Can I pass an argument as ?xxx=arg In Drupal 7, on the home page /home, I have a list of News items in the left column, and want to click on one of the News items in the list, and have the full article for that item show in the right column of the page.  

Is there a way to pass an argument that doesn't change the page, like /home?xxx=arg   Everything I read talks about passing arguments in ways that change the page path (i.e., home/news1, or home/news2).
As long as you have something (a custom module, for example) looking for the arguments, yes, you can pass as many arguments as you want.

Depending on the size of the articles, however, instead of requiring a page refresh, I would suggest either an AJAX call (more complicated) or using jQuery (less complicated) to hide the content, and simply show it on demand. If the articles are large though, the jQuery option would be cumbersome and slow the page, since it would load all of the material at page load.