MEETINGS AND CONFERENCES

TBILISI CONFERENCE ON THEORETICAL PHYSICS

From October 26 to 29, 1955, a conference on theoretical physics was held in Tbilisi. This conference, organized by the Institute of Physics of the Academy of Sciences of the Georgian SSR together with the theorists of the Physics Institute of the Tbilisi State University named after I. V. Stalin, was attended by theorists from Moscow, Kharkov, and Yerevan, as well as theoretical physicists from other cities of the Georgian SSR. Four plenary sessions were held, at which 17 papers were heard; among all the papers, six were read by Tbilisi theorists, seven by theorists from Moscow, and one paper each by theorists from Kharkov and Yerevan.

The conference was devoted mainly to three problems: nuclear theory, quantum electrodynamics and the theory of elementary particles, and the theory of the solid state.

The paper by G. R. Khutsishvili was devoted to considering the question of what data can be obtained by carrying out experiments with oriented nuclei. Investigation of the angular distribution of β- and γ-radiation from oriented nuclei makes it possible to determine the magnetic moments of β-active nuclei. Investigation of reactions between polarized nuclei and polarized nucleons makes it possible to obtain information on the spin dependence of nuclear forces and on the spins of composite nuclei. The speaker, in particular, presented the results of a calculation he had carried out of the angular distribution of β-particles for a β-transition \(\Delta I = \pm 2ga\). It was shown that polarization of the nuclei of ferromagnetic atoms can be achieved by applying to a ferromagnet, cooled to ultralow temperature, a magnetic field exceeding the saturation field. A calculation made by the author shows that the probability of reorientation of the proton spin upon ionization of a hydrogen atom by electron impact is small.

In the paper by Ya. A. Smorodinsky, the question is clarified of the number of experiments required, in the case of unpolarized targets, to obtain complete information about the amplitude of proton–proton scattering. This amplitude is determined by five complex functions. The analyticity condition for these functions gives a relation between their moduli and phases, so that in the general case the number of experiments is five. If the interaction does not depend on the velocity, then the number of required experiments is reduced to three. In this case relations are established between the cross sections. In the relativistic region the number of required experiments increases.

The paper by V. B. Berestetsky was devoted to consideration of certain properties of μ-mesons in connection with the limits of applicability of quantum electrodynamics. As was shown by Landau and Pomeranchuk, modern quantum field theory is untenable at distances smaller than a certain critical one.

lengths of the order of \(10^{-13}\)—\(10^{-14}\) cm. A calculation has been carried out of the magnetic moment of the \(\mu\)-meson. It turns out that if the \(\mu\)-meson is not characterized by interactions stronger than electromagnetic ones, then any deviation of its magnetic moment from the Dirac value serves as an indication of the magnitude of the critical length. A calculation has been carried out of the process of conversion of an electron-positron pair into a meson pair. The cross section of this process turns out to be equal to \(5\cdot 10^{-31}\,\text{cm}^2\) per atom.

The report by N. M. Polievktov-Nikoladze was devoted to the application of functional methods in quantum electrodynamics. A closed expression was constructed for the generating functional, with the aid of which all Green’s functions in quantum electrodynamics can be found. A rigorous renormalization of the charge was carried out without using perturbation theory, and it was shown that the experimental charge is not equal to zero only if the bare charge is assigned, in a suitable way, a chosen infinitely small imaginary value. The Green’s function for the photon was calculated. The result of Landau, Abrikosov, and Khalatnikov was obtained, but by a simpler method.

The report by V. L. Ginzburg was devoted to the present state of experimental tests of the general theory of relativity.

V. I. Mamasakhlisov and G. A. Chilashvili, in their report, introduce the hypothesis that, for small \(Z\), the atomic nucleus may be regarded as consisting of deuterons, tritons, and \(\alpha\)-particles. On the basis of this hypothesis, a number of features in the distribution of isotopes of atomic nuclei are explained. Then, conclusions from the formula for the density of nuclear levels, based on the gas model, are compared with experimental data obtained from an analysis of the effective cross sections for the capture of neutrons by a nucleus. It is shown that, in order to achieve agreement between theory and experiment, it is necessary to assume that the effective number of particles in the nucleus is two to three times smaller than the number of nucleons. This fact testifies in favor of the model described above. On the basis of this model, the cross sections of certain reactions were calculated, with agreement with the experimental data proving satisfactory.

The report by T. I. Kopaleishvili was devoted to the calculation of the \((d,t)\)-reaction on \(\mathrm{Be}^9\) and \(\mathrm{C}^{13}\). It is assumed that the unpaired neutron moves in an oscillator field created by the core of the nucleus. It is assumed that the incident deuteron interacts only with the unpaired neutron. The calculation was carried out in the Born approximation. The agreement of the angular distribution with the experimental data in the range of angles \(0\)—\(50^\circ\) is satisfactory.

In the report by M. I. Kobiashvili, a calculation was presented of the cross section for the electrodisintegration of a nucleus, in which the electron undergoes inelastic scattering and a nucleon flies out of the nucleus. Excitation functions of the nucleus were obtained for electric and magnetic dipole transitions. Further calculations were carried out according to the model of independent particles. The angular distribution of the scattered electrons and the integral cross section for electrodisintegration for dipole transitions were obtained.

The report by M. L. Ter-Mikaelyan was devoted to the quantum-mechanical calculation of inelastic collisions of fast particles with atoms. Macroscopic Maxwell equations were used, which makes it possible to take into account the influence of the medium. The following questions were analyzed: the separation of losses into near and distant ones, the possibility of introducing a dielectric constant, total energy losses, Cherenkov radiation, and others.

In the report by M. M. Mirianashvili, the incorrectness was shown of Caianiello’s assertion concerning the commutativity of the operators of space and time inversion and of the charge-conjugation operator in the case of fermions. Consideration of the Kronecker product of spinors and of its irreducible parts indicates the possibility of constructing field quantities differing...

of ordinary scalars, vectors, pseudoscalars, etc., by their transformation properties under inversion of space and time (reducing to multiplication by \(\pm i\)).

V. V. Chavchanidze’s report was devoted to a new method of introducing nonlinear interaction into the equations of boson-fermion fields. It is assumed that the nucleon is a complex particle and that the neutron—nucleoid—is described by the Dirac equation. To describe \(\pi\)-mesons that are neutral with respect to the electromagnetic interaction, conjugate field functions are introduced. This conjugation does not coincide with ordinary complex conjugation. In the general case the field functions are assumed to be quaternions. The inclusion of interaction proceeds analogously to how this is done in electrodynamics. A Lagrangian for the system of nucleons and mesons is constructed; some consequences of this Lagrangian are derived and the difficulties are analyzed.

In the report by I. M. Khalatnikov, Green’s functions in quantum electrodynamics were represented in the form of continual integrals in the space of functions of both the photon and spinor fields. In doing this, one has to overcome a difficulty connected with the integration of functions depending on noncommuting variables. Expressions were obtained for the mean vacuum value of the \(S\)-matrix and for the Green’s function of the one-electron problem.

The report by L. D. Landau, A. A. Abrikosov, and I. M. Khalatnikov was devoted to the study of liquid helium-3 at low temperatures. A functional relation was obtained between the energy of a Fermi excitation and the distribution function. Using experimental data on the temperature dependence of the heat capacity of helium-3, one can find the dependence of the Fermi-excitation energy on momentum, and then determine the magnetic moment, viscosity, and thermal conductivity of helium-3. In particular, the viscosity of helium-3 should be proportional to \(\frac{1}{T^2}\) at low temperatures (below the temperature at which Fermi degeneracy is removed) and constant at high temperatures.

The thermal conductivity of helium-3 should be proportional to \(\frac{1}{T}\) at low temperatures and to \(T\) at high temperatures; i.e., the thermal conductivity of helium-3 should have a minimum in an intermediate region. In addition, it is established that helium-3 should possess a second viscosity.

The report by I. A. Mirtskhulava was devoted to the kinetics of formation and relaxation of nonequilibrium centers when a semiconductor is illuminated by light. Stationary and relaxation solutions were found for the corresponding kinetic equation for electronic, hole, and mixed semiconductors. From the stationary and relaxation solutions one finds the change with time in the number of various centers under illumination of the semiconductor. The recombination coefficients are calculated according to Pekar’s theory.

In the report by E. M. Lifshitz, a theory was developed of the molecular forces of attraction between arbitrary bodies whose surfaces are brought close to small distances. In this treatment, the interaction of bodies is regarded as being effected by means of a fluctuating electromagnetic field. A general formula was obtained that determines the force of attraction at any distances; moreover, to calculate this force it is necessary to know only the dielectric properties of the bodies. The question of the influence of temperature on the forces of attraction was considered.

The report by Yu. V. Chkhartishvili was devoted to calculating the curve of \(F\)-absorption in mixed alkali-halide crystals. In these mixed crystals there can occur seven different types of \(F\)-centers. In experiment, the \(F\)-band is a superposition of \(F\)-bands corresponding to different types of \(F\)-centers. The calculations were carried out according to Pekar’s theory.

The report by I. M. Lifshitz, M. Ya. Azbel, and M. I. Kaganov was devoted to the theory of galvanomagnetic phenomena in metals; no assumptions are made about the dispersion law of conduction electrons or about the form of the collision integral. A solution of the kinetic equation in strong magnetic fields was found, and with its help the value of the conductivity tensor was calculated. It was shown that the dependence of the resistance on the magnetic field and on temperature is essentially determined by the topology of the Fermi surface. The character of the dependence of the conductivity on the magnetic field makes it possible to obtain information about the energy spectrum of the electrons.

Most of the reports provoked lively discussion.

In the closing remarks, V. I. Mamasakhlisov and Ya. A. Smorodinsky emphasized the important role that the conference should play in the further development of theoretical physics in Georgia, as well as in establishing close scientific contact between the theoreticians of Georgia and those of other republics of the Soviet Union.

G. R. Khutsishvili