Lang’s comments:
1. Asanna realm: Yes. The asanna satta has hadaya vatthu and pasada rupā (i.e., manomaya kaya). But it is inside a “physical body” that has no eyes, ears,.. or brain. That means the manomaya kaya is unable to contact the outside world. Thus, no citta can arise.
2. When an Arahant is in sannavedayita nirodha samapatti, the physical body is maintained by rupa jīvitindriya (kammic energy) but no sensory contacts are made. There it is the mind that “shuts off” external arammana.
– To get there an Arahant must systematically go to the fourth jhana, arupavacara samapatti, and then to sannavedayita nirodha samapatti.
3. Rest of the first comment is correct.
4. I am not sure what you mean in the second comment.
– Of course, Nibbana is NOT Samsara.
– Samsara is the rebirth process. To get to Nibbana one must attain Arahanthood. At the death of the physical body the Arahant (Parinibbana), Sansaric process ends, and Nibbana is complete.
– In the language of mathematics, Nibbana and Samsara (living in this world) are mutually exclusive. After the Parinibbana, an Arahant is totally disengaged from this world, i.e., no longer in Samsara or the rebirth process.