Wavefunction structure in quantum many-fermion systems with $k$-body interactions: conditional $q$-normal form of strength functions

Abstract

For finite quantum many-particle systems modeled with say $m$ fermions in $N$ single particle states and interacting with $k$-body interactions ($k\le m$), the wavefunction structure is studied using random matrix theory. Hamiltonian for the system is chosen to be $H=H_0(t)+\lambda V(k)$ with the unperturbed $H_0(t)$ Hamiltonian being a $t$-body operator and $V(k)$ a $k$-body operator with interaction strength $\lambda$. Representing $H_0(t)$ and $V(k)$ by independent Gaussian orthogonal ensembles (GOE) of random matrices in $t$ and $k$ fermion spaces respectively, first four moments, in $m$-fermion spaces, of the strength functions $F_{\kappa }(E)$ are derived; strength functions contain all the information about wavefunction structure. With $E$ denoting the $H$ energies or eigenvalues and $\kappa$ denoting unperturbed basis states with energy $E_{\kappa }$, the $F_{\kappa }(E)$ give the spreading of the $\kappa$ states over the eigenstates $E$. It is shown that the first four moments of $F_{\kappa }(E)$ are essentially same as that of the conditional $q$-normal distribution given in: P.J. Szabowski, Electronic Journal of Probability {\bf 15}, 1296 (2010). This naturally gives asymmetry in $F_{\kappa }(E)$ with respect to $E$ as $E_{\kappa }$ increases and also the peak value changes with $E_{\kappa }$. Thus, the wavefunction structure in quantum many-fermion systems with $k$-body interactions follows in general the conditional $q$-normal distribution.

arXiv comment23 pages, 3 figures

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