Dear Rabbi Kornfeld.
The way I understood it, Zikah is not a "bond" (between the widow and her late husband's brother(s) but it's a state, comparable to Niddah, in which the widow finds herself. If she waits a number of days after the stopping of her menses and goes to the mikveh she is no more Niddah, if one of her brothers in law does Yibbum/Halitza she is no more Zikah.
If we take Zikah to be state there has not to be question of Retroactive Retraction.
Thank you.
Kindest regards,
Richard
From the opinion that maintains "Yesh Zikah" it is clear that Zikah is a bond, similar to Kidushin. This is why it affects the Yavam as well, prohibiting him to marry relatives of the Yevamah (see Yevamos 17b etc.).
This is true even for the opinion that maintains Ein Zikah. We can demonstrate this from the fact that it can be removed retroactively, as you pointed out. It is for this reason, as well, that the Gemara differentiates between the Zikah of a single Yavam to a single Yevamah and the Zikah of multiple Yavam's or multiple Yevamos (which is weaker) - see 17b, 19a, etc.
Best wishes,
Mordecai Kornfeld
Dear Rabbi Kornfeld.
Thank you so much your answer.
As you pointed out " Zikah ...affects the Yavam as well, prohibiting him to marry relatives of the Yevamah" would the Yavam during this period (where his widowed sister in law is Zikah) be prevented from marrying an unrelated woman ?
Kindest regards,
Richard
No, Zikah only prevents the Yevamah from marrying (just like marriage).
By the way, according to the opinion that maintains Ein Zikah, it is possible that the definition of Zikah that you provided is correct (cf. Tosfos Yevamos 52b DH Iy Amar).
Be well,
Mordecai Kornfeld
Kollel Iyun Hadaf