Diphoton signal via Chern-Simons interaction in a warped geometry scenario

The Kalb-Ramond field, identifiable with bulk torsion in a five-dimensional Randall Sundrum (RS) scenario, has Chern-Simons interactions with gauge bosons, from the requirement of gauge anomaly cancellation. Its lowest Kaluza Klein (KK) mode on the visible 3-brane can be identified with a spin-0 $CP$-odd field, namely, the axion. By virtue of the warped geometry and Chern-Simons couplings, this axion has unsuppressed interactions with gauge bosons in contrast to ultra-suppressed interactions with fermions. The ensuing dynamics can lead to a peak in the diphoton spectrum, which could be observed at the LHC, subject to the prominence of the signal. Moreover, the results can be numerically justified when the warp factor is precisely in the range required for stabilization of the electroweak scale.

Figure 1

Diphoton cross sections at LHC-13 and LHC-14 for $m_a=1$, 1.5 and 2.5 TeV. The region on the right of the vertical line corresponds to a KK gauge boson below the existing bound.

Figure 2

Contours of constant cross section in the $m_a$ vs $k{r}_c$ plane. The region to the left of the vertical line is disallowed from the nonobservation of a diphoton resonance below 750 GeV. Similarly, the region above the horizontal line is disallowed from KK gauge boson searches.