Archivi tag: quantum chromodynamics

Looking for ‘new physics’ in the Universe

Con il termine “nuova fisica” si intende un nuovo campo di ricerca che tenta di spiegare quei fenomeni della natura che i fisici non sono ancora in grado di descrivere. Oggi, sta prendendo piede sempre più l’idea in base alla quale l’Universo può essere caratterizzato da una struttura diversa rispetto a quanto previsto dagli attuali modelli o teorie. In tal senso, un gruppo di fisici hanno avviato uno studio che avrà lo scopo di aiutare gli scienziati a rendere più facile, almeno in parte, la comprensione di alcuni fenomeni della fisica fondamentale.

New physics is about searching for unknown physical phenomena not known from the current perception of the Universe. Such phenomena are inherently very difficult to detect“, explains Matin Mojaza from CP3-Origins. Together with colleagues Stanley J. Brodsky from Stanford University in the U.S. and Xing-Gang Wu from Chongqing University in China, Mojaza has now succeeding in creating a new method that can make it easier to search for new physics in the Universe (post).

The method is a so called scalesetting procedure, and it fills out some empty, but very important, holes in the theories, models and simulations, which form the basis for all particle physics today.

With this method we can eliminate much of the uncertainty in theories and models of today“, says Matin Mojaza. Many theories and models in particle physics today has the problem that they, together with their predictions, provide some parameters that scientists do not know how to set. “Physicists do not know what values they should give these parameters. For example, when we study the Standard Model and see these unknown parameters, we cannot know whether they should be interpreted as conditions that support or oppose to the Standard Model, this makes it quite difficult to study the Standard Model accurately enough to investigate its value”, explains Matin Mojaza. With the new approach researchers can now completely clean their models for the unknown parameters and thus become better at assessing whether a theory or a model holds water.

The Standard Model has for the last 50 years been the prevailing theory of how the Universe is constructed. According to this theory, 16 (17 if we include the Higgs particle) subatomic particles form the basis for everything in the Universe.

But the Standard Model is starting to fall short, so it is now necessary to look for new physics in the Universe. One of the Standard Model’s major problems is that it cannot explain gravity, and another is that it cannot explain the existence of dark matter, believed to make up 25 percent of all matter in the Universe. In addition, the properties of the newly discovered Higgs particle, as described in the Standard Model, is incompatible with a stable Universe. “A part of the Standard Model is the theory of quantum chromodynamics, and this is one of the first things, we want to review with our new method, so that we can clean it from the uncertainties“, explains Matin Mojaza. The theory of quantum chromodynamics predicts how quarks (such as protons and neutrons) and gluons (particles that keeps quarks in place inside the protons and neutrons) interact. Matin and his Chinese and American colleagues now estimate that there may be a basis for reviewing many scientific calculations to clean the results from uncertainties and thus obtain a more reliable picture of whether the results support or contradict current models and theories. “Maybe we find new indications of new physics, which we would not have exposed if we had not had this new method”, says Matin Mojaza.

He believes that the Standard Model needs to be extended so that it can explain the Higgs particle, dark matter and gravity.

One possibility in this regard is to examine the so-called technicolor theory, and another is the theory of supersymmetry. According to the supersymmetry theory, each particle has a partner somewhere in the Universe (these have not yet been found though). According to the technicolor theory there is a special techni-force that binds so-called techni-quarks, which can form other particles, perhaps this is how the Higgs particle is formed. This could explain the problems with the current model of the Higgs particle. Also Rolf-Dieter Heuer, director of CERN in Switzerland, where the famous 27 km long particle accelerator, the LHC, is situated, believes that the search for new physics is important. According to him, the Standard Model cannot be the ultimate theory, and it is only capable of describing about 35 percent of the Universe. Like CP3-Origins, also CERN has put focus on weeding out old theories and search for new physics, this happening in 2015, when the accelerator starts up again (post).

University of Southern Denmark: New groundbreaking research may expose new aspects of the Universe

arXiv: A Systematic All-Orders Method to Eliminate Renormalization-Scale and Scheme Ambiguities in PQCD

Easy tests in high energy experiments

Tre fisici teorici hanno fatto un passo in avanti per eliminare alcune ambiguità che derivano dalle complesse formule matematiche che vengono utilizzate per studiare le interazioni tra i quark, le particelle più fondamentali della materia che compongono protoni e neutroni, e i gluoni, le particelle enigmatiche responsabili dell’interazione nucleare forte che lega i quark nei nucleoni. Secondo gli scienziati, semplificando questi calcoli è possibile facilitare, per così dire, il lavoro dei fisici per realizzare previsioni più accurate quando vengono eseguiti gli esperimenti di laboratorio.

The theory describing those interactions is known as quantum chromodynamics (QCD), and is an important component of the Standard Model, the reigning theory of the interactions of subatomic particles. “An important goal in high energy physics is to make predictions that are as precise as possible“, said SLAC theoretical physicist Stan Brodsky. “This makes tests of QCD more rigorous. Most important, if QCD doesn’t pass our experimental tests, it could reveal new physics beyond the Standard Model“. In a paper published in Physical Review Letters, Brodsky and his colleagues, Matin Mojaza of CP3-Origins at the University of Southern Denmark and Xing-Gang Wu of Chongqing University in China, have presented a method that will help theorists to automatically eliminate an important theoretical ambiguity of QCD predictions. Particle theorists attempt to put the quantum realm under a mathematical microscope. However, the world of subatomic particles operates according to very different rules than our familiar everyday world. Quantum uncertainties take hold.

On the scale of quarks and gluons, E=mcis not a slogan on a t-shirt, it’s the law of the land, if there’s a possibility for a particular particle to exist, it, and others, will pop into and out of existence, obscuring what lies under the physicists’ calculational lenses.

These “now you see them, now you don’t” particles, called virtual particles, give rise to infinite terms in quantum calculations, a big problem for theorists, who must remove the uncertainty in their calculations caused by these infinities without introducing new ambiguities. This problem has obscured the precision of the theorists’ mathematical microscope. Brodsky and his colleagues have been developing a method called the Principle of Maximum Conformality (PMC) which can focus the mathematical microscope into the quantum world.

Building on this work, in their new paper, Mojaza, Wu and Brodsky show how a novel generalization of a technique that many theorists employ to remove infinities, called modified minimal subtraction, can be used to identify patterns within the calculations.

This, along with PMC, makes the calculations easier to reduce to a form that can be used to make testable predictions, free of ambiguities, the heart of scientific progress. In addition to adding another tool to the theorists’ toolbox and providing testable predictions to experimenters, their technique has another advantage, said Brodsky: “Since the method is systematic, it can be used as the basis of a computer algorithm“, automating the calculations even further.

SLAC: SLAC Theorist Helps Sharpen Tests of Fundamental Theory in High Energy Experiments

arXiv:A Systematic All-Orders Method to Eliminate Renormalization-Scale and Scheme Ambiguities in PQCD