# Sensitivity analysis of random two-body interactions 

Calvin W. Johnson 1 and Plamen G. Krastev 1, 2 

$^{1}$Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1233 

$^{2}$Lawrence Livermore National Laboratory, P.O. Box 808, L-414, Livermore, CA 94551 

## Abstract 

The input to the configuration-interaction shell model includes many dozens or hundreds of inde- pendent two-body matrix elements. Previous studies have shown that when fitting to experimental low-lying spectra, the greatest sensitivity is to only a few linear combinations of matrix elements. Here we consider interactions drawn from the two-body random ensemble, or TBRE, and find that the low-lying spectra are also most sensitive to only a few linear combinations of two-body matrix elements, in a fashion nearly indistinguishable from an interaction empirically fit to data. We find in particular the spectra for both the random and empirical interactions are sensitive to similar matrix elements, which we analyze using monopole and contact interactions. 

