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 Physics , 2012, DOI: 10.1007/JHEP10(2012)134 Abstract: There is evidence for a 130 GeV gamma-ray line at the Galactic Center in the Fermi Large Area Telescope data. Dark matter candidates that explain this feature should also annihilate to Standard Model particles, resulting in a continuous spectrum of photons. To study this continuum, we analyze the Fermi data down to 5 GeV, restricted to the inner 3 degrees of the Galaxy. We place a strong bound on the ratio of continuum photons to monochromatic line photons that is independent of uncertainties in the dark matter density profile. The derived constraints exclude neutralino dark matter as an explanation for the line.
 Physics , 2012, Abstract: The gamma-ray line from dark matter (DM) annihilation is too weak to observe, but its observation will uncover much information, e.g., the DM mass and an nomalously large annihilation rate $\sim0.1$ pb into di-photon. In this work, we construct a minimal effective theory (EFT) incorporating DM and heavier charged particles. A large annihilation rate is obtained from operator coefficients with resonance or strong coupling enhancement. The EFT is stringently constrained by the XENON100 and WMAP data. Without resonance, Dirac DM or colored charged particles are ruled out. It is pointed out that the di-gluon mode may correctly determine the DM relic density. Interestingly, this framework also provides an origin for the Higgs di-photon excess at the LHC\@. We apply the general analysis to the NMSSM, which can elegantly interpret the tentative 130 GeV gamma-ray line. A top-window model is also proposed to explain the gamma-ray line.
 Physics , 2013, Abstract: We apply the axion-photon conversion mechanism to the 130 GeV $\gamma$-ray line observed by the Fermi satellite. Near the Galactic center, some astrophysical sources and/or particle dark matter can produce energetic axions (or axionlike particles), and the axions convert to $\gamma$ rays in Galactic magnetic fields along their flight to the Earth. Since continuum $\gamma$-ray and antiproton productions are sufficiently suppressed in axion production, the scenario fits the 130 GeV $\gamma$-ray line without conflicting with cosmic ray measurements. We derive the axion production cross section and the decay rate of dark matter to fit the $\gamma$-ray excess as functions of axion parameters. In the scenario, the $\gamma$-ray spatial distributions depend on both the dark matter profile and the magnetic field configuration, which will be tested by future $\gamma$-ray observations, e.g., H.E.S.S. II, CTA, and GAMMA-400. As an illustrative example, we study realistic supersymmetric axion models, and show the favored parameters that nicely fit the $\gamma$-ray excess.
 Bibhushan Shakya Physics , 2012, Abstract: The viability of neutralino dark matter as an explanation of the 130 GeV gamma ray signal from the Galactic Center recently observed by the Fermi Large Area Telescope is examined. It is found that the signal can be compatible with a sharp feature from internal bremsstrahlung from a mostly bino dark matter particle of mass around 145 GeV, augmented by a contribution from annihilation into gamma+Z via a small wino admixture. This scenario circumvents the problematic overproduction of lower energy continuum photons that plague line interpretations of this signal. Sleptons approximately degenerate in mass with the neutralino are required to enhance the internal bremsstrahlung feature.
 Physics , 2012, DOI: 10.1103/PhysRevD.86.043524 Abstract: Recent reports of a gamma-ray line feature at ~130 GeV in data from the Fermi Gamma-Ray Space Telescope have generated a great deal of interest in models in which dark matter particles annihilate with a sizable cross section to final states including photons. In this article, we take a model-independent approach, and discuss a number of possibilities for dark matter candidates which could potentially generate such a feature. While we identify several scenarios which could lead to such a gamma-ray line, these models are each fairly constrained. In particular, viable models require large couplings (g>1-3), and additional charged particles with masses in the range of approximately ~130-200 GeV. Furthermore, lower energy gamma-ray constraints from the Galactic Center force us to consider scenarios in which the dark matter annihilates in the early universe through velocity-suppressed processes, or to final states which yield relatively few gamma-rays (such as electrons, muons or neutrinos). An exception to these conclusions can be found in models in which the dark matter annihilates to heavy intermediate states which decay to photons to generate a line-like gamma-ray spectrum.
 James M. Cline Physics , 2012, DOI: 10.1103/PhysRevD.86.015016 Abstract: Based on tentative evidence for a peak in the Fermi gamma-ray spectrum originating from near the center of the galaxy, it has been suggested that dark matter of mass ~130 GeV is annihilating directly into photons with a cross section ~24 times smaller than that needed for the thermal relic density. We propose a simple particle physics model in which the DM is a scalar X, with a coupling lambda_X X^2|S|^2 to a scalar multiplet S carrying electric charge, which allows for XX -> gamma gamma at one loop due to the virtual S. We predict a second monochromatic photon peak at 114 GeV due to XX-> gamma Z. The S is colored under a hidden sector SU(N) or QCD to help boost the XX -> gamma gamma cross section. The analogous coupling lambda_h h^2 |S|^2 to the Higgs boson can naturally increase the partial width for h -> gamma gamma by an amount comparable to its standard model value, as suggested by recent measurements from CMS. Due to the hidden sector SU(N) (or QCD), S binds to its antiparticle to form S-mesons, which will be pair-produced in colliders and then decay predominantly to XX, hh, or to glueballs of the SU(N) which subsequently decay to photons. The cross section for X on nucleons is close to the Xenon100 upper limit, suggesting that it should be discovered soon by direct detection.
 High Energy Physics - Phenomenology , 2013, Abstract: Recent observations indicating the existence of a monochromatic gamma-ray line with energy ~130 GeV in the Fermi-LAT data have attracted great interest due to the possibility that the line feature stems from the annihilation of dark matter particles. Many studies examining the robustness of the putative line-signal have concentrated on its spectral attributes. Here, we study the morphological features of the gamma-ray line photons, which can be used to differentiate a putative dark matter signal from astrophysical backgrounds or instrumental artifacts. Photons stemming from dark matter annihilation will produce events tracing a specific morphology, with a statistical clustering that can be calculated based on models of the dark matter density profile in the inner Galaxy. We apply the DBSCAN clustering algorithm to Fermi gamma-ray data, and show that we can rule out the possibility that 1 (2, 4) or fewer point-like sources produce the observed morphology for the line photons at a 99% (95%, 90%) confidence level. Our study strongly disfavors the main astrophysical background envisioned to produce a line feature at energies above 100 GeV: cold pulsar winds. It is highly unlikely that 4 or more such objects have exactly the same monochromatic cosmic-ray energy needed to produce a gamma-ray line, to within instrumental energy resolution. Furthermore, we show that the larger photon statistics expected with Air Cherenkov Telescopes such as H.E.S.S.-II will allow for extraordinarily stringent morphological tests of the origin of the "line photons".
 Physics , 2013, DOI: 10.1103/PhysRevD.88.043006 Abstract: Recent observations indicating the existence of a monochromatic gamma-ray line with energy ~130 GeV in the Fermi-LAT data have attracted great interest due to the possibility that the line feature stems from the annihilation of dark matter particles. Many studies examining the robustness of the putative line-signal have concentrated on its spectral attributes. Here, we study the morphological features of the gamma-ray line photons, which can be used to differentiate a putative dark matter signal from astrophysical backgrounds or instrumental artifacts. Photons stemming from dark matter annihilation will produce events tracing a specific morphology, with a statistical clustering that can be calculated based on models of the dark matter density profile in the inner Galaxy. We apply the DBSCAN clustering algorithm to Fermi gamma-ray data, and show that we can rule out the possibility that 1 (2, 4) or fewer point-like sources produce the observed morphology for the line photons at a 99% (95%, 90%) confidence level. Our study strongly disfavors the main astrophysical background envisioned to produce a line feature at energies above 100 GeV: cold pulsar winds. It is highly unlikely that 4 or more such objects have exactly the same monochromatic cosmic-ray energy needed to produce a gamma-ray line, to within instrumental energy resolution. Furthermore, we show that the larger photon statistics expected with Air Cherenkov Telescopes such as H.E.S.S.-II will allow for extraordinarily stringent morphological tests of the origin of the "line photons".
 Physics , 2013, Abstract: Dark matter annihilation into photons in our galaxy would constitute an exciting indirect signal of its existence, as underscored by tentative evidence for 130 GeV dark matter in Fermi/LAT data. Models that give a large annihilation cross section into photons typically require the dark matter to couple to, or be composed of, new charged particles, that can be produced in colliders. We consider the LHC constraints on some representative models of these types, including the signals of same-sign dileptons, opposite-sign dileptons, events mimicking the production and decay of excited leptons, four-photon events, resonant production of composite vectors decaying into two photons, and monophoton events.
 Physics , 2012, DOI: 10.1016/j.physletb.2012.12.041 Abstract: The 130 GeV gamma-ray line based on tentative analyses on the Fermi-LAT data is hard to be understood with dark matter annihilation in the conventional framework of the MSSM. We point out that it can be nicely explained with two body decay of a scalar dark matter ($\tilde{\phi}_{\rm DM}\rightarrow\gamma\gamma$) by the dimension 6 operator suppressed with the mass of the grand unification scale ($\sim 10^{16}$ GeV), ${\cal L}\supset|\tilde{\phi}_{\rm DM}|^2F_{\mu\nu}F^{\mu\nu}/M_{\rm GUT}^2$, in which the scalar dark matter $\tilde{\phi}_{\rm DM}$ develops a TeV scale vacuum expectation value. We propose a viable model explaining the 130 GeV gamma-ray line.
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