Study of Gamow States in the Rigged Hilbert Space with Tempered Ultradistributions

In this work we show that it is possible to extend analitically, and with the use of tempered ultradistributions, the pseudonorm defined by T. Berggren for Gamow states. We define this pseudonorm for all states determined by the zeros of the Jost function for any short range potential. As an example we study the s-states corresponding to the square well potential.