cell Press journal Current Biology on June 23, a team of whale experts has found widespread tool manufacture and usage in an endangered population of resident killer whales living in the Salish Sea—part of the Pacific Ocean between British Columbia and Washington. The whales fashion tools from kelp and use them for grooming purposes.
“We found that southern resident killer whales regularly use lengths of bull kelp during social interactions, ...
Killer whales have been seen detaching lengths of seaweed and using them to massage each other – the first evidence of tool-making by marine mammals.
The whales bite off the end of a kelp stalk, position it between themselves and a partner, and roll the kelp between their bodies for prolonged periods.
Scientists spotted this behaviour in drone footage of “southern resident” killer whales in the Salish Sea, in the inland waters of Washington, USA.
Whales of all ages were seen doing this, possibly ...
Lower blood sugar and increased fat burning – without negatively affecting appetite or muscle mass. These are some of the most promising effects of a new potential drug treatment for people with type 2 diabetes and obesity, according to a new study published in the journal Cell by researchers from Karolinska Institutet and Stockholm University.
The new drug, which is taken in tablet form, has a completely different mechanism of action than the well-known GLP-1-based drugs, such as Ozempic, which is administered via injections. GLP-1 drugs affect hunger via signals between the gut and the brain, but often have side effects such as loss of appetite, ...
About The Study: The results of this study show that more screen time in late childhood was associated with more depressive symptoms, potentially due to shorter sleep and worse white matter organization during early adolescence. These findings emphasize the importance of promoting healthy habits and balancing screen time with adequate sleep.
Corresponding Author: To contact the corresponding author, João Paulo Lima Santos, MD, email limasantosjp2@upmc.edu.
To access the embargoed study: Visit our For The Media website at this link https://media.jamanetwork.com/
(doi:10.1001/jamapediatrics.2025.1718)
Editor’s ...
About The Study: U.S. neonatal mortality has generally decreased, likely due to medical advancements, improved prenatal care, and neonatal intensive care interventions. However, mortality from slow fetal growth and malnutrition has increased by nearly 2% annually, possibly reflecting impaired prenatal nutrition.
Corresponding Author: To contact the corresponding author, Muzamil Khan, MD, email muzamilkhan1411@gmail.com.
To access the embargoed study: Visit our For The Media website at this link https://media.jamanetwork.com/
(doi:10.1001/jamapediatrics.2025.1710)
Editor’s ...
For the first time, scientists using cryo-electron microscopy have discovered the structure and shape of key receptors connecting neurons in the brain’s cerebellum, which is located behind the brainstem and plays a critical role in functions such as coordinating movement, balance and cognition.
The research, published today in the journal Nature, provides new insight that could lead to the development of therapies to repair these structures when they are disrupted either by injury or genetic mutations affecting motor skills -- sitting, standing, walking, running, and jumping -- learning and memory.
The discovery by scientists at Oregon Health ...
PITTSBURGH, June 23, 2025 – In this digital era, both kids and adults are often glued to smartphone screens. Digital technology keeps users entertained, connected to friends, and in tune with important news. But some reports suggest that, particularly for adolescents, excessive time on these screens can be linked to mental health problems and even depression.
New research from the University of Pittsburgh School of Medicine published today in JAMA Pediatrics suggests that that association is driven by shorter ...
A rare gene mutation that delays Alzheimer’s disease does so by damping inflammatory signaling in brain-resident immune cells, according to a preclinical study led by investigators at Weill Cornell Medicine. The finding adds to growing evidence that brain inflammation is a major driver of neurodegenerative disorders such as Alzheimer’s—and that it may be a key therapeutic target for these disorders.
In the study, published June 23 in Immunity, the researchers examined the effects of the mutation APOE3-R136S—known as the “Christchurch ...
Researchers at the Center for Medicinal Cannabis Research at University of California San Diego School of Medicine have found that cannabidiol (CBD), a non-intoxicating compound found in cannabis, could help reduce problematic behaviors in autistic boys. The results provide valuable insights into the potential benefits and limitations of CBD as a therapeutic intervention for autism.
Autism spectrum disorder is a complex neurodevelopmental condition characterized by social communication difficulties, repetitive behaviors ...
CAR-T cells, which are genetically programmed to specifically recognize and kill target cells, have altered the therapeutic landscape of lymphoma. After the tumor antigens are identified by scFv, CAR-T cells execute anti-tumor activity through granzyme and perforin secretion, inducing cell apoptosis in a Fas-FasL-dependent pathway and producing inflammatory cytokines to antagonize the immunosuppressive tumor microenvironments (TME) and induce host immune responses. However, CAR-T cell therapy still faces many challenges owing to the heterogeneity of tumor cells, interference from TME, T cell exhaustion, as well as severe adverse events. Recent years, advances in tumor ...
