LHC and ILC probes of hidden-sector gauge bosons

TL;DR

The paper investigates hidden-sector gauge bosons that kinetically mix with hypercharge in brane-inspired models, formulating an EFT with SM × $U(1)_X$ and a kinetic-messenger sector. After diagonalizing kinetic terms and incorporating electroweak breaking, the exotic boson $X$ couples to SM fields with strength $\eta g_Y Q_Y$ and has mass $m_X$, with precision EW data constraining oblique effects via $\Upsilon = (\eta/0.1)^2 (250\,\text{GeV}/m_X)^2$. The authors quantify LHC/Tevatron reach for $pp \to X \to \mu^+\mu^-$ and show sensitivity to $\eta \gtrsim 0.03$ at the LHC (down to TeV scales), while ILC analyses of $e^+e^- \to \mu^+\mu^-$ and $e^+e^- \to \gamma X$ extend reach to $m_X<500$ GeV with $\eta$ as small as $\sim 0.10$–$0.15$, highlighting complementary search strategies. The results indicate a transition region around $m_X \approx 550$ GeV where LHC sensitivity surpasses ILC, and emphasize that higher-energy ILCs would broaden access to heavier hidden-sector gauge bosons. Overall, the work provides concrete collider benchmarks for hidden $U(1)_X$ scenarios and clarifies how LHC and ILC data together can constrain or reveal kinetic-mixing physics.

Abstract

Intersecting D-brane theories motivate the existence of exotic U(1) gauge bosons that only interact with the Standard Model through kinetic mixing with hypercharge. We analyze an effective field theory description of this effect and describe the implications of these exotic gauge bosons on precision electroweak, LHC and ILC observables.

Figures (4)

• Figure 1: LHC detection prospects for $100\,{\rm fb}^{-1}$ of integrated luminosity in the $\eta$-$M_X$ plane. The countours are of signal significance, which exceeds $5$ only when $\eta\hbox{$\;\stackrel{>}{\sim}\;$} 0.03$.
• Figure 2: Deviations of $e^+e^-\rightarrow \mu\bar{\mu}$ at ILC at $\sqrt{s}=500\, {\rm GeV}$ for $500\,{\rm fb}^{-1}$ integrated luminosity are represented in this plot as contours of the $\log_{10}(\%)$ of the excess of events produced compared to SM expectations. The line along the interface of the blue and maroon regions represents a $10^0=1\%$ (or $\sim 5\sigma$) deviation.
• Figure 3: Signal significance plot of $e^+e^-\rightarrow \gamma X\rightarrow \gamma\mu \bar{\mu}$ at ILC $\sqrt{s}=500\, {\rm GeV}$ with $500\,{\rm fb}^{-1}$ integrated luminosity. We assume that the $m_{\mu\bar{\mu}}$ can be measured to within 2%.
• Figure 4: Detection plot of estimated $5\sigma$ confidence level of $X$-boson that kinetically mixes with hypercharge. Detection for Tevatron ($8\,{\rm fb}^{-1}$), LHC ($100\,{\rm fb}^{-1}$), LEP ($\sqrt{s}=206\, {\rm GeV}$ and $725\,{\rm pb}^{-1}$), and ILC ($\sqrt{s}=500\, {\rm GeV}$ and $500\,{\rm fb}^{-1}$) can occur at points above their respective lines.