PHYS08200604018 Shamik Banerjee - Homi Bhabha National ...
PHYS08200604018 Shamik Banerjee - Homi Bhabha National ...
PHYS08200604018 Shamik Banerjee - Homi Bhabha National ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
4.5. EXAMPLES 69<br />
Note that Q and P are both primitive. Since Q · P is quantized in units of 2, we shall define<br />
Q s = Q √<br />
2<br />
, P s = P √<br />
2<br />
, ˇρ s = 2ˇρ, ˇσ s = 2ˇσ, ˇv s = 2ˇv . (4.5.5.3)<br />
Thus we have<br />
Q 2 s = − (2m + 1) , P 2 s = 2K + 1, Q s · P s = −J . (4.5.5.4)<br />
Since Q 2 s/2 is quantized in units of 1/2, we expect the partition function to have ˇσ s period<br />
2. However except for an overall additive factor of 1/2, Q 2 s/2 is actually quantized in integer<br />
units. Thus the partition function has the additional property that it is odd under ˇσ s → ˇσ s +1.<br />
Similarly since Ps<br />
2 is an odd integer, the partition function picks up a minus sign under ˇρ s →<br />
ˇρ s + 1. We shall call these symmetries of ̂Φ. Finally since Q s · P s is quantized in integer units,<br />
the period in the ˇv s direction is also unity. The corresponding symplectic transformations<br />
acting on (ˇρ s , ˇσ s , ˇv s ) are of the form<br />
⎛<br />
⎞<br />
1 0 ã 1 ã 3<br />
⎜ 0 1 ã 3 ã 2<br />
⎟<br />
⎝ 0 0 1 0 ⎠ , ã 1, ã 2 , ã 3 ∈ Z . (4.5.5.5)<br />
0 0 0 1<br />
Under this transformation the partition function picks up a multiplier factor of (−1) ea 1+ea 2<br />
.<br />
Our next task is to determine the subgroup of the S-duality group Γ 0 (2) that leaves the<br />
set B – defined( as the)<br />
T-duality orbit of A – invariant. For this let us apply the S-duality<br />
a b<br />
transformation ∈ Γ<br />
c d 0 (2) on the charge vector (4.5.5.1). This gives<br />
⎛<br />
Q ′ = aQ + bP = ⎜<br />
⎝<br />
b(2K + 1)<br />
(2m + 1)a/2 + bJ<br />
b<br />
−2a<br />
⎞<br />
⎟<br />
⎠ , P ′ = cQ + dP =<br />
⎛<br />
⎜<br />
⎝<br />
d(2K + 1)<br />
(2m + 1)c/2 + dJ<br />
d<br />
−2c<br />
(4.5.5.6)<br />
We need to choose a, b, c, d such that (4.5.5.6) is inside the set B, ı.e. it can be brought to the<br />
form (4.5.5.1) after a T-duality transformation. The T-duality transformations acting within<br />
this four dimensional subspace are generated by matrices of the form [24]:<br />
⎛<br />
⎞ ⎛<br />
n 1 −m 1<br />
⎜ −l 1 k 1 ⎟<br />
⎝<br />
k 1 l 1<br />
⎠ and ⎜<br />
⎝<br />
m 1 n 1 −m 2<br />
k 2 −l 2<br />
k 2 l 2<br />
m 2 n 2<br />
n 2<br />
⎞<br />
⎟<br />
⎠ , (<br />
ki l i<br />
⎞<br />
⎟<br />
⎠ .<br />
)<br />
∈ Γ<br />
m i n 0 (2) .<br />
i<br />
(4.5.5.7)