Dark matter and sub-GeV hidden U(1) in GMSB models

TL;DR

This paper investigates a dark matter scenario in which a sub-GeV hidden $U(1)_X$ sector is embedded in gauge mediated SUSY breaking (GMSB), yielding a heavy vector-like dark matter candidate charged under $U(1)_X$. The relic density is set by annihilation into hidden gauge bosons via $\tilde{\psi}_1\tilde{\psi}_1^* \to XX$, with $\alpha_X$ tied to the TeV-scale DM mass by $\alpha_X \simeq 1.58\,\alpha\, (m_{\tilde{\psi}_1}/\mathrm{TeV})$, and a Sommerfeld enhancement from the light mediator $m_X$ provides a sizable boost $S$ but falls short of explaining the PAMELA/ATIC data without extra boost factors. Direct detection constrains the kinetic-mixing angle to $\theta \lesssim 2\times 10^{-6} (m_X/0.4\ \mathrm{GeV})^2$, while collider phenomenology predicts visible displaced lepton vertices from $X\to \ell^+\ell^-$ decays following OLSP decays to the hidden sector. The ordinary LSP decays and the hidden sector mass spectrum yield distinctive LHC signatures, including $\ell^+\ell^- + \mathrm{MET}$ with $\mathcal{O}(10)$ cm displacements, enabling a test of the sub-GeV $U(1)_X$ scenario in GMSB.

Abstract

Motivated by the recent PAMELA and ATIC data, one is led to a scenario with heavy vector-like dark matter in association with a hidden $U(1)_X$ sector below GeV scale. Realizing this idea in the context of gauge mediated supersymmetry breaking (GMSB), a heavy scalar component charged under $U(1)_X$ is found to be a good dark matter candidate which can be searched for direct scattering mediated by the Higgs boson and/or by the hidden gauge boson. The latter turns out to put a stringent bound on the kinetic mixing parameter between $U(1)_X$ and $U(1)_Y$: $θ\lesssim 10^{-6}$. For the typical range of model parameters, we find that the decay rates of the ordinary lightest neutralino into hidden gauge boson/gaugino and photon/gravitino are comparable, and the former decay mode leaves displaced vertices of lepton pairs and missing energy with distinctive length scale larger than 20 cm for invariant lepton pair mass below 0.5 GeV. An unsatisfactory aspect of our model is that the Sommerfeld effect cannot raise the galactic dark matter annihilation by more than 60 times for the dark matter mass below TeV.

Figures (4)

• Figure 1: The Sommerfeld enhancement factor $S$ as a function of $m_{\widetilde{\psi}_1}$ for various $m_X$.
• Figure 2: Diagrams relevant to $\widetilde{\psi}_1$-nucleon elastic scattering.
• Figure 3: Exclusion plot for the spin-independent $\tilde{\psi}_1$-nucleon cross-section $\sigma_{\rm SI}$. The solid lines are the cross-sections via vector interactions with $m_X=0.4$ GeV corresponding to $\theta=10^{-5}, 10^{-6}$, and $10^{-7}$, respectively. The dashed lines are through Higgs exchange corresponding to $\lambda=1$ and 0.1, respectively, taking $m_h=115$ GeV. The thin solid (dashed) line shows the CDMS II limit for the vector (scalar) interaction.
• Figure 4: One-loop diagrams responsible for the decay of singlino $\widetilde{S}$ to $X\widetilde{X}$.