The existence of de-Sitter solutions and their stability within string theory
became, in recent years, one of the central research questions within the
string theory community. The so-called de-Sitter conjecture states that the
de-Sitter vacua are unstable within string theory. Here, we study the de-Sitter
solutions in string theory and their stability in the time direction using the
$O(d,d)$ symmetry approach allowing for the calculation of the generic form of
the string theory effective action. We study the undiscussed case of the
constant generalized dilaton as well as the general form of dilaton couplings.
Our findings suggest that de-Sitter solutions are unstable for the constant
generalized dilaton both with and without matter. Furthermore, we found that in
order for the theory to be weakly coupled the general form of dilaton coupling
is in the form of a cosmological constant.
