Electroweak precision measurements and collider probes of the Standard Model with large extra dimensions

TL;DR

This work builds a five-dimensional Standard Model to explore how large extra dimensions affect electroweak precision observables and collider signals. By separating bulk and wall-localized fields and introducing the key parameter $V$ to encode KK sums, the authors perform global fits to precision data, finding that a heavy Higgs is compatible provided KK effects are sizeable, with $M_c$ constrained to $>$ a few TeV. They translate these constraints into collider expectations, showing that indirect $e^+e^-$ searches at LEP2/NLC can probe $V$ down to $\sim 10^{-4}$–$10^{-3}$ (corresponding to $M_c$ up to tens of TeV), while direct searches at the Tevatron and LHC could discover or constrain first KK excitations up to several TeV (and up to ~31 TeV indirectly at future linear colliders). Overall, the paper demonstrates the continued viability and testability of TeV-scale extra dimensions through a coherent EFT framework and detailed collider projections.

Abstract

The elementary particles of the Standard Model may live in more than 3+1 dimensions. We study the consequences of large compactified dimensions on scattering and decay observables at high-energy colliders. Our analysis includes global fits to electroweak precision data, indirect tests at high-energy electron-positron colliders (LEP2 and NLC), and direct probes of the Kaluza-Klein resonances at hadron colliders (Tevatron and LHC). The present limits depend sensitively on the Higgs sector, both the mass of the Higgs boson and how many dimensions it feels. If the Higgs boson is trapped on a 3+1 dimensional wall with the fermions, large Higgs masses (up to 500 GeV) and relatively light Kaluza-Klein mass scales (less than 4 TeV) can provide a good fit to precision data. That is, a light Higgs boson is not necessary to fit the electroweak precision data, as it is in the Standard Model. If the Higgs boson propagates in higher dimensions, precision data prefer a light Higgs boson (less than 260 GeV), and a higher compactification scale (greater than 3.8 TeV). Future colliders can probe much larger scales. For example, a 1.5 TeV electron-positron linear collider can indirectly discover Kaluza-Klein excitations up to 31 TeV if 500 fb^-1 integrated luminosity is obtained.

Figures (4)

• Figure 1: $\chi^2$ to precision electroweak data with $\tan\phi =0$ (Higgs bosons in bulk only). The horizontal dashed line is for $\chi^2_{\rm SM,max}=22.1$, which reproduces the $\chi^2$ for $V=0$ and $m_h=260\hbox{\rm,GeV}$, which is currently the 95the Higgs mass in the SM. Requiring $\chi^2<\chi^2_{\rm SM,max}$ implies the limit $V<0.0015$, which translates to $M_c>3.8\hbox{\rm,TeV}$ in the 5DSM.
• Figure 2: $\chi^2$ to precision electroweak data with $\tan\phi =\infty$ (Higgs bosons on 3-brane wall only). The horizontal dashed line is for $\chi^2_{\rm SM,max}=22.1$, which reproduces the $\chi^2$ for $V=0$ and $m_h=260\hbox{\rm,GeV}$, which is currently the 95the Higgs mass in the SM. Requiring $\chi^2<\chi^2_{\rm SM,max}$ implies the limit $V<0.002$, which translates to $M_c>3.3\hbox{\rm,TeV}$ in the 5DSM. Furthermore, values of $m_h$ as high as $500\hbox{\rm,GeV}$ are allowed as long as $V>0$.
• Figure 3: Search reach in $V$ at LEP2 running at $\sqrt{s}=195\hbox{\rm,GeV}$ as a function of integrated luminosity. For the 5DSM the value of $V$ can be related to $M_c$, which is shown on the left vertical axis.
• Figure 4: Search reach in $V$ at NLC running at $\sqrt{s}=500\hbox{\rm,GeV}$, $1000\hbox{\rm,GeV}$ and $1500\hbox{\rm,GeV}$ as a function of integrated luminosity. For the 5DSM the value of $V$ can be related to $M_c$, which is shown on the left vertical axis.