If your home page is indexed with several different query strings attached, it can cause duplicate content issues. Generally, Google resolves these on its own over time, but it's best to take some action to repair this problem quickly.
You can set up 301 redirects to remove the query strings. You can tell Google to ignore these query string parameters through the Webmaster Tools console. You can add a rel="canonical" tag to your main page. Any or all of these steps will help. The 301 redirect is probably the best and most recommended solution. I've had good results with the rel="canonical" tag for this particular problem. The Webmaster Tools setting is also a good idea because it also repairs any other URLs from your site that might have been indexed with the same query string variables. Bing has a similar query string tool.