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  • 1.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Buchberger, Igor
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Enander, Jonas
    Stockholm University.
    Mörtsell, Edvard
    Stockholm University.
    Sjörs, Stefan
    Stockholm University.
    Growth Histories in Bimetric Massive Gravity2012In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 12, article id 021Article in journal (Refereed)
    Abstract [en]

    We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity for general homogeneous and isotropic backgrounds. In the de Sitter approximation, we obtain decoupled sets of massless and massive scalar gravitational fluctuations. Matter perturbations then evolve like in Einstein gravity. We perturb the future de Sitter regime by the ratio of matter to dark energy, producing quasi-de Sitter space. In this more general setting the massive and massless fluctuations mix. We argue that in the quasi-de Sitter regime, the growth of structure in bimetric gravity differs from that of Einstein gravity.

  • 2.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Buchberger, Igor
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Ghilencea, D.M.
    CERN, Switzerland.
    Petersson, Christoffer
    Université Libre de Bruxelles, Belgium.
    Higgs diphoton rate enhancement from supersymmetric physics beyond the MSSM2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 2Article in journal (Refereed)
    Abstract [en]

    We show that supersymmetric ‘‘new physics’’ beyond the minimal supersymmetric standard model can naturally accommodate a Higgs mass near 126 GeV and enhance the signal rate in the h to gamma gamma channel, while the signal rates in all the other Higgs decay channels coincide with Standard Model expectations, except possibly the h to Z gamma channel. The new physics that corrects the relevant Higgs couplings can be captured by two supersymmetric effective operators. We provide a simple example of an underlying model in which these operators are simultaneously generated. The scale of new physics that generates these operators can be around 5 TeV or larger, and outside the reach of the LHC.

  • 3.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Buchberger, Igor
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Schlotterer, Oliver
    Max Planck Institut, Potsdam, Germany.
    From maximal to minimal supersymmetry in string loop amplitudes2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 163Article in journal (Refereed)
  • 4.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Buchberger, Igor
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Schlotterer, Oliver
    ax-Planck-Institut für Gravitationsphysik, Germany.
    String-motivated one-loop amplitudes in gauge theories with half-maximal supersymmetry2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, article id 138Article in journal (Refereed)
    Abstract [en]

    We compute one-loop amplitudes in six-dimensional Yang-Mills theory with half-maximal supersymmetry from first principles: imposing gauge invariance and locality on an ansatz made from string-theory inspired kinematic building blocks yields unique expressions for the 3- and 4-point amplitudes. We check that the results are reproduced in the field-theory limit alpha' -> 0 of string amplitudes in K3 orbifolds, using simplifications made in a companion string-theory paper.

  • 5.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics. Stockholm University.
    Conlon, Joseph
    Oxford University, UK.
    Marsh, David
    Cornell University, USA.
    Witkowski, Lukas
    Oxford University, UK.
    Superpotential de-sequestering in string models2013In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 18, no FebruaryArticle in journal (Refereed)
    Abstract [en]

    Non-perturbative superpotential cross-couplings between visible sector matter and Kähler moduli can lead to significant flavour-changing neutral currents in compactifications of type IIB string theory. Here, we compute corrections to Yukawa couplings in orbifold models with chiral matter localised on D3-branes and non-perturbative effects on distant D7-branes. By evaluating a threshold correction to the D7-brane gauge coupling, we determine conditions under which the non-perturbative corrections to the Yukawa couplings appear. The flavour structure of the induced Yukawa coupling generically fails to be aligned with the tree-level flavour structure. We check our results by also evaluating a correlation function of two D7-brane gauginos and a D3-brane Yukawa coupling. Finally, by calculating a string amplitude between n hidden scalars and visible matter we show how non-vanishing vacuum expectation values of distant D7-brane scalars, if present, may correct visible Yukawa couplings with a flavour structure that differs from the tree-level flavour structure.

  • 6.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Conlon, Joseph P.
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Day, Francesca
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Jennings, Nicholas
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Krippendorf, Sven
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Powell, Andrew J.
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Rummel, Markus
    Rudolf Peierls Centre for Theoretical Physics, UK.
    Constraints on Axion-Like Particles from X-ray Observations of NGC12752017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 847, no 101, p. 1-22Article in journal (Refereed)
    Abstract [en]

    Axion-like particle s(ALPs) can induce localized oscillatory modulations in the spectra of photon sources passingthrough astrophysical magneticfields. Ultra-deep Chandraobservations of the Perseus cluster contain over 5 x 105counts from the active galactic nucleus (AGN) of the central cluster galaxy NGC1275 and represent a dataset of extraordinary quality for ALP searches. We use this data set to search for X-ray spectral irregularities fromthe AGN.

  • 7.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Haack, Michael
    LMU München.
    Kang, Jin U
    Kim Il Sung University.
    One-Loop Kähler Metric of D-Branes at Angles2012In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 1211, p. 091-Article in journal (Refereed)
    Abstract [en]

    We evaluate string one-loop contributions to the Kahler metric of D-brane moduli (positions and Wilson lines), in toroidal orientifolds with branes at angles. Contributions due to bulk states in the loop are known, so we focus on the contributions due to states localized at intersections of orientifold images. We show that these quantum corrections vanish. This does not follow from the usual nonrenormalization theorems of supersymmetric field theory.

  • 8.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Haack, Michael
    LMU München.
    Kang, Jin U
    Kim Il Sung.
    Sjörs, Stefan
    Heidelberg.
    Towards the One-loop Kahler Metric of Calabi-Yau Orientifolds2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 12, p. 077-Article in journal (Refereed)
    Abstract [en]

    We evaluate string one-loop contributions to the Kahler metric of closed string moduli in toroidal minimally supersymmetric (Calabi-Yau) orientifolds with D-branes. We focus on the poorly understood N = 1 sectors that receive contributions from all massive string states.

  • 9.
    Berg, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Haack, Michael
    LMU München.
    Pajer, Enrico
    LMU München.
    Perturbative quantum corrections and flux compactifications2008In: Fortschritte der Physik, ISSN 0015-8208, E-ISSN 1521-3978, Vol. 56, p. 356-362Article in journal (Refereed)
  • 10.
    Berg, Marcus
    et al.
    Stockholm University.
    Marsh, David
    Cornell University.
    McAllister, Liam
    Cornell University.
    Pajer, Enrico
    Cornell University.
    Sequestering in String Compactifications2011In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 134Article in journal (Refereed)
    Abstract [en]

    We study the mediation of supersymmetry breaking in string compactifications whose moduli are stabilized by nonperturbative effects. We begin with a critical review of arguments for sequestering in supergravity and in string theory. We then show that geometric isolation, even in a highly warped space, is insufficient to achieve sequestering: in type IIB compactifications, nonperturbative superpotentials involving the Kahler moduli introduce cross-couplings between well-separated visible and hidden sectors. The scale of the resulting soft terms depends on the moduli stabilization scenario. In the Large Volume Scenario, nonperturbative superpotential contributions to the soft trilinear A terms can introduce significant flavor violation, while in KKLT compactifications their effects are negligible. In both scenarios, the contributions to the mu and B mu parameters cannot be ignored in general. We conclude that sequestered supersymmetry breaking is possible in nonperturbatively-stabilized compactifications only if a mechanism in addition to bulk locality suppresses superpotential cross-couplings.

  • 11.
    Berg, Marcus
    et al.
    Oskar Klein Center for Cosmoparticle Physics and Department of Physics, Stockholm University.
    Pajer, Enrico
    Cornell University.
    Sjörs, Stefan
    Stockholm University.
    Two-field high-scale inflation in a sub-Planckian region of field space2010In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 81, no 10Article in journal (Refereed)
1 - 11 of 11
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