Let us consider the tangential modes as proposed by Thomsen and Reich. "Tangential modes refer to all phonon bands of a nanotube originating from the optical phonons of graphite. Their eigenvectors are characterized by an out-of-phase displacement of two neighboring carbon atoms. The displacement is directed parallel to the nanotube wall, along the circumference, the axis, or a direction in between. … The Raman-active vibrations of the tangential modes fall into two groups, the high-energy modes (HEM) just below 1600 cm -1 and the D mode ≈ 1350 cm -1 . The HEM is also called the G line in the nanotube literature" . "The double-peak structure close to 1600 cm -1 in Fig. [by Thomsen and Reich] is a unique feature of single-walled carbon nanotubes" (the Figure is from J. . This feature "is a more reliable Raman signature of single-walled tubes than the RBMs in the low energy range. Typically, the most intense peak in the high-energy range occurs between 1592 cm -1 and 1596 cm -1 (depending on diameter and excitation energy); it is always higher in frequency than the corresponding peak in graphite (1589 cm -1 , and the smaller peak between 1560 cm -1 to 1590 cm -1 changes dramatically for resonant excitation of metallic tubes" ). In the Fig. proposed by Thomsen and Reich, we can find the calculated line shapes of HEM in nanotubes. , made a theoretical work about "the origin of the broad line below the highest mode in the Raman spectrum. He worked out the proposal by , that the coupling of the tangential modes to the electronic continuum present in metallic nanotubes is the origin of the broad Raman line in the spectra. Semiconducting nanotubes, on the other hand, were responsible for uncoupled, Lorentzian-like peaks in the spectra". Therefore, Kempa assumed the plasmons in metallic tubes coupled to optical phonons. Due to the small wavevector of Raman excitation, a narrow peak is obtained. Therefore, Kempa added the presence of defects to have larger q-vectors in the phonon-plasmon scattering. "Alternatively, bundles of nanotubes form a plasmon continuum, similarly as electronic bands in a solid form from the discrete states of atoms. The calculated phonon-plasmon coupled lineshape for bundles is also shown in Fig. and displays a broad Fano lineshape, more similar to experiment" . "An alternative explanation for the low frequency of one of the tangential modes in metallic nanotubes was put forward by In the Section 9 of Thomsen and Reich's work, we find discussed the Electron-Phonon Interaction. "The interaction between electrons and phonons is also one step in the Raman process and thus determines the scattering cross section or Raman intensity. … On the other hand, electron-phonon coupling can also affect the phonon frequencies and drive structural phase transitions in solids". Section 9 reviews the electron-phonon coupling in carbon nanotubes, then "the Kohn anomaly (also called Peierls-like phonon softening) in metallic tubes" is discussed. "Conflicting reports exist on the presence and relative intensity of the G -band in isolated versus bundled metallic tubes. It has been claimed that this peak is as intense in isolated SWNTs as in bundles; that it is smaller; or that it can be absent. The G -peak is also thought to represent a Fano resonance due to phonon coupling with plasmons" (see in Lazzeri et al. the detailed further discussion and references therein). Lazzeri and coworkers "show that, like in graphite, the EPC per se gives the main contribution to the G - position and FWHM (Full Width at Half Maximum), even in the absence of phonon-plasmon coupling. Surprisingly, this has not been considered so far . However, it is clear that, if phonons do not couple to electrons, they certainly cannot couple to plasmons" . In Lazzeri et al., we find told that "in a metallic SWNT, the phonon frequencies corresponding to the graphene E2g mode are affected by a Kohn anomaly". "The strength of the Kohn anomaly also depends critically on the quantization of the electronic wave functions along the nanotube circumference confinement effects. On the contrary, the curvature of the nanotube has a small effect on the strength of the Kohn anomaly. In fact, the curvature can affect the Kohn anomaly by modifying the strength of the EPC and the band dispersion for the states near the Fermi energy".