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  • 1.
    Akrami, Yashar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Scott, Pat
    Stockholm University, Faculty of Science, Department of Physics.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    A Profile Likelihood Analysis of the Constrained MSSM with Genetic Algorithms2010In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, p. 057-Article in journal (Refereed)
    Abstract [en]

    The Constrained Minimal Supersymmetric Standard Model (CMSSM) is one of the simplest and most widely-studied supersymmetric extensions to the standard model of particle physics. Nevertheless, current data do not sufficiently constrain the model parameters in a way completely independent of priors, statistical measures and scanning techniques. We present a new technique for scanning supersymmetric parameter spaces, optimised for frequentist profile likelihood analyses and based on Genetic Algorithms. We apply this technique to the CMSSM, taking into account existing collider and cosmological data in our global fit. We compare our method to the MultiNest algorithm, an efficient Bayesian technique, paying particular attention to the best-fit points and implications for particle masses at the LHC and dark matter searches. Our global best-fit point lies in the focus point region. We find many high-likelihood points in both the stau co-annihilation and focus point regions, including a previously neglected section of the co-annihilation region at large m 0. We show that there are many high-likelihood points in the CMSSM parameter space commonly missed by existing scanning techniques, especially at high masses. This has a significant influence on the derived confidence regions for parameters and observables, and can dramatically change the entire statistical inference of such scans.

  • 2.
    Baltz, Edward A.
    et al.
    Stanford, USA.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Bringmann, Torsten
    Stockholm University, Faculty of Science, Department of Physics.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Sellerholm, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Pre-launch estimates for GLAST sensitivity to Dark Matter annihilation signals2008In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 0807, no 013Article in journal (Refereed)
    Abstract [en]

    We investigate the sensitivity of the Gamma-ray Large Area Space Telescope (GLAST) for indirectly detecting weakly interacting massive particles (WIMPs) through the γ-ray signal that their pair annihilation produces. WIMPs are among the favorite candidates for explaining the compelling evidence that about 80% of the mass in the Universe is non-baryonic dark matter (DM). They are serendipitously motivated by various extensions of the standard model of particle physics such as supersymmetry and universal extra dimensions (UED). With its unprecedented sensitivity and its very large energy range (20 MeV to more than 300 GeV) the main instrument on board the GLAST satellite, the Large Area Telescope (LAT), will open a new window of discovery. As our estimates show, the LAT will be able to detect an indirect DM signature for a large class of WIMP models given a cuspy profile for the DM distribution. Using the current state of the art Monte Carlo and event reconstruction software developed within the LAT collaboration, we present preliminary sensitivity studies for several possible sources inside and outside the Galaxy. We also discuss the potential of the LAT to detect UED via the electron/positron channel. Diffuse background modeling and other background issues that will be important in setting limits or seeing a signal are presented

  • 3.
    Bergstrom, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Dark Matter Candidates2009In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 11, p. 105006-Article in journal (Refereed)
    Abstract [en]

    An overview is given of various dark matter candidates. Among the many suggestions given in the literature, axions, inert Higgs doublet, sterile neutrinos, supersymmetric particles and Kaluza–Klein particles are discussed. The situation has recently become very interesting with new results on antimatter in the cosmic rays having dark matter as one of the leading possible explanations. Problems arising from this explanation and possible solutions are discussed, and the importance of new measurements is emphasized. If the explanation is indeed dark matter, a whole new field of physics, with unusual although not impossible mass and interaction properties, may soon open itself to discovery

  • 4.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    130 GeV fingerprint of right-handed neutrino dark matter2012In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 86, no 10, p. 103514-Article in journal (Refereed)
    Abstract [en]

    Recently, an interesting indication for a dark matter signal in the form of a narrow line, or maybe two lines and/or an internal bremsstrahlung feature, has been found in analyses of public data from the Fermi-LAT satellite detector. As recent analyses have also shown that there is little sign of extra contributions to continuum photons, it is natural to investigate leptophilic interacting massive particle models. We show that a model of radiatively generated neutrino masses may have the properties needed to explain the Fermi-LAT structure around 130 GeV. This model was proposed some 10 years ago, and predicted a clearly observable gamma-ray signal in the Fermi-LAT (then GLAST) detector. Here, we update and improve that analysis, and show as an example that a right-handed neutrino of mass 135 GeV should give rise to three conspicuous effects: a broad internal bremsstrahlung bump with maximum around 120 GeV, a 2 gamma line around 135 GeV, and a Z gamma line at 119.6 GeV (neglected in the previous work). These features together give a good fit to the 130 GeV structure, given the present energy resolution of the Fermi-LAT data. An attractive feature of the model is that the particle physics properties are essentially fixed, once the relic density and the mass of the right-handed neutrino dark matter particle have been set. Puzzling features of the data at present are a slight displacement of the signal from the galactic center, and a needed boost factor of order 5-15. This presents interesting challenges for numerical simulations including both baryons and dark matter on scales of 100 pc, and perhaps a need to go beyond the simplest halo models. With upcoming experiments having better energy resolution, or with future Fermi-LAT data, the double-peak structure with a definite predicted ratio of the strengths of the two lines and the internal bremsstrahlung feature should be seen, if this model is correct. With the planned satellite GAMMA-400, a striking fingerprint of this dark matter candidate should then appear.

  • 5.
    Bergström, Lars
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Cosmology and the dark matter frontier2013In: Physica scripta. T, ISSN 0281-1847, Vol. T158, no Art.nr., p. UNSP 014014-Article in journal (Refereed)
    Abstract [en]

    A brief overview is given about some issues in current astroparticle physics, focusing on the dark matter (DM) problem, where the connection to Large Hadron Collider (LHC) physics is particularly strong . New data from the Planck satellite has made the evidence in favour of the existence of DM even stronger. The favourite, though not the only, candidates for cosmological DM, weakly interacting massive particles, are being probed by a variety of experiments—direct detection through scattering in terrestrial detectors, indirect detection by observing products of annihilation of DM in the Galaxy and finally searches at accelerators such as the LHC. The field is in the interesting situation that all of these search methods are reaching sensitivities where signals of DM may plausibly soon be found, and a vast array of models will be probed in the next few years. Of course, expectations for a positive signature are high, which calls for caution regarding ‘false alarms’. Some of the presently puzzling and partly conflicting pieces of evidence for DM detection are discussed as well as expectations for the future.

  • 6.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dark matter and imaging air Cherenkov arrays2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 44-49Article in journal (Refereed)
    Abstract [en]

    The CIA will mean a significant increase of the potential for dark matter detection, compared to present-day detectors like MAGIC, HESS and VERITAS. In particular, if - as it might be indicated from early LHC results - the dark matter sector is heavy, perhaps in the TeV mass range, imaging air Cherenkov arrays have a good opportunity to detect gamma-rays from dark matter annihilation in the galactic halo, the galactic center, dwarf galaxies, or galaxy clusters. A review of the present situation is given and a few of the miracles that may enhance chances for detection in CTA are discussed, such as Sommerfeld enhancement and internal bremsstrahlung radiation. A few templates for dark matter are studied, and the importance of the acceptance of the detector at low energies is pointed out. Finally, the idea of a complement to CIA in the form of a high-altitude, low energy threshold dedicated dark matter array, DMA, is discussed.

  • 7.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dark matter evidence, particle physics candidates and detection methods2012In: Annalen der Physik, ISSN 0003-3804, E-ISSN 1521-3889, Vol. 524, no 9-10, p. 479-496Article, review/survey (Refereed)
    Abstract [en]

    The problem of the dark matter in the universe is reviewed. A short history of the subject is given, and several of the most obvious particle candidates for dark matter are identified. Particular focus is given to weakly interacting, massive particles (WIMPs) of which the lightest supersymmetric particle is an interesting special case and a useful template. The three detection methods: in particle accelerators, by direct detections of scattering in terrestrial detectors, and indirect detection of products from dark matter particle annihilation in the galactic halo, are discussed and their complementarity is explained. Direct detection experiments have revealed some possible indications of a dark matter signal, but the situation is quite confusing at the moment. Very recently, also indirect detection has entered a sensitivity region where some particle candidates could be detectable. Indeed, also here there are some (presently non-conclusive) indications of possible dark matter signals, like an interesting structure at 130 GeV ?-ray energy found in publicly available data from the Fermi-LAT space detector. The future of the field will depend on whether WIMPs are indeed the dark matter, something that may realistically be probed in the next few years. If this exciting scenario turns out to be true, we can expect a host of other, complementary experiments in the coming decade. If it is not true, the time scale and methods for detection will be much more uncertain.

  • 8.
    Bergström, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bertone, Gianfranco
    Bringmann, Torsten
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taoso, Marco
    Gamma-ray and Radio Constraints of High Positron Rate Dark Matter Models Annihilating into New Light Particles2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 79, no 8, p. 081303-Article in journal (Refereed)
    Abstract [en]

    The possibility of explaining the positron and electron excess recently found by the PAMELA and ATIC collaborations in terms of dark matter (DM) annihilation has attracted considerable attention. Models surviving bounds from, e.g, antiproton production generally fall into two classes, where either DM annihilates directly with a large branching fraction into light leptons, or, as in the recent models of Arkani-Hamed et al., and of Nomura and Thaler, the annihilation gives low-mass (pseudo)scalars or vectors $\phi$ which then decay into $\mu^+\mu^-$ or $e^+e^-$. While the constraints on the first kind of models have recently been treated by several authors, we study here specifically models of the second type which rely on an efficient Sommerfeld enhancement in order to obtain the necessary boost in the annihilation cross section. We compute the photon flux generated by QED radiative corrections to the decay of $\phi$ and show that this indeed gives a rather spectacular broad peak in $E^2d\sigma/dE$, that for these extreme values of the cross section violate gamma-ray observations of the Galactic center for DM density profiles steeper than that of Navarro, Frenk and White. The most stringent constraint comes from the comparison of the predicted synchrotron radiation in the central part of the Galaxy with radio observations of Sgr A*. For the most commonly adopted DM profiles, the models that provide a good fit to the PAMELA and ATIC data are ruled out, unless there are physical processes that boost the local anti-matter fluxes more than one order of magnitude, while not affecting the gamma-ray or radio fluxes.

  • 9.
    Bergström, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bertone, Gianfranco
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Weniger, Christoph
    Investigating gamma ray lines from dark matter with future observatories2012In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 11, p. 025-Article in journal (Refereed)
    Abstract [en]

    We study the prospects for studying line features in gamma-ray spectra with upcoming gamma-ray experiments, such as HESS-II, the Cherenkov Telescope Array (CTA), and the GAMMA-400 satellite. As an example we use the narrow feature at 130 GeV seen in public data from the Fermi-LAT satellite. We found that all three experiments should be able to confidently confirm or rule out the presence of this 130 GeV feature. If it is real, it should be confirmed with a confidence level higher than 5 sigma. Assuming it to be a spectral signature of dark matter origin, GAMMA-400, thanks to a projected energy resolution of about 1.5 % at 100 GeV, should also be able to resolve both the gamma gamma line and a corresponding Z gamma or H gamma feature, if the corresponding branching ratio is comparable to that into two photons. It will also allow to distinguish between a gamma-ray line and the similar feature resulting from internal bremsstrahlung photons.

  • 10.
    Bergström, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bringmann, Torsten
    Cholis, Ilias
    Hooper, Dan
    Weniger, Christoph
    New Limits on Dark Matter Annihilation from Alpha Magnetic Spectrometer Cosmic Ray Positron Data2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 17, article id 171101Article in journal (Refereed)
    Abstract [en]

    The Alpha Magnetic Spectrometer experiment onboard the International Space Station has recently provided cosmic ray electron and positron data with unprecedented precision in the range from 0.5 to 350 GeV. The observed rise in the positron fraction at energies above 10 GeV remains unexplained, with proposed solutions ranging from local pulsars to TeV-scale dark matter. Here, we make use of this high quality data to place stringent limits on dark matter with masses below similar to 300 GeV, annihilating or decaying to leptonic final states, essentially independent of the origin of this rise. We significantly improve on existing constraints, in some cases by up to 2 orders of magnitude.

  • 11.
    Bergström, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bringmann, Torsten
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Complementarity of direct dark matter detection and indirect detection through gamma rays2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 83, no 4, p. 045024-Article in journal (Refereed)
    Abstract [en]

    We show, by using an extensive sample of viable supersymmetric models as templates, that indirect detection of dark matter through gamma rays may have a large potential for identifying the nature of dark matter. This is, in particular, true also for models that give too weak dark matter-nucleon scattering cross sections to be probed by present and planned direct detection experiments. Also models with a mass scale too high to be accessible at CERN's LHC accelerator may show up in next-generation imaging Cherenkov telescope arrays. Based on our findings, we therefore suggest to view indirect searches as genuine particle physics experiments, complementing other strategies to probe so far unknown regions in the parameter space of e.g. supersymmetric models, and propose a new approach that would make use of telescopes dedicated for dark matter searches. As a concrete example for the potential of such an approach, we consider an array of imaging air Cherenkov telescopes, the Dark Matter Array (DMA), and show that such an experiment could extend present-day limits by several orders of magnitude, reaching a large class of models that would remain undetected in both direct detection experiments and searches at the LHC. In addition, in a sizable part of the parameter space, signals from more than one type of dark matter detection experiment would be possible, something that may eventually be necessary in order to identify the dark matter candidate.

  • 12. Bringmann, Torsten
    et al.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gondolo, Paolo
    Ullio, Piero
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    DarkSUSY 6: an advanced tool to compute dark matter properties numerically2018In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 7, article id 033Article in journal (Refereed)
    Abstract [en]

    The nature of dark matter remains one of the key science questions. Weakly Interacting Massive Particles (WIMPs) are among the best motivated particle physics candidates, allowing to explain the measured dark matter density by employing standard big-bang thermodynamics. Examples include the lightest supersymmetric particle, though many alternative particles have been suggested as a solution to the dark matter puzzle. We introduce here a radically new version of the widely used DarkSUSY package, which allows to compute the properties of such dark matter particles numerically. With DarkSUSY 6 one can accurately predict a large variety of astrophysical signals from dark matter, such as direct detection rates in low-background counting experiments and indirect detection signals through antiprotons, antideuterons, gamma rays and positrons from the Galactic halo, or high-energy neutrinos from the center of the Earth or of the Sun. For thermally produced dark matter like WIMPs, high-precision tools are provided for the computation of the relic density in the Universe today, as well as for the size of the smallest dark matter protohalos. Furthermore, the code allows to calculate dark matter self-interaction rates, which may affect the distribution of dark matter at small cosmological scales. Compared to earlier versions, DarkSUSY 6 introduces many significant physics improvements and extensions. The most fundamental new feature of this release, however, is that the code has been completely reorganized and brought into a highly modular and flexible shape. Switching between different pre-implemented dark matter candidates has thus become straight-forward, just as adding new - WIMP or non-WIMP - particle models or replacing any given functionality in a fully user-specified way. In this article, we describe the physics behind the computer package, along with the main structure and philosophy of this major revision of DarkSUSY. A detailed manual is provided together with the public release at www.darksusy.org.

  • 13.
    Gustafsson, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lundström, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Significant Gamma Lines from Inert Higgs Dark Matter2007In: Physical Review Letters, Vol. 99, no 041301Article in journal (Refereed)
    Abstract [en]

    One way to unambiguously confirm the existence of particle dark matter and determine its mass would be to detect its annihilation into monochromatic gamma-rays in upcoming telescopes. One of the most minimal models for dark matter is the inert doublet model, obtained by adding another Higgs doublet with no direct coupling to fermions. For a mass between 40 and 80 GeV, the lightest of the new inert Higgs particles can give the correct cosmic abundance of cold dark matter in agreement with current observations. We show that for this scalar dark matter candidate, the annihilation signal of monochromatic γγ and Zγ final states would be exceptionally strong. The energy range and rates for these gamma-ray line signals make them ideal to search for with the soon upcoming GLAST satellite.

  • 14. Leonov, A. A.
    et al.
    Galper, A. M.
    Bonvicini, V.
    Topchiev, N. P.
    Adriain, O.
    Aptekar, R. L.
    Arkhangelskaja, I. V.
    Arkhangelskiy, A. I.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Berti, E.
    Bigongiari, G.
    Bobkov, S. G.
    Boezio, M.
    Bogomolov, E. A.
    Bonechi, S.
    Bongi, M.
    Bottai, S.
    Castellini, G.
    Cattaneo, P. W.
    Cumani, P.
    Dedenko, G. L.
    De Donato, C.
    Dogiel, V. A.
    Gorbunov, M. S.
    Gusakov, Yu. V.
    Hnatyk, B. I.
    Kadilin, V. V.
    Kaplin, V. A.
    Kaplun, A. A.
    Kheymits, M. D.
    Korepanov, V. E.
    Larsson, J.
    Loginov, V. A.
    Longo, F.
    Maestro, P.
    Marrocchesi, P. S.
    Mikhailov, V. V.
    Mocchiutti, E.
    Moiseev, A. A.
    Mori, N.
    Moskalenko, I. V.
    Naumov, P. Yu.
    Papini, P.
    Pearce, M.
    Picozza, P.
    Rappoldi, A.
    Ricciarini, S.
    Runtso, M. F.
    Ryde, F.
    Serdin, O. V.
    Sparvoli, R.
    Spillantini, P.
    Suchkov, S. I.
    Taraskin, A. A.
    Tavani, M.
    Tiberio, A.
    Tyurin, E. M.
    Ulanov, M. V.
    Vacchi, A.
    Vannuccini, E.
    Vasilyev, G. I.
    Yurkin, Yu. T.
    Zampa, N.
    Zirakashvili, V. N.
    Zverev, V. G.
    Separation of electrons and protons in the GAMMA-400 gamma-ray telescope2015In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 56, no 7, p. 1538-1545Article in journal (Refereed)
    Abstract [en]

    The GAMMA-400 telescope will measure the fluxes of gamma rays and cosmic-ray electrons and positrons in the energy range from 100 MeV to several TeV. These measurements will allow it to achieve the following scientific objectives: search for signatures of dark matter, investigation of gamma-ray point-like and extended sources, study of the energy spectrum of the Galactic and extragalactic diffuse emission, study of gamma-ray bursts and gamma-ray emission from the active Sun, together with high-precision measurements of the high-energy electrons and positrons spectra, protons and nuclei up to the knee. The bulk of cosmic rays are protons and helium nuclei, whereas the lepton component in the total flux is similar to 10(-3) at high energy. In the present paper, the simulated capability of the GAMMA-400 telescope to distinguish electrons and positrons from protons in cosmic rays is addressed. The individual contribution to the proton rejection from each detector system of GAMMA-400 is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of the order of similar to 4 x 10(5) for vertical incident particles and similar to 3 x 10(5) for particles with initial inclination of 30 degrees in the electron energy range from 50 GeV to 1 TeV. (C) 2015 COSPAR.

  • 15.
    Pinzke, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pfrommer, Christoph
    CITA, Toronto.
    Bergstrom, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Gamma-rays from dark matter annihilations strongly constrain the substructure in halos2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 18, p. 181302-Article in journal (Refereed)
    Abstract [en]

    Recently, it has been shown that electrons and positrons from dark matter (DM) annihilations provide an excellent fit to the Fermi, PAMELA, and HESS data. Using this DM model, which requires an enhancement of the annihilation cross section over its standard value to match the observations, we show that it immediately implies an observable level of gamma-ray emission for the Fermi telescope from nearby galaxy clusters such as Virgo and Fornax. We show that this DM model implies a peculiar feature from final state radiation that is a distinctive signature of DM. Using the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures within DM halos to be > 5x10^-3 M_sun -- about four orders of magnitudes larger than the expectation for cold dark matter. This limits the cutoff scale in the linear matter power spectrum to k < 35/kpc which can be explained by e.g., warm dark matter. Very near future Fermi observations will strongly constrain the minimum mass to be > 10^3 M_sun: if the true substructure cutoff is much smaller than this, the DM interpretation of the Fermi/PAMELA/HESS data must be wrong. To address the problem of astrophysical foregrounds, we performed high-resolution, cosmological simulations of galaxy clusters that include realistic cosmic ray (CR) physics. We compute the dominating gamma-ray emission signal resulting from hadronic CR interactions and find that it follows a universal spectrum and spatial distribution. If we neglect the anomalous enhancement factor and assume standard values for the cross section and minimum subhalo mass, the same model of DM predicts comparable levels of the gamma-ray emission from DM annihilations and CR interactions. This suggests that spectral subtraction techniques could be applied to detect the annihilation signal.

  • 16. Pinzke, Anders
    et al.
    Pfrommer, Christoph
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Prospects of detecting gamma-ray emission from galaxy clusters: Cosmic rays and dark matter annihilations2011In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, no 12, p. 123509-Article in journal (Refereed)
    Abstract [en]

    We study the possibility for detecting gamma-ray emission from galaxy clusters. We consider (1) leptophilic models of dark matter (DM) annihilation that include a Sommerfeld enhancement (SFE), (2) different representative benchmark models of supersymmetric DM, and (3) cosmic-ray (CR) induced pion decay. Among all clusters/groups of a flux-limited x-ray sample, we predict Virgo, Fornax, and M49 to be the brightest DM sources and find a particularly low CR-induced background for Fornax. For a minimum substructure mass given by the DM free-streaming scale, cluster halos maximize the substructure boost for which we find a factor of greater than or similar to 1000. Since regions around the virial radius dominate the annihilation flux of substructures, the resulting surface brightness profiles are almost flat. This makes it very challenging to detect this flux with imaging atmospheric Cherenkov telescopes since their sensitivity drops approximately linearly with radius and they typically have 5-10 linear resolution elements across a cluster. Assuming cold dark matter with a substructure mass distribution down to an Earth mass and using extended Fermi upper limits, we rule out the leptophilic models in their present form in 28 clusters, and limit the boost from SFE in M49 and Fornax to be less than or similar to 5. This corresponds to a limit on SFE in the Milky Way of less than or similar to 3, which is too small to account for the increasing positron fraction with energy as seen by PAMELA and challenges the DM interpretation. Alternatively, if SFE is realized in nature, this would imply a limiting substructure mass of M(lim) > 10(4)M(circle dot)-a problem for structure formation in most particle physics models. Using individual cluster observations, it will be challenging for Fermi to constrain our selection of DM benchmark models without SFE. The Fermi upper limits are, however, closing in on our predictions for the CR flux using an analytic model based on cosmological hydrodynamical cluster simulations. We limit the CR-to-thermal pressure in nearby bright galaxy clusters of the Fermi sample to less than or similar to 10% and in Norma and Coma to less than or similar to 3%. Thus, we will soon start to constrain the underlying CR physics such as shock acceleration efficiencies or CR transport properties.

  • 17.
    Scott, P.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Farnier, C.
    Akrami, Yashar
    Stockholm University, Faculty of Science, Department of Physics.
    Direct constraints on minimal supersymmetry from Fermi-LAT observations of the dwarf galaxy Segue 12010In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 1, p. 31-50Article in journal (Refereed)
    Abstract [en]

    The dwarf galaxy Segue 1 is one of the most promising targets for the indirect detection of dark matter. Here we examine what constraints 9 months of Fermi-LAT gamma-ray observations of Segue 1 place upon the Constrained Minimal Supersymmetric Standard Model (CMSSM), with the lightest neutralino as the dark matter particle. We use nested sampling to explore the CMSSM parameter space, simultaneously fitting other relevant constraints from accelerator bounds, the relic density, electroweak precision observables, the anomalous magnetic moment of the muon and B-physics. We include spectral and spatial fits to the Fermi observations, a full treatment of the instrumental response and its related uncertainty, and detailed background models. We also perform an extrapolation to 5 years of observations, assuming no signal is observed from Segue 1 in that time. Results marginally disfavour models with low neutralino masses and high annihilation cross-sections. Virtually all of these models are however already disfavoured by existing experimental or relic density constraints.

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