V. E. Korepin, S. Lukyanov, Y. Nishiyama, M. Shiroishi
Asymptotic Behavior of the Emptiness Formation Probability 
in the Critical Phase of XXZ Spin Chain
(197K, Postscript)

ABSTRACT.  We study the 
Emptiness Formation Probability 
(EFP) for the spin 1/2 $XXZ$ spin chain. 
EFP $P(n)$ detects a formation of ferromagnetic string of the 
length $n$ in the ground state. 
It is expected that EFP decays in a Gaussian way for large strings 
Here, we propose the explicit expressions for 
the rate of Gaussian decay ${C}$ as well as for the exponent $\gamma$.In order to confirm the validity of our formulae, 
we employed an {\it ab initio} simulation technique of the 
density-matrix renormalization group to simulate 
$XXZ$ spin chain of sufficient length. 
Furthermore, we performed Monte-Carlo integration of 
the Jimbo-Miwa multiple integral for ${P(n)}$. 
Those numerical results for ${P(n)}$ support our formulae 
fairly definitely.