• Asiri Nanayakkara

      Articles written in Pramana – Journal of Physics

    • Higher-order semiclassical energy expansions for potentials with non-integer powers

      Asiri Nanayakkara

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      In this paper, we present a semiclassical eigenenergy expansion for the potential |x|α when α is a positive rational number of the form2n/m (n is a positive integer and m is an odd positive integer). Remarkably, this expansion is found to be identical to the WKB expansion obtained for the potentialxN(N-even), if2n/m is replaced byN. Taking the limitm → 2 of the above expansion, we obtain an explicit asymptotic energy expansion of symmetric odd power potentials |x|2j+1 (j- positive integer). We then show how to develop approximate semiclassical expansions for potentials |x|α when α is any positive real number.

    • Application of Lie transform perturbation method for multidimensional non-Hermitian systems

      Asiri Nanayakkara

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      Three-dimensional non-Hermitian systems are investigated using classical perturbation theory based on Lie transformations. Analytic expressions for total energy in terms of action variables are derived. Both real and complex semiclassical eigenvalues are obtained by quantizing the action variables. It was found that semiclassical energy eigenvalues calculated with the classical perturbation theory are in very good agreement with exact energies and for certain non-Hermitian systems second-order classical perturbation theory performed better than the secondorder Rayleigh–Schroedinger perturbation theory.

    • Effects of complex parameters on classical trajectories of Hamiltonian systems

      Asiri Nanayakkara Thilagarajah Mathanaranjan

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      Anderson et al have shown that for complex energies, the classical trajectories of real quartic potentials are closed and periodic only on a discrete set of eigencurves. Moreover, recently it was revealed that when time is complex $t(t = t_r e^{i\theta_\tau})$, certain real Hermitian systems possess close periodic trajectories only for a discrete set of values of $\theta_\tau$. On the other hand, it is generally true that even for real energies, classical trajectories of non-PT symmetric Hamiltonians with complex parameters are mostly non-periodic and open. In this paper, we show that for given real energy, the classical trajectories of complex quartic Hamiltonians $H = p^2 + ax^4 + bx^k$ (where 𝑎 is real, 𝑏 is complex and $k = 1$ or 2) are closed and periodic only for a discrete set of parameter curves in the complex 𝑏-plane. It was further found that given complex parameter 𝑏, the classical trajectories are periodic for a discrete set of real energies (i.e., classical energy gets discretized or quantized by imposing the condition that trajectories are periodic and closed). Moreover, we show that for real and positive energies (continuous), the classical trajectories of complex Hamiltonian $H = p^2 + \mu x^4$, ($\mu= \mu_r$ e$^{i\theta}$) are periodic when $\theta = 4 \tan^{−1}$[($n/(2m + n)$)] for $\forall n$ and $m \epsilon \mathbb{Z}$.

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