Is it possible in Drupal to find out which user modified a particular field? Not just the whole node. After saving the content I want to display the author name next to that field.
Not sure if this is possible or not.
This is not provided by Drupal core, and (As far as I know) it is not provided by any contributed modules on drupal.org.
So, in order to do that, you would probably need to create a custom module.
A simple module to achieve that would have a database table with (nid, uid, current field value) and hook_node_presave implementation (compare field values, then update/insert/ignore saving new data to your database table).