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Publications (10 of 11) Show all publications
Berg, M., Conlon, J. P., Day, F., Jennings, N., Krippendorf, S., Powell, A. J. & Rummel, M. (2017). Constraints on Axion-Like Particles from X-ray Observations of NGC1275. Astrophysical Journal, 847(101), 1-22
Open this publication in new window or tab >>Constraints on Axion-Like Particles from X-ray Observations of NGC1275
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2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 847, no 101, p. 1-22Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2017
Keywords
elementary particles, X-rays, galaxies, clusters, individual (NGC1275)
National Category
Other Physics Topics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-65797 (URN)10.3847/1538-4357/aa8b16 (DOI)000411890700001 ()
Available from: 2018-01-23 Created: 2018-01-23 Last updated: 2019-07-11Bibliographically approved
Berg, M., Buchberger, I. & Schlotterer, O. (2017). From maximal to minimal supersymmetry in string loop amplitudes. Journal of High Energy Physics (JHEP), 163
Open this publication in new window or tab >>From maximal to minimal supersymmetry in string loop amplitudes
2017 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 163Article in journal (Refereed) Published
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-41950 (URN)10.1007/JHEP04(2017)163 (DOI)000401067200002 ()
Available from: 2016-04-29 Created: 2016-04-29 Last updated: 2018-01-04Bibliographically approved
Berg, M., Buchberger, I. & Schlotterer, O. (2017). String-motivated one-loop amplitudes in gauge theories with half-maximal supersymmetry. Journal of High Energy Physics (JHEP) (7), Article ID 138.
Open this publication in new window or tab >>String-motivated one-loop amplitudes in gauge theories with half-maximal supersymmetry
2017 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, article id 138Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Scattering Amplitudes, Superstrings and Heterotic Strings, Supersymmetric Gauge Theory, Supersymmetric Effective Theories
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-65726 (URN)10.1007/JHEP07(2017)138 (DOI)000406884500007 ()
Available from: 2018-01-18 Created: 2018-01-18 Last updated: 2019-07-11Bibliographically approved
Berg, M., Haack, M., Kang, J. U. & Sjörs, S. (2014). Towards the One-loop Kahler Metric of Calabi-Yau Orientifolds. Journal of High Energy Physics (JHEP), 12, 077
Open this publication in new window or tab >>Towards the One-loop Kahler Metric of Calabi-Yau Orientifolds
2014 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 12, p. 077-Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
New York: Springer, 2014
Keywords
Strings and branes phenomenology
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-33810 (URN)10.1007/JHEP12(2014)077 (DOI)000349601900001 ()
Available from: 2014-09-23 Created: 2014-09-23 Last updated: 2019-11-28Bibliographically approved
Berg, M., Buchberger, I., Ghilencea, D. & Petersson, C. (2013). Higgs diphoton rate enhancement from supersymmetric physics beyond the MSSM. Physical Review D, 88(2)
Open this publication in new window or tab >>Higgs diphoton rate enhancement from supersymmetric physics beyond the MSSM
2013 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 2Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2013
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-30079 (URN)10.1103/PhysRevD.88.025017 (DOI)000321738200011 ()
External cooperation:
Available from: 2013-11-21 Created: 2013-11-21 Last updated: 2019-07-11Bibliographically approved
Berg, M., Conlon, J., Marsh, D. & Witkowski, L. (2013). Superpotential de-sequestering in string models. Journal of High Energy Physics (JHEP), 18(February)
Open this publication in new window or tab >>Superpotential de-sequestering in string models
2013 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 18, no FebruaryArticle in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Berlin: Springer, 2013
Keywords
Supersymmetry Breaking, Compactification and String Models, Intersecting branes models, Conformal Field Models in String Theory
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-26947 (URN)10.1007/JHEP02(2013)018 (DOI)000316272900018 ()
External cooperation:
Available from: 2013-04-15 Created: 2013-04-15 Last updated: 2019-07-11Bibliographically approved
Berg, M., Buchberger, I., Enander, J., Mörtsell, E. & Sjörs, S. (2012). Growth Histories in Bimetric Massive Gravity. Journal of Cosmology and Astroparticle Physics (12), Article ID 021.
Open this publication in new window or tab >>Growth Histories in Bimetric Massive Gravity
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2012 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 12, article id 021Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Bristol: Institute of Physics (IOP), 2012
Keywords
modified gravity, cosmological parameters from LSS, dark energy theory
National Category
Physical Sciences Algebra and Logic Mathematical Analysis
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-26948 (URN)10.1088/1475-7516/2012/12/021 (DOI)000312959800021 ()
Available from: 2013-04-15 Created: 2013-04-15 Last updated: 2019-07-11Bibliographically approved
Berg, M., Haack, M. & Kang, J. U. (2012). One-Loop Kähler Metric of D-Branes at Angles. Journal of High Energy Physics (JHEP), 1211, 091
Open this publication in new window or tab >>One-Loop Kähler Metric of D-Branes at Angles
2012 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 1211, p. 091-Article in journal (Refereed) Published
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.

National Category
Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-16169 (URN)10.1007/JHEP11(2012)091 (DOI)000312198500026 ()
Funder
Swedish Research Council
Available from: 2012-12-12 Created: 2012-12-12 Last updated: 2019-07-11Bibliographically approved
Berg, M., Marsh, D., McAllister, L. & Pajer, E. (2011). Sequestering in String Compactifications. Journal of High Energy Physics (JHEP), 134
Open this publication in new window or tab >>Sequestering in String Compactifications
2011 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 134Article in journal (Refereed) Published
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.

Keywords
Flux compactifications; Supersymmetry Breaking
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-30895 (URN)10.1007/JHEP06(2011)134 (DOI)000293136600061 ()
Available from: 2014-01-15 Created: 2014-01-15 Last updated: 2019-07-11Bibliographically approved
Berg, M., Pajer, E. & Sjörs, S. (2010). Two-field high-scale inflation in a sub-Planckian region of field space. Physical Review D, 81(10)
Open this publication in new window or tab >>Two-field high-scale inflation in a sub-Planckian region of field space
2010 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 81, no 10Article in journal (Refereed) Published
National Category
Natural Sciences
Research subject
Political Science; Physics
Identifiers
urn:nbn:se:kau:diva-30896 (URN)10.1103/PhysRevD.81.103535 (DOI)
Available from: 2014-01-15 Created: 2014-01-15 Last updated: 2019-07-11Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9611-2450

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