“…In one line of thinking, to relax the assumption of Gaussian distribution in the one factor Gaussian copula model, student-t copula [5][6][7][8][9][10][11][12], double-t copula [13,14], Clayton copula [12,[15][16][17][18][19][20], Archimedian copula [21,22], Marshall Olkin copula [23][24][25][26] are studied. And default correlations are made stochastic and correlated with the systematic factor in [27,28] to relax the assumption that default correlations are constant through time and independent of the firms default probabilities.…”