Let \( \alpha, \beta \) be the roots of the equation \( x^2 - ax - b = 0 \) with \( \text{Im}(\alpha) <\text{Im(\beta) \). Let \( P_n = \alpha^n - \beta^n \). If}
\[
P_3 = -5\sqrt{7}, \, P_4 = -3\sqrt{7}, \, P_5 = 11\sqrt{7}, \, P_6 = 45\sqrt{7},
\]
then \( |\alpha^4 + \beta^4| \) is equal to: