Searcharxiv⌕ Search

arXiv subjects

Luca Salasnich

Publications and source records attributed to Luca Salasnich.

At least 181 records · Page 10Linked to original sources
arXiv1998

Classical and Quantum Perturbation Theory for two Non--Resonant Oscillators with Quartic Interaction

We study the classical and quantum perturbation theory for two non--resonant oscillators coupled by a nonlinear quartic interaction. In particular we analyze the question of quantum corrections to the torus quantization of the classical perturbation theory (semiclassical mechanics). We obtain up to the second order of perturbation theory an explicit analytical formula for the quantum energy levels, which is the semiclassical one plus quantum corrections. We compare the "exact" quantum levels obtained numerically to the semiclassical levels studying also the effects of quantum corrections.

quant-ph↗
arXiv1998

Structure and stability of bosonic clouds: alkali atoms with negative scattering length

We investigate the form and stability of a cloud of atoms confined in a harmonic trap when the scattering length is negative. We find that, besides the known low density metastable solution, a new branch of Bose condensate appears at higher density when non locality effects in the attractive part are taken into account. The transition between the two classes of solutions as a function of the number $N$ of atoms can be either sharp or smooth according to the strength and range of the attractive interaction. Use of tight traps is favorable for investigating the evolution of the system as the strength of the effective interaction increases with $N$.

cond-mat↗
arXiv1998

Reply to a Comment on "the Role of Dimensionality in the Stability of a Confined Condensed Bose Gas"

As pointed out by the authors of the comment quant-ph/9712046, in our paper quant-ph/9712030 we studied in detail the metastability of a Bose-Einstein Condensate (BEC) confined in an harmonic trap with zero-range interaction. As well known, the BEC with attractive zero-range interaction is not stable but can be metastable. In our paper we analyzed the role of dimensionality for the metastability of the BEC with attractive and repulsive interaction.

quant-ph↗
arXiv1997

The Role of dimensionality in the stability of a confined Bose gas

We study analytically the ground-state stability of a Bose-Einstein condensate (BEC) confined in an harmonic trap with repulsive or attractive zero-range interaction by minimizing the energy functional of the system. In the case of repulsive interaction the BEC mean radius grows by increasing the number of bosons, instead in the case of attractive interaction the BEC mean radius decreases by increasing the number of bosons: to zero if the system is one-dimensional and to a minimum radius, with a maximum number of bosons, if the system is three-dimensional.

quant-ph↗
arXiv1997

WKB corrections to the energy splitting in double-well potentials

By using the WKB quantization we deduce an analytical formula for the energy splitting in a double-well potential which is the usual Landau formula with additional quantum corrections. Then we analyze the accuracy of our formula for the double square well potential and the parabolic double-well potential.

chao-dyn↗
arXiv1997

On the Convergence of the WKB Series for the Angular Momentum Operator

In this paper we prove a recent conjecture [Robnik M and Salasnich L 1997 J. Phys. A: Math. Gen. 30 1719] about the convergence of the WKB series for the angular momentum operator. We demonstrate that the WKB algorithm for the angular momentum gives the exact quantization formula if all orders are summed.

quant-ph↗
arXiv1997

SWKB for the Angular Momentum

In this paper we solve the eigenvalue problem of the angular momentum operator by using the supersymmetric semiclassical quantum mechanics (SWKB), and show that it gives the correct quantization already at the leading order.

quant-ph↗
arXiv1997

Quantum Transition from Order to Chaos in the Nuclear Shell Model

We discuss the role of quantum chaos in atomic nuclei. After reviewing the basic assumptions of the nuclear shell model, we analyze the spectral statistics of the energy levels obtained with realistic shell-model calculations in the fp shell. In particular, for Ca isotopes we observe a transition from order to chaos by increasing the excitation energy and a clear quantum signature of the breaking of integrability by changing the single-particle spacings.

nucl-th↗
arXiv1997

Quantum Signature of the Chaos-Order Transition in a Homogeneous SU(2) Yang-Mills-Higgs System

We analyze a spatially homogeneous SU(2) Yang-Mills-Higgs system both in classical and quantum mechanics. By using the Toda criterion of the Gaussian curvature we find a classical chaos-order transition as a function of the Higgs vacuum, the Yang-Mills coupling constant and the energy of the system. Then, we study the nearest-neighbour spacing distribution of the energy levels, which shows a Wigner-Poisson transition by increasing the value of the Higgs field in the vacuum. This transition is a clear quantum signature of the classical chaos-order transition of the system.

nucl-th↗
arXiv1997

Convergence of the Splitting Method for Shallow Water Equations

In this paper we analyze the convergence of the splitting method for shallow water equations. In particular, we give an analytical estimation of the time step which is necessary for the convergence and then we study the behaviour of the motion of the shallow water in the Venice lagoon by using the splitting method with a finite element space discretization. The numerical calculations show that the splitting method is convergent if the time step of the first part is sufficiently small and that it gives a good agreement with the experimental data.

funct-an↗
arXiv1997

Quantum Chaos in a Yang-Mills-Higgs System

We study the energy fluctuations of a spatially homogeneous SU(2) Yang-Mills-Higgs system. In particular, we analyze the nearest-neighbour spacing distribution which shows a Wigner-Poisson transition by increasing the value of the Higgs field in the vacuum. This transition is a clear quantum signature of the classical chaos-order transition of the system.

quant-ph↗
arXiv1996

On the Limit Cycle of an Inflationary Universe

We study the dynamics of a scalar inflaton field with a symmetric double--well potential and prove rigorously the existence of a limit cycle in its phase space. By using analytical and numerical arguments we show that the limit cycle is stable and give an analytical formula for its period.

gr-qc↗
arXiv1996

WKB to all orders and the accuracy of the semiclassical quantization

We perform a systematic WKB expansion to all orders for a one-dimensional system with potential $V(x)=U_0/\cos^2{(αx)}$. We are able to sum the series to the exact energy spectrum. Then we show that at any finite order the error of the WKB approximation measured in the natural units of the mean energy level spacing does not go to zero when the quantum number goes to infinity. Therefore we make the general conclusion that the semiclassical approximations fail to predict the individual energy levels within a vanishing fraction of the mean energy level spacing.

quant-ph↗
arXiv1996

Chaotic features in classical scattering processes between ions and atoms

A numerical study has been done of collisions between protons and hydrogen atoms, treated as classical particles, at low impact velocities. The presence of chaos has been looked for by investigating the processes with standard techniques of the chaotic--scattering theory. The evidence of a sharp transition from nearly regular scattering to fully developed chaos has been found at the lower velocities.

chao-dyn↗
arXiv1996

WKB to all orders and accuracy of the semiclassical quantization

We perform a systematic WKB expansion to all orders for a one--dimensional system with potential $V(x)=U_0/\cos^2{(αx)}$. We are able to sum the series to the exact energy spectrum. Then we show that any finite order WKB approximation fails to predict the individual energy levels within a vanishing fraction of the mean energy level spacing.

chao-dyn↗
arXiv1996

Non--Hyperbolic Dynamics: a Family of Special Functions

In this paper we present some theorems for a class of non--hyperbolic fixed points on ${\bf R}^N$ and then analyze a family of functions $f_θ$ on the plane which have a non--hyperbolic fixed point in the origin. The dynamical properties of the family near the fixed point, like the basin of attraction, are studied. Finally the limits of applicability of the characterization by the eigenvalues of the Jacobian are discussed.

chao-dyn↗