Ray Line Research Articles

Cosmic–ray and gamma–ray constraints on dark matter stability

We examine different constraints on dark matter stability from cosmic–ray and gamma–ray observations and their complementarity through higher–order effects. Two–body and three–body decays of dark matter particles into charged leptons and quarks generically induce decays into monochromatic photons at the quantum level, giving rise to distinct signatures. We also present a general model–independent analysis of hadronic constraints in the mass–lifetime parameter space and compare those constraints to current and projected limits on gamma–ray lines. Furthermore, we discuss how the production of monochromatic photons can be enhanced by kinematic effects, potentially giving rise to observable lines in the gamma–ray sky.

Fundamental physics from the sky: Cosmic rays, gamma rays and the hunt for dark matter

Can we learn about New Physics with astronomical and astro–particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental nature of dark matter. I will discuss some of the recent puzzling findings in cosmic–ray electron–positron data and in gamma–ray observations that might be related to dark matter. I will argue that recent cosmic–ray data, most notably from the Pamela and Fermi satellites, indicate that previously unaccounted–for powerful sources in the Galaxy inject high–energy electrons and positrons. Interestingly, this new source class might be related to new fundamental particle physics, and specifically to pair–annihilation or decay of galactic dark matter. This exciting scenario is directly constrained by Fermi gamma–ray observations, which also inform us on astrophysical source counterparts that could also be responsible for the high–energy electron–positron excess. Observations of gamma–ray emission from the central regions of the Galaxy as well as claims on a gamma–ray line at around 130 GeV also recently triggered a wide–spread interest: I will address the question of whether we are really observing signals from dark matter annihilation, how to test this hypothesis, and which astrophysical mechanisms constitute the relevant background.

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.

Corrigendum to “From gamma ray line signals of dark matter to the LHC” [Phys. Dark Universe 2(1) (2013) 22-34

Corrigendum to “From gamma ray line signals of dark matter to the LHC” [Phys. Dark Universe 2(1) (2013) 22-34

Simple dark matter recipe for the 111 and 128 GeV Fermi-LAT lines

Recently evidence for gamma ray lines at energies of approximately 111 and 128 GeV has been found in Fermi-LAT data from the center of the galaxy and from unassociated point sources. Many explanations in terms of dark matter particle pairs annihilating to gamma gamma and gamma Z have been suggested, but these typically require very large couplings or mysterious coincidences in the masses of several new particles to fit the signal strength. We propose a simple novel explanation in which dark matter is part of a multiplet of new states which all have mass near 260 GeV as a result of symmetry. Two dark matter particles annihilate to a pair of neutral particles in this multiplet which subsequently decay to gamma gamma and gamma Z. For example, one may have a triplet of pseudo-Nambu-Goldstone bosons, charged pions and a neutral pion, where the charged pions are stabilized by their charge under a new U(1) symmetry and the slightly lighter neutral pion state decays to gamma gamma and gamma Z. The symmetry structure of such a model explains the near degeneracy in masses needed for the resulting photons to have a line-like shape and the large observed flux. The tunable lifetime of the neutral state allows such models to go unseen at direct detection or collider experiments that can constrain most other explanations. However, nucleosynthesis constraints on the neutral pion lifetime fix a minimum necessary coupling between the new multiplet and the Standard Model. The spectrum is predicted to be not a line but a box with a width of order a few GeV, smaller than but on the order of the Fermi-LAT resolution.

130 GeV gamma ray line and enhanced Higgs di-photon rate from Triplet-Singlet extended MSSM

We propose an economic extension of minimal supersymmetric standard model with a SU(2) singlet and Y=0 triplet, which can explain (i) the 125 GeV Higgs boson without fine tuning, (ii) the 130 GeV $\gamma$-ray line seen at Fermi-LAT, (as well as a second photon line at 114 GeV)(iii) an enhanced Higgs di-photon decay rate seen by ATLAS, while being consistent with dark matter relic density and recent XENON 100 exclusion limits on spin-independent direct detection cross-section. We obtain the required cross-section of $10^{-27}cm^3s^{-1}$ for the 130 GeV $\gamma$-ray flux through the resonant annihilation of dark matter via pseudoscalar triplet Higgs of mass $\sim$260 GeV. The dark matter is predominantly bino-higgsino which has large couplings with photons (through higgsino) and gives correct relic density (through bino). We get the enhanced Higgs diphoton decay rate, $R_{\gamma \gamma}\simeq 1.24$ dominantly contributed by the light chargino-loops, which can account for the reported excess seen in the $h\rightarrow \gamma \gamma$ channel by ATLAS.

The 111 and 129 GeVγ-ray lines from annihilations in the Milky Way dark matter halo, dark disk and subhalos

Recently a series of indications have been put forward suggesting the presence of two -ray lines at 110-130 GeV (centered at 111 and 129 GeV). Signals of these lines have been observed toward the Galactic center, at some galaxy clusters and among some of the unassociated point sources of the 2 years Fermi catalogue. Such a combination of signals could be generated by dark matter annihilations in the main dark matter halo, its substructures and nearby galaxy clusters. We discuss in this work the consistency between the number of events observed at the line energies in the sky and the predictions using results from the Via Lactea II numerical simulation and extrapolations below its mass resolution, taking into account that the annihilation cross-section to the lines can be estimated from the Galactic center signal. We find that some extrapolations to small substructures can naturally account for the point sources signal, although the hypothesis of background only cannot be rejected. We also study the morphology of the -ray sky at the 2 lines energies, testing different Galactic diffuse background models to account for interstellar medium uncertainties and different assumptions on the DM diffuse component profile. We find from template fits that within reasonable diffuse background uncertainties the presence of a spherical halo component is preferred with cuspier dark matter halo profiles being preferable even from the full sky fit. We finally check the impact of a dark disk component suggested by cosmological simulations that include baryons and find that thin dark disks can not be disfavored, thus possibly accounting for the preferentially closer to the Galactic disk distribution of the point sources lines signal.

Gamma-ray lines and one-loop continuum from s-channel dark matter annihilations

The era of indirect detection searches for dark matter has begun, withthe sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation,although they are typically suppressed compared to the continuum.In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced.We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the ``forbidden channel mechanism" advocated a few years ago in the ``Higgs in space" scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400.Constraints from the relic abundance, direct detection and collider bounds are also discussed.

Vector Higgs-portal dark matter and Fermi-LAT gamma ray line

We propose a renormalizable model for vector dark matter with extra $U(1)$ gauge symmetry, which is broken by the vacuum expectation value of a complex singlet scalar. When the singlet scalar has a quartic coupling to a heavy charged scalar, the resonance effect enhances the annihilation cross section of vector dark matter into two photons such that a Fermi gamma ray line at about 130 GeV is obtained. In the presence of a tiny mixing between the singlet scalar and the Standard Model Higgs doublet, the relic density is determined dominantly by $WW/ZZ$ and two-photon channels near the resonance pole of the singlet scalar. We also show that various phenomenological bounds coming from the Higgs-to-diphoton decay rate, precision data, and collider searches for the charged scalar and vacuum stability are satisfied in the model.

Probing charged matter through h → γγ, gamma ray lines, and EDMs

Numerous experiments currently underway offer the potential to indirectly probe new charged particles with masses at the weak scale. For example, the tentative excess in Higgs diphoton decay and the tentative gamma-ray line in Fermi-LAT data have recently attracted attention as possible one-loop signatures of new charged particles. We explore the interplay between such signals, dark matter direct detection through Higgs exchange, and measurements of the electron EDM, by studying the size of these effects in several models. We compute one-loop effects to explore the relationship among couplings probed by different experiments. In particular, models in which dark matter and the Higgs both interact with charged particles at a detectable level typically induce, at loop level, couplings between dark matter and the Higgs that are around the level of current direct detection sensitivity. Intriguingly, one-loop Higgs diphoton decay and DM annihilation into two photons, two-loop EDMs, and loop-induced direct detection rates are all coming within range of existing experiments for approximately the same range of charged particle masses, offering the prospect of an exciting coincidence of signals at collider, astrophysical, underground and atomic physics measurements.

From gamma ray line signals of dark matter to the LHC

We explore the relationship between astrophysical gamma-ray signals and LHC signatures for a class of phenomenologically successful secluded dark matter models, motivated by recent evidence for a ~130 GeV gamma-ray line. We consider in detail scenarios in which interactions between the dark sector and the standard model are mediated by a vev-less scalar field \phi, transforming as an N-plet (N > 3) under SU(2)_L. Since some of the component fields of \phi carry large electric charges, loop induced dark matter annihilation to \gamma \gamma and \gamma Z can be enhanced without the need for non-perturbatively large couplings, and without overproduction of continuum gamma-rays from other final states. We discuss prospects for other experimental tests, including dark matter-nucleon scattering and production of \phi at the LHC, where future searches for anomalous charged tracks may be sensitive. The first LHC hints could come from the Higgs sector, where loop corrections involving \phi lead to significantly modified h to \gamma \gamma and h to \gamma Z branching ratios.

Top quark mediated dark matter

We study the top quark portal dominated dark matter interactions, and its implications for the gamma ray line searches. In this picture, the dark matter interactions with photons and gluons are loop induced by the axial anomaly of the top quark current. We show there can be a natural suppression of the tree-level annihilation of dark matter, and the photon channel in turn has a substantial rate when the main annihilation proceeds into gluons. We observe a competition between the indirect detection of gamma ray line and the search with monojet plus missing energy events at LHC, and the 7 TeV data already set an upper bound of ∼10−28 cm3s−1 on the photonic annihilation cross section. This upper limit is compatible with a thermal WIMP scenario.

DE-EXCITATION NUCLEAR GAMMA-RAY LINE EMISSION FROM LOW-ENERGY COSMIC RAYS IN THE INNER GALAXY

Recent observations of high ionization rates of molecular hydrogen in diffuse interstellar clouds point to a distinct low-energy cosmic-ray component. Supposing that this component is made of nuclei, two models for the origin of such particles are explored and low-energy cosmic-ray spectra are calculated, which, added to the standard cosmic-ray spectra, produce the observed ionization rates. The clearest evidence of the presence of such low-energy nuclei between a few MeV nucleon{sup -1} and several hundred MeV nucleon{sup -1} in the interstellar medium would be a detection of nuclear {gamma}-ray line emission in the range E {sub {gamma}} {approx} 0.1-10 MeV, which is strongly produced in their collisions with the interstellar gas and dust. Using a recent {gamma}-ray cross section compilation for nuclear collisions, {gamma}-ray line emission spectra are calculated alongside the high-energy {gamma}-ray emission due to {pi}{sup 0} decay, the latter providing normalization of the absolute fluxes by comparison with Fermi-LAT observations of the diffuse emission above E {sub {gamma}} = 0.1 GeV. Our predicted fluxes of strong nuclear {gamma}-ray lines from the inner Galaxy are well below the detection sensitivities of the International Gamma-Ray Astrophysics Laboratory, but a detection, especially of the 4.4 MeV line, seems possible with new-generationmore » {gamma}-ray telescopes based on available technology. We also predict strong {gamma}-ray continuum emission in the 1-8 MeV range, which, in a large part of our model space for low-energy cosmic rays, considerably exceeds the estimated instrument sensitivities of future telescopes.« less

Axion-mediated dark matter and Higgs diphoton signal

Abstract We consider axion-mediated dark matter models motivated by Fermi gamma ray line at 130 GeV, where an axion-like scalar couples to a singlet Dirac fermion dark matter (DM) so its anomaly interactions with electroweak gauge bosons allow the DM to annihilate into monochromatic photon(s). In these models, extra vector-like leptons generate the necessary anomaly interactions for the axion and can also modify the Higgs-to-diphoton rate by their Yukawa couplings to the SM Higgs boson. We can distinguish models by the branching fraction of the DM annihilation into a photon pair, favoring the model with a triplet fermion. From the condition that the lighter charged extra lepton must be heavier than dark matter for no tree-level DM annihilations, we also show that the ratio of Higgs-to-diphoton rate to the SM value is constrained by vacuum stability to 1.4 (1.5) for the cutoff scale of 10 (1) TeV.

Fermi gamma ray line at 130 GeV from axion-mediated dark matter

We consider a singlet Dirac fermion with Peccei-Quinn (PQ) symmetry as dark matter. A singlet complex scalar is introduced to mediate between dark matter and the Standard Model through Higgs portal interaction and electroweak PQ anomalies. We show that a resonant annihilation of dark matter with axion mediation can explain the monochromatic photon line of the Fermi Large Area Telescope data at 130 GeV by anomaly interactions while the annihilation cross section with Higgs portal interaction is $p$-wave suppressed. We discuss the interplay between the direct detection of the fermion dark matter and the collider search of Higgs-like scalars. We also present an ultraviolet completion of the dark matter model into the Next-to-Minimal Supersymmetric Standard Model with PQ symmetry.

NEW DEVELOPMENT OF HYPERGAM AND ITS TEST OF PERFORMANCE FOR γ-RAY SPECTRUM ANALYSIS

The HyperGam program was developed for the analysis of complex HPGe <TEX>${\gamma}$</TEX>-ray spectra. The previous version of HyperGam was mainly limited to the analysis of <TEX>${\gamma}$</TEX>-ray peaks and the manual logging of the result. In this study, it is specifically developed into a tool for the isotopic analysis of spectra. The newly developed features include nuclide identification and activity determination. An algorithm for nuclide identification was developed to identify the peaks in the spectrum by considering the yield, efficiency, energy and peak area for the <TEX>${\gamma}$</TEX>-ray lines emitted from the radionuclide. The detailed performance of nuclide identification and activity determination was accessed using the IAEA 2002 set of test spectra. By analyzing the test spectra, the numbers of radionuclides identified truly (true hit), falsely (false hit) or missed (misses) were counted and compared with the results from the IAEA 2002 tests. The determined activities of the radionuclides were also compared for four test spectra of several samples. The result of the performance test is promising in comparison with those of the well-known software packages for <TEX>${\gamma}$</TEX>-ray spectrum analysis.

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.

THE RELATIONSHIP BETWEEN LEARNERS’ DISTRUST OF SCIENTIFIC MODELS, THEIR SPATIAL ABILITY, AND THE VIVIDNESS OF THEIR MENTAL IMAGES

The purpose of the current study was to examine the nature of the relationship between learners’ distrust of scientific models that represent unseen entities and phenomena, their spatial ability, and the vividness of their mental images. The sample consisted of 302 tenth grade students in the Sultanate of Oman. Three measures were used for this study: the Epistemologies about the Credibility of Scientific Models instrument, the Water Level Task (WLT), and the Vividness of Microscopic Mental Images. It was found that students’ distrust was greater for theoretical and abstract models such as the electron clouds, photons, magnetic lines of force, DNA, electron transfer, atomic orbits, and alpha rays. The findings also show that there was a statistically significant negative correlation between students’ distrust of scientific models and their spatial ability, as indicated by their performance on the WLT. There was a positive relationship between the distrust of scientific models and the vividness of mental images and a weak negative relationship between spatial ability and the vividness of mental images. Based on the findings, it might be plausible to conclude that as the abstraction level for scientific models increases, such as for theoretical models which lack defined structure and known details, imaginative learners’ difficulty to construct colorful and detailed mental images for natural entities and phenomena increases. It would also be recommended that learners with vivid mental images should be provided with and directed to use more spatial techniques such as computerized visualization tools and mental manipulation of 3D objects.

Emission and strain in InGaAs/GaAs quantum wells with InAs quantum dots obtained at different temperatures

The photoluminescence (PL), its temperature dependence and X ray diffraction (XRD) have been studied in the symmetric In0.15Ga0.85As/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs), obtained with the variation of QD growth temperatures (470–535°C). The increase of QD growth temperatures is accompanied by the enlargement of QD lateral sizes (from 12 up to 28nm) and by the shift non monotonously of PL peak positions. The fitting procedure has been applied for the analysis of the temperature dependence of PL peaks. The obtained fitting parameters testify that in studied QD structures the process of In/Ga interdiffusion between QDs and capping/buffer layers takes place partially. However this process cannot explain the difference in PL peak positions.The XRD study has revealed the high intensity peaks which correspond to the diffraction of X ray line from the (200) crystal planes of cubic GaAs. It was shown that the XRD peak is the superposition of the diffraction from the GaAs substrate and GaAs layers of quantum wells. The position of diffraction peaks related to the cubic GaAs substrate coincides with the very well-known XRD data for the bulk GaAs. At the same time the (200) diffraction peaks in GaAs epitaxial layers shift to the high angles in comparison with the bulk GaAs, testifying the compression strain in GaAs epitaxial layers. The value of elastic strain has been estimated. The minimum of elastic strain is detected in the structure with QD grown at 510°C that manifests itself by the higher QD PL intensity and lower PL peak energy.

Pharmacognostic profile of root of Cryptolepis sanguinolenta (Lindl.) Schlechter

Medicinal plants are traditionally found to be useful for many ailments. The present study highlights the pharmacognostical as well as phytochemical studies including parameters such as macroscopic, microscopic characters, physicochemical evaluation, chemomicroscopy and preliminary phytochemical studies of the root of Cryptolepis sanguinolenta. The morphological studies shows a root light to medium brown in color with hard and brittle texture, prisms of calcium oxalate crystals, sclereids and parenchyma cells. The transverse section showed parenchyma cells, vascular cambium, ray lines and phelloderm. Physico-chemical standards and their percentage values w/w were found to be: total ash (14.02±0.12), acid insoluble ash (5.08±0.18, %), water soluble ash (4.02±0.27%), sulphated ash (4.26±0.11%), alcohol soluble extractive (6.20±0.45%), water soluble extractive (28.40±0.75%) and moisture content (6.80±0.25%). Chemomicroscopical investigation revealed presence of lignin, tannin, oils, cellulose and calcium oxalate. Phytochemical analysis of the root revealed the presence of carbohydrates, alkaloids, glycosides, saponins, resins, proteins, steroids and terpenoids. These findings will help in identification, standardization of the root of Cryptolepis sanguinolenta (Lindl.) Schlechter and also distinguish it from its adulterants.