Anomalous U(1) Gauge Bosons and String Physics at the Forward Physics Facility

Looking forward to forward physics at the CERN's LHC

“…The mass of the dark photon is usually generated through spontaneous symmetry breaking; namely, through the vacuum expectation value (vev) of a hidden SM singlet Higgs field which carries a U(1) charge. In LST models this is possible provided we tolerate a hierarchy between the vev and M s that increases as M 3/2 s [11]. As noted above, the U(1) does not couple directly to the visible sector, but does it via kinetic mixing with the hypercharge.…”

“…We now consider a specific Little String Theory (LST) model, in which the weakness of gravity (or equivalently the enormity of the Planck mass) is attributed to the tiny value of the string coupling g s [10]. In spite of the small g s , in type II string theories with gauge interactions localized in the M s connection in LST models [11]. Adapted from [16].…”

“…We remind the reader that within LST models the SM lives on NS5 branes, but since the U(1) gauge boson comes from D-branes the SM is generically neutral under U(1) as desired. The U(1) gauge coupling is found to be [11]:…”

“…where µ 2 denotes the renormalization scale (which in string theory is replaced by M s ), e is the elementary charge, and where we absorbed also the constant contribution in C Log ∼ 3 [11]. Substituting ( 9) into (10) we obtain the region of the parameter space to be probed by FASER2, which is shown in Fig.…”

“…The grey shaded regions are excluded by previous experiments. The vertical axis on the right indicates theM s connection in LST models[11]. Adapted from[16].…”