Symbol b

The passage around this formula

…, exactly the units of $\hbar$/$\text{mass}$ , so $\Phi$ is dimensionless as a phase must be, and mass is recoverable from it as $m_{\rm op}[\mathcal L_{\rm G}]=\frac{\hbar\,\Phi[\mathcal L_{\rm G}]}{\mathbf b\cdot\mathbf v}$. Because m enters only through the fixed central charge and $\mathbf b$,$\mathbf v$ are the loop’s own declared parameters, $m_{\rm op}$[$\mathcal L_{\rm G}$] does not depend on which inertial frame is used to describe the apparatus from outside: boosting the whole laboratory changes how an external observer labels positions and velocities, but it does not change which…

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