What is the weak force in physics? Weak interaction
The reader is familiar with the forces of different nature, which manifest themselves in interactions between bodies. But deeply differing in principle types interactions very little. Apart from gravity, which plays a significant role only in the presence of huge masses, only three types of interactions are known: strong, electromagnetic and weak.
electromagnetic interactions everyone is familiar. Thanks to them, an unevenly moving electric charge (say, an electron in an atom) emits electromagnetic waves(for example, visible light). All chemical processes are associated with this class of interactions, as well as all molecular phenomena - surface tension, capillarity, adsorption, fluidity. electromagnetic interactions, the theory of which is brilliantly confirmed by experience, are deeply connected with the electric charge elementary particles.
Strong interactions became known only after the disclosure internal structure atomic nucleus. In 1932 it was discovered that it consists of nucleons, neutrons and protons. And exactly strong interactions connect nucleons in the nucleus - they are responsible for nuclear forces, which, unlike electromagnetic ones, are characterized by a very small radius of action (about 10-13, i.e. one ten-trillionth of a centimeter) and high intensity. Besides, strong interactions appear on collision particles high energies involving pions and the so-called "strange" particles.
It is convenient to estimate the intensity of interactions by the so-called mean free path particles in some substance, i.e. By average the path that particle can pass in this substance to a destructive or strongly deflecting impact. It is clear that the longer the mean free path, the less intense the interaction.
If we consider particles very high energy, then the collisions caused by strong interactions, are characterized by the mean free path particles corresponding in order of magnitude to tens of centimeters in copper or iron.
The situation is different for weak interactions. As we have already said, the mean free path of a neutrino in dense matter is measured in astronomical units. This indicates a surprisingly low intensity of weak interactions.
Any process interactions elementary particles characterized by some time that determines it average duration. Processes caused by weak interactions, are often referred to as "slow" because their time is relatively long.
True, the reader may be surprised that a phenomenon that occurs in, say, 10-6 (one millionth) of a second is classified as slow. Such a lifetime is typical, for example, for muon decay caused by weak interactions. But everything is relative. In the world elementary particles such a period of time is indeed quite long. The natural unit of length in the microcosm is 10-13 centimeters - the radius of action of nuclear forces. And since elementary particles high energy have a speed close to the speed of light (of the order of 1010 centimeters per second), then the "normal" time scale for them will be 10-23 seconds.
This means that the time of 10-6 seconds for the "citizens" of the microcosm is much longer than for you and me the entire period of the existence of life on Earth.
In 1896, the French scientist Henri Becquerel discovered the radioactivity of uranium. This was the first experimental signal about previously unknown forces of nature - the weak interaction. We now know that the weak force is behind many familiar phenomena - for example, it takes part in some thermonuclear reactions that support the radiation of the Sun and other stars.
The name "weak" went to this interaction due to a misunderstanding - for example, for a proton it is 1033 times stronger than the gravitational interaction (see Gravitation, Unity of this nature). Rather, it is a destructive interaction, the only force of nature that does not hold matter together, but only destroys it. One could also call it "unprincipled", since in destruction it does not take into account the principles of spatial parity and temporal reversibility, which other forces observe.
The basic properties of the weak interaction became known as early as the 1930s, mainly due to the work of the Italian physicist E. Fermi. It turned out that, unlike gravitational and electrical forces, weak forces have a very small radius of action. In those years, it seemed that there was no radius of action at all - the interaction takes place at one point in space, and, moreover, instantly. This interaction is virtual a short time) turns each proton of the nucleus into a neutron, a positron into a positron and a neutrino, and each neutron into a proton, an electron and an antineutrino. In stable nuclei (see atomic nucleus) these transformations remain virtual, like the virtual production of electron-positron pairs or proton-antiproton pairs in vacuum.
If the difference in the masses of nuclei that differ by one in charge is large enough, these virtual transformations become real, and the nucleus changes its charge by 1, throwing out an electron and an antineutrino (electron-decay) or a positron and a neutrino (positron-decay). Neutrons have a mass that is approximately 1 MeV greater than the sum of the masses of a proton and an electron. Therefore, a free neutron decays into a proton, an electron, and an antineutrino with an energy release of approximately 1 MeV. The lifetime of a free neutron is about 10 minutes, although in a bound state, for example, in a deuteron, which consists of a neutron and a proton, these particles live indefinitely.
A similar event occurs with the muon (see Peptons) - it decays into an electron, a neutrino and an antineutrino. Before decaying, the muon lives about c - much less than the neutron. Fermi's theory explained this by the difference in the masses of the particles involved. The more energy released during decay, the faster it goes. The release of energy during -decay is about 100 MeV, approximately 100 times greater than during the decay of a neutron. The lifetime of a particle is inversely proportional to the fifth power of this energy.
As it turned out in recent decades, the weak interaction is nonlocal, i.e., it does not occur instantly and not at one point. According to modern theory, weak interaction is not transmitted instantly, and a virtual electron-antineutrino pair is born in c after the muon passes into a neutrino, and this happens at a distance of cm. Not a single ruler, not a single microscope, of course, can measure such a small distance, just as no stopwatch can measure such a small interval of time. As is almost always the case, modern physics we must be content with indirect data. Physicists build various hypotheses about the mechanism of the process and test all possible consequences of these hypotheses. Those hypotheses that contradict at least one reliable experiment are swept aside, and new experiments are put to verify the remaining ones. This process in the case of the weak interaction continued for about 40 years, until physicists came to the conclusion that the weak interaction is carried by supermassive particles - 100 times heavier than the proton. These particles have spin 1 and are called vector bosons (discovered in 1983 at CERN, Switzerland - France).
There are two charged vector bosons and one neutral (the icon at the top, as usual, indicates the charge in proton units). A charged vector boson "works" in the decays of a neutron and a muon. The course of muon decay is shown in Fig. (above, right). Such drawings are called Feynman diagrams, they not only illustrate the process, but also help to calculate it. This is a kind of shorthand formula for the probability of a reaction; it is used here for illustration only.
The muon transforms into a neutrino, emitting a -boson, which decays into an electron and an antineutrino. The released energy is not enough for the real production of -boson, so it is born virtually, ie, for a very short time. In this case it is s. During this time, the field corresponding to the -boson does not have time to form a wave, or otherwise, a real particle (see Fields and particles). A cm-sized field bunch is formed, and after c an electron and an antineutrino are born from it.
For the decay of the neutron, one could draw the same diagram, but here it would already mislead us. The fact is that the size of a neutron is cm, which is 1000 times greater than the range of weak forces. Therefore, these forces act inside the neutron, where the quarks are located. One of the three quarks of the neutron emits a -boson, while passing into another quark. Charges of quarks in a neutron: -1/3, - 1/3 and so one of the two quarks with a negative charge -1/3 passes into a quark with a positive charge. The result will be quarks with charges - 1/3, 2/3, 2/3, which together make up the proton. The reaction products - an electron and an antineutrino - freely fly out of the proton. But it's a quark that emitted a -boson. received feedback and began to move in the opposite direction. Why doesn't he fly?
It is held by the strong force. This interaction will drag its two inseparable satellites behind the quark, resulting in a moving proton. The weak decays (associated with the weak interaction) of the remaining hadrons occur according to a similar scheme. All of them are reduced to the emission of a vector boson by one of the quarks, the transition of this vector boson into leptons (, and -particles) and the further expansion of the reaction products.
Sometimes, however, hadronic decays also occur: a vector boson can decay into a quark-antiquark pair, which will turn into mesons.
So, a large number of various reactions is reduced to the interaction of quarks and leptons with vector bosons. This interaction is universal, that is, it is the same for quarks and leptons. The universality of the weak interaction, in contrast to the universality of the gravitational or electromagnetic interaction, has not yet received an exhaustive explanation. IN modern theories the weak interaction is combined with the electromagnetic interaction (see Unity of the Forces of Nature).
For symmetry breaking by the weak interaction, see Parity, Neutrino. The article The unity of the forces of nature tells about the place of weak forces in the picture of the microworld
This is the third fundamental interaction that exists only in the microcosm. It is responsible for the transformation of some fermion particles into others, while the color of weakly interacting peptons and quarks does not change. A typical example of a weak interaction is the beta decay process, during which a free neutron decays into a proton, an electron, and an electron antineutrino in an average of 15 minutes. The decay is caused by the transformation of a flavor quark d into a flavor quark u inside the neutron. The emitted electron ensures the conservation of the total electric charge, and the antineutrino allows the conservation of the total mechanical momentum of the system.
Strong interaction
The main function of the strong force is to combine quarks and antiquarks into hadrons. The theory of strong interactions is in the process of creation. It is a typical field theory and is called quantum chromodynamics. Its starting position is the postulate of the existence of three types of color charges (red, blue, green), expressing the ability inherent in matter to combine quarks in a strong interaction. Each of the quarks contains some combination of such charges, but their full mutual compensation does not occur, and the quark has a resulting color, that is, it retains the ability to interact strongly with other quarks. But when three quarks, or a quark and an antiquark, combine to form a hadron, the total combination of color charges in it is such that the hadron as a whole is color neutral. Color charges create fields with their inherent quanta - bosons. The exchange of virtual color bosons between quarks and (or) antiquarks serves as the material basis for the strong interaction. Before the discovery of quarks and color interaction, nuclear interaction was considered fundamental, uniting protons and neutrons in the nuclei of atoms. With the discovery of the quark level of matter, the strong interaction began to be understood as color interactions between quarks that combine into hadrons. Nuclear forces are no longer considered fundamental, they must somehow be expressed through colored forces. But this is not easy to do, because the baryons (protons and neutrons) that make up the nucleus are generally color neutral. By analogy, we can recall that atoms as a whole are electrically neutral, but at the molecular level, chemical forces appear, which are considered as echoes of electrical atomic forces.
The considered four types of fundamental interactions underlie all other known forms of motion of matter, including those that have arisen at the highest stages of development. Any complex shapes motions, when they are decomposed into structural components, are revealed as complex modifications of these fundamental interactions.
2. Development of scientific views on the interaction of particles before the evolutionary creation of the theory of "Great Unification"
The Grand Unified Theory is a theory that combines electromagnetic, strong and weak interactions. Mentioning the theory of "Grand Unification", it comes to the fact that all the forces that exist in nature are a manifestation of one universal fundamental force. There are a number of considerations that give reason to believe that at the moment of the Big Bang that gave birth to our universe, only this force existed. However, over time, the universe expanded, which means it cooled down, and the single force split into several different ones, which we are now observing. The theory of "Grand Unification" should describe the electromagnetic, strong, weak and gravitational forces as a manifestation of one universal force. There is already some progress: scientists have managed to build a theory that combines the electromagnetic and weak interactions. However, the main work on the theory of "Great Unification" is still ahead.
Modern particle physics is forced to discuss issues that, in fact, worried even ancient thinkers. What is the origin of particles and chemical atoms built from these particles? And how can the Cosmos, the Universe we see, be built from particles, no matter how we call them? And one more thing - was the Universe created, or has it existed from eternity? If this is the right question, what are the ways of thought that can lead to convincing answers? All these questions are similar to the search for the true principles of being, questions about the nature of these principles.
Whatever we say about the Cosmos, one thing is clear that everything in the natural world is somehow composed of particles. But how is this composition to be understood? It is known that particles interact - they attract or repel each other. Particle physics studies various interactions. [Popper K. On the sources of knowledge and ignorance // Vopr. history of natural science and technology, 1992, no. 3, p. 32.]
Electromagnetic interaction attracted special attention in the 18th–19th centuries. Similarities and differences between electromagnetic and gravitational interactions were found. Like gravity, electromagnetic interaction forces are inversely proportional to the square of the distance. But, unlike gravity, electromagnetic "gravity" not only attracts particles (different in sign of charge), but also repels them from each other (equally charged particles). And not all particles are carriers of an electric charge. For example, the photon and neutron are neutral in this respect. In the 50s of the XIX century. the electromagnetic theory of D. C. Maxwell (1831–1879) unified electrical and magnetic phenomena and thereby clarified the action of electromagnetic forces. [Grunbaum A. Origin versus creation in physical cosmology (theological distortions of modern physical cosmology). - Q. philosophy, 1995, no. 2, p. 19.]
The study of the phenomena of radioactivity led to the discovery of a special kind of interaction between particles, which was called the weak interaction. Since this discovery is related to the study of beta radioactivity, one could call this interaction beta decay. However, in the physical literature it is customary to talk about weak interaction - it is weaker than the electromagnetic one, although it is much stronger than the gravitational one. The discovery was facilitated by the research of W. Pauli (1900–1958), who predicted that during beta decay, a neutral particle emerges, compensating for the apparent violation of the law of conservation of energy, called the neutrino. And besides, the discovery of weak interactions was facilitated by the studies of E. Fermi (1901–1954), who, along with other physicists, suggested that electrons and neutrinos, before they leave the radioactive nucleus, do not exist in the nucleus, so to speak, in finished form, but are formed during the radiation process. [Grunbaum A. Origin versus creation in physical cosmology (theological distortions of modern physical cosmology). - Q. philosophy, 1995, no. 2, p. 21.]
Finally, the fourth interaction turned out to be related to intranuclear processes. Named strong interaction, it manifests itself as an attraction of intranuclear particles - protons and neutrons. Due to its large size, it turns out to be a source of enormous energy.
The study of four types of interactions followed the path of searching for their deep connection. On this obscure, largely obscure path, only the principle of symmetry guided the investigation and led to the identification of the alleged connection. various types interactions.
To reveal such connections, it was necessary to turn to the search for a special type of symmetry. A simple example This type of symmetry can be the dependence of the work done when lifting the load on the height of the lift. The energy expended depends on the height difference, but does not depend on the nature of the ascent path. Only the height difference is significant and it does not matter at all from what level we start the measurement. It can be said that we are dealing here with symmetry with respect to the choice of reference point.
Similarly, you can calculate the energy of movement of an electric charge in an electric field. The analog of the height here is the field voltage or, otherwise, the electric potential. The energy expended during the movement of the charge will depend only on the potential difference between the end and start points in the space of the field. We are dealing here with the so-called gauge or, in other words, with scale symmetry. Gauge symmetry referred to electric field, is closely related to the law of conservation of electric charge.
Gauge symmetry turned out to be the most important tool that gives rise to the possibility of resolving many difficulties in the theory of elementary particles and in numerous attempts to unify various types of interactions. In quantum electrodynamics, for example, various divergences arise. These divergences can be eliminated because the so-called renormalization procedure, which eliminates the difficulties of the theory, is closely related to gauge symmetry. The idea appears that the difficulties in constructing the theory of not only electromagnetic, but also other interactions can be overcome if it is possible to find other, hidden symmetries.
Gauge symmetry can take on a generalized character and can be related to any force field. In the late 1960s S. Weinberg (b. 1933) from Harvard University and A. Salam (b. 1926) from Imperial College in London, relying on the work of S. Glashow (b. 1932), undertook a theoretical unification of the electromagnetic and weak interactions. They used the idea of gauge symmetry and the concept of a gauge field related to this idea. [Yakushev A. S. Basic concepts of modern natural science. - M., Fact-M, 2001, p. 29.]
Applicable for electromagnetic interaction simplest form gauge symmetry. It turned out that the symmetry of the weak interaction is more complicated than that of the electromagnetic one. This complexity is due to the complexity of the process itself, so to speak, the mechanism of weak interaction.
In the process of weak interaction, for example, the decay of a neutron occurs. Such particles as neutron, proton, electron and neutrino can participate in this process. Moreover, due to the weak interaction, the mutual transformation of particles occurs.
Conceptual provisions of the theory of "Great Unification"
In modern theoretical physics, two new conceptual schemes set the tone: the so-called "Grand Unified" theory and supersymmetry.
These scientific directions together lead to a very attractive idea, according to which all of nature is ultimately subject to the action of some kind of superpower, which manifests itself in various "persons". This force is powerful enough to create our Universe and endow it with light, energy, matter and structure. But superpower is more than just a creative principle. In it, matter, space-time and interaction are merged into an inseparable harmonious whole, generating such a unity of the Universe that no one had previously imagined. The purpose of science is, essentially, to seek such unity. [Ovchinnikov N. F. Structure and symmetry // System Research, M., 1969, p. 137.]
Based on this, there is a certain confidence in the unification of all phenomena of animate and inanimate nature within the framework of a single descriptive scheme. To date, four fundamental interactions or four forces in nature are known, responsible for all known interactions of elementary particles - strong, weak, electromagnetic and gravitational interactions. Strong interactions bind quarks together. Weak interactions are responsible for some types of nuclear decays. Electromagnetic forces act between electric charges, and gravitational forces act between masses. The presence of these interactions is a sufficient and necessary condition for the construction of the world around us. For example, without gravity, not only would there be no galaxies, stars and planets, but the Universe could not have arisen - after all, the very concepts of the expanding Universe and the Big Bang, from which space-time originates, are based on gravity. Without electromagnetic interactions, there would be no atoms, no chemistry or biology, and no solar heat and light. Without strong nuclear interactions, the nucleus would not exist, and consequently, atoms and molecules, chemistry and biology, and stars and the Sun could not generate heat and light due to nuclear energy.
Even weak nuclear forces play a role in the formation of the universe. Without them, nuclear reactions in the Sun and stars would be impossible, apparently, supernova explosions would not occur, and the heavy elements necessary for life could not spread in the Universe. Life might as well not exist. If we agree with the opinion that all these four completely different interactions, each of which is necessary in its own way for the emergence of complex structures and determining the evolution of the entire Universe, are generated by a single simple superpower, then the presence of a single fundamental law that operates both in living and in inanimate nature, is beyond doubt. Modern research shows that at one time these four forces could have been combined into one.
This was possible at the enormous energies characteristic of the era of the early universe shortly after the Big Bang. Indeed, the theory of unification of electromagnetic and weak interactions has already been confirmed experimentally. "Grand Unification" theories should unify these interactions with strong forces, and "All That Is" theories uniformly describe all four fundamental interactions as manifestations of one interaction. Thermal history of the Universe, starting from 10–43 sec. after the Big Bang to the present day, shows that most of the helium-4, helium-3, deuterons (nuclei of deuterium - a heavy isotope of hydrogen) and lithium-7 were formed in the Universe approximately 1 minute after the Big Bang.
Heavier elements appeared inside stars tens of millions or billions of years later, and the emergence of life corresponds to the final stage of the evolving Universe. Based on the theoretical analysis carried out and the results of computer simulation of dissipative systems operating far from equilibrium, under the action of a code-frequency low-energy flow, we concluded that there are two parallel processes in the Universe - entropy and information. Moreover, the entropy process of transformation of matter into radiation is not dominant. [Soldatov VK Theory of the "Great Unification". - M., Postscript, 2000, p. 38.]
Under these conditions, a new type of evolutionary self-organization of matter arises, linking the coherent space-time behavior of the system with dynamic processes within the system itself. Then, on the scale of the Universe, this law will be formulated as follows: "If the Big Bang led to the formation of 4 fundamental interactions, then the further evolution of the space-time organization of the Universe is connected with their unification." Thus, in our view, the law of entropy increase must be applied not to individual parts of the Universe, but to the entire process of its evolution. At the moment of its formation, the Universe turned out to be quantized according to the space-time levels of the hierarchy, each of which corresponds to one of the fundamental interactions. The resulting fluctuation, perceived as an expanding picture of the Universe, at a certain moment proceeds to restore its equilibrium. The process of further evolution takes place in a mirror image.
In other words, two processes take place simultaneously in the observable universe. One process - anti-entropy - is associated with the restoration of disturbed equilibrium, through the self-organization of matter and radiation into macroquantum states (as physical example such well-known states of matter as superfluidity, superconductivity, and the quantum Hall effect). This process, apparently, determines the consistent evolution of the processes thermonuclear fusion in the stars, the formation of planetary systems, minerals, flora, unicellular and multicellular organisms. This automatically follows the self-organizing orientation of the third principle of the progressive evolution of living organisms.
Another process is purely entropic in nature and describes the processes of cyclic evolutionary transition of self-organizing matter (decay - self-organization). It is possible that these principles can serve as the basis for creating a mathematical apparatus that allows you to combine all four interactions into one superpower. As already noted, it is precisely this problem that the majority of theoretical physicists are currently occupied with. Further argumentation of this principle goes far beyond the scope of this article and is connected with the construction of the theory of the Evolutionary Self-Organization of the Universe. Therefore, let us make the main conclusion and see how applicable it is to biological systems, the principles of their control, and most importantly, to new technologies for the treatment and prevention of pathological conditions of the body. First of all, we will be interested in the principles and mechanisms of maintaining the self-organization and evolution of living organisms, as well as the causes of their violations, manifested in the form of various pathologies.
The first of them is the principle of code-frequency control, the main purpose of which is to maintain, synchronize and control energy flows within any open self-organizing dissipative system. The implementation of this principle for living organisms requires the presence at each structural hierarchical level of a biological object (molecular, subcellular, cellular, tissue, organoid, organismic, population, biocenotic, biotic, landscape, biospheric, cosmic) the presence of a biorhythmological process associated with the consumption and consumption of transformable energy, which determines the activity and sequence of processes within the system. This mechanism occupies a central place in the early stages of the emergence of life in the formation of the DNA structure and the principle of reduplication of discrete codes of hereditary information, as well as in such processes as cell division and subsequent differentiation. As you know, the process of cell division always occurs in a strict sequence: prophase, metaphase, telophase, and then anaphase. You can violate the conditions of division, prevent it, even remove the nucleus, but the sequence will always be preserved. Without a doubt, our body is equipped with the most perfect synchronizers: a nervous system that is sensitive to the slightest changes in the external and internal environment, slower humoral system. At the same time, the infusoria-shoe, in the complete absence of the nervous and humoral systems, lives, feeds, excretes, reproduces, and all these complex processes do not proceed randomly, but in strict sequence: any reaction predetermines the next, and that, in turn, allocates products needed to start the next reaction. [Soldatov VK Theory of the "Great Unification". - M., Postscript, 2000, p. 59.]
It should be noted that even Einstein's theory marked such an important progress in understanding nature that soon a revision of views on other forces of nature also became inevitable. At this time, the only "other" force whose existence was firmly established was the electromagnetic force. However, outwardly it did not look like gravity at all. Moreover, a few decades before the creation of Einstein's theory of gravity, Maxwell's theory successfully described electromagnetism, and there was no reason to doubt the validity of this theory.
Throughout his life, Einstein dreamed of creating a unified field theory in which all the forces of nature would merge together on the basis of pure geometry. Einstein devoted most of his life to the search for such a scheme after the creation of the general theory of relativity. However, ironically, the closest thing to the realization of Einstein's dream came the little-known Polish physicist Theodor Kaluza, who, back in 1921, laid the foundations for a new and unexpected approach to unifying physics, which still boggles the imagination with its audacity.
With the discovery of weak and strong interactions in the 1930s, the ideas of unifying gravity and electromagnetism have largely lost their appeal. A consistent unified field theory was supposed to include not two, but four forces. Obviously, this could not be done without achieving a deep understanding of the weak and strong interactions. In the late 1970s, thanks to a fresh breeze brought by the Grand Unified Theories (GUT) and supergravity, the old Kaluza-Klein theory was remembered. She was "dusted off, dressed in fashion" and included in it all the interactions known today.
In the GUT, the theorists managed to collect three very different types of interactions within the framework of one concept; this is due to the fact that all three interactions can be described using gauge fields. The main property of gauge fields is the existence of abstract symmetries, thanks to which this approach acquires elegance and opens up wide possibilities. The presence of force field symmetries quite definitely indicates the manifestation of some hidden geometry. In the Kaluza-Klein theory brought back to life, the symmetries of gauge fields acquire concreteness - these are geometric symmetries associated with additional dimensions of space.
As in the original version, interactions are introduced into the theory by adding additional spatial dimensions to space-time. However, since we now have to accommodate three types of interactions, we have to introduce a few extra dimensions. A simple count of the number of symmetry operations involved in the GUT leads to a theory with seven additional spatial dimensions (so that their total number reaches ten); if time is taken into account, then the whole space-time has eleven dimensions. [Soldatov VK Theory of the "Great Unification". - M., Postscript, 2000, p. 69.]
The main provisions of the theory of "Grand Unification" from the point of view of quantum physics
In quantum physics, each length scale is associated with an energy (or equivalent mass) scale. The smaller the length scale under study, the higher the energy required for this. To study the quark structure of the proton requires energies equivalent to at least ten times the mass of the proton. Much higher on the energy scale is the mass corresponding to the Great Unification. If we ever manage to achieve such a huge mass (energy), which we are very far from today, then it will be possible to study the world of X-particles, in which the distinctions between quarks and leptons are erased.
What kind of energy is needed to penetrate "inside" the 7-sphere and explore additional dimensions of space? According to the Kaluza-Klein theory, it is required to surpass the scale of the Grand Unification and reach energies equivalent to 10 19 proton masses. Only with such unimaginably huge energies would it be possible to directly observe the manifestations of additional dimensions of space.
This huge value - 10 19 proton masses - is called the Planck mass, since it was first introduced by Max Planck, the creator of quantum theory. With an energy corresponding to the Planck mass, all four interactions in nature would merge into a single superforce, and ten spatial dimensions would be completely equal. If it were possible to concentrate a sufficient amount of energy, "ensuring the achievement of the Planck mass, then the full dimension of space would manifest itself in all its splendor. [Yakushev A. S. Basic concepts of modern natural science. - M., Fact-M, 2001, p. 122. ]
Giving free rein to the imagination, one can imagine that one day humanity will master the superpower. If this happened, then we would gain power over nature, since superpower ultimately gives rise to all interactions and all physical objects; in this sense, it is the fundamental principle of all things. Having mastered the superpower, we could change the structure of space and time, bend the void in our own way and put matter in order. By controlling the superpower, we could create or transform particles at will, generating new exotic forms of matter. We could even manipulate the dimensionality of space itself, creating bizarre artificial worlds with unthinkable properties. We would truly be masters of the universe!
But how can this be achieved? First of all, you need to get enough energy. To give an idea of what we are talking about, recall that the linear accelerator at Stanford, 3 km long, accelerates electrons to energies equivalent to 20 proton masses. To achieve the Planck energy, the accelerator would have to be extended by a factor of 1018, making it the size of the Milky Way (about a hundred thousand light years). Such a project is not one of those that can be implemented in the foreseeable future. [Wheeler J.A. Quantum and Universe // Astrophysics, quanta and theory of relativity, M., 1982, p. 276.]
There are three distinct thresholds, or scales, of energy in the Grand Unified Theory. First of all, this is the Weinberg–Salam threshold, equivalent to almost 90 proton masses, above which the electromagnetic and weak interactions merge into a single electroweak one. The second scale, corresponding to 10 14 proton masses, is characteristic of the Great Unification and the new physics based on it. Finally, the ultimate scale, the Planck mass, equivalent to 10 19 proton masses, corresponds to the complete unification of all interactions, as a result of which the world is amazingly simplified. One of the biggest unresolved problems is explaining the existence of these three scales, as well as the reasons for such a strong difference between the first and second of them. [Soldatov VK Theory of the "Great Unification". - M., Postscript, 2000, p. 76.]
Modern technology is capable of achieving only the first scale. Proton decay could give us an indirect means to study physical world on the scale of the Grand Unification, although at present there seems to be no hope of reaching this limit directly, let alone on the scale of the Planck mass.
Does this mean that we will never be able to observe the manifestations of the original superpower and the invisible seven dimensions of space. Using such technical means as the superconducting supercollider, we are rapidly moving up the scale of energies achievable under terrestrial conditions. However, the technology created by people by no means exhausts all the possibilities - there is nature itself. The Universe is a gigantic natural laboratory in which the greatest experiment in the field of elementary particle physics was "carried out" 18 billion years ago. We call this experiment the Big Bang. As will be discussed later, this initial event was enough to release - albeit for a very short moment - superpower. However, this, apparently, was enough for the ghostly existence of a superpower to forever leave its mark. [Yakushev A. S. Basic concepts of modern natural science. - M., Fact-M, 2001, p. 165.]
MINISTRY OF EDUCATION AND SCIENCE OF RUSSIA
federal state budgetary educational institution
higher vocational education
"St. Petersburg State Electrotechnical University "LETI" named after V. I. Ulyanov (Lenin)"
(SPbGETU)
Faculty of Economics and Management
Department of Physics
In the discipline "Concepts of modern natural science"
on the topic "Weak interaction"
Checked:
Altmark Alexander Moiseevich
Performed:
student gr. 3603
Kolisetskaya Maria Vladimirovna
Saint Petersburg
1. The Weak Force is One of the Four Fundamental Forces
History of study
Role in nature
The weak force is one of the four fundamental forces
The weak force, or weak nuclear force, is one of the four fundamental forces
Weak interaction is short-range - it manifests itself at distances much smaller than the size of the atomic nucleus
Weak interaction carriers are vector bosons
For the first time, weak interactions were observed in the β-decay of atomic nuclei. And, as it turned out, these decays are associated with the transformations of a proton into a neutron in the nucleus and vice versa:
R? n + e+ + ?e, n? p + e- + e,
where n is a neutron, p is a proton, e- is an electron, ??e is an electron antineutrino.
Elementary particles are usually divided into three groups:
) photons; this group consists of only one particle - a photon - a quantum electromagnetic radiation;
) leptons (from the Greek "leptos" - light), participating only in electromagnetic and weak interactions. The leptons include the electron and muon neutrinos, the electron, the muon and the heavy lepton discovered in 1975 - the t-lepton, or taon, with a mass of approximately 3487 me, as well as their corresponding antiparticles. The name leptons is due to the fact that the masses of the first known leptons were less than the masses of all other particles. The leptons also include the taon neutrino, whose existence in Lately also installed;
) hadrons (from the Greek "adros" - large, strong). Hadrons have a strong interaction along with electromagnetic and weak. Of the particles discussed above, these include the proton, neutron, pions, and kaons.
Properties of the weak interaction
The weak interaction has distinctive properties:
All fundamental fermions take part in the weak interaction
Operation P changes the sign of any polar vector
The operation of spatial inversion transforms the system into mirror symmetry. Mirror symmetry is observed in processes under the action of strong and electromagnetic interactions. Mirror symmetry in these processes means that in mirror-symmetric states, transitions are realized with the same probability.
G. ? Yang Zhenning, Li Zongdao received nobel prize in physics. For deep research into the so-called laws of parity, which led to important discoveries in the field of elementary particles.
In addition to spatial parity, the weak interaction also does not preserve the combined space-charge parity, that is, the only known interaction violates the CP invariance principle
Charge symmetry means that if there is any process involving particles, then when they are replaced by antiparticles (charge conjugation), the process also exists and occurs with the same probability. Charge symmetry is absent in processes involving neutrinos and antineutrinos. In nature, only left-handed neutrinos and right-handed antineutrinos exist. If each of these particles (for definiteness we will consider the electron neutrino? e and antineutrino e) is subjected to charge conjugation, then they will turn into non-existent objects with lepton numbers and helicities.
Thus, both P- and C-invariance are violated in weak interactions. However, if two consecutive operations are performed on a neutrino (antineutrino)? P- and C-transformations (the order of operations is not important), then again we get neutrinos that exist in nature. The sequence of operations and (or in reverse order) is called the CP-transformation. The result of the CP transform (combined inversion) of ?e and e is the following:
Thus, for neutrinos and antineutrinos, the operation that transforms a particle into an antiparticle is not a charge conjugation operation, but a CP transformation.
History of study
The study of weak interactions continued for a long period.
In 1896, Becquerel discovered that uranium salts emit penetrating radiation (?-decay of thorium). This was the beginning of the study of the weak interaction.
In 1930, Pauli put forward the hypothesis that light neutral particles are emitted along with electrons (e) during? decay? neutrino (?). In the same year, Fermi proposed the quantum field theory of?-decay. The decay of a neutron (n) is a consequence of the interaction of two currents: the hadron current converts the neutron into a proton (p), the lepton current creates a pair of electron + neutrino. In 1956, Reines first observed the reaction ep? ne+ in experiments near a nuclear reactor.
Lee and Yang explained the paradox in the decays of K + mesons (? ~ ? riddle) ? decay into 2 and 3 pions. It is related to nonconservation of spatial parity. Mirror asymmetry has been found in the decay of nuclei, decays of muons, pions, K-mesons, and hyperons.
In 1957, Gell-Mann, Feynman, Marshak, Sudarshan proposed a universal theory of the weak interaction based on the quark structure of hadrons. This theory, called V-A theory, led to the description of the weak interaction using Feynman diagrams. At the same time, fundamentally new phenomena were discovered: violation of CP invariance and neutral currents.
In the 1960s by Sheldon Lee Glashow
In 1991-2001, Z0-boson decays were studied at the LEP2 accelerator (CERN), which showed that there are only three generations of leptons in nature: ?e, ?? And??.
Role in nature
nuclear force is weak
The most common process due to the weak interaction is the b-decay of radioactive atomic nuclei. The phenomenon of radioactivity<#"justify">Bibliography
1. Novozhilov Yu.V. Introduction to the theory of elementary particles. Moscow: Nauka, 1972
Okun B. Weak interaction of elementary particles. Moscow: Fizmatgiz, 1963
The carriers of the weak interaction are the vector bosons W + , W− and Z 0 . In this case, the interaction of the so-called charged weak currents and neutral weak currents is distinguished. Interaction of charged currents (with the participation of charged bosons W± ) leads to a change in particle charges and the transformation of some leptons and quarks into other leptons and quarks. Interaction of neutral currents (with the participation of a neutral boson Z 0 ) does not change the particle charges and transforms leptons and quarks into the same particles.
Encyclopedic YouTube
-
1 / 5
Using the Pauli hypothesis, Enrico Fermi developed in 1933 the first theory of beta decay. Interestingly, his work was refused to be published in the journal Nature, referring to the excessive abstractness of the article. Fermi's theory is based on the use of the secondary quantization method, similar to that which had already been applied by that time for the processes of emission and absorption of photons. One of the ideas voiced in the work was also the assertion that the particles emitted from the atom were not initially contained in it, but were born in the process of interaction.
For a long time it was believed that the laws of nature are symmetrical with respect to mirror reflection, that is, the result of any experiment should be the same as the result of an experiment carried out on a mirror-symmetric installation. This symmetry with respect to spatial inversion (which is usually denoted as P) is related to the law conservation parity . However, in 1956, while theoretically considering the process of K-meson decay, Yang Zhenning and Li Zongdao suggested that the weak interaction may not obey this law. As early as 1957, Wu Jiansong's group confirmed this prediction in a beta decay experiment, which earned Yang and Li the 1957 Nobel Prize in Physics. Later, the same fact was confirmed in the decay of the muon and other particles.
To explain the new experimental facts, in 1957 Murray Gell-Mann, Richard Feynman, Robert Marshak and George Sudarshan developed universal theory four-fermion weak interaction, called V − A-theory.
In an effort to preserve the maximum possible symmetry of interactions, L. D. Landau suggested in 1957 that although P-symmetry is broken in weak interactions, combined symmetry must be preserved in them CP- a combination of mirror reflection and replacement of particles by antiparticles. However, in 1964, James-Cronin and Wahl-Fitch found a weak violation in the decays of neutral kaons CP-parity. It was the weak interaction that also turned out to be responsible for this violation, moreover, the theory in this case predicted that in addition to the two generations of quarks and leptons known by that time, there should be at least one more generation. This prediction was confirmed first in 1975 with the discovery of the tau lepton, and then in 1977 with the discovery of the b quark. Cronin and Fitch received the 1980 Nobel Prize in Physics.
Properties
All fundamental fermions (leptons and quarks) take part in the weak interaction. This is the only interaction in which neutrinos participate (apart from gravity, which is negligible in the laboratory), which explains the colossal penetrating power of these particles. Weak interaction allows leptons, quarks and their antiparticles to exchange energy, mass, electric charge and quantum numbers - that is, to turn into each other.
The weak force gets its name from the fact that its characteristic intensity is much lower than that of electromagnetism. In elementary particle physics, the intensity of an interaction is usually characterized by the rate of processes caused by this interaction. The faster the processes proceed, the higher the intensity of interaction. At energies of interacting particles of the order of 1 GeV, the characteristic rate of processes due to weak interaction is about 10 −10 s, which is approximately 11 orders of magnitude higher than for electromagnetic processes, that is, weak processes are extremely slow processes.
Another characteristic of the intensity of interaction is the length free path of particles in a substance. So, in order to stop a flying hadron due to the strong interaction, a plate of iron several centimeters thick is required. And a neutrino, which only participates in the weak interaction, can fly through a plate billions of kilometers thick.
Among other things, the weak interaction has a very small radius of action - about 2 10 -18 m (this is approximately 1000 times smaller size nuclei). It is for this reason that, despite the fact that the weak interaction is much more intense than the gravitational one, the range of which is unlimited, it plays a noticeably smaller role. For example, even for nuclei located at a distance of 10 −10 m, the weak interaction is weaker not only electromagnetic, but also gravitational.
In this case, the intensity of weak processes strongly depends on the energy of the interacting particles. The higher the energy, the higher the intensity. For example, due to the weak interaction, the neutron, the energy release during beta decay of which is approximately 0.8 MeV, decays in about 10 3 s, and the Λ-hyperon, with an energy release of about a hundred times more, already in 10 −10 s. The same is true for energetic neutrinos: the cross section for interaction with a nucleon of a neutrino with an energy of 100 GeV is six orders of magnitude larger than that of a neutrino with an energy of about 1 MeV. However, at energies of the order of several hundred GeV (in the center-of-mass system of colliding particles), the intensity of the weak interaction becomes comparable to the energy of the electromagnetic interaction, as a result of which they can be described in a unified way as the electroweak interaction.
The weak interaction is the only one of the fundamental interactions for which the law conservation parity does not hold, which means that the laws that weak processes obey change when the system is mirrored. Violation of the law of conservation of parity leads to the fact that only the left particles (whose spin is directed opposite to the momentum) are subject to weak interaction, but not the right ones (whose spin is co-directed with the momentum), and vice versa: the right antiparticles interact in a weak way, but the left ones are inert.
In addition to spatial parity, the weak interaction also does not preserve the combined space-charge parity, that is, the only known interaction violates the principle CP-invariance .
Theoretical description
Fermi theory
The first theory of the weak interaction was developed by Enrico Fermi in the 1930s. His theory is based on a formal analogy between the process of β-decay and the electromagnetic processes of photon emission. Fermi's theory is based on the interaction of the so-called hadron and lepton currents. In this case, unlike electromagnetism, it is assumed that their interaction is of a contact nature and does not imply the presence of a carrier similar to a photon. In modern notation, the interaction between the four main fermions (proton, neutron, electron, and neutrino) is described by an operator of the form
G F 2 p ¯ ^ n ^ ⋅ e ¯ ^ ν ^ (\displaystyle (\frac (G_(F))(\sqrt (2)))(\hat (\overline (p)))(\hat (n) )\cdot (\hat (\overline (e)))(\hat (\nu ))),Where G F (\displaystyle G_(F))- the so-called Fermi constant, numerically equal to approximately 10 −48 J/m³ or 10 − 5 / m p 2 (\displaystyle 10^(-5)/m_(p)^(2)) (m p (\displaystyle m_(p))- proton mass) in units, where ℏ = c = 1 (\displaystyle \hbar =c=1); p ¯ ^ (\displaystyle (\hat (\overline (p))))- proton creation operator (or antiproton annihilation), n ^ (\displaystyle (\hat(n)))- neutron annihilation operator (antineutron creation), e ¯ ^ (\displaystyle (\hat (\overline (e))))- operator of electron creation (positron annihilation), ν ^ (\displaystyle (\hat (\nu )))- neutrino annihilation operator (antineutrino generation).
Work p ¯ ^ n ^ (\displaystyle (\hat (\overline (p)))(\hat (n))), responsible for the conversion of a neutron into a proton, was called the nucleon current, and e ¯ ^ ν ^ , (\displaystyle (\hat (\overline (e)))(\hat (\nu )),) converting an electron into a neutrino - lepton. It is postulated that these currents, similarly to electromagnetic currents, are 4-vectors p ¯ ^ γ μ n ^ (\displaystyle (\hat (\overline (p)))\gamma _(\mu )(\hat (n))) And e ¯ ^ γ μ ν ^ (\displaystyle (\hat (\overline (e)))\gamma _(\mu )(\hat (\nu ))) (γ μ , μ = 0 … 3 (\displaystyle \gamma _(\mu ),~\mu =0\dots 3)- Dirac matrices). Therefore, their interaction is called vector.
The essential difference between the weak currents introduced by Fermi and the electromagnetic ones is that they change the charge of the particles: a positively charged proton becomes a neutral neutron, and a negatively charged electron becomes a neutral neutrino. In this regard, these currents are called charged currents.
Universal V-A Theory
The universal theory of the weak interaction, also called V−A-theory, was proposed in 1957 by M. Gell-Mann, R. Feynman, R. Marshak and J. Sudarshan. This theory took into account the recently proved fact of parity violation ( P-symmetries) in the case of weak interaction. For this, weak currents were represented as the sum of the vector current V and axial A(hence the name of the theory).
The vector and axial currents behave in exactly the same way under Lorentz transformations. However, during spatial inversion, their behavior is different: the vector current remains unchanged during such a transformation, while the axial current changes sign, which leads to parity violation. In addition, currents V And A differ in the so-called charge parity (violate C-symmetry).
Similarly, the hadronic current is the sum of the quark currents of all generations ( u- top, d- bottom, c- enchanted s- strange, t- true, b- lovely quarks):
u ¯ ^ d ′ ^ + c ¯ ^ s ′ ^ + t ¯ ^ b ′ ^ . (\displaystyle (\hat (\overline (u)))(\hat (d^(\prime )))+(\hat (\overline (c)))(\hat (s^(\prime ))) +(\hat (\overline (t)))(\hat (b^(\prime ))).)Unlike the lepton current, however, here the operators d ′ ^ , (\displaystyle (\hat (d^(\prime ))),) s ′ ^ (\displaystyle (\hat (s^(\prime )))) And b ′ ^ (\displaystyle (\hat (b^(\prime )))) are a linear combination of operators d ^ , (\displaystyle (\hat (d)),) s ^ (\displaystyle (\hat(s))) And b ^ , (\displaystyle (\hat (b)),) that is, the hadron current contains a total of not three, but nine terms. These terms can be combined into a single 3×3 matrix called the Cabibbo - Kobayashi - Maskawa matrix. This matrix can be parameterized with three angles and a phase factor. The latter characterizes the degree of violation CP-invariance in the weak interaction.
All terms in the charged current are the sum of the vector and axial operators with multipliers equal to one.
L = G F 2 j w ^ j w † ^ , (\displaystyle (\mathcal (L))=(\frac (G_(F))(\sqrt (2)))(\hat (j_(w)))(\ hat (j_(w)^(\dagger ))),)Where j w ^ (\displaystyle (\hat (j_(w)))) is the charged current operator, and j w † ^ (\displaystyle (\hat (j_(w)^(\dagger ))))- conjugate to it (obtained by replacing e ¯ ^ ν e ^ → ν e ¯ ^ e ^ , (\displaystyle (\hat (\overline (e)))(\hat (\nu _(e)))\rightarrow (\hat (\overline (\ nu _(e))))(\hat (e)),) u ¯ ^ d ^ → d ¯ ^ u ^ (\displaystyle (\hat (\overline (u)))(\hat (d))\rightarrow (\hat (\overline (d)))(\hat (u ))) etc.)
Theory of Weinberg - Salam
IN modern form the weak interaction is described as part of the unified electroweak interaction in the framework of the Weinberg-Salam theory. This is a quantum field theory with a gauge group SU(2)× U(1) and the spontaneously broken symmetry of the vacuum state caused by the action of the Higgs boson field. The proof of the renormalizability of such a model by Martinus Veltman and Gerard "t Hooft was awarded the 1999 Nobel Prize in Physics.
In this form, the theory of the weak interaction is included in the modern Standard Model, and it is the only interaction that breaks symmetries P And CP .
According to the theory of the electroweak interaction, the weak interaction is not a contact, but has its own carriers - vector bosons W + , W− and Z 0 with non-zero mass and spin equal to 1. The mass of these bosons is about 90 GeV / s², which causes a small range of weak forces.
In this case, charged bosons W± are responsible for the interaction of charged currents, and the existence of a neutral boson Z 0 means the existence of neutral currents as well. Such currents, indeed, were discovered experimentally. An example of interaction with their participation is, in particular, the elastic scattering of a neutrino by a proton. In such interactions, both the type of particles and their charges are preserved.
To describe the interaction of neutral currents, the Lagrangian must be supplemented with a term of the form
L = G F ρ 2 2 f 0 ^ f 0 ^ , (\displaystyle (\mathcal (L))=(\frac (G_(F)\rho )(2(\sqrt (2))))(\hat ( f_(0)))(\hat (f_(0))),)where ρ is a dimensionless parameter, equal to unity in the standard theory (experimentally it differs from unity by no more than 1%), f 0 ^ = ν e ¯ ^ ν e ^ + ⋯ + e ¯ ^ e ^ + ⋯ + u ¯ ^ u ^ + … (\displaystyle (\hat (f_(0)))=(\hat (\overline ( \nu _(e))))(\hat (\nu _(e)))+\dots +(\hat (\overline (e)))(\hat (e))+\dots +(\hat (\overline (u)))(\hat (u))+\dots )- self-adjoint neutral current operator.
Unlike charged currents, the neutral current operator is diagonal, that is, it translates particles into themselves, and not into other leptons or quarks. Each of the terms of the neutral current operator is the sum of a vector operator with a multiplier and an axial operator with a multiplier I 3 − 2 Q sin 2 θ w (\displaystyle I_(3)-2Q\sin ^(2)\theta _(w)), Where I 3 (\displaystyle I_(3))- the third projection of the so-called weak
Search
We may notify you of new articles,