[en] The N-quantum approximation (NQA) method is examined in the light of its application to bound state problems. Bound state wave functions are obtained as expansion coefficients in a truncated Haag expansion. From the equations of motion for the Heisenberg field and the NQA expansion, an equation satisfied by the wave function is derived. Two different bound state systems are considered. In one case, the bound state problem of two identical scalars by scalar exchange is analyzed using the NQA. An integral equation satisfied by the wave function is derived. In the nonrelativistic limit, the equation is shown to reduce to the Schroedinger equation. The equation is solved numerically, and the results compared with those obtained for this system by other methods. The NQA method is also applied to the bound state of two spin 1/2 particles with electromagnetic interaction. The integral equation for the wave function is shown to agree with the corresponding Bethe Salpeter equation in the nonrelativistic limit. Using the Dirac (4 x 4) matrices the wave function is expanded in terms of structure functions and the equation for the wave function is reduced to two disjoint sets of coupled equation for the structure functions

[en] Superstring theories lead to supersymmetric E₆ based models which contain exotic charge -1/3 quarks, h. We find that if the h mixes with the b quark then CP-violation and mixing are dramatically affected. (author). 9 refs

[en] Ksub(L)-Ksub(S) mass difference and the CP violation parameter, epsilon, of the K₀-K₀ system are used to set bounds on the right-handed Cabibbo-like angle and the CP violating phase angle in the left-right symmetric electroweak model of four quarks. The corresponding mixing and phase angles in typical left-right asymmetric models (gsub(L)not=gsub(R)) are also determined. (author)

[en] The question of low energy restoration of parity is examined using a left-right asymmetric model implied by the gauge group SU(2)sub(L)xSU(2)sub(R)xU(1)sub(B-L) with gsub(L)>gsub(R), both from a phenomenological point of view and also exploiting the possibility that such an asymmetry may be a consequence of two-stage symmetry breaking of SU(2)sub(R) allowed in the SU(16) grand unification scheme. We carry out all the charged and neutral current tests with somewhat increased errors of the measured values of neutral current parameters. The phenomenological asymmetric model passes all the tests permitting 1<=(gsub(L)/gsub(R))²<=2 and 0.23<=sin²thetasub(w)<=0.29, where the case gsub(L)/gsub(R)=1 corresponds to the symmetric model investigated by Rizzo and Senjanovic. Whereas low-energy parity restoration and low mass gauge bosons may be possible in the symmetric model, the phenomenological asymmetric model allows a low mass right-handed charged gauge boson (86-230 GeV) and a low mass neutral boson (190-455 GeV), in addition to the two gauge bosons of first generation, but no parity restoration. It is shown that all the results of analysis of the phenomenological asymmetric model, for the case of no mixing between left- and right-handed charged gauge bosons still hold true in the case where the left-right asymmetry arises out of two stage symmetry breaking of SU(2)sub(R) allowed by SU(16) grand unification, but only with the replacement of the charged right-handed boson by a heavier one (>10⁴ GeV). The SU(16) interpretation of left-right asymmetry and the available charged and neutral current data allow the second neutral boson to be observed, together with the two gauge bosons of first generation, but no restoration of parity at ISABELLE energies. However, the parity restoration, if any, may be possible at energies > or approx. 10⁴ GeV. Several other observable distinctions of the asymmetric model from the standard one and the symmetric model are pointed out

[en] We present a complete calculation of the lowest-order gluino-induced corrections to the weak form factors. In an exact supersymmetric theory the two tensorial form factors cancel out. In a realistically broken supersymmetry these corrections turn out to be small and possibly inadequate to bring out the signature of supersymmetry

[en] Deuteron disintegration by reactor antineutrinos is examined in the light of neutrino oscillations. Different spectra are compared and recent experimental results are used to set limits on the mass squared difference and mixing angle of a two neutrino system. (orig.)

[en] Superstring theories lead to supersymmetric E₆ based models which contain exotic charge -1/3 quarks, h. We find that if the h mixes with the b quark then CP-violation and mixing is dramatically affected. (orig.)

[en] It is shown that the assertion that some recently obtained new solutions are of lower energy than the magnetic dipole solutions is unjustified. (orig.)

[en] Ksub(L)-Ksub(S) mass difference and the CP violation parameter, epsilon, of the K₀- anti K₀ system are used to set bounds on the right-handed Cabibbo-like angle and the CP violating phase angle in the left-right symmetric electroweak model of four quarks. The corresponding mixing and phase angles in typical left-right asymmetric models (gsub(L)not=gsub(R)) are also determined. (orig.)

[en] Experimental results on the inverse β decay of the proton are interpreted in terms of neutrino oscillations to set limits on the difference in (mass)² and mixing angle of a two-neutrino system. (author)