Weak interaction
Strong interaction
Strong interaction is short-acting. Its range of action is about 10-13 cm.
Particles participating in strong interactions are called hadrons. In an ordinary stable substance, not too much high temperature strong interaction does not call any processes. Its role is to create a strong bond between nucleons (protons and neutrons) in nuclei. The binding energy averages about 8 MeV per nucleon. Moreover, in collisions of nuclei or nucleons with sufficient high energy(on the order of hundreds of MeV), strong interaction leads to numerous nuclear reactions: fission of nuclei, transformation of some nuclei into others, etc.
Starting from energies of colliding nucleons of the order of several hundred MeV, strong interaction leads to the production of P-mesons. At even higher energies, K-mesons and hyperons, and many meson and baryon resonances are born (resonances are short-lived excited states of hadrons).
At the same time, it turned out that not all particles experience strong interaction. Thus, protons and neutrons experience it, but electrons, neutrinos and photons are not subject to it. Usually only heavy particles participate in strong interactions.
The theoretical explanation of the nature of the strong interaction has been difficult to develop. A breakthrough emerged only in the early 1960s, when the quark model was proposed. In this theory, neutrons and protons are considered not as elementary particles, but as composite systems, built from quarks
The strong interaction quanta are eight gluons. Gluons get their name from English word glue (glue), because they are responsible for the confinement of quarks. The rest masses of gluons are zero. At the same time, gluons have a colored charge, due to which they are capable of interacting with each other, as they say, of self-interaction, which leads to difficulties in describing the strong interaction mathematically due to its nonlinearity.
Its range of action is less than 10-15 cm. The weak interaction is several orders of magnitude weaker not only than the strong one, but also the electromagnetic one. Moreover, it is much stronger than gravitational force in the microcosm.
The first discovered and most common process caused by the weak interaction is radioactive nuclear b-decay.
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This type of radioactivity was discovered in 1896 by A.A. Becquerelem. During the process of radioactive electron /b - -/ decay, one of the neutrons / n/ the atomic nucleus turns into a proton / R/ with electron emission / e-/ and electron antineutrino //:
n ® p + e-+
In the process of positronic /b + -/ decay the following transition occurs:
p® n + e++
In the first theory of b-decay, created in 1934 by E. Fermi, to explain this phenomenon it was necessary to introduce the hypothesis of the existence of a special type of short-range forces that cause the transition
n ® p + e-+
Further research showed that the interaction introduced by Fermi has a universal character.
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It causes the decay of all unstable particles, whose masses and selection rules based on quantum numbers do not allow them to decay due to strong or electromagnetic interaction. Weak interaction is inherent in all particles except photons. The characteristic time of weak interaction processes at energies of the order of 100 MeV is 13-14 orders of magnitude longer than the characteristic time for strong interaction.
The weak interaction quanta are three bosons - W + , W − , Z°- bosons. The superscripts indicate the sign of the electric charge of these quanta. Weak interaction quanta have a significant mass, which leads to the fact that weak interaction appears at very short distances.
It must be taken into account that today the weak and electromagnetic interactions are already combined into a single theory. There are a number of theoretical schemes that attempt to create a unified theory of all types of interaction. However, these schemes have not yet been developed enough to be tested experimentally.
26. Structural physics. Corpuscular approach to the description and explanation of nature. Reductionism
The objects of structural physics are the elements of the structure of matter (for example, molecules, atoms, elementary particles) and more complex education of them. This:
1) plasma - it is a gas in which a significant portion of the molecules or atoms are ionized;
2) crystals- This solids, in which atoms or molecules are arranged in an orderly manner and form a periodically repeating internal structure;
3) liquids- this is the aggregate state of a substance, which combines the features of a solid state (conservation of volume, a certain tensile strength) and a gaseous state (shape variability).
The liquid is characterized by:
a) short-range order in the arrangement of particles (molecules, atoms);
b) a small difference in the kinetic energy of thermal motion and their potential interaction energy.
4) stars,ᴛ.ᴇ. glowing gas (plasma) balls.
When identifying structural equations of a substance, the following criteria are used:
Spatial dimensions: particles of the same level have spatial dimensions of the same order (for example, all atoms have dimensions of the order of 10 -8 cm);
Process time: at one level it is approximately the same order of magnitude;
Objects of the same level consist of the same elements (for example, all nuclei consist of protons and neutrons);
The laws that explain processes at one level are qualitatively different from the laws that explain processes at another level;
Objects at different levels differ in their basic properties (for example, all atoms are electrically neutral, and all nuclei are positively electrically charged).
As new levels of structure and states of matter are discovered, the object domain of structural physics is expanding.
It must be taken into account that when solving specific physical problems, issues related to elucidating structure, interaction and motion are closely intertwined.
At the root of structural physics is a corpuscular approach to describing and explaining nature.
For the first time, the concept of the atom as the last and indivisible particle of the body arose in Ancient Greece within the framework of the natural philosophical teachings of the school of Leucippus-Democritus. According to this view, there are only atoms in the world that move in the void. The ancient atomists considered the continuity of matter to be apparent. Different combinations of atoms form different visible bodies. This hypothesis was not based on experimental data. She was just a brilliant guess. But it determined everything for many centuries to come. further development natural sciences.
The hypothesis of atoms as indivisible particles of matter was revived in natural science, in particular in physics and chemistry, to explain some laws that were established experimentally (for example, the Boyle-Mariotte and Gay-Lussac laws for ideal gases, thermal expansion of bodies, etc.). d.). Indeed, the Boyle-Marriott law states that the volume of a gas is inversely proportional to its pressure, but it does not explain why this is so. Likewise, when a body is heated, its size increases. But what is the reason for this expansion? In the kinetic theory of matter, these and other experimentally established patterns are explained with the help of atoms and molecules.
Indeed, the directly observed and measurable decrease in gas pressure with an increase in its volume in the kinetic theory of matter is explained as an increase in the free path of its constituent atoms and molecules. It is as a result of this that the volume occupied by the gas increases. Similarly, the expansion of bodies when heated in the kinetic theory of matter is explained by an increase average speed moving molecules.
Explanations in which they try to reduce the properties of complex substances or bodies to the properties of their simpler elements or components, called reductionism. This method of analysis made it possible to solve a large class of problems in natural science.
Up to late XIX V. It was believed that an atom is the smallest, indivisible, structureless particle of matter. At the same time, the discoveries of the electron and radioactivity showed that this is not so. Rutherford's planetary model of the atom emerges. Then she is replaced by the model N. Bora. But as before, the thought of physicists is aimed at reducing the whole variety of complex properties of bodies and natural phenomena to simple properties a small number of primary particles. Subsequently, these particles were called elementary. Now their total number exceeds 350. For this reason, it is unlikely that all such particles can be called truly elementary, not containing other elements. This belief is strengthened by the hypothesis of the existence of quarks. According to it, known elementary particles consist of particles with fractional electric charges. They are called quarks.
According to the type of interaction in which elementary particles participate, all of them, except the photon, are classified into two groups:
1) hadrons. It is worth saying that they are characterized by the presence of strong interaction. Moreover, they can also participate in weak and electromagnetic interactions;
2) leptons. Οʜᴎ participate only in electromagnetic and weak interactions;
According to their lifespan, they are distinguished:
a) stable elementary particles. These are the electron, photon, proton and neutrino;
b) quasi-stable. These are particles that decay due to electromagnetic and weak interactions. For example, to + ® m + +;
c) unstable. Οʜᴎ decay due to strong interaction, for example, neutron.
The electric charges of elementary particles are multiples of the smallest charge inherent in the electron. At the same time, elementary particles are divided into particle – antiparticle pairs, for example e - - e + (they have all the same characteristics, and the signs of the electric charge are opposite). Electrically neutral particles also have antiparticles, for example, P -,- .
So, the atomistic concept is based on the idea of the discrete structure of matter. The atomistic approach explains the properties of a physical object based on the properties of its components tiny particles, which at a certain stage of cognition are considered indivisible. Historically, such particles were first recognized as atoms, then as elementary particles, and now as quarks. The difficulty of this approach is the complete reduction of the complex to the simple, which does not take into account the qualitative differences between them.
Until the end of the first quarter of the twentieth century, the idea of the unity of the structure of the macro- and microcosmos was understood mechanistically, as the complete identity of laws and as the complete similarity of the structure of both.
Microparticles were interpreted as miniature copies of macrobodies, ᴛ.ᴇ. like extremely small balls (corpuscles) moving in precise orbits, which are completely similar to planetary orbits, with the only difference that the celestial bodies are connected by forces gravitational interaction, and microparticles - by electrical interaction forces.
After the discovery of the electron (Thomson, 1897), the creation of the theory of quantum (Planck, 1900), and the introduction of the concept of photon (Einstein, 1905), atomic theory acquired a new character.
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The idea of discreteness was extended to the field of electrical and light phenomena, to the concept of energy (in the 19th century, the doctrine of energy served as the sphere of ideas about continuous quantities and functions of state). The most important feature of modern atomic teaching is the atomism of action. It is due to the fact that the movement, properties and states of various micro-objects are amenable to quantization, ᴛ.ᴇ. are expressed in the form of discrete quantities and ratios. New atomism recognizes the relative stability of each discrete type of matter, its qualitative certainty, its relative indivisibility and intransformability within the known boundaries of natural phenomena. For example, being divisible by some by physical means, the atom is indivisible chemically, ᴛ.ᴇ. V chemical processes he behaves as something whole, indivisible. A molecule, being divisible chemically into atoms, thermal movement(up to certain limits) behaves as a whole, indivisible, etc.
Particularly important in the concept of new atomism is the recognition of the interconvertibility of any discrete types of matter.
Different levels of the structural organization of physical reality (quarks, microparticles, nuclei, atoms, molecules, macrobodies, megasystems) have their own specific physical laws. But no matter how different the phenomena being studied are from the phenomena studied by classical physics, all experimental data must be described using classical concepts. There is a fundamental difference between the description of the behavior of the microobject being studied and the description of the action measuring instruments. This is the result of the fact that the action of measuring instruments, in principle, should be described in the language of classical physics, but the object under study may not be described by this language.
The corpuscular approach in explaining physical phenomena and processes has always been combined with the continuum approach since the emergence of interaction physics. It was expressed in the concept of the field and the disclosure of its role in physical interaction. The representation of the field as a flow of a certain kind of particles (quantum field theory) and the attribution of wave properties to any physical object (Louis de Broglie's hypothesis) brought together these two approaches to the analysis of physical phenomena.
Weak interaction - concept and types. Classification and features of the category "Weak interaction" 2017, 2018.
This is the third fundamental interaction, existing 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 weak interaction is the process of beta decay, 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 quark of flavor d into a quark of flavor u inside the neutron. The emitted electron ensures the conservation of the total electrical charge, and the antineutrino allows the total mechanical momentum of the system to be preserved.
The main function of the strong interaction is to combine quarks and antiquarks into hadrons. The theory of strong interactions is in the process of being created. It is a typical field theory and is called quantum chromodynamics. Its starting point is the postulate of the existence of three types of color charges (red, blue, green), expressing the inherent ability of matter to unite quarks in strong interaction. Each of the quarks contains some combination of such charges, but their complete 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 net 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 interactions, the nuclear force that unites protons and neutrons in the nuclei of atoms was considered fundamental. With the discovery of the quark level of matter, the strong interaction began to be understood as color interactions between quarks combining 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, considered as echoes of electric atomic forces.
The four types of fundamental interactions considered underlie all other known forms of matter motion, including those that arose at higher stages of development. Any complex forms of motion, when decomposed into structural components, are revealed as complex modifications of these fundamental interactions.
The "Grand Unification" theory is a theory that unifies electromagnetic, strong and weak interactions. Mentioning the theory of the “Great Unification”, we are talking about 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, which gave birth to our universe, only this force existed. However, over time, the universe expanded, which means it cooled, and the single force split into several different ones, which we now observe. The "Grand Unification" theory would describe the electromagnetic, strong, weak and gravitational forces as manifestations of one universal force. There has already been some progress: scientists have managed to construct a theory that combines electromagnetic and weak interactions. However, the main work on the theory of the “Great Unification” is still ahead.
Modern particle physics is forced to discuss questions that, in fact, worried ancient thinkers. What is the origin of particles and chemical atoms built from these particles? And how can the Cosmos, the Universe visible to us, be built from particles, no matter what we call them? And also – was the Universe created, or has it existed from eternity? If one can ask this, what are the pathways of thought that can lead to convincing answers? All these questions are similar to the search for the true principles of existence, questions about the nature of these principles.
Whatever we say about the Cosmos, one thing is clear: everything in the natural world is made up of particles in one way or another. But how to understand this composition? It is known that particles interact - they attract or repel each other. Particle physics studies a variety of 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 particular attention in the 18th–19th centuries. Similarities and differences between electromagnetic and gravitational interactions were discovered. Like gravity, electromagnetic forces are inversely proportional to the square of the distance. But, unlike gravity, electromagnetic “gravity” not only attracts particles (different charge signs), but also repels them from each other (equally charged particles). And not all particles are carriers of electric charge. For example, the photon and neutron are neutral in this regard. 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. [Grünbaum A. Origin versus creation in physical cosmology (theological distortions of modern physical cosmology). – Question. Philosophy, 1995, No. 2, p. 19.]
The study of the phenomena of radioactivity led to the discovery of a special kind of particle interaction, which was called 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 electromagnetic interaction, although much stronger than gravitational interaction. The discovery was facilitated by the research of W. Pauli (1900–1958), who predicted that during beta decay a neutral particle is released, compensating for the apparent violation of the law of conservation of energy, called a neutrino. And in addition, the discovery of weak interactions was facilitated by the research of E. Fermi (1901–1954), who, along with other physicists, suggested that electrons and neutrinos, before their departure from the radioactive nucleus, do not exist in the nucleus, so to speak, in a ready-made form, but are formed during the radiation process. [Grünbaum A. Origin versus creation in physical cosmology (theological distortions of modern physical cosmology). – Question. Philosophy, 1995, No. 2, p. 21.]
Finally, the fourth interaction turned out to be associated with intranuclear processes. Called the strong interaction, it manifests itself as the 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 the four types of interactions followed the path of searching for their deep connection. On this unclear, largely dark path, only the principle of symmetry guided the research and led to the identification of the supposed connection various types interactions.
To identify such connections, it was necessary to turn to a search for a special type of symmetries. A simple example This type of symmetry can be represented by the dependence of the work performed when lifting a load on the height of the lift. The energy expended depends on the difference in height, but does not depend on the nature of the ascent path. Only the difference in height is significant and it does not matter at all from what level we start the measurement. We can say that we are dealing here with symmetry with respect to the choice of origin.
In a similar way, you can calculate the energy of motion of an electric charge in an electric field. The analogue of height here will be field voltage or, in other words, electric potential. The energy expended during charge movement will depend only on the potential difference between the final and initial points in the field space. We are dealing here with the so-called gauge or, in other words, 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, giving 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. It is possible to eliminate these divergences due to the fact that 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 a theory of not only electromagnetic, but also other interactions can be overcome if other, hidden symmetries can be found.
Gauge symmetry can take on a generalized character and can be attributed to any force field. At the end of the 1960s. S. Weinberg (b. 1933) from Harvard University and A. Salam (b. 1926) from Imperial College in London, based on the work of S. Glashow (b. 1932), undertook a theoretical unification of electromagnetic and weak interactions. They used the idea of gauge symmetry and the concept of a gauge field associated with this idea. [Yakushev A. S. Basic concepts of modern natural science. – M., Fakt-M, 2001, p. 29.]
Applicable for electromagnetic interaction simplest form gauge symmetry. It turned out that the symmetry of the weak interaction is more complex than that of the electromagnetic interaction. 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. Particles such as neutron, proton, electron and neutrino can participate in this process. Moreover, due to weak interaction, mutual transformation of particles occurs.
Conceptual provisions of the theory of “Grand Unification”
In modern theoretical physics, two new conceptual schemes set the tone: the so-called “Grand Unified” theory and supersymmetry.
These scientific trends together lead to a very attractive idea, according to which all of nature is ultimately subject to the action of some superpower, manifesting itself in various “guises.” This force is powerful enough to create our Universe and endow it with light, energy, matter and give it structure. But superpower is more than just a creative force. In it, matter, space-time and interaction are fused into an indivisible harmonious whole, generating such a unity of the Universe that no one had previously imagined. The purpose of science is essentially the search for 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 living and inanimate nature within the framework of a single descriptive scheme. Today, 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 decay. Electromagnetic forces act between electric charges, and gravitational forces act between masses. The presence of these interactions is a sufficient and necessary condition for building 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 or light. Without strong nuclear interactions, nuclei would not exist, and therefore atoms and molecules, chemistry and biology would not exist, and stars and the Sun would not be able to generate heat and light using nuclear energy.
Even weak nuclear interactions 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 throughout the Universe. Life might well not have arisen. If we agree with the opinion that all these four completely different interactions, each of which is in its own way necessary 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 operating in both living and nonliving nature is beyond doubt. Modern research shows that these four forces may once 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. The “Grand Unification” theories should combine these interactions with the strong ones, and the “All That Is” theories should unify 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 and the results of computer modeling 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 entropic process of converting matter into radiation is not dominant. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 38.]
Under these conditions, a new type of evolutionary self-organization of matter arises, connecting the coherent spatiotemporal 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 associated with their unification.” Thus, in our view, the law of increasing entropy 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 in space-time hierarchy levels, 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 begins to restore its equilibrium. The process of further evolution occurs in a mirror image.
In other words, two processes are happening 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 (physical examples include such well-known states of matter as superfluidity, superconductivity and the quantum Hall effect). This process, apparently, determines the consistent evolution of thermonuclear fusion processes in 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.
The other 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 us to combine all four interactions into one superforce. As already noted, this is the problem that most 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 Evolutionary Self-Organization of the Universe. Therefore, let us draw 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 self-organization and evolution of living organisms, as well as the causes of their violations, manifested in the form of all kinds of 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, organismal, population, biocenotic, biotic, landscape, biosphere, cosmic) presence of a biorhythmological process associated with the consumption and consumption of the transformed 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 processes of formation of DNA structure and the principle of reduplication of discrete codes of hereditary information, as well as in processes such 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, interfere with 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, and a slower humoral system. At the same time, the slipper ciliate, in the complete absence of the nervous and humoral systems, lives, feeds, excretes, reproduces, and all these complex processes do not occur chaotically, but in strict sequence: any reaction predetermines the next one, and that in turn releases products , which are necessary to start the next reaction. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 59.]
It should be noted that Einstein’s theory marked such important progress in understanding nature that a revision of views on other forces of nature soon became inevitable. At this time, the only "other" force whose existence was firmly established was electromagnetic interaction. However, outwardly it did not resemble gravity at all. Moreover, several decades before the creation of Einstein’s theory of gravity, electromagnetism was successfully described by Maxwell’s theory, 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 creating the general theory of relativity. However, ironically, the person who came closest to realizing Einstein’s dream was the little-known Polish physicist Theodor Kaluza, who back in 1921 laid the foundations for a new and unexpected approach to the unification of physics, which still amazes the imagination with its audacity.
With the discovery of weak and strong interactions in the 30s of the 20th century, the ideas of unifying gravity and electromagnetism largely lost their attractiveness. A consistent unified field theory should have included not two, but four forces. Obviously, this could not be done without achieving a deep understanding of weak and strong interactions. In the late 1970s, thanks to the fresh wind brought by Grand Unified Theories (GUT) and supergravity, the old Kaluza-Klein theory was remembered. They “blowed off the dust, dressed it up in fashion” and included in it all the interactions known to date.
In GUT, theorists managed to bring together three very different types of interactions within 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 gains elegance and opens up wide possibilities. The presence of force field symmetries quite clearly indicates the manifestation of some hidden geometry. In the Kaluza-Klein theory brought back to life, the symmetries of gauge fields become concrete - 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 need to accommodate interactions of three types, we have to introduce several additional dimensions. Simply counting the number of symmetry operations involved in GUT leads to a theory with seven additional spatial dimensions (bringing the total to ten); if we take into account time, then space-time has eleven dimensions in total. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 69.]
Basic 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 scale (or equivalent masses). The smaller the length scale being studied, the higher the energy required for this. Studying the quark structure of a proton requires energies equivalent to at least ten times the proton's mass. Significantly 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 differences 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 exceed the Grand Unification scale and achieve energies equivalent to 10 19 proton masses. Only with such unimaginably enormous energies would it be possible to directly observe the manifestations of additional dimensions of space.
This huge value - 10 19 masses of a proton - is called the Planck mass, since it was first introduced by Max Planck, the creator of quantum theory. At 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 appear in all its splendor [Yakushev A. S. Basic concepts of modern natural science. – M., Fakt-M, 2001, p. 122. ]
By giving free rein to the imagination, one can imagine that one day humanity will gain superpowers. 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 superpower, we could change the structure of space and time, bend the void in our own way and put matter in order. By controlling superpowers, we could create or transform particles at will, generating exotic new forms of matter. We could even manipulate the dimension of space itself, creating bizarre artificial worlds with unimaginable properties. We would truly become masters of the Universe!
But how to achieve this? First of all, it is necessary to obtain a sufficient amount of energy. To get an idea of what we're talking about, remember that the 3 km long linear accelerator at Stanford accelerates electrons to energies equivalent to 20 proton masses. To achieve the Planck energy, the accelerator would need to be lengthened by 10 18 times, making it the size of the Milky Way (about one hundred thousand light years). Such a project is not one that can be implemented in the foreseeable future. [Wheeler J. A. Quantum and the Universe // Astrophysics, quanta and the theory of relativity, M., 1982, p. 276.]
Grand Unified Theory clearly distinguishes three thresholds, or scales, of energy. First of all, this is the Weinberg–Salam threshold, equivalent to almost 90 proton masses, above which electromagnetic and weak interactions merge into a single electroweak interaction. The second scale, corresponding to 10 14 proton masses, is characteristic of the Grand 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 to explain the existence of these three scales, as well as the reason for such a strong difference between the first and second of them. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 76.]
Modern technology is capable of achieving only the first scale. Proton decay could provide us with an indirect means of studying the physical world at the Grand Unified scale, although at present there appears to be no hope of directly reaching this limit, let alone at the Planck mass scale.
Does this mean that we will never be able to observe manifestations of the original superpower and the invisible seven dimensions of space. Using technical means such as a superconducting supercollider, we are rapidly moving up the scale of energies achievable under terrestrial conditions. However, the technology created by people does not exhaust all possibilities - nature itself also exists. The Universe is a gigantic natural laboratory in which the greatest experiment in the field of elementary particle physics was “conducted” 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 superpower to leave its mark forever. [Yakushev A. S. Basic concepts of modern natural science. – M., Fakt-M, 2001, p. 165.]
This interaction is the weakest of the fundamental interactions experimentally observed in the decays of elementary particles, where quantum effects are fundamentally significant. Let us recall that quantum manifestations of gravitational interaction have never been observed. Weak interactions are highlighted using next rule: if an elementary particle called a neutrino (or antineutrino) is involved in the interaction process, then this interaction is weak.
A typical example of the weak interaction is the beta decay of a neutron, where n– neutron, p– proton, e– – electron, e+ – electron antineutrino. It should, however, be borne in mind that the above rule does not mean at all that any act of weak interaction must be accompanied by a neutrino or antineutrino. It is known that a large number of neutrinoless decays occur. As an example, we can note the decay process of lambda hyperon D into a proton p+ and negatively charged pion p– . By modern ideas The neutron and proton are not true elementary particles, but are composed of elementary particles called quarks.
The intensity of the weak interaction is characterized by the Fermi coupling constant G F. Constant G F dimensional. To form a dimensionless quantity, it is necessary to use some reference mass, for example the mass of a proton m p. Then the dimensionless coupling constant will be. It can be seen that the weak interaction is much more intense than the gravitational interaction.
The weak interaction, unlike the gravitational interaction, is short-range. This means that the weak force between particles only comes into play if the particles are close enough to each other. If the distance between particles exceeds a certain value called the characteristic radius of interaction, the weak interaction does not manifest itself. It has been experimentally established that the characteristic radius of weak interaction is about 10–15 cm, that is, weak interaction is concentrated at distances smaller than the size of the atomic nucleus.
Why can we talk about weak interaction as an independent type of fundamental interaction? The answer is simple. It has been established that there are processes of transformation of elementary particles that are not reduced to gravitational, electromagnetic and strong interactions. Good example, showing that there are three qualitatively different interactions in nuclear phenomena, is associated with radioactivity. Experiments indicate the presence of three various types radioactivity: α-, β- and γ-radioactive decays. In this case, α-decay is due to strong interaction, γ-decay is due to electromagnetic interaction. The remaining β decay cannot be explained by the electromagnetic and strong interactions, and we are forced to accept that there is another fundamental interaction, called the weak. In the general case, the need to introduce weak interaction is due to the fact that processes occur in nature in which electromagnetic and strong decays are prohibited by conservation laws.
Although the weak interaction is significantly concentrated within the nucleus, it has certain macroscopic manifestations. As we have already noted, it is associated with the process of β-radioactivity. In addition, the weak interaction plays an important role in the so-called thermonuclear reactions responsible for the mechanism of energy release in stars.
The most amazing property weak interaction is the existence of processes in which mirror asymmetry is manifested. At first glance, it seems obvious that the difference between the concepts left and right is arbitrary. Indeed, the processes of gravitational, electromagnetic and strong interaction are invariant with respect to spatial inversion, which carries out mirror reflection. It is said that in such processes the spatial parity P is conserved. However, it has been experimentally established that weak processes can proceed with non-conservation of spatial parity and, therefore, seem to sense the difference between left and right. Currently, there is solid experimental evidence that parity nonconservation in weak interactions is universal in nature; it manifests itself not only in the decays of elementary particles, but also in nuclear and even atomic phenomena. It should be recognized that mirror asymmetry is a property of Nature at the most fundamental level.
Parity nonconservation in weak interactions seemed such an unusual property that almost immediately after its discovery, theorists began trying to show that there was in fact complete symmetry between left and right, only it had a deeper meaning than previously thought. Mirror reflection must be accompanied by the replacement of particles with antiparticles (charge conjugation C), and then all fundamental interactions must be invariant. However, it was later established that this invariance is not universal. There are weak decays of the so-called long-lived neutral kaons into pions p + , p – , forbidden if the indicated invariance actually took place. Thus, distinctive feature weak interaction is its CP non-invariance. It is possible that this property is responsible for the fact that matter in the Universe significantly prevails over antimatter, built from antiparticles. The world and the antiworld are asymmetrical.
The question of which particles are carriers of the weak interaction has been unclear for a long time. Understanding was achieved relatively recently within the framework of the unified theory of electroweak interactions - the Weinberg-Salam-Glashow theory. It is now generally accepted that the carriers of the weak interaction are the so-called W + - and Z 0 -bosons. These are charged W + and neutral Z 0 elementary particles with spin 1 and masses equal in order of magnitude to 100 m p.
Time is like a river carrying passing events, and its current is strong; As soon as something appears before your eyes, it has already been carried away, and you can see something else that will also soon be carried away.
Marcus Aurelius
Each of us strives to create a holistic picture of the world, including a picture of the Universe, from the smallest subatomic particles to the greatest scale. But the laws of physics are sometimes so strange and counterintuitive that this task can become overwhelming for those who have not become professional theoretical physicists.
A reader asks:
Although this is not astronomy, maybe you can give me a hint. The strong force is carried by gluons and binds quarks and gluons together. Electromagnetic is carried by photons and binds electrically charged particles. Gravity is supposedly carried by gravitons and binds all particles to mass. The weak is carried by W and Z particles, and... is associated with decay? Why is the weak force described this way? Is the weak force responsible for the attraction and/or repulsion of any particles? And which ones? And if not, why then is it one of the fundamental interactions if it is not associated with any forces? Thank you.
And all this is interaction, force. For particles whose state can be measured, the application of a force changes its moment - in ordinary life, in such cases we talk about acceleration. And for three of these forces this is true.
In the case of gravity, the total amount of energy (mostly mass, but all energy is included) bends spacetime, and the motion of all other particles changes in the presence of everything that has energy. This is how it works in the classical (non-quantum) theory of gravity. Maybe there are more general theory, quantum gravity, where gravitons are exchanged, leading to what we observe as gravitational interaction.
Before you continue, please understand:
In electromagnetism, the main property is electric charge. Unlike gravity, it can be positive or negative. A photon, a particle that carries the force associated with a charge, causes like charges to repel and dissimilar charges to attract.
It is worth noting that moving charges, or electric currents, experience another manifestation of electromagnetism - magnetism. The same thing happens with gravity, and it is called gravitomagnetism (or gravitoelectromagnetism). We won’t go deeper - the point is that there is not only a charge and a force carrier, but also currents.
There is also a strong nuclear interaction, which has three types of charges. Although all particles have energy and are all subject to gravity, and although quarks, half the leptons and a pair of bosons contain electrical charges - only quarks and gluons have a colored charge and can experience the strong nuclear force.
There are a lot of masses everywhere, so gravity is easy to observe. And since the strong force and electromagnetism are quite strong, they are also easy to observe.
But what about the latter? Weak interaction?
We usually talk about it in the context of radioactive decay. A heavy quark or lepton decays into lighter and more stable ones. Yes, weak interaction has something to do with this. But in in this example it is somehow different from other forces.
It turns out that weak interaction is also a force, it’s just not often talked about. She's weak! 10,000,000 times weaker than electromagnetism over a distance the diameter of a proton.
A charged particle always has a charge, regardless of whether it is moving or not. But electricity, created by it, depends on its movement relative to other particles. Current determines magnetism, which is as important as electrical part electromagnetism. Compound particles like the proton and neutron have significant magnetic moments, just like the electron.
Quarks and leptons come in six flavors. Quarks - up, down, strange, charmed, charming, true (according to them letter designations in Latin u, d, s, c, t, b - up, down, strange, charm, top, bottom). Leptons - electron, electron-neutrino, muon, muon-neutrino, tau, tau-neutrino. Each of them has an electrical charge, but also a scent. If we combine electromagnetism and the weak force to get the electroweak force, then each of the particles will have some weak charge, or electroweak current, and a weak force constant. All this is described in the Standard Model, but it was quite difficult to test it because electromagnetism is so strong.
In a new experiment, the results of which were recently published, the contribution of the weak interaction was measured for the first time. The experiment made it possible to determine the weak interaction of up and down quarks
And the weak charges of the proton and neutron. The Standard Model's predictions for weak charges were:
Q W (p) = 0.0710 ± 0.0007,
Q W (n) = -0.9890 ± 0.0007.
And based on the scattering results, the experiment produced the following values:
Q W (p) = 0.063 ± 0.012,
Q W (n) = -0.975 ± 0.010.
Which coincides very well with the theory, taking into account the error. The experimenters say that by processing more data, they will further reduce the error. And if there are any surprises or divergences from the Standard Model, that will be cool! But nothing indicates this:
Therefore, particles have a weak charge, but we do not talk about it, since it is unrealistically difficult to measure. But we did it anyway, and it appears that we have reconfirmed the Standard Model.
Vector bosons are carriers of the weak interaction W + , W− and Z 0 . In this case, a distinction is made between the interaction of so-called charged weak currents and neutral weak currents. 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 charges of the particles and converts leptons and quarks into the same particles.
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Using the Pauli hypothesis, Enrico Fermi developed the first theory of beta decay in 1933. It’s interesting that his work was refused publication in the magazine Nature, citing the excessive abstractness of the article. Fermi's theory is based on the use of a secondary quantization method, similar to that which had already been applied at that time for the processes of emission and absorption of photons. One of the ideas voiced in the work was also the statement that particles flying out of an 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 is relative to spatial inversion (which is usually denoted as P) is associated with the law of conservation of parity. However, in 1956, when theoretically considering the process of decay of K-mesons, Yang Zhenning and Li Zongdao suggested that the weak interaction may not obey this law. Already in 1957, Wu Jiansong's group confirmed this prediction in an experiment on β-decay, which earned Yang and Li the Nobel Prize in Physics for 1957. 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 Marchak and George Sudarshan developed a universal theory of four-fermion weak interaction, called V − A-theories.
In an effort to preserve the maximum possible symmetry of interactions, L. D. Landau in 1957 suggested that although P-symmetry is broken in weak interactions; combined symmetry must be preserved in them C.P.- a combination of mirror reflection and replacement of particles with antiparticles. However, in 1964, James Cronin and Val Fitch found a weak violation in the decays of neutral kaons C.P.-parity. The weak interaction 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.
All fundamental fermions (leptons and quarks) take part in weak interaction. This is the only interaction in which neutrinos participate (apart from gravity, which is negligible in laboratory conditions), which explains the colossal penetrating power of these particles. The weak interaction allows leptons, quarks and their antiparticles to exchange energy, mass, electric charge and quantum numbers - that is, turn into each other.
The weak interaction 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 occur, the higher the intensity of interaction. At energies of interacting particles of the order of 1 GeV, the characteristic rate of processes caused by weak interaction is about 10 −10 s, which is approximately 11 orders of magnitude greater than for electromagnetic processes, that is, weak processes are extremely slow processes.
Another characteristic of the intensity of interaction is the free path of particles in a substance. So, in order to stop a flying hadron due to strong interaction, a plate of iron several centimeters thick is required. And a neutrino, which participates only in the weak interaction, can fly through a plate billions of kilometers thick.
Among other things, the weak interaction has a very small range of action - about 2·10 -18 m (this is approximately 1000 times smaller size kernels). It is for this reason that, despite the fact that the weak interaction is much more intense than the gravitational interaction, the radius of which is unlimited, it plays a noticeably lesser role. For example, even for nuclei located at a distance of 10−10 m, the weak interaction is weaker not only than electromagnetic, but also gravitational.
In this case, the intensity of weak processes strongly depends on the energy of interacting particles. The higher the energy, the higher the intensity. For example, due to weak interaction, a neutron, the energy release during beta decay of which is approximately 0.8 MeV, decays in a time of about 10 3 s, and a 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 greater than that of a neutrino with an energy of about 1 MeV. However, at energies of the order of several hundred GeV (in the frame of the center of mass 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 manner as the electroweak interaction.
The weak interaction is the only fundamental interaction for which the law of conservation of parity is not satisfied, this means that the laws that govern weak processes change when the system is mirrored. Violation of the law of conservation of parity leads to the fact that only left-handed particles (whose spin is directed opposite to the momentum), but not right-handed ones (whose spin is in the same direction as the momentum), are subject to weak interaction, and vice versa: right-handed antiparticles interact weakly, but left-handed 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 C.P.-invariance.
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 hadronic and lepton currents. Moreover, in contrast to 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 the system of units, where ℏ = c = 1 (\displaystyle \hbar =c=1); p ¯ ^ (\displaystyle (\hat (\overline (p))))- operator of proton creation (or destruction of antiproton), n ^ (\displaystyle (\hat (n)))- operator of neutron destruction (antineutron birth), e ¯ ^ (\displaystyle (\hat (\overline (e))))- operator of electron creation (destruction of positron), ν ^ (\displaystyle (\hat (\nu )))- operator of neutrino destruction (antineutrino birth).
Work p ¯ ^ n ^ (\displaystyle (\hat (\overline (p)))(\hat (n))), responsible for the transfer of a neutron into a proton, is 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, similar 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.
A significant difference between the weak currents introduced by Fermi and electromagnetic ones is that they change the charge of 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.
The universal theory of 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 proven fact of parity violation ( P-symmetry) with weak interaction. For this purpose, weak currents were represented as the sum of the vector current V and axial A(hence the name of the theory).
Vector and axial currents behave exactly the same under Lorentz transformations. However, during spatial inversion, their behavior is different: the vector current remains unchanged during this transformation, but the axial current changes sign, which leads to parity violation. In addition, currents V And A differ in so-called charge parity (violate C-symmetry).
Similarly, the hadronic current is the sum of quark currents of all generations ( u- upper, d- lower, c- enchanted, s- strange, t- true, b- cute 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 )))) represent a linear combination of operators d ^ , (\displaystyle (\hat (d)),) s ^ (\displaystyle (\hat (s))) And b ^ , (\displaystyle (\hat (b)),) that is, the hadronic current contains a total of not three, but nine terms. These terms can be combined into one 3x3 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 C.P.-invariance in weak interaction.
All terms in the charged current are the sum of the vector and axial operators with factors 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.)
IN modern form the weak interaction is described as part of a single electroweak interaction within the framework of the Weinberg-Salam theory. This is a quantum field theory with a gauge group S.U.(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 Nobel Prize in Physics for 1999.
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 C.P. .
According to the theory of electroweak interaction, the weak interaction is not 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 / c², which determines the small radius of action of weak forces.
At the same time, 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 have indeed been 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 appearance of the 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 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 transfers 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
