index for or relation

Hi All !
Maybe that a basic question ,sorry.
I have to 2 tables :
Column | Type | Modifiers
----------------+-----------------------------+-----------
yaadid | numeric(19,0) |
populationtype | character varying(50) |
population | numeric(20,0) |
insert_trans_id | numeric(16,0) |
invalidate_trans_id | numeric(16,0) |
nextval('public.population2yaad_journal_journalid_seq'::text)
Indexes: population2yaad_insert_trans_id_idx btree (insert_trans_id),
population2yaad_invalidate_trans_id_idx btree (invalidate_trans_id)

and
Column | Type | Modifiers
----------------+-----------------------------+-----------
action | character varying(50) |
transaction_id | numeric(16,0) |
worker_login | character varying(10) |
time | timestamp without time zone |
param | character varying(100) |
studentid | numeric(9,0) |
Indexes: journal_action_idx btree ("action"),
journal_trans_id_idx btree (transaction_id)

I am trying to join it like this:

select pj.populationtype,getPopulationName(pj.populationtype,pj.population) as populationname,pj.population,pj.yaadid,
pj.insert_trans_id,pj.invalidate_trans_id,
j.time,w.login as worker_login,j.action,j.transaction_id as j_transaction_id
from journal j
INNER JOIN population2yaad_journal pj on (j.transaction_id=pj.insert_trans_id
OR j.transaction_id=pj.invalidate_trans_id)
where j.action = 'add_yaad' or j.action = 'delete_yaad' or j.action = 'change_yaad' order by j.time

However this does not use the indexes because of the OR in the INNER JOIN.
How should i create indexes to make this work right?

Thanks
--
Evgeny.