An investigation of PT -symmetry breaking in tight-binding chains

We consider non-Hermitian PT -symmetric tight-binding chains where gain/loss optical potentials of equal magnitudes ±iγ are arbitrarily distributed over all sites. The main focus is on the threshold γ c beyond which PT -symmetry is broken. This threshold generically falls off as a power of the chain length, whose exponent depends on the configuration of optical potentials, ranging between 1 (for balanced periodic chains) and 2 (for unbalanced periodic chains, where each half of the chain experiences a non-zero mean potential). For random sequences of optical potentials with zero average and finite variance, the threshold is itself a random variable, whose mean value decays with exponent 3/2 and whose fluctuations have a universal distribution. The chains yielding the most robust PT -symmetric phase, i.e. the highest threshold at fixed chain length, are obtained by exact enumeration up to 48 sites. This optimal threshold exhibits an irregular dependence on the chain length, presumably decaying asymptotically with exponent 1, up to logarithmic corrections.

An investigation of the elastic scattering of 17O projectiles by different target nuclei using the CDCC method

The Continuum Discretized Coupled Channels (CDCC) method is a convenient method that was developed in order to examine weakly bound nuclei. For this purpose, the elastic scattering data of 17 O projectile for 90 Zr, 124 Sn and 208 P b target nuclei were investigated at 340 MeV using the CDCC method. In calculations using this method, 17 O projectiles were taken to be .Optical potentials were selected as the interaction potentials. It was seen that the results obtained were compatible with the experimental data. The effects of excited channels in all three systems were also determined.