For D=4, N=2 QFTs, there are two "standard" forms of the Seiberg-Witten curve: hyperelliptic form, and a form which looks like y2=ϕ(z), where ϕ(z) appears in a quadratic differential q=ϕ(z)dz2. Converting between these two forms is meant to be standard. For example, Tachikawa describes how to go from the former to the latter in the case of the SU(2) theory with four flavours in section 9.1 of his summary paper. Let's use this theory as an example. To recap, the hyperelliptic form of the Seiberg-Witten curve looks like:
Σ:f(˜x−˜μ1)(˜x−˜μ2)˜z+f′⋅(˜x−˜μ3)(˜x−˜μ4)˜z=˜x2−u
To convert to "quadratic differential form", rescale ˜z to make f′=1 and collect terms in ˜x, and complete the square in ˜x. We find (dropping tildes):
x2=(f(μ1+μ2)+z2(μ3+μ4))2−4(f+(z−1)z)(fμ1μ2+z(u+zμ3μ4))4(f+(z−1)z)2
As Tachikawa tells us, we have for the Seiberg-Witten differential λ=xdz/z and λ2=q, so q=x2dz2/z2, i.e., using the above notation:
ϕ(z)=(f(μ1+μ2)+z2(μ3+μ4))2−4(f+(z−1)z)(fμ1μ2+z(u+zμ3μ4))4(f+(z−1)z)2z2
Now, to get to my question. There's meant to be a one-one mapping between these two forms of the Seiberg-Witten curve. So given a specific expression for ϕ(z), we should be able to work backwards to compute a specific form of the SW curve in hyperelliptic form, i.e. find the parameters {μ1,μ2,μ3,μ4,f,u}. Consider the following specific example of such a ϕ(z):
ϕ(z)=−576z(z3−1)4π2(1+8z3)2
Comparing with the previous general expression and equating coefficients of the numerators and denominators, we should be able to find the {μ1,μ2,μ3,μ4,f,u}. But doing so, I find multiple possible sets of values for these parameters. Moreover, plugging these parameters back into the Seiberg-Witten curve in its original "hyperelliptic form" (the first equation), they seem to give different curves.
But I thought there was meant to be a one-one correspondence between these two forms of the curves! So I feel I must have either done something wrong, or I am missing that somehow these curves look different but are nevertheless equivalent, or I just got wrong that there's a one-one correspondence between the two forms of the curves. Can anyone help me out here? Thanks in advance!!