Study of unstable particle through the spectral function in O(4) \(\phi^4\) theory

Abstract: We test application of the maximum entropy method to decompose the states contributing to the unstable

s i g m a

correlation function through the spectral function in the four dimensional O(4)

p h i^{4}

theory. Reliable results are obtained for the

s i g m a

mass and two-particle

p i p i

state energy using only the

s i g m a

correlation function. We also find that the property of the

s i g m a

particle is different between the unstable (

m_{s i g m a} / m_{p i} > 2

) and stable (

m_{s i g m a} / m_{p i} < 2

) cases.