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Merle, Alexander
Publications (10 of 15) Show all publications
Melbéus, H., Merle, A. & Ohlsson, T. (2012). Continuum photon spectrum from Z1Z1 annihilations in universal extra dimensions. Physics Letters B, 706(4-5), 329-332
Open this publication in new window or tab >>Continuum photon spectrum from Z1Z1 annihilations in universal extra dimensions
2012 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 706, no 4-5, p. 329-332Article in journal (Refereed) Published
Abstract [en]

We calculate the continuum photon spectrum from the pair annihilation of a Z1 LKP in non-minimal universal extra dimensions. We find that, due to the preferred annihilation into W+ W- pairs, the continuum flux of collinear photons is relatively small compared to the standard case of the B1 as the LKP. This conclusion applies in particular to the spectral endpoint, where also the additional fermionic contributions are not large enough to increase the flux significantly. When searching for the line signal originating from Z1 Z1 annihilations, this is actually a perfect situation, since the continuum signal can be regarded as background to the smoking gun signature of a peak in the photon flux at an energy that is nearly equal to the mass of the dark matter particle. This signal, in combination with (probably) a non-observation of the continuum signal at lower photon energies, constitutes a perfect handle to probe the hypothesis of the Z1 LKP being the dominant component of the dark matter observed in the Universe.

Place, publisher, year, edition, pages
Elsevier B.V., 2012
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-50386 (URN)10.1016/j.physletb.2011.11.018 (DOI)000299756800011 ()2-s2.0-84155165683 (Scopus ID)
Funder
Swedish Research Council, 621-2008-4210
Note

This is the author’s version of a work that was accepted for publication in Physics Letters B. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Physics Letters B, VOL 706, ISSUE 4-5, (15 November 2011) DOI:10.1016/j.physletb.2011.11.018. QC 20120223  Correction ISI: 000306305000041  Doi: 10.1016/j.physletb.2012.05.059

Available from: 2012-02-23 Created: 2011-12-05 Last updated: 2024-03-18Bibliographically approved
Melbéus, H., Merle, A. & Ohlsson, T. (2012). Erratum to: Continuum photon spectrum from Z(1)Z(1) annihilations in universal extra dimensions. Physics Letters B, 713(3), 350-350
Open this publication in new window or tab >>Erratum to: Continuum photon spectrum from Z(1)Z(1) annihilations in universal extra dimensions
2012 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 713, no 3, p. 350-350Article in journal (Refereed) Published
Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2012
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-245297 (URN)10.1016/j.physletb.2012.05.059 (DOI)000306305000041 ()2-s2.0-84862668334 (Scopus ID)
Note

QC 20190315

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2022-06-26Bibliographically approved
de Woul, J., Merle, A. & Ohlsson, T. (2012). Establishing analogies between the physics of extra dimensions and carbon nanotubes. Physics Letters B, 714(1), 44-47
Open this publication in new window or tab >>Establishing analogies between the physics of extra dimensions and carbon nanotubes
2012 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 714, no 1, p. 44-47Article in journal (Refereed) Published
Abstract [en]

We point out a conceptual analogy between the physics of extra spatial dimensions and the physics of carbon nanotubes which arises for principle reasons, although the corresponding energy scales are at least ten orders of magnitude apart. For low energies, one can apply the Kaluza-Klein description to both types of systems, leading to two completely different but consistent interpretations of the underlying physics. In particular, we discuss in detail the Kaluza-Klein description of armchair and zig-zag carbon nanotubes. Furthermore, we describe how certain experimental results for carbon nanotubes could be re-interpreted in terms of the Kaluza-Klein description. Finally, we present ideas for new measurements that could allow to probe concepts of models with extra spatial dimensions in table-top experiments, providing further links between condensed matter and particle physics.

Place, publisher, year, edition, pages
Elsevier, 2012
Keywords
Tev, Millimeter, Hierarchy, Graphene
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-100304 (URN)10.1016/j.physletb.2012.06.047 (DOI)000306877400008 ()2-s2.0-84864024235 (Scopus ID)
Funder
Swedish Research Council, 621-2011-3985EU, European Research Council, PIEF-GA-2011-297557
Note

QC 20120807

Available from: 2013-02-26 Created: 2012-08-06 Last updated: 2024-03-18Bibliographically approved
Merle, A. & Zwicky, R. (2012). Explicit and spontaneous breaking of SU(3) into its finite subgroups. Journal of High Energy Physics (JHEP) (2), 128
Open this publication in new window or tab >>Explicit and spontaneous breaking of SU(3) into its finite subgroups
2012 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, p. 128-Article in journal (Refereed) Published
Abstract [en]

We investigate the breaking of SU(3) into its subgroups from the viewpoints of explicit and spontaneous breaking. A one-to-one link between these two approaches is given by the complex spherical harmonics, which form a complete set of SU(3)-representation functions. An invariant of degrees p and q in complex conjugate variables corresponds to a singlet, or vacuum expectation value, in a (p; q)-representation of SU(3). We review the formalism of the Molien function, which contains information on primary and secondary invariants. Generalizations of the Molien function to the tensor generating functions are discussed. The latter allows all branching rules to be deduced. We have computed all primary and secondary invariants for all proper finite subgroups of order smaller than 512, for the entire series of groups Delta(3n(2)), Delta(6n(2)), and for all crystallographic groups. Examples of sufficient conditions for breaking into a subgroup are worked out for the entire Tn[a]-, Delta(3n(2))-, Delta(6n(2))-series and for all crystallographic groups Sigma(X). The corresponding invariants provide an alternative definition of these groups. A Mathematica package, SUtree, is provided which allows the extraction of the invariants, Molien and generating functions, syzygies, VEVs, branching rules, character tables, matrix (p; q)(SU(3))-representations, Kronecker products, etc. for the groups discussed above.

Keywords
Discrete and Finite Symmetries, Spontaneous Symmetry Breaking, Beyond Standard Model
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-96743 (URN)10.1007/JHEP02(2012)128 (DOI)000301453400048 ()2-s2.0-84857808986 (Scopus ID)
Note
QC 20120613Available from: 2012-06-13 Created: 2012-06-11 Last updated: 2024-03-18Bibliographically approved
Melbéus, H., Merle, A. & Ohlsson, T. (2012). Higgs dark matter in UEDs: A good WIMP with bad detection prospects. Physics Letters B, 715(1-3), 164-169
Open this publication in new window or tab >>Higgs dark matter in UEDs: A good WIMP with bad detection prospects
2012 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 715, no 1-3, p. 164-169Article in journal (Refereed) Published
Abstract [en]

We study the first Kaluza-Klein excitation of the Higgs boson in universal extra dimensions as a dark matter candidate. The first-level Higgs boson could be the lightest Kaluza-Klein particle, which is stable due to the conservation of Kaluza-Klein parity, in non-minimal models where boundary localized terms modify the mass spectrum. We calculate the relic abundance and find that it agrees with the observed dark matter density if the mass of the first-level Higgs boson is slightly above 2 TeV, not considering coannihilations and assuming no relative mass splitting among the first-level Kaluza-Klein modes. In the case of coannihilations and a non-zero mass splitting, the mass of the first-level Higgs boson can range from 1 TeV to 4 TeV. We study also the prospects for detection of this dark matter candidate in direct as well as indirect detection experiments. Although the first-level Higgs boson is a typical weakly interacting massive particle, an observation in any of the conventional experiments is very challenging.

Place, publisher, year, edition, pages
Elsevier, 2012
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-103976 (URN)10.1016/j.physletb.2012.07.037 (DOI)000308519000022 ()2-s2.0-84865319214 (Scopus ID)
Funder
Swedish Research Council, 621-2011-3985
Note

QC 20121026

Available from: 2013-02-20 Created: 2012-10-25 Last updated: 2024-03-18Bibliographically approved
Merle, A. (2012). keV sterile Neutrino Dark Matter and Neutrino Model Building. Paper presented at 12th International Conference on Topics in Astroparticle and Underground Physics (TAUP2011), Munich, Germany, 5-9 Sep 2011. Journal of Physics, Conference Series, 375(Part 2), 012047
Open this publication in new window or tab >>keV sterile Neutrino Dark Matter and Neutrino Model Building
2012 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 375, no Part 2, p. 012047-Article in journal (Refereed) Published
Abstract [en]

A sterile neutrino with a mass around the keV scale could be an interesting candidate for warm dark matter. Although there are several scenarios and production mechanisms known in which such a particle could yield the correct abundance, there are astonishingly few models around that can actually yield an explanation for the appearance of a keV-like scale. We here review three main classes of such mass models for keV sterile neutrino dark matter, based on split seesaw, on L-e - L-mu - L-tau symmetry, and on the Froggatt-Nielsen mechanism, respectively.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2012
Keywords
Dark matter, Mass models, Production mechanisms, Sterile neutrinos
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-79880 (URN)10.1088/1742-6596/375/1/012047 (DOI)000307776500047 ()2-s2.0-84864995930 (Scopus ID)
Conference
12th International Conference on Topics in Astroparticle and Underground Physics (TAUP2011), Munich, Germany, 5-9 Sep 2011
Note

QC 20120516

Available from: 2012-05-16 Created: 2012-02-09 Last updated: 2024-03-18Bibliographically approved
Bonnevier, J., Melbéus, H., Merle, A. & Ohlsson, T. (2012). Monoenergetic gamma rays from nonminimal Kaluza-Klein dark matter annihilations. Physical Review D, 85(4), 043524
Open this publication in new window or tab >>Monoenergetic gamma rays from nonminimal Kaluza-Klein dark matter annihilations
2012 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 85, no 4, p. 043524-Article in journal (Refereed) Published
Abstract [en]

We investigate monoenergetic gamma-ray signatures from annihilations of dark matter comprised of Z(1), the first Kaluza-Klein (KK) excitation of the Z boson in a nonminimal universal extra dimensions (UED) model. The self interactions of the non-Abelian Z(1) gauge boson give rise to a large number of contributing Feynman diagrams that do not exist for annihilations of the Abelian gauge boson B-1, which is the standard Kaluza-Klein dark matter (KKDM) candidate. We find that the annihilation rate is indeed considerably larger for the Z(1) than for the B-1. Even though relic density calculations indicate that the mass of the Z(1) should be larger than the mass of the B-1, the predicted monoenergetic gamma fluxes are of the same order of magnitude. We compare our results to existing experimental limits, as well as to future sensitivities, for image air Cherenkov telescopes, and we find that the limits are reached already with a moderately large boost factor. The realistic prospects for detection depend on the experimental energy resolution.

Place, publisher, year, edition, pages
The American Physical Society, 2012
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-50382 (URN)10.1103/PhysRevD.85.043524 (DOI)000300571500006 ()2-s2.0-84857700861 (Scopus ID)
Funder
Swedish Research Council, 621-2008-4210
Note
QC 20111208Available from: 2012-02-23 Created: 2011-12-05 Last updated: 2024-03-18Bibliographically approved
Bouchand, R. & Merle, A. (2012). Running of radiative neutrino masses: the scotogenic model. Journal of High Energy Physics (JHEP) (7), 084
Open this publication in new window or tab >>Running of radiative neutrino masses: the scotogenic model
2012 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, p. 084-Article in journal (Refereed) Published
Abstract [en]

We study the renormalization group equations of Ma's scotogenic model, which generates an active neutrino mass at 1-loop level. In addition to other benefits, the main advantage of the mechanism exploited in this model is to lead to a natural loop-suppression of the neutrino mass, and therefore to an explanation for its smallness. However, since the structure of the neutrino mass matrix is altered compared to the ordinary type I seesaw case, the corresponding running is altered as well. We have derived the full set of renormalization group equations for the scotogenic model which, to our knowledge, had not been presented previously in the literature. This set of equations reflects some interesting structural properties of the model, and it is an illustrative example for how the running of neutrino parameters in radiative models is modified compared to models with tree-level mass generation. We also study a simplified numerical example to illustrate some general tendencies of the running. Interestingly, the structure of the RGEs can be exploited such that a bimaximal leptonic mixing pattern at the high-energy scale is translated into a valid mixing pattern at low energies, featuring a large value of theta(13). This suggests very interesting connections to flavour symmetries.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-103394 (URN)10.1007/JHEP07(2012)084 (DOI)000307298400084 ()2-s2.0-84864451485 (Scopus ID)
Note

QC 20121011

Available from: 2012-10-11 Created: 2012-10-11 Last updated: 2022-06-24Bibliographically approved
King, S. F. & Merle, A. (2012). Warm Dark Matter from keVins. Journal of Cosmology and Astroparticle Physics (8), 016
Open this publication in new window or tab >>Warm Dark Matter from keVins
2012 (English)In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 8, p. 016-Article in journal (Refereed) Published
Abstract [en]

We propose a simple model for Warm Dark Matte (WDM) in which two femions are added to the Standard,Model: (quasi-) stable "keVins" (keV inert fermions) which account for WDM and their unstable brothers, the "GeVins" (GeV inert fermions), both of which carry zero electric charge and zero lepton number, and are (approximately) "inert", in the sense that their only interactions are via suppressed couplings to the Z. We consider scenarios in which stable keVins are thermally produced and their abundance is subsequently diluted by entropy production from the decays of the heavier unstable GeVins. This mechanism could be implemented in a wide variety of models, including E-6 inspired supersymmetric models or models involving sterile neutrinos.

Keywords
dark matter theory, cosmology of theories beyond the SM, cosmological neutrinos
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-105023 (URN)10.1088/1475-7516/2012/08/016 (DOI)000308800700017 ()2-s2.0-84865272666 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, PIEF-GA-2011-297557
Note

QC 20121119

Available from: 2012-11-19 Created: 2012-11-15 Last updated: 2024-03-18Bibliographically approved
Bergström, J., Merle, A. & Ohlsson, T. (2011). Constraining new physics with a positive or negative signal of neutrino-less double beta decay. Journal of High Energy Physics (JHEP), 2011(05), 122
Open this publication in new window or tab >>Constraining new physics with a positive or negative signal of neutrino-less double beta decay
2011 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2011, no 05, p. 122-Article in journal (Refereed) Published
Abstract [en]

We investigate numerically how accurately one could constrain the strengths of different short-range contributions to neutrino-less double beta decay in effective field theory. Depending on the outcome of near-future experiments yielding information on the neutrino masses, the corresponding bounds or estimates can be stronger or weaker. A particularly interesting case, resulting in strong bounds, would be a positive signal of neutrino-less double beta decay that is consistent with complementary information from neutrino oscillation experiments, kinematical determinations of the neutrino mass, and measurements of the sum of light neutrino masses from cosmological observations. The keys to more robust bounds are improvements of the knowledge of the nuclear physics involved and a better experimental accuracy.

Keywords
Rare Decays, Beyond Standard Model, Neutrino Physics
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-34849 (URN)10.1007/JHEP05(2011)122 (DOI)000291364500054 ()2-s2.0-80053161286 (Scopus ID)
Funder
Swedish Research Council, 621-2008-4210
Note
QC 20110616Available from: 2011-09-26 Created: 2011-06-16 Last updated: 2024-03-18Bibliographically approved
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