Search

Self-conjugate nuclei in the A≈70–80 region have attracted a great deal of attention due to phenomena such as shape coexistence and increasing collectivity along the N=Z line. We investigate the structure of nuclei in this region through lifetime measurements using the GRETINA array. The first implementation of the Differential Recoil Distance Doppler Shift technique with fast radioactive beams is demonstrated and verified through a measurement of the well-known B(E2;21+→01+) transition strength in 74Kr. The method is then applied to determine the B(E2;21+→01+) transition strength in 74Rb, the heaviest odd–odd N=Z nucleus for which this quantity has been determined. This result and extended systematics along N=Z suggest the dominance of the isoscalar part of the quadrupole transition strengths in self-conjugate nuclei, as well as the possible presence of shape coexistence in 74Rb.

Self-conjugate nuclei in the A≈70–80 region have attracted a great deal of attention due to phenomena such as shape coexistence and increasing collectivity along the N=Z line. We investigate the structure of nuclei in this region through lifetime measurements using the GRETINA array. The first implementation of the Differential Recoil Distance Doppler Shift technique with fast radioactive beams is demonstrated and verified through a measurement of the well-known B(E2;21+→01+) transition strength in 74Kr. The method is then applied to determine the B(E2;21+→01+) transition strength in 74Rb, the heaviest odd–odd N=Z nucleus for which this quantity has been determined. This result and extended systematics along N=Z suggest the dominance of the isoscalar part of the quadrupole transition strengths in self-conjugate nuclei, as well as the possible presence of shape coexistence in 74Rb.

A new route to the Dirac equation and its symmetries is outlined on the basis of the four-vector representation of the Lorentz group (LG). This way permits one to linearize the first Casimir operator of the LG in terms of the energy–momentum four-vector and enables one to derive an extended Dirac equation that naturally reveals the S U (2) symmetry in connection with an isospin associated with the LG. The procedure gives a spin-one-half fermion doublet, which we interpret as the electron and neutrino or the up-and-down quark doublet. Similarly, the second Casimir operator can be linearized by invoking an abstract isospin that is not connected with the LG, but with the two basic empirical fermion types. Application of the spinor helicity formalism yields two independent singlet and triplet fermion states—which we interpret as being related to U (1) and the lepton, respectively—to the S U (3) symmetry group of the three colors of the quarks. The way in which we obtain these results indicates the genuine yet very different physical natures of these basic symmetries. This new notion does not need the idea of grand unification. However, by still combining them in the product group S U (4) = S U (3) ⊗ U (1) and then further combining all groups into S U (2) ⊗ S U (4) , one may get a symmetry scheme that perhaps supports the notion of unification by the group S U (8) . We also argue that the simpler S O (4) group—instead of S U (4) —seems more appropriate for achieving unification. [ABSTRACT FROM AUTHOR]

Theoretical analysis of three exclusive decays, Bc→ψ(′)+R, where R=K+4π, KK+3π, or 7π, is given. Using the factorization method and the resonance approximation (methods proved to be very useful in the analysis of some other similar decays), we have obtained analytical expressions of the required amplitudes and created distributions over some interesting mass combinations. Presented results could be used for comparison with forthcoming experimental data and better understanding of the nature of heavy quarkonia.

For large isospin asymmetries, perturbation theory predicts the quantum chromodynamic (QCD) ground state to be a superfluid phase of u and d ¯ Cooper pairs. This phase, which is denoted as the Bardeen-Cooper-Schrieffer (BCS) phase, is expected to be smoothly connected to the standard phase with Bose-Einstein condensation (BEC) of charged pions at μ I ≥ m π / 2 by an analytic crossover. A first hint for the existence of the BCS phase, which is likely characterised by the presence of both deconfinement and charged pion condensation, comes from the lattice observation that the deconfinement crossover smoothly penetrates into the BEC phase. To further scrutinize the existence of the BCS phase, in this article we investigate the complex spectrum of the massive Dirac operator in 2+1-flavor QCD at nonzero temperature and isospin chemical potential. The spectral density near the origin is related to the BCS gap via a generalization of the Banks-Casher relation to the case of complex Dirac eigenvalues (derived for the zero-temperature, high-density limits of QCD at nonzero isospin chemical potential).

A new route to the Dirac equation and its symmetries is outlined on the basis of the four-vector representation of the Lorentz group (LG). This way permits one to linearize the first Casimir operator of the LG in terms of the energy–momentum four-vector and enables one to derive an extended Dirac equation that naturally reveals the SU(2) symmetry in connection with an isospin associated with the LG. The procedure gives a spin-one-half fermion doublet, which we interpret as the electron and neutrino or the up-and-down quark doublet. Similarly, the second Casimir operator can be linearized by invoking an abstract isospin that is not connected with the LG, but with the two basic empirical fermion types. Application of the spinor helicity formalism yields two independent singlet and triplet fermion states—which we interpret as being related to U(1) and the lepton, respectively—to the SU(3) symmetry group of the three colors of the quarks. The way in which we obtain these results indicates the genuine yet very different physical natures of these basic symmetries. This new notion does not need the idea of grand unification. However, by still combining them in the product group SU(4)=SU(3)⊗U(1) and then further combining all groups into SU(2)⊗SU(4), one may get a symmetry scheme that perhaps supports the notion of unification by the group SU(8). We also argue that the simpler SO(4) group—instead of SU(4)—seems more appropriate for achieving unification.

The collective Hamiltonian including isovector pairing and α -particle-type correlation degrees of freedom is constructed. The Hamiltonian is applied to description of the relative energies of the ground states of even–even nuclei around 5 6 Ni. A satisfactory description of the experimental data is obtained. A significant improvement of the agreement with the experimental data compared to our previous calculations is explained by inclusion in the Hamiltonian of the dynamical variables describing α -particle-type correlations. [ABSTRACT FROM AUTHOR]