Electroweak and Conformal Symmetry Breaking by a Strongly Coupled Hidden Sector

TL;DR

The paper investigates a Planck-scale compliant, classically conformal framework in which a QCD-like hidden sector undergoes spontaneous chiral symmetry breaking. The breaking is transmitted to the Standard Model through a real singlet scalar via a Higgs portal, triggering electroweak symmetry breaking and yielding dark pions as stable dark matter. Using the NJL model in a self-consistent mean-field approach, the authors compute the effective potential, scalar mass spectrum, dark-meson couplings, relic abundance, and finite-temperature phase transitions. They find a weakly first-order electroweak transition and resonant DM annihilation required to obtain the correct relic density, while direct-detection signals are predicted to be suppressed, limiting near-future detection prospects. The work highlights a concrete mechanism by which conformal symmetry and strong dynamics can explain the EW scale and DM phenomenology, while also outlining clear avenues for refinement and extensions.

Abstract

The LHC and other experiments show so far no sign of new physics and long-held beliefs about naturalness should be critically reexamined. We discuss therefore in this paper a model with a combined breaking of conformal and electroweak symmetry by a strongly coupled hidden sector. Even though the conformal symmetry is anomalous, this may still provide an explanation of the smallness of electroweak scale compared to the Planck scale. Specifically we start from a classically conformal model, in which a strongly coupled hidden sector undergoes spontaneous chiral symmetry breaking. A coupling via a real scalar field transmits the breaking scale to the Standard Model Higgs and triggers electroweak symmetry breaking. The model contains dark matter candidates in the form of dark pions, whose stability is being guaranteed by the flavor symmetry of hidden quark sector. We study its relic abundance and direct detection prospects with the Nambu-Jona-Lasinio method and discuss the phase transition in the dark sector as well as in the electroweak sector.

Figures (11)

• Figure 1: The RG evolution of an exemplary set of values of model parameters for different energy scale are shown with the boundary values at $Q=\unit[1]{TeV}$ given as $g_4^2=4\pi$, $\lambda_H=0.13$, $\lambda_S=0.15$, $\lambda_{HS}=0.1$, $y=0.3$. The SM gauge coupling constants are denoted as $g_Y=\sqrt{5/3}g_1$, $g_2$ and $g_3$.
• Figure 2: The allowed regions for the parameters $\lambda_S$ and $y$ (the $Q=\unit[1]{TeV}$ scale) are shaded for different value of $\lambda_{HS}$.
• Figure 3: The mass of DM $m_{\rm DM}$ and constituent quark mass $M$ as a function of $y$, where the scalar couplings are fixed at the values given in Eq. (\ref{['eq:exm1']}).
• Figure 4: One-loop diagrams contributing to the DM-DM-$S$ coupling.
• Figure 5: One-loop contributions to the DM-DM-$S$-$S$ coupling.