I dug more into the problem and noticed some points which may help:
when a user is registered, Hikashop notices that the user do not need login step. so it redirect to next step. afterwards at next step it checks whether user is registered and authorized to continue the check out , at this point hikashop realizes that the user is not a registered user thus redirects him again to login page, and this way the redirect loop occurs.
My guess is that because joomla uses database for handling sessions in case of database server's low performance due to high traffic or something, redirect happens before processing cookies . Is there any timeout set for processing session ? I mean is there a False return after a specified period of time before actually session queries are executed ?