abstract

It is shown in the framework of the affine theory of gravitation that the surface of a neutron star differs slightly from sphere because of the contact spin–spin interaction of polarized neutrons.

abstract

In this paper, the point of view is stressed that the total four momentum must primarily be defined with respect to a certain set of spacelike hypersurfaces which do not intersect. Each total four momentum defined with respect to a single hypersurface can then be handled like a free vector under affine transformations of coordinates, It may be possible that the total four momentum does not depend on the choice of a certain hypersurface from this set, which means a conservation law. This set of hypersurfaces is the main ingredient of the frame of reference. Replacing such a set of spacelike hypersurfaces by another, whose elements intersect those of the former one, is in principle equivalent to changing the frame of reference. It is also, on the other hand, possible that certain sets of spacelike hypersurfaces be equivalent, which means the principle of relativity. Then the problem is whether the total four momentum can be defined in the same way with respect to different frames of reference and whether it behaves like a four Vector under the invariance group of mappings between the equivalent frames of reference. Not for all energy-momentum tensors the answer to this is affirmative. Several examples are discussed. They demonstrate the difference between such concepts as a transformation of coordinates and changing the frame of reference.

abstract

We consider the generation of the D\(^{\ast }\) by the exchange of a p meson in the crossed channel in an \(N/D\) determinantal approach. The D\(^{\ast }\) width turns out to be 56 keV.

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Within the framework of the impulse approximation and the intermediate coupling shell model we have calculated the cross sections for the \(\gamma ^6\)Li \(\to \pi ^0\,^6\)Li\(^{\ast }(\varepsilon )\) partial reactions for the levels of the \(^6\)Li nucleus with the excitation energies \(\varepsilon = 0.0\), 2.18, 3.56, 4.27 and 5.37 MeV and also for the \(\gamma ^6\)Li \(\to \pi ^0\,^6\)Li \(^{\ast }(\varepsilon )\to \pi ^0\gamma ^{\prime 6}\)Li two-step processes at \(\varepsilon = 3.56\) and 5.37 MeV. It is shown that the reactions with a change in the nuclear isospin turn out to be suppressed in the energy region of the photoexcitation of the first and second nucleon resonances where the isoscalar amplitudes of photoproduction on a nucleon are small. The possibility of using the described processes to extract an additional information on the single-nucleon photoproduction amplitudes and on the nuclear structure is discussed.

abstract

Differential cross-section and polarisation data for the pair of line reversed reactions \(\pi ^+\)p \(\to \) K\(^+ \Sigma ^+\) and K\(^-\)p \(\to \) \(\pi ^-\Sigma ^+\) is analysed in the range \(p_{\rm lab} \geq \) 7 GeV/\(c\) and \(|t| \leq 1\) (GeV/\(c)^2\) using non degenerate K\(^{\ast }\)–K\(^{\ast \ast }\) trajectories. The K\(^{\ast }\) residues are taken to be peripheral in impact-parameter space while the K\(^{\ast \ast }\) residue is taken as non-peripheral in nature. It is found that, contrary to popular belief, a satisfactory fit to the data can be obtained without invoking Regge cut terms. Comparison of our results with several models is made.

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We reanalyse critically the suggestion of using hypothetical heavy stable particles for industrial catalysis of nuclear fusion reactions at low temperatures.

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The principles of detectors are discussed following the list of the basic quantities to be measured by experiment: position, time and identity, energy and momentum.

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The convergence of the linked graph expansion for the binding energy of \(^{40}\)Ca is discussed in the 2\(\hslash \omega \) model space. It is found that when the lowest energy of the 2\(\hslash \omega \) states matrix is above the closed shell energy the expansion can be always made convergent. Under this condition, the first few terms of the expansion can be used to approximate the full result even if the expansion is not convergent.