Queens Gambit Accepted 3rd move Side Lines (White) What are rationals/inherent preferences behind the following novelties performed by White? I'm open to those to either logically deduced them or explain the deviated lines through experience/practice playing them.

The traditional line:

[FEN ""]
1.d4 d5
2.c4 dxc4
3.Qa4+ Bd7
4.Qxc4 ...


Novelty 1:

[FEN ""]
1.d4 d5
2.c4 dxc4
3.Bf4!?


Novelty 2:

[FEN ""]
1.d4 d5
2.c4 dxc4
3.Nd2!?


Novelty 3:

[FEN ""]
1.d4 d5
2.c4 dxc4
3.b4!?
Short answer

3.Qa4+ and 3.Bf4 are reasonnable enough moves but not dangerous for Black.

3.Nd2?! and 3.b4? are very dubious.

1. "Traditional line"

I don't know why you name it that way, 3.Nf3 or 3.e4 are much more common than 3.Qa4+. By the way your "novelties" are certainly not that "new" either.

The idea of 3.Qa4+ is to regain the pawn at once. Its minus is that the queen goes out too early and will lose some tempi later on. Note that beside 3...Bd7, 3...Nc6 is possible too.

2. "Novelty 1"

3.Bf4 is just a developing move, so it cannot be too bad. However, it doesn't adress the main issues in the QGA (fight for the center, for the light squares, for the Pc4...), so it should be pretty harmless for Black after, say, 3...Nf6 4.e3 c5!?, or 4...Bg4!?, or simply 4...e6 followed by a6,c5 in traditional QGA-style.

3. "Novelty 2"

I suppose 3.Nd2?! aims at taking back on c4 with that knight. Fair enough, but it becomes a real (double-)gambit after 3...Qxd4!? 4.Nf3 [or 4.e3 Qd7 5.Bxc4 e6 and White doesn't have enough for one pawn.] Qc5, and White has to prove his compensation. If Black is less adventurous, 3...Nc6 4.e3 e5 should already be advantageous for him: he has more influence in the center and White hasn't got his gambitted pawn back yet.

4. "Novelty 3"

3.b4? sets a record: There is no faster way to give your opponent a passed pawn after only 5 plies. It also doesn't develop, doesn't make a threat and weaken your queenside.

If Black takes en passant, White will get a bit of compensation for his pawn but probably not enough. If black just develops with 3...Nf6 or 3...e6 (already hiting b4!), he enjoys a great position with as much of an advantage as you can dream for on move 3 as Black. The solid 3...c6 planning either 4...a5 attacking the weakness on b4 or 4...b5 securing an extra protected passed pawn also looks logical to me. 3...e5!? is a more aggressive option, and a tempting one as well since 4.de5 Bxb4+ 5.Bd2 Qd4 6.Bxb4 Qxa1 is probably just winning for Black.

Maybe White's idea is the trap 3...Nc6?! 4.d5 Nxb4?? [even here, 4...Ne5 should be okay.] 5.Qa4+ winning the knight, but well, that's just a cheapo and once Black avoids it he can be very happy.