Phi(vect{x}, t | vect{x}_0)

documentclass{pnastwo}
    usepackage{PNAStwoF}
    usepackage{amssymb, amsfonts, amsmath}
    usepackage{url, graphicx, subfig, bbold}
    usepackage[usenames,dvipsnames,svgnames,table]{xcolor}
    usepackage{multirow}
    usepackage{footmisc}

%% Dvipsone Names:
deftimesroman{tir}
deftimesbold{tib}
deftimesitalic{tii}
deftimesbolditalic{tibi}

%% Karl Berry Names:
%deftimesroman{ptmr8t}
%deftimesbold{ptmb8t}
%deftimesitalic{ptmri8t}
%deftimesbolditalic{ptmbi8t}

%% BlueSky or other TeX Systems, write in appropriate font name:
deftimesroman{du801btr7t}
deftimesbold{du801btb7t}
deftimesitalic{du801bti7t}
deftimesbolditalic{du801btbi7t}

globalletrmdefaulttimesroman
DeclareFontFamily{encodingdefault}{rmdefault}{}
DeclareFontShape{encodingdefault}{rmdefault}{m}{n}{
    <-> timesroman
}{}
DeclareSymbolFont{operators}{encodingdefault}{rmdefault}{m}{n}

%% Times-Roman

    %% Dvipsone Names:
    %deftimesroman{tir}
    %deftimesbold{tib}
    %deftimesitalic{tii}
    %deftimesbolditalic{tibi}

    %% Karl Berry Names:
    %deftimesroman{ptmr8t}
    %deftimesbold{ptmb8t}
    %deftimesitalic{ptmri8t}
    %deftimesbolditalic{ptmbi8t}

    %% BlueSky or other TeX Systems, write in appropriate font name:
    %deftimesroman{du801btr7t}
    %deftimesbold{du801btb7t}
    %deftimesitalic{du801bti7t}
    %deftimesbolditalic{du801btbi7t}