When a person dies, s/he goes to heaven or hell based on present life karma and any past karmas. In Buddhism, if there is no soul, who is punished in hell and who enjoys in heaven? as there is no physical body to feel pain and pleasure. If that person has learnt the art of detachment, how can s/he suffer/enjoy in hell/heaven? Does different realms really exists and do we travel through them?
-- “What is it, Nàgasena, that is reborn?”
-- “Mind and matter (namarupa).”
-- “Is it this very mind and matter that is reborn?”
-- “No, it is not, but by this mind and matter deeds are done and because of those deeds another mind and matter is reborn; but that mind and matter is not thereby released from the results of its previous deeds.
Just like an adult "inherits" results of the choices made by the child - even though most of the original body cells are gone, similarly future existence "inherits" karma from the past existence.
--“Can there be any rebirth where there is no transmigration?”
--“Yes there can, just as a man can light one oil-lamp from another but nothing moves from one lamp to the other; or as a pupil can learn a verse by heart from a teacher but the verse does not transmigrate from teacher to pupil.”
It is information and causation that is reborn, or is re-embodied. Or, as Chogyam Trungpa said, it is our neuroses that are reborn.
as there is no physical body to feel pain and pleasure?
Oh yes, there is definitely a body every time. Information always needs some kind of media, it does not exist without media... But that media could be virtual as well -- after all, form is emptiness and emptiness is form. Depending on a particular realm it may not be a crude material body. Besides, pain and pleasure do not require a body. Did you never experience mental pleasure and mental pain?
If that person has learnt the art of detachment, how can s/he suffer/enjoy in hell/heaven?
If that person has learnt the art of detachment, why would he or she be reborn in heaven or hell?
Does different realms really exists and do we travel through them?
Of course they really exist, just not necessarily in a naive way below the ground or above the sky ;) Yes, we do travel through them. Even in this world some people live in hell - don't you agree?
When one dies, one goes to heaven or hell or animal realms or ghost or human or higher heaven realm based on present life karma and any past karmas. In Buddhism, if one dies , one goes to any of the 6 realms based on present life karma and any past karmas. In Buddhism, since there is no soul, it is the minds that are punished in hell and it is the mind that enjoys in heaven. If one becomes a buddhist and has learnt the art of detachment, one will not suffer/enjoy in hell/heaven or any other realms. Different realms does exists and we do cycle through them in our countless number of past lives.
The aim of Buddhism is to be free from cycling through these 6 realms which are suffering or eventually leads to sufferings.
Another example of understanding the 6 realms is through ones' everyday life when our mind goes from happy to sad to neutral to any moods which are beyond one's control. Buddhism teaches one to have control over the mind and become free from these cycles. So that one is prepared when death comes
This is a similar question in the Sutta, to this question, where the Buddha says not to consider whether the one in the previous birth is the one causing the karmic responses in the current birth or not. Both assumptions are based on eternalism and annihilationism. Rather, the Buddha asks to consider dependent origination.
For the rest of the questions, I think Andrei has replied them well.
Again, when the Buddha was asked by the naked ascetic Kassapa whether suffering was of one's own making or of another's or both or neither, the Buddha replied "Do not put it like that." When asked whether there was no suffering or whether the Buddha neither knew nor saw it, the Buddha replied that there was, and that he both knew and saw it. He then said "Kassapa, if one asserts that 'He who makes (it) feels (it): being one existent from the beginning, his suffering is of his own making,' then one arrives at eternalism. But if one asserts that one makes (it), another feels (it); being one existent crushed out by feeling, his suffering is of another's making,' then one arrives at annihilationism. Instead of resorting to either extreme a Tathaagata teaches the Dhamma by the middle way (by dependent origination)" (S. XII, 17/vol. ii, 20).