We derive universal relations for the radio-frequency (rf) spectroscopy of a
two-dimensional Fermi gas consisting of two spin states with a resonant S-wave
interaction. The rf transition rate has a high-frequency tail that is
proportional to the contact and displays logarithmic scaling violations,
decreasing asymptotically like 1/(Ο2ln2Ο). Its coefficient is
proportional to ln2(a2Dβ²β/a2Dβ), where a2Dβ and a2Dβ²β are the
2-dimensional scattering lengths associated with initial-state and final-state
interactions. The clock shift is proportional to the contact and to
ln(a2Dβ²β/a2Dβ). If β£ln(a2Dβ²β/a2Dβ)β£β«1, the clock shift arises
as a cancellation between much larger contributions proportional to
ln2(a2Dβ²β/a2Dβ) from bound-bound and bound-free rf transitions.Comment: 4 pages, 1 figur