Peer authentication failed ???

Hi there.

Using the 'sudo -u postgres psql' command I created a group and two
accounts in the group, I also created a database for one of the
accounts. Now, I'd like to login PG-15, using my new account and
connecting to my new database, but PG-15 complains. See the example
below, I think it is clear than my English.

*CREATE ROLE my_group; // Create a group**
**CREATE ROLE my_group_admin LOGIN PASSWORD 'AdminPassword' CREATEDB
CREATEROLE; // Create admin**
**CREATE ROLE my_group_worker LOGIN PASSWORD 'WorkerPassword' CREATEDB;
// Create Worker**
**GRANT my_group TO my_group_admin WITH INHERIT TRUE;**
**GRANT my_group TO my_group_worker WITH INHERIT TRUE;**
**
**CREATE DATABASE my_group_db WITH OWNER my_group_worker;**
**\q**
**psql -U my_group_worker -d my_group_db*

/psql: error: connection to server on socket
"/var/run/postgresql/.s.PGSQL.5432" failed: FATAL:  Peer authentication
failed for user "my_group_worker/*"*

*** What am I doing wrong?

Thanks in advance.