PHYS08200604018 Shamik Banerjee - Homi Bhabha National ...
PHYS08200604018 Shamik Banerjee - Homi Bhabha National ...
PHYS08200604018 Shamik Banerjee - Homi Bhabha National ...
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Chapter 4<br />
Generalities of Quarter BPS Dyon<br />
Partition Function<br />
Our goal in this chapter is to draw insight from the known results to postulate the general<br />
structure of dyon partition function for any class of quarter BPS dyons in any N = 4 supersymmetric<br />
string theory.<br />
The results of our analysis can be summarized as follows.<br />
1. Definition of the partition function: Let (Q, P ) denote the electric and magnetic<br />
charges carried by a dyon, and Q 2 , P 2 and Q · P be the T-duality invariant quadratic<br />
forms constructed from these charges. 1 In order to define the dyon partition function<br />
we first need to identify a suitable infinite subset B of dyons in the theory with the<br />
property that if we have two pairs of charges (Q, P ) ∈ B and (Q ′ , P ′ ) ∈ B with Q 2 = Q ′2 ,<br />
P 2 = P ′2 and Q · P = Q ′ · P ′ , then they must be related by a T-duality transformation.<br />
Furthermore given a pair of charge vectors (Q, P ) ∈ B, all other pairs of charge vectors<br />
related to it by T-duality should be elements of the set B. We shall generate such a set B<br />
by beginning with a family A of charge vectors (Q, P ) labelled by three integers such that<br />
Q 2 , P 2 and Q·P are independent linear functions of these three integers, and then define<br />
B to be the set of all (Q, P ) which are in the T-duality orbit of the set A. We denote by<br />
d(Q, P ) the degeneracy, – or more precisely an index measuring the number of bosonic<br />
supermultiplets minus the number of fermionic supermultiplets – of quarter BPS dyons<br />
of charge (Q, P ). Since d(Q, P ) should be invariant under a T-duality transformation,<br />
for (Q, P ) ∈ B it should depend on (Q, P ) only via the T-duality invariant combinations<br />
1 Irrespective of what description we are using, we shall denote by S-duality transformation the symmetry<br />
that acts on the complex scalar belonging to the gravity multiplet. In heterotic string compactification this<br />
would correspond to the axion-dilaton modulus. On the other hand T-duality will denote the symmetry that<br />
acts on the matter multiplet scalars. In the heterotic description these scalars arise from the components of<br />
the metric, anti-symmetric tensor fields and gauge fields along the compact directions.<br />
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