Extending the limits of nuclear landscape via new physical mechanisms*

   The detailed investigation of new physical mechanisms which allow to extend the boundaries of

the nuclear landscape beyond the traditional limits has been performed over recent years.  In the region

of hyperheavy (Z>126) nuclei, the transition from ellipsoid-like nuclear shapes to toroidal ones

provides a substantial increase of nuclear landscape [1-3].  Rotational excitations in the nuclei

near proton and neutron drip lines provide an alternative mechanism for an extension of the nuclear

landscape beyond the  limits defined at spin zero [4,5]. In both cases, the collective coordinates related

to nuclear shapes play an important role in extending nuclear landscape.  In hyperheavy nuclei, they

drive the nuclear systems from ellipsoidal-like to toroidal shapes. In rotating  nuclei, triggered by

particle-hole excitations they transform the system from spherical or normal deformed ground 

states to extremely elongated  (super-,  hyper and mega-deformed) shapes or rotation-induced

proton halos at high spins. Rotational frequency acts as an additional collective degree of freedom

(coordinate) in rotating nuclei. At the microscopic level, the impact  of these collective coordinates drives

the single-particle orbitals, which are otherwise located at positive energy in a given nucleonic

configuration, below the  continuum  threshold. As a consequence, it allows to extend the limits of nuclear 

landscape beyond  traditional limits (for example, beyond spin-zero drip lines in rotating nuclei). The

similarities and differences of these mechanisms  will be discussed. The roles of underlying single-particle

and shell structures will be analyzed.