Hidden gauginos of an unbroken U(1): Cosmological constraints and phenomenological prospects

TL;DR

This work analyzes supersymmetric models with an unbroken hidden U(1) whose gaugino serves as dark matter and communicates with the MSSM via kinetic mixing with hypercharge. A radiatively generated bino–hidden gaugino mixing yields an extended neutralino sector, and the authors derive stringent cosmological bounds from thermal overproduction, BBN, and structure formation, delineating viable NLSP configurations. They find that neutralino NLSP scenarios are largely excluded, while slepton NLSPs survive only for χ in the range ~10^{-10}–10^{-13}, potentially producing detectable long-lived charged tracks at colliders; gravitino DM scenarios can have relaxed reheating-temperature bounds due to hidden-sector contributions. In the limit of extremely small χ, the neutralino can become decaying DM, with gamma-ray data imposing stringent constraints (χ ≲ 10^{-20}–10^{-21} for representative masses). The results illustrate rich cosmological and collider phenomenology arising from a hidden, kinetically mixed U(1) sector coupled to MSSM physics.

Abstract

We study supersymmetric scenarios where the dark matter is the gaugino of an unbroken hidden U(1) which interacts with the visible world only via a small kinetic mixing with the hypercharge. Strong constraints on the parameter space can be derived from avoiding overclosure of the Universe and from requiring successful Big Bang Nucleosynthesis and structure formation. We find that for typical values of the mixing parameter, scenarios with neutralino NLSP are excluded, while scenarios with slepton NLSP are allowed when the mixing parameter lies in the range chi~O(10^(-13) - 10^(-10)). We also show that if the gravitino is the LSP and the hidden U(1) gaugino the NLSP, the bounds on the reheating temperature from long lived charged MSSM relics can be considerably relaxed and we comment on the signatures of these scenarios at future colliders. Finally, we discuss the case of an anomalously small mixing, chi<<10^(-16), where the neutralino becomes a decaying dark matter candidate, and derive constraints from gamma ray experiments.

Figures (6)

• Figure 1: Summary of bounds on the hidden $U(1)$ gaugino parameter space for the case of a slepton NLSP. We use $M_{\tilde{l}}=150\,{\rm GeV}$ and $M_B=180\,{\rm GeV}$. The upper dark blue region is excluded by thermal overproduction. Below this region, the hidden $U(1)$ gaugino is dominantly produced via late decaying sleptons. The light blue region is excluded by energy injection during BBN KKM05, whereas the light green region is excluded by catalysis of $^6\text{Li}$ production Pospelov07. We also show the region which would be excluded solely by free streaming arguments. The dotted lines show the slepton lifetime. In the presence of a gravitino with $M_{\tilde{G}} = 100\,{\rm GeV}$ the slepton would dominantly decay into the hidden $U(1)$ gaugino, except in the red lower region. The dashed lines show the region that is potentially excluded by bounds on $\Lambda$CWDM models in scenarios where the thermally produced hidden $U(1)$ gaugino decays into a gravitino LSP with large free streaming length (see Fig. \ref{['fig:FSXandGravitino']}). The lines correspond to a dark matter fraction $f=0.02$ and $f=0.2$ which is allowed to be warm.
• Figure 2: Summary of bounds on the hidden $U(1)$ gaugino parameter space for the case of a bino-like neutralino NLSP. We take $M_B=150\,{\rm GeV}$. The dark blue region is excluded by thermal overproduction. Below this region, the hidden $U(1)$ gaugino would be dominantly produced via late decaying neutralinos. This scenario is totally excluded by BBN KKM05 (light blue region). The bound actually strongly overlaps with the overproduction region (dashed line). We also show the region (in yellow) that would be solely excluded by free streaming arguments. The dotted lines show the lifetime of the neutralino. (We used $M_\text{sf}=400\,{\rm GeV}$ and $\mu=300\,{\rm GeV}$ for the branching ratios).
• Figure 3: Spectra for (a) gravitino NLSP and (b) gravitino LSP ( cf. last two cases in Tab. \ref{['tab:Spectra']}). We show the widths for the different decay processes for typical particle masses. The mixing parameter is assumed to lie in the allowed region of Fig. \ref{['fig:boundsSlepton']}.
• Figure 4: Contour plot of free streaming lengths in units of $\text{Mpc}$. The upper left (lower right) corner shows the free streaming length of gravitinos (hidden $U(1)$ gauginos) that stem from the late decay of hidden $U(1)$ gauginos (gravitinos).
• Figure 5: Bounds on the reheating temperature as function of the gravitino mass, using Eq. \ref{['eqn:GravitinoProduction']} with $m_{\tilde{g}}=800\,{\rm GeV}$. The mass of the hidden $U(1)$ gaugino is fixed to $M_X=120\,{\rm GeV}$. If the gravitino is the LSP (left part), the reheating temperature is only bounded by overproduction arguments (dark red region), which are only slightly strengthened when, say, 20% of the gravitino abundance is due to non-thermal production (light red region). A gravitino NLSP (right part) would late decay into the hidden $U(1)$ gaugino, yielding a warm dark matter component. If only a fraction of $20\%$ or $2\%$ of dark matter is allowed to be warm (with free streaming lengths as shown in Fig. \ref{['fig:FSXandGravitino']}), the corresponding blue regions are excluded.