Custom field and Doc boost

I can add new fields using xpath clause in the config parameter.
But is it possible to access this kind of field in the Doc Boost groovy script?

For example if I create following field, can I access it in the Doc boost:

I only want to use the field in the Doc Boost. I do not want to store it.

I think you can use it.
To ignore the field, you need to edit doc.json and create the index.
For excluding fields, please see elasticsearch document.

I can confirm it can be used in the Doc boost.
But if the custom field does not always contain a value, then the existence of variable must be checked in the groovy script: binding.hasVariable('meta_published_time') && ...