Cluster X-ray line at $$3.5~\mathrm{keV}$$ 3.5 keV from axion-like dark matter

We show that the required high quality of the Peccei-Quinn symmetry can be naturally explained in the aligned QCD axion models where the QCD axion arises from multiple axions with decay constants much smaller than the axion window, e.g., around the weak scale. Even in the presence of general Planck-suppressed Peccei-Quinn symmetry breaking operators, the effective strong CP phase remains sufficiently small in contrast to the standard axion models without the alignment. The QCD axion potential has small or large modulations due to the symmetry breaking operators, which can significantly affect the axion cosmology. When the axions are trapped in different minima, domain walls appear and their scaling behavior suppresses the axion isocurvature perturbations at super-horizon scales. Our scenario predicts many axions and saxions coupled to gluons, and they may be searched for at collider experiments. In particular, the recently found diphoton excess at 750 GeV could be due to one of such (s)axions.

Section: Jhep06(2016)150mentioning

confidence: 99%

Quality of the Peccei-Quinn symmetry in the aligned QCD axion and cosmological implications

Higaki

Jeong

Kitajima

et al. 2016

“…Nevertheless, a large number of DM models have been proposed to explain this signal. The ideas that have been proposed include sterile neutrinos , axions [70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85], supersymmetry [86][87][88][89][90][91][92] and a number of other mechanisms . We now show that the 3.5 keV line, if confirmed, can be easily accommodated within the framework of the minimal model.…”

Section: The 35 Kev Linementioning

confidence: 99%

A couplet from flavored dark matter

Agrawal

Chacko

Kılıç

et al. 2015

We show that a couplet, a pair of closely spaced photon lines, in the X-ray spectrum is a distinctive feature of lepton flavored dark matter models for which the mass spectrum is dictated by Minimal Flavor Violation. In such a scenario, mass splittings between different dark matter flavors are determined by Standard Model Yukawa couplings and can naturally be small, allowing all three flavors to be long-lived and contribute to the observed abundance. Then, in the presence of a tiny source of flavor violation, heavier dark matter flavors can decay via a dipole transition on cosmological timescales, giving rise to three photon lines. Two of these lines are closely spaced, and constitute the couplet. Provided the flavor violation is sufficiently small, the ratios of the line energies are determined in terms of the charged lepton masses, and constitute a prediction of this framework. For dark matter masses of order the weak scale, the couplet lies in the keV-MeV region, with a much weaker line in the eV-keV region. This scenario constitutes a potential explanation for the recent claim of the observation of a 3.5 keV line. The next generation of X-ray telescopes may have the necessary resolution to resolve the double line structure of such a couplet.

“…It is because the Lagrangian (2.1) has additional symmetry, i.e. scale invariance for the transformation 8) in the limit µ 2 η → 0. We should get non-trivial mixing in ψ i states to generate TMDO.…”

Section: Jhep08(2015)023mentioning

confidence: 99%

3.5 keV X-ray line signal from dark matter decay in local U(1)B−L extension of Zee-Babu model

Baek¹

2015

We consider a local U(1) B−L extension of Zee-Babu model to explain the recently observed 3.5 keV X-ray line signal. The model has three Standard model (SM)-singlet Dirac fermions with different U(1) B−L charges. A complex scalar field charged under U(1) B−L is introduced to break the U(1) B−L symmetry. After U(1) B−L symmetry breaking a remnant discrete symmetry stabilizes the lightest state of the Dirac fermions, which can be a stable dark matter (DM). The second lightest state, if mass splitting with the stable DM is about 3.5 keV, decays dominantly to the stable DM and 3.5 keV photon through two-loop diagrams, explaining the X-ray line signal. Two-loop suppression of the decay amplitude makes its lifetime much longer than the age of the universe and it can be a decaying DM candidate in large parameter region. We also introduce a real scalar field which is singlet under both the SM and U(1) B−L and can explain the current relic abundance of the Dirac fermionic DMs. If the mixing with the SM Higgs boson is small, it does not contribute to DM direct detection. The main contribution to the scattering of DM off atomic nuclei comes from the exchange of U(1) B−L gauge boson, Z ′ , and is suppressed below current experimental bound when Z ′ mass is heavy ( 10 TeV). If the singlet scalar mass is about 0.1-10 MeV, DM self-interaction can be large enough to solve small scale structure problems in simulations with the cold DM, such as, the core-vs-cusp problem and too-big-to-fail problem.