In postgresql binary replication, indexes are replicated or not? And if i dont like it? I want to know if indexes are replicated in a binary replication in postgresql.

And if it is, how can i disable this behavior?

So if slave becomes master i can start to index it using reindex?
The postgres replication works at the WAL (Write-Ahead-Log) level, which basically contains a copy of each disk block that is modified. The slave just streams the WAL records and play them back. So, everything that modifies the disk, which includes indexes, are replicated. 

This also means that the slave will use exactly same amount of disk space (for the database) as that of the master, and will use exactly the same query plan as that of the master etc.

It is not possible to change that behavior as long as you are using postgres in-built replication.

When the slave is promoted as master, there is no need to run reindex as index is already available.