Monochromatic Gamma-ray Lines Research Articles

Studying dark matter with MadDM: lines and loops

Automated tools for the computation of amplitudes and cross sections have become the backbone of phenomenological studies beyond the standard model. We present the latest developments in MadDM, a calculator of dark-matter observables based on MadGraph5_aMC@NLO. The new version enables the fully automated computation of loop-induced annihilation processes, relevant for indirect detection of dark matter. Of particular interest is the direct annihilation into photons, γγ, γX. These processes lead to monochromatic gamma-ray lines that are smoking-gun signatures for dark-matter annihilation in our Galaxy. MadDM computes the predictions for the expected photon fluxes near Earth and derives constraints from the gamma-ray line searches by Fermi-LAT and HESS. As an application, we present the implications for the parameter space of the Inert Doublet Model.

Pseudo-Goldstone dark matter confronts cosmic ray and collider anomalies

Persistent excesses in the spectra of gamma rays from the galactic center and cosmic ray antiprotons can be explained by dark matter of mass $50\sim 65$\,GeV annihilating into $b$ quarks, but this is typically hard to reconcile with direct detection constraints. We resolve this tension using a simple class of models, where dark matter is a pseudo-Nambu-Goldstone boson, having naturally momentum-suppressed couplings to nuclei. Exploring the parameter space of the model, we find that it can explain the cosmic ray anomalies while remaining compatible with constraints from the relic abundance and annihilation in dwarf spheroidal galaxies. In certain regions of parameter space, the Higgs-dark matter coupling can help stabilize the Higgs potential up to the Planck scale. The scalar partner of the dark matter is an extra Higgs boson, that can explain a tentative diphoton excess observed by CMS, and an excess of $b\bar b$ signal from LEP, if its mass is $\sim 96$\,GeV and the model is extended to include a heavy scalar quark. This extended model predicts a monochromatic gamma-ray line near 64 GeV, at a level close to current experimental sensitivity, from dark matter annihilations in the galaxy.

Dark matter decay to a photon and a neutrino: The double monochromatic smoking gun scenario

In the energy range from few TeV to 25 TeV, upper bounds on the dark matter decay rate into high energy monochromatic neutrinos have recently become comparable to those on monochromatic gamma-ray lines. This implies clear possibilities of a future double "smoking-gun" evidence for the dark matter particle, from the observation of both a gamma and a neutrino line at the same energy. In particular, we show that a scenario where both lines are induced from the same dark matter particle decay leads to correlations that can already be tested. We study this "double monochromatic" scenario by considering the complete list of lowest dimensional effective operators that could induce such a decay. Furthermore, we argue that, on top of lines from decays into two-body final states, three-body final states can also be highly relevant. In addition to producing a distinct hard photon spectrum, three-body final states also produce a line-like feature in the neutrino spectrum that can be searched for by neutrino telescopes.

Perspective of monochromatic gamma-ray line detection with the High Energy cosmic-Radiation Detection (HERD) facility onboard China’s space station

HERD is the High Energy cosmic-Radiation Detection instrument proposed to operate onboard China’s space station in the 2020s. It is designed to detect energetic cosmic ray nuclei, leptons and photons with a high energy resolution ( ∼1% for electrons and photons and 20% for nuclei) and a large geometry factor (>3 m2 sr for electrons and diffuse photons and > [2]m2 sr for nuclei). In this work we discuss the capability of HERD to detect monochromatic γ-ray lines, based on simulations of the detector performance. It is shown that HERD will be one of the most sensitive instruments for monochromatic γ-ray searches at energies between ∼ 10 to a few hundred GeV. Above hundreds of GeV, Cherenkov telescopes will be more sensitive due to their large effective area. As a specific example, we show that a good portion of the parameter space of a supersymmetric dark matter model can be probed with HERD.

Closing in on singlet scalar dark matter: LUX, invisible Higgs decays and gamma-ray lines

We study the implications of the Higgs discovery and of recent results from dark matter searches on real singlet scalar dark matter. The phenomenology of the model is defined by only two parameters, the singlet scalar mass $m_S$ and the quartic coupling $a_2$ between the SU(2) Higgs and the singlet scalar. We concentrate on the window $5 < m_S/{\rm GeV} < 300$. The most dramatic impact on the viable parameter space of the model comes from direct dark matter searches with LUX, and, for very low masses in the few GeV range, from constraints from the invisible decay width of the Higgs. In the resonant region the best constraints come from gamma-ray line searches. We show that they leave only a small region of viable parameter space, for dark matter masses within a few percent of half the mass of the Higgs. We demonstrate that direct and indirect dark matter searches (especially the search for monochromatic gamma-ray lines) will play a key role in closing the residual parameter space in the near future.

Enhanced line signals from annihilating Kaluza-Klein dark matter

Monochromatic gamma ray lines have long been known to provide potential smoking gun signals for annihilating dark matter. Here, we demonstrate that the situation is particularly interesting for Kaluza-Klein dark matter because resonant annihilation is generically expected for small, but not necessarily vanishing relative velocities of the annihilating particles. We calculate the contribution from those hitherto neglected resonances and show that the annihilation rate into monochromatic photons can be significantly enhanced, in a way that is much more pronounced than for the associated production of continuum photons. For favorable astrophysical conditions, this leads to promising prospects for the detection of TeV-scale Kaluza-Klein dark matter. We also point out that the situation may be even more interesting in the vicinity of black holes, like the supermassive black hole at the center of our Galaxy, where in principle center-of-mass energies much larger than the rest mass are available. In this case, annihilating Kaluza-Klein dark matter may show the striking and unique signature of several gamma ray lines, with an equidistant spacing corresponding to twice the compactification radius of the extra dimension.

Testing no-scale supergravity with the Fermi Space Telescope LAT

We describe a methodology for testing no-scale supergravity by the LAT instrument onboard the Fermi Space Telescope via observation of gamma ray emissions from lightest supersymmetric (SUSY) neutralino annihilations. For our test vehicle we engage the framework of the SUSY grand unified model no-scale flipped SU(5) with extra vector-like flippon multiplets derived from F-theory, known as -SU(5). We show that through compression of the light stau and light bino neutralino mass difference, where internal bremsstrahlung photons give a dominant contribution, the photon yield from annihilation of SUSY dark matter can be elevated to a number of events potentially observable by the Fermi-LAT in the coming years. Likewise, the increased yield in no-scale -SU(5) may also have rendered the existing observation of a 133 GeV monochromatic gamma ray line visible, if additional data should exclude systematic or statistical explanations. The question of intensity aside, no-scale -SU(5) can indeed provide a natural weakly interacting massive particle candidate with a mass in the correct range to yield γγ and γZ emission lines at mχ ∼ 133 GeV and mχ ∼ 145 GeV, respectively. Additionally, we elucidate the emerging empirical connection between recent Planck satellite data and no-scale supergravity cosmological models which mimic the Starobinsky model of inflation. Together, these experiments furnish rich alternate avenues for testing no-scale -SU(5), and similarly structured models, the results of which may lend independent credence to observations made at the Large Hadron Collider.

Clustering analysis of the morphology of the 130 GeV gamma-ray feature

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".

Extra U(1) as natural source of a monochromatic gamma ray line

Abstract Extensions of the Standard Model with an extra U′(1) abelian group generically generate terms coming from loops of heavy fermions, leading to three gauge boson couplings, in particular Z′Zγ. We show that WMAP data constrains the gauge coupling of the group g D to values comparable with the electro-weak ones, rather independently of the mass of Z′. Moreover, the model predicts a monochromatic γ-ray line which can fit a 130 GeV signal at the FERMI telescope for natural values of the Chern-Simons terms and a dark matter mass around 144.5 GeV.

Fermi LAT search for dark matter in gamma-ray lines and the inclusive photon spectrum

Dark matter particle annihilation or decay can produce monochromatic gamma-ray lines and contribute to the diffuse gamma-ray background. Flux upper limits are presented for gamma-ray spectral lines from 7 to 200 GeV and for the diffuse gamma-ray background from 4.8 GeV to 264 GeV obtained from two years of Fermi Large Area Telescope data integrated over most of the sky. We give cross section upper limits and decay lifetime lower limits for dark matter models that produce gamma-ray lines or contribute to the diffuse spectrum, including models proposed as explanations of the PAMELA and Fermi cosmic-ray data.

Fermi LAT search for internal bremsstrahlung signatures from dark matter annihilation

A commonly encountered obstacle in indirect searches for galacticdark matter is how to disentangle possible signals from astrophysicalbackgrounds. Given that such signals are most likely subdominant, the searchfor pronounced spectral features plays a key role for indirect detectionexperiments; monochromatic gamma-ray lines or similar features related tointernal bremsstrahlung, in particular, provide smoking gun signatures. Weperform a dedicated search for the latter in the data taken by the Fermigamma-ray space telescope during its first 43 months. To this end, we use anew adaptive procedure to select optimal target regions that takes intoaccount both standard and contracted dark matter profiles. The behaviour ofour statistical method is tested by a subsampling analysis of the full skydata and found to reproduce the theoretical expectations very well. Thelimits on the dark matter annihilation cross-section that we derive arestronger than what can be obtained from the observation of dwarf galaxies and,at least for the model considered here, collider searches. While theselimits are still not quite strong enough to probe annihilation rates expectedfor thermally produced dark matter, future prospects to do so are very good.In fact, we already find a weak indication, with a significance of 3.1σ(4.3σ) when (not) taking into account the look-elsewhere effect, foran internal bremsstrahlung-like signal that would correspond to a dark mattermass of ∼150 GeV; the same signal is also well fitted by a gamma-rayline at around 130 GeV. Although this would be a fascinating possibility, wecaution that a much more dedicated analysis and additional data will benecessary to rule out or confirm this option.

Gamma ray line constraints on effective theories of dark matter

A monochromatic gamma ray line results when dark matter particles in the galactic halo annihilate to produce a two body final state which includes a photon. Such a signal is very distinctive from astrophysical backgrounds, and thus represents an incisive probe of theories of dark matter. We compare the recent null results of searches for gamma ray lines in the galactic center and other regions of the sky with the predictions of effective theories describing the interactions of dark matter particles with the Standard Model. We find that the null results of these searches provide constraints on the nature of dark matter interactions with ordinary matter which are complementary to constraints from other observables, and stronger than collider constraints in some cases.

Indirect detection of light neutralino dark matter in the next-to-minimal supersymmetric standard model

We explore the prospects for indirect detection of neutralino dark matter in supersymmetric models with an extended Higgs sector (next-to-minimal supersymmetric standard model, or NMSSM). We compute, for the first time, one-loop amplitudes for NMSSM neutralino pair annihilation into two photons and two gluons, and point out that extra diagrams (with respect to the minimal supersymmetric standard model, or MSSM), featuring a potentially light $CP$-odd Higgs boson exchange, can strongly enhance these radiative modes. Expected signals in neutrino telescopes due to the annihilation of relic neutralinos in the Sun and in the Earth are evaluated, as well as the prospects of detection of a neutralino annihilation signal in space-based gamma-ray, antiproton and positron search experiments, and at low-energy antideuteron searches. We find that in the low mass regime the signals from capture in the Earth are enhanced compared to the MSSM, and that NMSSM neutralinos have a remote possibility of affecting solar dynamics. Also, antimatter experiments are an excellent probe of galactic NMSSM dark matter. We also find enhanced two-photon decay modes that make the possibility of the detection of a monochromatic gamma-ray line within the NMSSM more promising than in the MSSM, although likely below the sensitivity of next generation gamma-ray telescopes.

Cosmological evolution of homogeneous universal extra dimensions

Recent observational achievements within cosmology and astrophysics have lead to a concordance model in which the energy content in our Universe is dominated by presumably fundamentally new and exotic ingredients – dark energy and dark matter. To reveal the nature of these ingredients is one of the greatest challenges in physics.The detection of a signal in gamma rays from dark matter annihilation would significantly contribute to revealing the nature of dark matter. This thesis presents derived imprints in gamma-ray spectra that could be expected from dark matter annihilation. In particular, dark matter particle candidates emerging in models with extra space dimensions, extending the standard model to be supersymmetric, and introducing an inert Higgs doublet are investigated. In all these scenarios dark matter annihilation induces sizeable and distinct signatures in their gamma-ray spectra. The predicted signals are in the form of monochromatic gamma-ray lines or a pronounced spectrum with a sharp cutoff at the dark matter particle’s mass. These signatures have no counterparts in the expected astrophysical background and are therefore well suited for dark matter searches.Furthermore, numerical simulations of galaxies are studied to learn how baryons, that is, stars and gas, affect the expected dark matter distribution inside disk galaxies such as the Milky Way. From regions of increased dark matter concentrations, annihilation signals are expected to be the strongest. Estimations of dark matter induced gamma-ray fluxes from such regions are presented.The types of dark matter signals presented in this thesis will be searched for with existing and future gamma-ray telescopes.Finally, a claimed detection of dark matter annihilation into gamma rays is discussed and found to be unconvincing.

Design of a Liquid Xenon Calorimeter for the Observation of Cosmic Gamma Ray Lines in the 1∼100 GeV Region

A liquid xenon calorimeter has recently been designed. The main purpose is to show the capability of observing monochromatic cosmic gamma ray lines in the 1∼100 GeV region. The calorimeter has a geometric factor of ∼1 m2·sr, an energy resolution of ∼0.4% and an angular resolution of about 1 degree for GeV-region gamma rays. These characteristics will meet the conditions required for the observation of gamma ray lines produced by the pair annihilation of hypothetical SUSY heavy Majorana fermions which might exist in the galactic halo as dark matter. The calorimeter is also applicable to the search for point sources emitting gamma rays as well as the investigation of diffuse gamma rays at high energies.