Constraints on variation of fine structure constant from joint SPT-SZ
  and XMM-Newton observations
  We search for a variation of the electromagnetic fine structure constant
($\alpha \equiv e^2/\hbar c$) using a sample of 58 SZ selected clusters in the
redshift range ($0.2<z<1.5$) detected by the South Pole Telescope, along with
X-ray measurements using the XMM-Newton observatory. We use the ratio of the
integrated SZ Compto-ionization to its X-ray counterpart as our observable for
this search. We first obtain a model-independent constraint on $\alpha$ of
about 0.7%, using the fact that the aforementioned ratio is constant as a
function of redshift. We then look for a logarithmic dependence of $\alpha$ as
a function of redshift: $\Delta \alpha/\alpha = -\gamma \ln(1+z)$, as this is
predicted by runaway dilaton models. We find that $\gamma$ = $-0.046 \pm 0.1$,
which indicates that there is no logarithmic variation of $\alpha$ as a
function of redshift. We also search for a dipole variation of the fine
structure constant using the same cluster sample. We do not find any evidence
for such a spatial variation.
