Non-abelian dark matter solutions for Galactic gamma-ray excess and Perseus 3.5 keV X-ray line

Abstract

We attempt to explain simultaneously the Galactic center gamma-ray excess and the 3.5 keV X-ray line from the Perseus cluster based on a class of non-abelian SU (2) DM models, in which the dark matter and an excited state comprise a "dark" SU (2) doublet. The non-abelian group kinetically mixes with the standard model gauge group via dimensions-5 operators. The dark matter particles annihilate into standard model fermions, followed by fragmentation and bremsstrahlung, and thus producing a continuous spectrum of gamma-rays. On the other hand, the dark matter particles can annihilate into a pair of excited states, each of which decays back into the dark matter particle and an X-ray photon, which has an energy equal to the mass difference between the dark matter and the excited state, which is set to be 3.5 keV. The large hierarchy between the required X-ray and γ-ray annihilation cross-sections can be achieved by a very small kinetic mixing between the SM and dark sector, which effectively suppresses the annihilation into the standard model fermions but not into the excited state.A gamma-ray excess around a few GeV near the Galactic center (GC) region, seen by the Fermi-LAT collaboration (see, for instance, the recent analysis by the collaboration [1]), has been widely discussed based on dark matter (DM) annihilations into standard model (SM) fermions [2][3][4][5][6][7][8][9][10][11][12][13][14][15], which hadronize into neutral pions followed by π 0 → γγ, or electromagnetic bremsstrahlung. On the other hand, recent reports of the 3.5 keV X-ray line [16,17] from the XMM-Newton data have triggered many studies in the context of DM, for example, Refs. . Roughly speaking, they can be classified into two categories: (i) DM undergoes upscattering into an excited stated followed by the decay back into DM and an X-ray photon; and (ii) decaying DM matter, such as a 7 keV sterile neutrino decaying into an active neutrino and the X-ray photon. The excited DM, however, has a advantage of explaining some null results on X-ray line searches due to a low local DM velocity as shown in Ref [66].There is a very interesting connection between the γ-ray excess and X-ray line as follows. The GC γ-ray excess can be explained by annihilating DM with a mass from 10 to 60 GeV [2, 5-8, 10-12], depending on the final state of the annihilation. On the other hand, due to the fact that the current DM velocity is around 10 −3 c in the Perseus cluster, where the X-ray line is observed, the DM with a mass of 10 to 60 GeV coincidently has a kinetic energy of a few keV. It implies if there exists an excited state with a 3.5 keV mass splitting from the DM particle, then the DM particles can annihilate into the excited state, followed by the decay back into the DM particle with a photon accounting for the observed X-ray line.In this work, we employ a class of non-abelian SU (2) X DM models proposed in Refs. [18,67], where the DM particle and the excited state form an SU (2) X doublet with a 3.5 keV mass splitting. The SU (2) X kinetically mixes with ...

Dark sector portal with vectorlike leptons and flavor sequestering

“…and with v = 246 GeV. Defining the column vector Υ ≡ (e, χ (1) , χ (2) ) T , which displays the two components of the χ doublet, we may write the mass matrix that is produced after spontaneous symmetry breaking by…”

“…IV), and that the dark gauge bosons are heavier than the dark matter fermion. The coupling matrices U † R T a U R , for a = 1 and a = 3 allow decays of A 1 D and A 3 D directly to e + e − ; the same is not true for a = 2, but the A 2 D boson does couple to the two different ψ mass eigenstates, which we will call ψ (1) (the lighter, dark matter component) and ψ (2) (the heavier). The eigenstate ψ (2) can decay to dark matter…”

“…Examples of non-Abelian dark matter models can be found in Refs. [1][2][3][4][5][6][7] and [8,9], though we will not focus on models like those in Refs. [8,9] where the dark gauge boson is itself the dark matter.…”

“…Our focus differs from that of Refs. [1][2][3][4][5][6][7], where the origin of higher-dimension operators connecting the dark and visible sectors was either unspecified, or assumed to arise from a sector whose flavor structure and phenomenology was not explicitly investigated.…”

The dark penguin shines light at colliders

“…As a consequence, these operators play important roles in the possible explanation of various γ-ray excesses observed at indirect detection experiments [52][53][54][55][56][57][58]. Moreover, being chirality-flipping, these operators can possess a non-trivial flavor structure when more than one species of dark fermions χ i is present.…”