Phenomenology of the Littlest Higgs with T-Parity

TL;DR

Addressing the little hierarchy problem, the paper analyzes the Littlest Higgs model with T-parity, proposing T-parity as a way to satisfy EW precision data and provide a stable dark matter candidate. It identifies the heavy photon A_H as the dark matter WIMP and computes relic densities to constrain the symmetry-breaking scale f as a function of the Higgs mass, including Higgs-mediated annihilation and gauge final states. The work then maps out LHC phenomenology, highlighting SUSY-like missing-energy signatures from pair-produced T-odd states and the unique role of the T-even and lighter T-odd top partners in shaping collider signals. It also surveys alternative T-parity implementations and outlines directions for future collider and dark matter studies to distinguish this framework from other TeV-scale scenarios.

Abstract

Little Higgs models offer an interesting approach to weakly coupled electroweak symmetry breaking without fine tuning. The original little Higgs models were plagued by strong constraints from electroweak precision data which required a fine tuning to be reintroduced. An economical solution to this problem is to introduce a discrete symmetry (analogous to R-parity of SUSY) called T-parity. T-parity not only eliminates most constraints from electroweak precision data, but it also leads to a promising dark matter candidate. In this paper we investigate the dark matter candidate in the littlest Higgs model with T-parity. We find bounds on the symmetry breaking scale f as a function of the Higgs mass by calculating the relic density. We begin the study of the LHC phenomenology of the littlest Higgs model with T-parity. We find that the model offers an interesting collider signature that has a generic missing energy signal which could "fake" SUSY at the LHC. We also investigate the properties of the heavy partner of the top quark which is common to all littlest Higgs models, and how its properties are modified with the introduction of T-parity. We include an appendix with a list of Feynman rules specific to the littlest Higgs with T-parity to facilitate further study.

Figures (8)

• Figure 1: We plot a sample spectrum for the littlest Higgs with T-parity. The top quark mass and two values of the Higgs mass are plotted as a reference. The spectrum of heavy particles is plotted for $f=1$ TeV. The $\Phi$ mass is plotted for two different values of the Higgs mass, $M_H=115,130$ GeV. A value of $s_\lambda=\frac{1}{\sqrt{2}}$ is used to determine the masses of $t'_+$ and $t'_-$.
• Figure 2: The $A_H$ annhilates predominantly to SM gauge and Higgs bosons. These are the diagrams which give the largest contributions to the annihilation coefficient $\langle \sigma_A v \rangle$ for the ranges of $f$ and $m_H$ that we examine.
• Figure 3: This plot depicts the variation of the relic density with respect to the Higgs mass and the symmetry breaking scale, $f$. In order from lightest to darkest regions, the $A_H$ makes up ($0-10\%$, $10-50\%$, $50-70\%$, $70-100\%$, $100\%$, $> 100\%$) of the observed relic abundance of dark matter.
• Figure 4: The cross section for the production of a pair of T-odd heavy vector bosons at the LHC is plotted as a function of the symmetry breaking scale $f$. The number of events for $300\;\mathrm{fb}^{-1}$ is plotted on the second y-axis. $M_{W_H^{\pm}}$ is plotted on the second x-axis. $M_{Z_H}$ is degenerate in mass with $M_{W_H^{\pm}}$, and $M_{A_H}\sim .16 f$.
• Figure 5: The cross section for the production of a pair of T-odd triplets at the LHC is plotted as a function of the symmetry breaking scale $f$. The cross section is plotted for $m_H=100,200 \;\mathrm{GeV}$ since the triplet mass, $M_\Phi$, is determined by $f$ and $m_H$. The number of events for $300\;\mathrm{fb}^{-1}$ is plotted on the second y-axis. $M_\Phi$ for a Higgs mass of $100$ GeV is plotted on the second x-axis, for a Higgs mass of $200$ GeV simply scale the second x-axis by a factor of $2$.