Collective P-and T-odd moments produced by parity and time invariance violating forces in reflection asymmetric nuclei are considered. The enhanced collective Schiff, electric dipole and octupole moments appear due to the mixing of rotational levels of opposite parity. These moments can exceed singleparticle moments by more than two orders of magnitude. The enhancement is due to the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. In turn these nuclear moments induce enhanced T-and P-odd effects in atoms and molecules. First a simple estimate is given and then a detailed theoretical treatment of the collective T-, P-odd electric moments in reflection asymmetric, odd-mass nuclei is presented and various corrections evaluated. Calculations are performed for octupole deformed long-lived odd-mass isotopes of Rn, Fr, Ra, Ac and Pa and the corresponding atoms. Experiments with such atoms may improve substantially the limits on time reversal violation.

Parity and time invariance violating forces produce collective P-and T-odd moments in nuclei with static octupole deformation. Collective Schiff moment, electric octupole and dipole and also magnetic quadrupole appear due to the mixing of rotational levels of opposite parity and can exceed singleparticle moments by more than a factor of 100. This enhancement is due to two factors, the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. The above moments induce T-and P-odd effects in atoms and molecules. Experiments with such systems may improve substantially the limits on time reversal violation.Parity and time invariance nonconserving nuclear moments induced by P-, T-odd nuclear forces were discussed e.g. in Refs. [1][2][3][4][5][6]. These moments can be enhanced in nuclei which have close to the ground state (g.s.) levels of the same spin as the g.s. but opposite parity [3,4]. An interesting possibility to enhance the effect is to consider mechanisms producing collective T-, P-odd moments. In Ref. [7] it was shown that the "spin hedgehog" mechanism produces a collective magnetic quadrupole. In the present paper we want to consider a different mechanism: mixing of opposite parity rotational levels (parity doublets) by T-, Podd interaction in the nuclei with octupole deformation. This deformation was demonstrated to exist in nuclei from the Ra-Th and Ba-Sm region and produces such effects as parity doublets, large dipole and octupole moments in the intrinsic frame of reference and enhanced E1 and E3 transitions (see review [8]).Let us start our consideration from the expression for the electrostatic potential of a nucleus screened by the electrons of the atom. If we consider only the dipole T-, P-odd part of screening (Purcell-Ramsey-Schiff theorem [9]) one finds [4]: 1

In view of the recent experiments on neutrino oscillations performed by the LSND and KARMEN collaborations as well as of future experiments, we present new theoretical results of the flux averaged 12 C(νe, e − ) 12 N and 12 C(νµ, µ − ) 12 N cross sections. The approaches used are charge-exchange RPA, charge-exchange RPA among quasi-particles (QRPA) and the Shell Model. With a large-scale shell model calculation the exclusive cross sections are in nice agreement with the experimental values for both reactions. The inclusive cross section for νµ coming from the decay-in-flight of π + is 15.2 × 10 −40 cm 2 (when Hartree-Fock wavefunctions are used), to be compared to the experimental value of 12.4 ± 0.3 ± 1.8 × 10 −40 cm 2 , while the one due to νe coming from the decay-at-rest of µ + is 16.4 × 10 −42 cm 2 which agrees within experimental error bars with the measured values. The shell model prediction for the decay-in-flight neutrino cross section is reduced compared to the RPA one, namely 19.2 × 10 −40 cm 2 . This is mainly due to the different kind of correlations taken into account in the calculation of the spin modes (in particular, because of the quenching in the 1 + channel) and partially due to the shell-model configuration basis which is not large enough, as we show using arguments based on sum-rules. Results for exclusive and inclusive muon capture rates and beta decay are given and are close to the experimental findings.

The phenomenon of super-radiance (Dicke effect, coherent spontaneous radiation by a gas of atoms coupled through the common radiation field) is well known in quantum optics. The review discusses similar physics that emerges in open and marginally stable quantum many-body systems. In the presence of open decay channels, the intrinsic states are coupled through the continuum. At sufficiently strong continuum coupling, the spectrum of resonances undergoes the restructuring with segregation of very broad super-radiant states and trapping of remaining long-lived compound states. The appropriate formalism describing this phenomenon is based on the Feshbach projection method and effective non-Hermitian Hamiltonian. A broader generalization is related to the idea of doorway states connecting quantum states of different structure. The method is explained in detail and the examples of applications are given to nuclear, atomic and particle physics. The interrelation of the collective dynamics through continuum and possible intrinsic many-body chaos is studied, including universal mesoscopic conductance fluctuations. The theory serves as a natural framework for general description of a quantum signal transmission through an open mesoscopic system.

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