Abstract
We construct a thermal dark matter model with annihilation mediated by a resonance to explain the positron excess observed by PAMELA, Fermi-LAT and AMS-02, while satisfying constraints from cosmic microwave background (CMB) measurements. The challenging requirement is that the resonance has twice the dark matter mass to one part in a million. We achieve this by introducing an $SU(3{)}_{f}$ dark flavor symmetry that is spontaneously broken to $SU(2{)}_{f}\ifmmode\times\else\texttimes\fi{}U(1{)}_{f}$. The resonance is the heaviest state in the dark matter flavor multiplet, and the required mass relation is protected by the vacuum structure and supersymmetry from radiative corrections. The pseudo-Nambu-Goldstone bosons (PNGBs) from the dark flavor symmetry breaking can be slightly lighter than one GeV and dominantly decay into two muons just from kinematics, with subsequent decay into positrons. The PNGBs are produced in resonant dark matter semiannihilation, where two dark matter particles annihilate into an anti--dark matter particle and a PNGB. The dark matter mass in our model is constrained to be below around 1.9 TeV from fitting thermal relic abundance, AMS-02 data and CMB constraints. The superpartners of Standard Model (SM) particles can cascade decay into a light PNGB along with SM particles, yielding a correlated signal of this model at colliders. One of the interesting signatures is a resonance of a SM Higgs boson plus two collimated muons, which has superb discovery potential at LHC Run 2.
Highlights
It is beyond doubt that the majority of matter in the Universe is composed of dark matter, yet we still don’t know how to describe the particle properties, if any, of dark matter as we can with other particles in the Standard Model (SM)
We explore a new and natural way to realize resonant dark matter annihilation based on the symmetry breaking vacuum structure of non-Abelian global symmetry
The tiny mass splittings among different components could be crucial for the dark matter phenomenology and provide a natural model for the dark matter annihilation mediated by a resonance
Summary
It is beyond doubt that the majority of matter in the Universe is composed of dark matter, yet we still don’t know how to describe the particle properties, if any, of dark matter as we can with other particles in the Standard Model (SM). One of the simplest ways to explain the small mass splitting is to have the resonance be a bound state of two dark matter particles This scenario requires a long-range force to provide the binding energy and suffers the additional 1/v Sommerfeld enhancement for the annihilation rate at the CMB era. If the unbroken symmetry is nearly exact in the low energy theory, the vacuum structure of Φ should stay fairly stable and is not modified by quantum correction or higher-dimensional operators If this symmetry-breaking spurion, Φ, couples linearly to other matter fields that is fundamental under SUð3Þf, the SUð2Þfdoublet field should have a mass half of the SUð2Þf-singlet field, which is exactly the required condition to realize resonant dark matter or Breit-Wigner features for dark matter annihilations. Knowing the vacuum structure of the SRDM model, we first work out the particle spectrum and properties, followed by the dark matter annihilation rate
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