“…It is worth mentioning that the inverse Gaussian subordinator represents a particular case of the α ‐stable one with (see Louati, Masmoudi, & Mselmi, 2015b; 2017,2020; 2018c). Its first‐exit time is defined by , where X ( t ) is inverse Gaussian distributed (see Meerschaert & Scheffler, 2008; Meerschaert, Nane, & Vellaisamy, 2011, 2018a, 2018a, 2018b, 2018b). Using the same notations of Mselmi (2018a), we denote by Q y ( dz ), ρ t ( dy ), and the distributions of G ( y ), Y ( t ), ( Y ( t ), Z ( t )) and Z ( t ) respectively.…”