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

Abstract

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.

Scalar dark matter search from the extended νTHDM

“…Hence v 1 is considered to be smaller than the other VEVs. It also interesting to notice that µ = 0 restores the symmetry of the Lagrangian hence a technically natural small value of µ is acceptable [15,16]. It is also interesting to notice that µ = 0 enhances the symmetry of the Lagrangian in the sense that we can assign arbitrary U (1) X charge to Φ 1 , which ensures the radiative generation of the µ-term is proportional to µ itself.…”

“…They correspond to massive pseudo-scalar, the masslesss Nambu-Goldstone (NG) mode which is absorbed by the Z boson, and a massless physical Goldstone boson associated with the U (1) X breaking, respectively. Hence the mass of A is given by 16) which is at the electroweak scale. It can be shown [12] that the Goldstone boson, a, is safe from the phenomenological constraints such as Z → H i a(i = 1, 2, 3) decay, stellar cooling from the interaction aeγ 5 e, etc., because it interacts with the SM particles only via highly-suppressed (∼ v 1 /v 2,S ) mixing with the SM Higgs.…”

Dark matter physics in neutrino specific two Higgs doublet model

“…From (2.5) we find that v 1 is proportonial to and of the same order with µ: [5,6] because µ ≡ 0 enhances the symmetry of the Lagrangian (2.1) to additional U(1) under which only the S field is charged while all the others are neutral.…”

Flavour dependent gauged radiative neutrino mass model

“…The original model based on the idea of radiative generation of neutrino masses is known as the Zee model [1] proposed in early 80's, where neutrino masses are generated at the one-loop level. After the Zee model, the Zee-Babu model [2][3][4][5][6][7] has also been proposed, where neutrino masses are explained at the two-loop level. In 2000's, radiative neutrino mass models have been extended so as to include a dark matter (DM) candidate by introducing an unbroken symmetry such as a discrete Z 2 symmetry known as; e.g., the models by Krauss-Nasri-Trodden [8,9] and by Ma [10][11][12][13][14][15][16][17].…”