So you initially set it up gamma neutral but during the trade do you dynamically delta hedge? I mean it's not good if you profit from a vol spike and then lose from the drop in spot.
The amount of delta-hedging is pretty small, given that you are gamma neutral at inception. As you are drifting away from spot, you will actually gain gamma because shorter-dated options have much higher change in gamma per change in spot. As I said, given that you by definition have hedged away gamma/theta, your main risk is the level of forward volatility and other risks start appearing once either enough time passes or spot moves enough for the trade to lose it's gamma/theta neutrality.
Yes. There are other risks. Those term structure drifts can become material. So you still can't really structure a view that's on vol like you can on stock (where there aren't any material carrying costs or other risks). Also, in vol spikes term structure behaves differently (like 2008 vs 2010).
Root-time vega is regular vega rescaled by the root of time (rtVega = Vega / (sqrt(t)). It is a better representation of volatility risk for relatively short-dated trades, as the curve moves in a root-time manner (e.g. 1 vol move in 1 year bucket would usually be accompanied with 2 vol move in 3m bucket).
Vega time adjusted.... such that you can compare different Vegas across time..... Squaring and dividing is at the very beginning is statistics... squaring cumulating and the dividing by n is standard deviation...... I can see why one would wanna do this..you can graph the term structure of Vegas across the Calender like this
I opened 143/147/151 IB on 09/19 for 2.66 credit and closed it on 9/21 for 2.46. Gain was ~11% after commissions. Have you tried a similar trade?