Publications (12)45.38 Total impact

Article: Delving into extra dimensions
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ABSTRACT: Henrik Melbéus and Tommy Ohlsson describe three different theories of extra dimensions – universal, large and warped – and how these unseen dimensions could be observed, if they exist at all.Physics World 09/2012; 25(9):2730. · 0.45 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We study the first KaluzaKlein excitation of the Higgs boson in universal extra dimensions as a dark matter candidate. The firstlevel Higgs boson could be the lightest KaluzaKlein particle, which is stable due to the conservation of KaluzaKlein parity, in nonminimal 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 firstlevel Higgs boson is slightly above 2 TeV, not considering coannihilations and assuming no relative mass splitting among the firstlevel KaluzaKlein modes. In the case of coannihilations and a nonzero mass splitting, the mass of the firstlevel 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 firstlevel Higgs boson is a typical weakly interacting massive particle, an observation in any of the conventional experiments is very challenging.Physics Letters B 07/2012; 715(13):164169. · 4.57 Impact Factor 
Article: Erratum to
Physics Letters B 07/2012; 713(3):350350. · 4.57 Impact Factor  Physical review D: Particles and fields 05/2012; 85(10).
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ABSTRACT: We study how the recent ATLAS and CMS Higgs mass bounds affect the renormalization group running of the physical parameters in universal extra dimensions. Using the running of the Higgs selfcoupling constant, we derive bounds on the cutoff scale of the extradimensional theory itself. We show that the running of physical parameters, such as the fermion masses and the CKM mixing matrix, is significantly restricted by these bounds. In particular, we find that the running of the gauge couplings cannot be sufficient to allow gauge unification at the cutoff scale.Physics Letters B 05/2012; 712(45):419424. · 4.57 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We investigate monoenergetic gammaray signatures from annihilations of dark matter comprised of Z1, the first KaluzaKlein (KK) excitation of the Z boson in a nonminimal universal extra dimensions (UED) model. The self interactions of the nonAbelian Z1 gauge boson give rise to a large number of contributing Feynman diagrams that do not exist for annihilations of the Abelian gauge boson B1, which is the standard KaluzaKlein dark matter (KKDM) candidate. We find that the annihilation rate is indeed considerably larger for the Z1 than for the B1. Even though relic density calculations indicate that the mass of the Z1 should be larger than the mass of the B1, 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.Physical Review D 02/2012; 85(4):043524. · 4.69 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We calculate the continuum photon spectrum from the pair annihilation of a Z^1 LKP in nonminimal 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 Z^1 Z^1 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 nonobservation 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.Physics Letters B 11/2011; 706(45):329332. · 4.57 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We study the renormalization group (RG) running of the neutrino masses and the leptonic mixing parameters in two different extradimensional models, namely, the Universal Extra Dimensions (UED) model and a model, where the Standard Model (SM) bosons probe an extra dimension and the SM fermions are confined to a fourdimensional brane. In particular, we derive the beta function for the neutrino mass operator in the UED model. We also rederive the beta function for the chargedlepton Yukawa coupling, and confirm some of the existing results in the literature. The generic features of the RG running of the neutrino parameters within the two models are analyzed and, in particular, we observe a powerlaw behavior for the running. We note that the running of the leptonic mixing angle \theta_{12} can be sizable, while the running of \theta_{23} and \theta_{13} is always negligible. In addition, we show that the tribimaximal and the bimaximal mixing patterns at a highenergy scale are compatible with lowenergy experimental data, while a trismall mixing pattern is not. Finally, we perform a numerical scan over the lowenergy parameter space to infer the highenergy distribution of the parameters. Using this scan, we also demonstrate how the highenergy \theta_{12} is correlated with the smallest neutrino mass and the Majorana phases.Journal of High Energy Physics 04/2011; 2011(4):052. · 5.62 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We study the generation of small neutrino masses in an extradimensional model, where righthanded neutrinos are allowed to propagate in the extra dimension, while the Standard Model particles are confined to a brane. Motivated by the fact that extradimensional models are nonrenormalizable, we truncate the KaluzaKlein towers at a maximal extradimensional momentum. The structure of the bulk Majorana mass term, motivated by the SherkSchwarz mechanism, implies that the righthanded KaluzaKlein neutrinos pair to form Dirac neutrinos, except for a number of unpaired Majorana neutrinos at the top of each tower. These heavy Majorana neutrinos are the only sources of lepton number breaking in the model, and similarly to the typeI seesaw mechanism, they naturally generate small masses for the lefthanded neutrinos. The lower KaluzaKlein modes mix with the light neutrinos, and the mixing effects are not suppressed with respect to the lightneutrino masses. Compared to conventional fermionic seesaw models, such mixing can be more significant. We study the signals of this model at the Large Hadron Collider, and find that the current lowenergy bounds on the nonunitarity of the leptonic mixing matrix are strong enough to exclude an observation.Physical Review D 08/2010; 82(4):045023. · 4.69 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We investigate indirect neutrino signals from annihilations of KaluzaKlein dark matter in the Sun. Especially, we examine a five as well as a sixdimensional model, and allow for the possibility that boundary localized terms could affect the spectrum to give different lightest KaluzaKlein particles, which could constitute the dark matter. The dark matter candidates that are interesting for the purpose of indirect detection of neutrinos are the first KaluzaKlein mode of the U(1) gauge boson and the neutral component of the SU(2) gauge bosons. Using the DarkSUSY and WimpSim packages, we calculate muon fluxes at an Earthbased neutrino telescope, such as IceCube. For the fivedimensional model, the results that we obtained agree reasonably well with the results that have previously been presented in the literature, whereas for the sixdimensional model, we find that, at treelevel, the results are the same as for the fivedimensional model. Finally, if the first KaluzaKlein mode of the U(1) gauge boson constitutes the dark matter, IceCube can constrain the parameter space. However, in the case that the neutral component of the SU(2) gauge bosons is the LKP, the signal is too weak to be observed.Journal of Cosmology and Astroparticle Physics 01/2010; 2010(1):018. · 6.04 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We investigate a model of large extra dimensions where the internal space has the geometry of a hyperbolic disc. Compared with the ADD model, this model provides a more satisfactory solution to the hierarchy problem between the electroweak scale and the Planck scale, and it also avoids constraints from astrophysics. In general, a novel feature of this model is that the physical results depend on the position of the brane in the internal space, and in particular, the signal almost disappears completely if the brane is positioned at the center of the disc. Since there is no known analytic form of the KaluzaKlein spectrum for our choice of geometry, we obtain a spectrum based on a combination of approximations and numerical computations. We study the possible signatures of our model for hadron colliders, especially the LHC, where the most important processes are the production of a graviton together with a hadronic jet or a photon. We find that the signals are similar to those of the ADD model, regarding both qualitative behavior and strength. For the case of hadronic jet production, it is possible to obtain relatively strong signals, while for the case of photon production, this is much more difficult.Journal of High Energy Physics 08/2008; 2008(8):077. · 5.62 Impact Factor 
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12  Citations  
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45.38  Total Impact Points  
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Institutions

2010–2012

KTH Royal Institute of Technology
 Department of Theoretical Physics
Tukholma, Stockholm, Sweden
