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  • 1.
    Edsjö, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Elevant, Jessica
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Enberg, R.
    Niblaeus, Carl
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Neutrinos from cosmic ray interactions in the Sun2017In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 6, article id 033Article in journal (Refereed)
    Abstract [en]

    Cosmic rays hitting the solar atmosphere generate neutrinos that interact and oscillate in the Sun and oscillate on the way to Earth. These neutrinos could potentially be detected with neutrino telescopes and will be a background for searches for neutrinos from dark matter annihilation in the Sun. We calculate the flux of neutrinos from these cosmic ray interactions in the Sun and also investigate the interactions near a detector on Earth that give rise to muons. We compare this background with both regular Earth-atmospheric neutrinos and signals from dark matter annihilation in the Sun. Our calculation is performed with an event-based Monte Carlo approach that should be suitable as a simulation tool for experimental collaborations. Our program package is released publicly along with this paper.

  • 2.
    Niblaeus, Carl
    Stockholm University, Faculty of Science, Department of Physics.
    Studies of dark matter annihilation and production in the Universe2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this PhD thesis we investigate various aspects of particle dark matter. The proper identification of dark matter developed during the second half of the twentieth century to become one of the biggest endeavours in modern physics and astronomy. Although observations currently favour the explanation that dark matter consists of a new form of particle, no experimental search has yet provided unequivocal evidence of such a particle. 

    Of particular importance in this thesis is the field of indirect detection of dark matter, where one searches for the particles emerging from annihilations of dark matter particles out in the Universe. Specifically, we consider dark matter annihilations in the centre of the Sun. As the Sun moves through the galaxy, some dark matter particles scatter in the Sun and lose enough energy to become bound to the Sun. They settle in the solar core and begin to annihilate, which leads to an annihilation signal from the solar direction.

    The thesis is built on novel research consisting of three papers and a monograph-type chapter. In the first paper we calculate the flux of high energy neutrinos coming from cosmic ray cascades in the solar atmosphere and investigate the role it plays as a background in solar dark matter searches. In the second paper we consider dark matter annihilating into long-lived mediators in the Sun, which leads to interesting new detection possibilities. A third paper explores more generally the fluxes of secondary particles from dark matter annihilations that are searched for in indirect detection. We look at the effects of changing the Monte Carlo event generator that generates the fluxes and of having polarized final states in the annihilations. Finally, we consider in a monograph-type chapter the production of dark matter in the early Universe through the freeze-out mechanism, looking at effects of higher order corrections in the calculation of the relic abundance in the minimal supersymmetric standard model.

  • 3.
    Niblaeus, Carl
    Stockholm University, Faculty of Science, Department of Physics.
    The Sun as a laboratory for particle physics2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the paper attached to this thesis, Paper I, we have calculated the flux of neutrinos that emanate from cosmic ray collisions in the solar atmosphere. These neutrinos are created in the cascades that follow the primary collision and can travel from their production point to a detector on Earth, interacting with the solar material and oscillating on the way. The motivation is both a better understanding of the cosmic ray interactions in the solar environment but also the fact that this neutrino flux presents an almost irreducible background for the searches for neutrinos from annihilations between dark matter particles in the Sun’s core.

    This interesting connection between neutrinos and dark matter make use of the Sun as a laboratory to investigate new models of particle physics. If dark matter consists of weakly interacting massive particles (WIMPs), the Sun will sweep up some of these WIMPs when it moves through the halo of dark matter that our galaxy lies in. These WIMPs will become gravitationally bound to the Sun and over time accumulate in the Sun’s core. In most models WIMPs can annihilate to Standard Model particles when encountering each other. The only particle that can make it out of the Sun without being absorbed is the neutrino. The buildup of WIMPs in the solar interior can therefore lead to a detectable flux of neutrinos.

    Neutrino telescopes therefore search for an excess of neutrinos from the Sun. To be able to ensure that a detected flux is in fact coming from dark matter annihilations one must properly account for all other sources of neutrinos. At higher energies these are primarily neutrinos created in energetic collisions between cosmic rays and particles in the Earth’s atmosphere, but also the solar atmospheric neutrinos. The latter will be tougher to disentangle from a WIMP signal since they also come from the Sun.

    We calculate in Paper I the creation of the neutrinos in the solar atmosphere and propagate these neutrinos to a detector on Earth, including oscillations and interactions in the Sun and vacuum oscillations between the Sun and the Earth. We find that the expected flux is small but potentially detectable by current neutrino telescopes, although further studies are needed to fully ascertain the possibility of discovery as well as how to properly disentangle this from a potential WIMP-induced neutrino signal. 

  • 4.
    Niblaeus, Carl
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Beniwal, Ankit
    Stockholm University, Faculty of Science, Department of Physics. Université catholique de Louvain, Belgium.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Neutrinos and gamma rays from long-lived mediator decays in the SunIn: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516Article in journal (Refereed)
    Abstract [en]

    We investigate a scenario where dark matter (DM) particles can be captured and accumulate in the Sun, and subsequently annihilate into a pair of long-lived mediators. These mediators can decay further out in the Sun or outside of the Sun. Compared to the standard scenario where DM particles annihilate directly into Standard Model particles close to the solar core, here we also obtain fluxes of gamma rays and charged cosmic rays. We simulate this scenario using a full three-dimensional model of the Sun, and include interactions and neutrino oscillations. In particular, we perform a model-independent study of the complementarity between neutrino and gamma ray fluxes by comparing the recent searches from IceCube, Super-Kamiokande, Fermi-LAT, ARGO and HAWC.

    We find that the resulting neutrino fluxes are significantly higher at high energy when the mediators decay further out in the Sun. We also find that gamma ray searches place stronger constraints than neutrino searches on these models even in cases where the mediators decay mainly inside the Sun, except in the approximately inner 10% of the Sun where neutrino searches are more powerful. We present our results in a model-independent manner and release a new version of the WimpSim code that can be used to simulate this scenario for arbitrary mediator models.

  • 5.
    Niblaeus, Carl
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Cornell, Jonathan
    University of Cincinnati, USA.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Effect of polarisation and change of event generator on dark matter annihilation fluxesManuscript (preprint) (Other academic)
    Abstract [en]

    If indirect detection searches are to be used to discriminate between dark matter particle models, it is crucial to understand the expected energy spectra of secondary particles such as neutrinos, charged antiparticles and gamma rays emerging from dark matter annihilations in the local Universe. We simulate the dark matter annihilation processes and collect the fluxes of the stable end products in the annihilation. In order to get an estimate of the impact of different modelling of the physics in the annihilation process, we compare fluxes obtained with two popular event generators, Pythia8 and Herwig7. We also consider the possible impact of polarisation of the final state in the annihilation, with a specific focuson the impact on neutrino fluxes from dark matter annihilations in the centre of the Sun. We find that differences between the event generators are larger for yields of hadronic end products such as antiprotons, than for leptonic end products. Concerning polarisation, we conversely find the largest differences in the leptonic spectra. We find that for neutrino fluxes from dark matter annihilations in the Sun, differences between the polarisations of the final state are to some extent washed out by neutrino oscillations and interactions in the Sun.

  • 6. Perotti, E.
    et al.
    Niblaeus, Carl
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Uppsala University, Sweden.
    Leupold, S.
    Lifetime of the eta ' meson at low temperature2016In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 950, p. 29-63Article in journal (Refereed)
    Abstract [en]

    This work constitutes one part of an investigation of the low-temperature changes of the properties of the eta ' meson. In turn these properties are strongly tied to the U(1)(A) anomaly of Quantum Chromodynamics. The final aim is to explore the interplay of the chiral anomaly and in-medium effects. We determine the lifetime of an eta ' meson being at rest in a strongly interacting medium as a function of the temperature. To have a formally well-defined low-energy limit we use in a first step Chiral Perturbation Theory for a large number of colors. We determine the pertinent scattering amplitudes in leading and next-to-leading order. In a second step we include resonances that appear in the same mass range as the eta ' meson. The resonances are introduced such that the low-energy limit remains unchanged and that they saturate the corresponding low-energy constants. This requirement fixes all coupling constants. We find that the width of the eta ' meson is significantly increased from about 200 keV in vacuum to about 10 MeV at a temperature of 120 MeV.

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