  We provide a comprehensive theoretical study of the radio-frequency (rf)
spectra of a two-component Fermi gas with balanced populations in the normal
region of the temperature-vs-coupling phase diagram. In particular, rf spectra
are analyzed in terms of two characteristic peaks, which can be either distinct
or overlapping. On the BEC side of the crossover, these two contributions are
associated with a fermionic quasi-particle peak and a bosonic-like contribution
due to pairing. On the BCS side of the crossover, the two peaks are instead
associated with interactions between particles occurring, respectively, at high
or low relative momenta. Through this two-peak analysis, we show how and to
what extent the correlation between the widths of the rf spectra and the pair
size, previously identified in the superfluid phase at low temperature, can be
extended to the normal phase, as well as how the temperature-vs-coupling phase
diagram of the BCS-BEC crossover can be partitioned in a number of distinct
physical sectors. Several analytic results for the shape and widths of the rf
spectra are also derived in appropriate temperature and coupling limits.
