is $site_name , $logo ,$site_slogan variables values are store in render array $page? or they are independent from $page? if they are independent.then list of variables that have same nature?
The variables you use in templates aren't really part of the render arrays themselves. They are created by the various preprocess and process functions and added to the
$variables array. By default, those you list are added in either a
template_preprocess_html(), which your theme can have, too. Look at the source to see what is going on. For example, the stock
$variables['site_slogan'] = (theme_get_setting('toggle_slogan') ? filter_xss_admin(variable_get('site_slogan', '')) : '');
to get a dump of everything in the
$variables array, or you can do
to poke through the
$page object via Krumo, which is included in Devel.