Meditation

What is the exact line of discussion...modern day meditation techniques,or the samadhi or dhyan of sikhism?

Actually, there is no perfectly suited word in english language for these two,meditation is the nearest.
Buddist' Zen'style of meditation actully originated from' Dhyan' of Vedic times,
Dhyan means focus on the inner senses "Anta-Karan",the inner-self,where in lies a hidden powerful inner sense ,which when accessed connects one to the pre-mordial eternal energy of "Nada' sound or wavelength or frequency or whatever you may call it.Its in this state the great saints herd the inner sound of AUM..........; The reveleations.....The inner melodies(which Guru ji has mentioned in the Bani of Anand(Bliss)Sahib-Anand bhayaa meri maa'e,Satguru main paaya,Satguru ta paaya man mere man vajeean vadhaayeean Raag ratan parivar bhareean shabad gaavan aayeean...)
When a person is in the truly' Dhyan' state ,his external senses are temporarily all disconnected from external world of senses and they are all fully focussed inawards.
To understand Dhyana you will need to grasp the concept of MIND.
The whole story is of taming the monkey mind which by nature is highly unstable,in a constant fluctuating state..Man jeete jag jeet...Aye mana mereya! tu sadaa raho har(god) nale,har naal raho tu man mere dookh sabh visaarna.......
You must have heard of the concept 'man marna'(Kill the mind),empty your mind,clean your mind,....Our mind is like a highly sophisticated computer diskette...if you have already a recording there then you cant record over it.To do so you will have to erase the previuos content and reformat it.Similarly,those who desire to practice Dhyana,they have to prepare their mind first with such thoughts that will make it easier for them to go inward,with concepts and things the mind will want to wander and connect to when going inward,otherwise it'll keep coming back to the external sensual world thoughts by default,for it knows nothing else and it's comfortable for it go back there.
The same principle mind applies for habbits,addictions,attachments,fear,and other learned behaviour.To break it out of its mould you have to teach it with a whip of discipline.
Initially the practice of 'Dhyana' might reward you of such a state of Bliss(Ananda)for fractions of a second only,slowly building up to just a second or two or max a miserable few moments.But if done regurly it will definitely show better rewards
' Dhyan' done with love for lord in the heart ,with deep devotion,no doubts,no expectations,no frustration, done by such people who have first managed to clean up their heart and mind of pollution (of bad or negative thoughts,)and who respect their body as the one and only sacred vehicle or instrument of Liberation or connection to God's essence (and thus believing keeping it healthy and all senses fully funtional,)
Bani says our Conciosness needs uplifting Through Bramh gian(sacred knowledge of the nature of the Self and the gods creation).
For this we need to fine tune our intellect(IQ for surviving in the world,EQ for dealing with the social and personal aspect and peace of mind and stability (being the cool dude):and SQ for the spiritual factor for the skills to know and unveil The Truth/The Reality of the Supreme Transcedental /The Parbrahmn-The Cosmic mind(THE JEEVA MANA IS THE INDIVIDUAL HUMAN MIND)/The Paramatman-The eternal Omnipresent Soul essense of god(The jeeva atman being the individual human soul which is the latent tiny spark connecting the entire world with god).
Now it is this spark that grows and makes saints of ordinary people.

So the question now is how to awaken this dormant energy lying within every soul.The secret to this is 'The Thought Power' acc to bani.Those who have good,kind,sharing,caring,non violent,non lustin,non greedy,non attaching,Loving,,just,and such good thoughts are happy and grounded people who are not afraid to share ,help,loose out,or selfish----fearless and without enemity.Such people can be poor or filthy rich.....its the thoughts that set them apart.They are satisfied with their lot and go out of the way to reach out to others and carry the love of selfless contribution to others.

Sikhism has the concept ff Miri-Piri(Saint-Soldier) or SAHAJ-which is akin to the balanced person of modern day .Scientifically,(IQ)left and right brain balanced people;(EQ)people who have very developed pre frontal cortex emotionally balanced as well:(SQ) and those who are deeply devoted to God and live a spiritually correct life.
To know what is this spiritually correct life you will need to do your daily japa.have a Tapa(Determination and discipline in your life of following the spiritually correct life).
Hope this will put you on the path of exploring more Truths.

Black Magic
It actually means negative energies that harm yhe mind ,Body and Soul.
Only the weak minded are susceptible to it.A weak mind is that which is very superficial,only carrying the sensual external world energies ,devoid of powerful inner energies.Inner energies are build up with good thoughts(vichaar) and good intellect(budhi)and strengthen the connection to god essence by constant japa.
Black magic cannot harm inner pwer of mind ,it only affects the external mind.So one needs to build on that to deflect any such attack.
There is one sakhi in which one of our Guru's tried to give this message by deflecting all the wutches attacks of black magic just by sitting at the river bank and praying while the witches attacked him from across the banks.
If your mind is afraid or fearful that it is going to be affected by the B.M. then it sure will.By doing so the mind is actually attaching itself to the wavelenth of the attack and unknowingly attracts it ,by making itself weaker it lets itself br taken over by the attack..depending on how strong is the attack.
MInd is constantly doubting your own capabilities and setting limits and manifesting that limit for itself.Beleive in yourself,think positive,ignore and reprimand and even banish them if you want set higher limits.
In sikhism the concept of :"Chardi Kala"is way to tackle this.IT means always aim higher,think positive,never cry over the past and move on ,dont despair or feel sad or depressed.You will start a vicios circle by attracting more of such negativity in your life.What frequency you put yourself at is what you are going to attract in the universe.It all boils down to your thoughts and the inner mind strength and having a chat line established with god at all times.God connects to those who exist at a similar range of frequency as him, the rest unfortunately are responsible for cutting themselves out of his range of grace.ITs peoples own actions(Karma)that bring them closer to god or keep them away from his grace...karmi apo apni ke nere ke door...jini naam dhiaaya gaye masakat ghaal...(those who do japa and maintain the inner thought level or frequency as he wants ,their hard work never goes unrewarded)
Nanak naam chardi kala tere bhane sarbat da bhalla...Nanak says that NAAM(god ) always remians in chardi kala mode and his desire and will never has any thoughts of harm or punishment or suffering for anyone for he has only love and good for all his creation.So it's the creation which is responsible for bringing the suffering on itself'People dont realise this and go on and on......why me,what did I do to be punushed in this way,Why I am always so unlucky,I'll complain to god;If god is so good then why there is so much suffering in the world;when peoples desires sre not fulfilled they curse god or forsake him,and so on.This is done in IGNORANCE.....not understanding the true nature of god and the TRUTH.