Decaying into the Hidden Sector

TL;DR

This work presents a natural, modular framework for decaying DM into a GeV-scale hidden sector that communicates with the SM via gauge kinetic mixing. DM decays are driven by dimension-6 operators suppressed by the GUT scale, yielding lifetimes near $10^{26}$ s and GeV-scale cascades that produce observable leptons and photons while avoiding antiproton and CMB constraints. The authors develop tools to construct viable models across energy scales (GUT, weak, GeV, MeV), and provide four explicit realizations, including a minimal $U(1)_d$ model, a UV-completed $SU(2)_d$ setup, a SM-charged DM model with correlated neutrinos, and a double kinetic-mixing $U(1)_\chi \times U(1)_d$ scenario. Cosmology is shown to accommodate a thermal relic and GeV-scale dynamics without conflicting with BBN or recombination, while predicting sharp indirect signatures such as primary photons and correlated neutrinos that can distinguish decaying from annihilating DM in upcoming experiments.

Abstract

The existence of light hidden sectors is an exciting possibility that may be tested in the near future. If DM is allowed to decay into such a hidden sector through GUT suppressed operators, it can accommodate the recent cosmic ray observations without over-producing antiprotons or interfering with the attractive features of the thermal WIMP. Models of this kind are simple to construct, generic and evade all astrophysical bounds. We provide tools for constructing such models and present several distinct examples. The light hidden spectrum and DM couplings can be probed in the near future, by measuring astrophysical photon and neutrino fluxes. These indirect signatures are complimentary to the direct production signals, such as lepton jets, predicted by these models.

Figures (5)

• Figure 1: We summarize our notations, organized by energy scale. $X$ and $Y$ denote GUT scale fields that are integrated out to generate dimension-6 operators that induce DM decays. We use $\langle H \rangle$ to denote a GUT scale VEV, which can partially break the dark gauge group, $G_{d}^\prime \rightarrow G_{d}$, as demonstrated in section \ref{['sec:SU2']}. The DM may be composed of multiple species, $\chi_i$, with mass at the TeV scale. This scale is naturally generated through the VEV of a singlet, $S$, that communicates with the SUSY breaking sector. Here, $N_i$ denote electroweak scale fields that participate in the mechanism that generates a DM mass splitting. Such splittings can help evade the bounds from direct detection, as we discuss in section \ref{['sec:mev-scale']}. The dark gauge group, with gauge bosons $\gamma_d^i$, is entirely broken at the GeV scale by the VEVs of light Higgses. DM decays by dimension-6 operators into these GeV scale states. We use $h_i$ to denote light fields charged under the dark gauge group, at least some of which will receive VEVs, and we use $n$ to denote a light singlet.
• Figure 2: A sample DM 3-body decay induced by one of the two last operators of Eq. \ref{['eq:decayop3bod']}. The DM decays to a GeV-scale gauge boson, gaugino, and a neutrino or the lighter field, $\chi_1$. The gauge boson decays through the kinetic mixing to a lepton pair and the gaugino decays through the kinetic mixing to a photon and gravitino, assuming that the gaugino is lighter than, or degenerate with, the dark photon. The resulting leptons can explain the PAMELA and FERMI excesses while the gamma rays and neutrinos lead to hard and sharp spectral features that can be probed by upcoming experiments Ruderman:2009ta.
• Figure 3: The setup of our minimal model. DM is charged under the hidden sector, $U(1)_{d}$, and decays through dimension-6 GUT scale suppressed operators into the dark sector gauge multiplet. $U(1)_{d}$ kinetically mixes with hypercharge, and this kinetic mixing has three important effects: (i) D-term mixing causes $U(1)_{d}$ to break at the GeV scale, (ii) dark gauge bosons decay through the kinetic mixing to leptons while decays into antiprotons are kinematically forbidden, and (iii) DM stays in kinetic equilibrium with the SM through the kinetic mixing, allowing for the usual 'WIMP Miracle' cosmology (see section \ref{['sec:cosmology']}).
• Figure 4: A model with DM charged under the SM. DM is the neutral component of a $\bf 5 + \bar{5}$ representation of $SU(5)_{\rm SM} \supset SU(3)_C\times SU(2)_W \times U(1)_Y$. DM decays through a dimension-6 operator into the gauge multiplet of $U(1)_{d}$, which kinetically mixes with hypercharge. The conservation of hypercharge (at the GUT scale) implies that this decay must be accompanied by the associated production of a neutrino. This results in a primary neutrino spectrum that is correlated with the leptonic cosmic rays, and will be tested by upcoming experiments such as IceCube/DeepCore Ruderman:2009ta.
• Figure 5: A model with double kinetic mixing. DM, $\chi_2$, is charged under $U(1)_\chi$, which is broken by a different species, $\chi_1$, at the TeV scale. Decays are induced by a dimension-6 GUT suppressed operator into the $U(1)_{d}$ gauge multiplet, which kinetically mixes with both hypercharge and $U(1)_\chi$. This double kinetic mixing is sufficient to keep DM in kinetic equilibrium with the SM, preserving the usual WIMP cosmology (see section \ref{['sec:cosmology']}). There is no strong constraint from direct detection because the DM does not couple directly to the $Z$ or $U(1)_{d}$ gauge boson, and therefore no DM splitting is required.