Professor Maxim Khlopov on Сosmoparticle physics, the science of the fundamental relationship between the theory of the Universe and the physics of the microworld

Maxim Yurievich Khlopov ( is the professor, doctor of physical and mathematical sciences. He is the Principal Researcher, Institute of Physics, Southern Federal University, Professor, Department of Elementary Particle Physics, NRNU MEPhI, Director of the Virtual Institute of Astroparticle physics (VIA), President of the Center for Cosmoparticle physics “Cosmion.”

He graduated with honors from the Moscow Institute of Physics and Technology in 1974, the topic of his PhD thesis is “Physical and Astrophysical Effects of Weak Interactions” (1977), the theme of his Doctor of Science thesis is “Astrophysical manifestations of super weak interactions of elementary particles” (1986). Khlopov worked in Ya.B. Zeldovich’s group in Keldysh Institute of Applied Mathematics in 1977-2004, served as visiting scientist in Special Astrophysical Observatory (N.Arkhyz, Russia) in 1987-1990, a MIUR Professor in Rome University “La Sapienza) in 2002-2004, a visiting specialist at the INFN Sector of Lecce (Italy), the Center for Research of Very Low Temperatures (CRTBT, Grenoble, France), and the Laboratory of Subnuclear Physics and Cosmology (LPSC, Grenoble, France) in 2005-2006.

He has been carrying out scientific management of the project of the Virtual Institute of Astroparticle physics, based on the APC laboratory (Paris, France) while having retained his positions at MEPhI and Cosmion since 2007.

Along with A.D. Sakharov he created USSR Academy of Science Scientific Council on Cosmoparticle physics in 1989 and the Center for Cosmoparticle physics “Cosmion” in 1992 for the implementation of a research program elaborated by this Council. Khlopov was the organizer of the International Conferences on Cosmoparticle physics Cosmion-94 (Moscow), Cosmion-96 (Moscow), Cosmion-97 (Moscow), Cosmion-99 (Moscow), Cosmion-2001 (Moscow-St. Petersburg) and Cosmion-2004 (Moscow-St.Petersburg-Paris), at which the results of this research were presented.

He organizes annual Bled Workshops called “What comes beyond the Standard models?” in Bled, Slovenia since 2010.

He has been holding the position of chief researcher at the Institute of Physics of the Southern Federal University, carrying out scientific management of the “Cosmoparticle physics studies of various types of extension of the Standard Model based on restrictions on the nature of the dark matter of the Universe from the data of high-energy physics and astrophysics” project N-18-12-00213 supported by Russian Science Foundation since 2018.

He is a member of Gravitation and Cosmology, International Journal of Modern Physics D, Symmetry, Particles, Universe, Physics international scientific journals Editorial Board.

Khlopov is the author of 24 books, textbooks and chapters in books. Among them is the “Cosmoparticle Physics” monograph. (, published in 1999 by World Scientific, “Cosmological Pattern of Microphysics in the Inflationary Universe” (, published by Kluwer Academic Publishers in 2004, Basics of Cosmoparticle Physics, published by the URSS in 2004 (2nd edition 2011) and the “Fundamentals of Cosmic Particle Physics” (, published by CISP – Springer in 2012.

Field of research: cosmoparticle physics, dark matter, primordial black holes, elementary particle physics.

What is Сosmoparticle physics?

Cosmoparticle physics is a science that studies the fundamentals of the micro- and macrocosm and their fundamental relationship, manifested in a complex combination of microphysical, astrophysical and cosmological effects. Its appearance is a natural stage in the development of cosmology and elementary particle physics, in which their theoretical constructions and a whole series of fundamental principles are forced to rely on ideas, processes, and phenomena that are inaccessible to direct laboratory verification and require, therefore, indirect actions, including astronomical, research methods.

Answering questions about the causes of cosmological expansion, about the origin of baryonic matter and the existence in the Universe of other, non-baryonic forms of matter, modern cosmology goes beyond the experimentally studied field of physics and inevitably attracts such predictions of the elementary particle theory, the verification of which, in turn, is based on their cosmological effects. The way out from this vicious circle of problems is associated with the cosmo particle physics development. This science genesis reflected the inevitable stage of internal development of both cosmology and elementary particle physics.

What other unexplored observable phenomena are interested in Сosmoparticle physics?

Neutrino mass physics and its cosmological manifestations, physical foundations and possibilities of astronomical search for mirror and shadow matter, unstable massive neutrinos, invisible axion, nonequilibrium fluxes of energetic particles in the Universe and nonequilibrium cosmic nucleosynthesis theory, inhomogeneous baryosynthesis, sources of antinucleons and antimatter domains in baryon asymmetric universe, primordial black holes, a variety of stable and unstable particles of dark matter is far from a complete list of those elements of Сosmoparticle physics analysis, which will allow us to approach a comprehensive study of the Universe and the physical laws that determined its origin, structure and evolution. Particular attention should be paid to the role of domestic research and the heritage of Russian scientific schools in the cosmo particle physics formation, their significance in the context of the world science modern development.

The most serious barrier to the perception of cosmo particle physics is the psychological. It’s research subject is doubly unusual. This science is interested in rare unknown interactions. Rare events or a new interpretation of already known facts is of interest in astronomy. It attracts and excites the imagination like any exotic. To the same extent, one perceives it remotely, precisely as an exotic, bright, catchy, beautiful thing, but giving nothing but a slight excitement, which gives nothing to the mind and heart. The other side of Сosmoparticle physics, which does not fit into the framework of prevailing stereotypes, is the absence of direct experiments to verify its ideas, the need to combine heterogeneous observational and experimental methods for such verification.

It will take billions of years to test the theory of the Universe!

It seems that the usual logic of scientific development, which is the expectation of experimental confirmation of each new theoretical assumption, does not work here, since these assumptions relate to processes in the elementary particles world, which is often inaccessible to laboratory studies, and involve stages of the Universe’s evolution, which one cannot record directly in astronomical observations.

However, these barriers are surmountable. Science assimilates unusual concepts quickly, they become generally accepted and necessary, and the method of testing them only at first glance is strikingly different from the approved methods of laboratory research.

Having arisen on the basis of the ideas of the grand unification of the natural fundamental forces, cosmoparticle physics necessarily combine analysis with synthesis in it’s construction. This is it’s specificity; or perhaps the specificity of it today.

Historically, what developed the relationship of astronomy and physics, and which led to the Сosmoparticle physics origin?

Cosmoparticle physics is a natural result of the internal development of elementary particles physics’ and cosmology. This science origin is due to the merging of two trends – the development of the elementary particles theory, non-trivial manifestations of which are revealed only in processes at ultrahigh energies, and the emergence of ideas about new forms of matter necessary for a self-consistent description of the observed phenomena collection in the Universe. A clear understanding of the relationship between the determination problem of the microworld structure and the foundation problem of the macrocosm structure brought the joint consideration of the micro and macrocosms to a new level, at which these tasks merge, forming a new quality. The microworld structure in the cosmo particle physics is voiced by the harmony of the celestial spheres.

One traces the connection of ideas about the micro- and macrocosm at all stages of their development. Judgments about the universe and its arches, making up a single whole, remained purely speculative for a long time. Such judgments sources were observations and conclusions based on them.

Optical instruments, which armed the eye of the observer, came then. Interestingly, that the same physical principle allows one to approach phenomena depth with a microscope and to expand the worldview with a telescope. There is probably no coincidence that Galileo Galilei was the scientist, who originated both the physical experiment and optical astronomy. The optical astronomy and experimental physics began to develop independently from that moment on. Their specificity was clearly revealed also.

Astronomy was given only a close look at the external manifestations of extraterrestrial objects, the bowels of which are closed to the eyes, to observe the results of processes, the causes and course of which are beyond control. It is possible to fragment the objects of research, digging into their essence in a physical experiment; you can change the initial conditions and control the process. Therefore, it is not surprising that in the relationship between astronomy and physics, scientists paid the increased attention to the development of the latter, which determined both the progress of astronomy and the degree of understanding astronomical results.

Thus, physics investigated the structure of atoms and of their radiation spectra; it armed astronomy with spectral analysis methods. The physical laws of the matter interaction and radiation formed the basis for understanding of the star radiation laws, and the nuclear physics development has opened astronomers the energy sources of this radiation. One can count on fingers responsible astrophysical signs of gratitude to physics. One can mention the discovery of helium from the solar emission lines and the existence of the excitation level in carbon, theoretically predicted to explain the thermonuclear helium combustion in stars among them. It seemed that astrophysics was doomed only to the development of physical laws firmly confirmed in laboratories, to the role of a kind of polygon that refracts the known effects with bizarre combinations of unearthly conditions for the study.

However, the nonstationary Universe appeared in front of Friedman’s mental gaze in the 20s of the XX century, and Hubble’s observation confirmed its variability. In place of the eternal and unchanging Universe, a picture of the Universe has opened, expanding in a finite time from a superdense phase to a modern state.

Thus, astronomy provided physics with a natural accelerator, the scale and significance of which is becoming fully recognized by the particle physics only now. The creation of the unsteady Universe theory was almost a decade ahead of the revolutionary overthrow made in the 1930s in the concept of elementary particles.

The particle physics found a way out of the painful problems associated with the conservation of energy and momentum in beta decay, with a “nitrogen” catastrophe and a mystery of the nucleus structure in rejecting the idea of eternal and unchanging particles, in the transition to ideas about the possibility of their creation and annihilation in processes of their interactions. Another lesson taught in the 1930s was that the number of elementary particles in Nature turned out to be significantly larger than what a simple and economical picture of the structure of matter requires.

Revolutions in elementary particle physics and in the science of the Universe as a whole, cosmology took place in one decade, and although they covered knowledge areas that did not intersect at that time, the proximity in time of these two events was far from being accidental. Awareness of the Universe unsteadiness fact has psychologically prepared a change of ideas about the elementary particles’ properties; there is no place for eternal and unchanging particles in the Universe, which over time radically changes its state. Hence, there is a change of view on the physics foundations, the laws of elementary particles conservation and interaction.

Thus, the electric charge conservation was not a simple consequence of the eternal electrically charged particles’ conservation, but a non-trivial rules determining a strict local balance of the charged particles’ annihilation and creation. The idea of a charge as the electromagnetic interaction measure has also changed from an inherent characteristic of an eternal and unchanging particle to a characteristic of the law of transformation, in which the annihilation of the initial and the creation of the final charged particles were accompanied by the creation or annihilation of the electromagnetic quantum.

This change of mind contained a wealth of room for generalizations. One could describe the laws of nuclear transformations under the influence of strong and weak interactions in a similar way. The particles’ annihilation and birth is accompanied in such transformations by the strong or weak interactions’ field quanta creation and annihilation.

Scientists could have made a logical step towards a uniform description of all fundamental interactions back in the 1930s, but in fact, it took half a century to implement it. The difficulty of the path to a unified description of all interactions was due to the need to combine the similarity of the description with the difference in these interactions observed properties. It was necessary to explain why the weak interaction manifests itself only at small distances, the transformation of which particular particles cause a strong interaction, and with what charges its field quanta interact.

These and other questions answers formed the basis of the electromagnetic, weak and strong interactions modern theory, based on the symmetry of particle transformations and explaining the observed differences in their properties by breaking this symmetry. It was possible by expanding symmetry to move from the different interactions description uniformity to their fundamental unity. Such a step, initially supported by the hope of experimental confirmation of proton decay, and by a rigid, consistent with experimental data, connection of the weak and electromagnetic interactions charges, meant a jump in the theory to the region of super high energies, inaccessible to direct experimental study.

The theory lost direct support in experimental high-energy physics with this step. The theory should have passed from the usual direct experimental verification of its predictions to the indirect manifestations combination analysis of its fundamental constructions. The world of high-energy physics, which hitherto relied on its own experimental capabilities, has opened up all permissible indirect methods of studying hypothetical phenomena, the direct experimental study of which is not possible. In this context, the relationship of the particle physics with cosmology is of particular importance, becoming a necessary pillar of the particle theory development.

This relationship grows into the necessary basis for the modern cosmology development. The expanding universe theory developed relatively independently initially. The electromagnetic radiation’s thermal background discovery in 1965 confirmed the so-called hot model of the expanding Universe put forward by G. Gamov. The current temperature of this radiation is low (2.7K), its energy density is low in comparison with the atoms rest energy density, but, tracing the well-known expansion law, we come to the picture of not only the dense, but also the hot state of the substance with the dominant radiation energy density.

The early Universe’s data is very interesting. Was it “cold” or “hot”?

Simple estimates show that matter and radiation were in thermodynamic equilibrium in the early Universe. The combination of the Universe’s expansion law with the thermodynamics laws made it possible to obtain a logically closed picture of the matter and radiation cosmological evolution, into which elementary particles discovered by high-energy physics introduced only small quantitative corrections. Astronomical observations qualitatively confirmed this picture of the radiation-dominated hot plasma transformation into the modern inhomogeneous matter structure penetrated by uniform background radiation.

Qualitatively internally self-consistent, this picture required, however, the certain initial conditions specification at very high temperatures and densities at very early stages of the Universe expansion, observational information about which is absent. To justify these initial conditions, cosmology should have turned to such predictions of the elementary particles theory that turned out to be inaccessible to laboratory verification.

On the basis of exactly these particle physics notions, which were not verified in laboratories, modern cosmology succeeded in substantiating the causes of expansion and the remarkable homogeneity of the observed part of the Universe, creating a theory of the inflationary Universe, explaining its baryon asymmetry and the nature of small initial inhomogeneities, the development of which led to the formation of the modern Universe large-scale structure, quantitatively coordinate the formation of this structure with the observed relict radiation isotropy.

We achieved these successes of modern cosmology at the cost of attracting hypothetical forms of matter into the theory that determined the dark matter of the Universe at various stages of its evolution. Thus, the modern cosmology fundamentals inaccessible to direct verification in astronomical observations merge with the fundamentals of the modern particle theory inaccessible to direct experience.

Until the particle physics was limited to the study of individual transformations of known elementary particles, an appeal to the world as a whole seemed unnecessary in its theoretical constructions. On the other hand, knowledge of the Universe’s general evolution laws at first glance also had little in common with detailed representations of elementary particles individual processes.

What is the elementary particle physics role in the theory of the Universe origin and its structure?

Turning to the foundations of both particle symmetry and the Universe expansion initial conditions, we find an inextricable link between elementary particle physics and cosmology. There is a single foundation for the micro- and macrocosm. The study of this single foundation in all the variety of its manifestations is the cosmo particle physics subject.

On the way to a unified description of the micro- and macrocosm structure, cosmoparticle physics naturally combines theoretical studies, a computational experiment, and all possible methods of obtaining indirect information in laboratory experiments and astronomical observations.

These constituent elements of Cosmoparticle physics are based on the experimental methods development progress not only in high-energy physics, but also in cosmology. The high, literally “astronomical” accuracy of determining the Universe expansion parameters, its structure and evolution allows us to speak of the onset of a “precision cosmology” era. The discovery of gravitational waves complements the Universe study based on data on cosmic rays, on cosmic radiation in various spectral bands (from radio waves to gamma rays), and on cosmic neutrino fluxes. This paves the way for “multi-messenger” astronomy, which will provide a comprehensive understanding of the structure of astronomical objects and astrophysical processes in them.

How much do Large Hadron Collider experiments contribute to cosmo particle physics research?

The current situation’s paradox is that, although the modern cosmology physical foundations are based on the elementary particles’ standard model extensions, the Large Hadron Collider experiments do not yet yield positive results for the search for new effects (for example, new particles) predicted in popular versions of such extensions.

Historical experience, however, shows that Nature never justifies our simplest ideas about new phenomena in it. Therefore, the fact that we live in a Universe filled with 95% unknown matter and energy forms gives us confidence that the cosmo particle physics methods will allow us to approach their physical nature and master the power of these new fundamental forces of Nature.

Interview: Ivan Stepanyan

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