Johan Rathsman

Lund University, Lund, Skåne, Sweden

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Publications (71)163.64 Total impact

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    ABSTRACT: In this note we give recommendations on how to evaluate LHC cross sections for (neutral) Higgs production and Higgs branching ratios in the general (CP-conserving) Two-Higgs-Doublet Model (2HDM). The current status of available higher-order corrections to Higgs production and decay in this model is discussed, and the existing public codes implementing these calculations are described. Numerical results are presented for a set of reference scenarios, demonstrating the very good agreement between the results obtained using different programs.
    12/2013;
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    Rikard Enberg, Johan Rathsman, Glenn Wouda
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    ABSTRACT: We analyze a model for the Higgs sector with two scalar doublets and a softly broken $Z_2$ symmetry. One of the doublets breaks the electroweak symmetry and has tree-level Yukawa couplings to fermions. The other doublet has no vacuum expectation value and no tree-level couplings to fermions. Because the $Z_2$ parity is broken the two doublets can mix, which leads to a distinct and novel phenomenology. This Stealth Doublet Model can be seen as a generalization of the Inert Doublet Model with a broken $Z_2$ symmetry. We outline the model and present constraints from theory, electroweak precision tests and collider searches, including the recent observation of a Higgs boson at the LHC. The CP-odd scalar $A$ and the charged scalar $H^\pm$ couple to fermions at one-loop level. We compute the decays of $A$ and $H^\pm$ and in particular the one-loop decays $A \to f \bar{f}$, $H^\pm \to f \bar{f}^\prime $, $H^\pm \to W^\pm Z $ and $H^\pm \to W^\pm \gamma$. We also describe how to calculate and renormalize such processes in our model. We find that if one of $H^\pm$ or $A$ is the lightest scalar, $H^\pm \to W^\pm \gamma$ or $ A \to b \bar{b} $ are typically their respective dominating decay channels. Otherwise, the dominating decays of $H^\pm$ and $A$ are into a scalar and a vector. Due to the absence of tree-level fermion couplings for $H^\pm$ and $A$, we consider pair production and associated production with vector bosons and scalars at the LHC. If the parameter space of the model that favors $H^\pm \to W^\pm \gamma$ is realized in Nature, we estimate that there should be a considerable amount of such events in the present LHC data.
    11/2013;
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    Rikard Enberg, Johan Rathsman, Glenn Wouda
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    ABSTRACT: We consider a model for the Higgs sector with two scalar doublets and a softly broken Z_2 symmetry, the Stealth Doublet Model. This model can be seen as a generalization of the Inert Doublet Model. One of the doublets is the Higgs doublet that participates in electroweak symmetry breaking and couples to fermions. The other doublet does not couple to fermions at tree level and does not acquire a vacuum expectation value. The broken Z_2 symmetry leads to interesting phenomenology such as mixing between the two doublets and charged and CP-odd scalars that can be light and have unusual decay channels. We present theoretical and experimental constraints on the model and consider the recent observation of a Higgs boson at the LHC. The data on the H to \gamma\gamma\ channel can be naturally accommodated in the model, with either the lightest or the heaviest CP-even scalar playing the role of the observed particle.
    Journal of High Energy Physics 04/2013; · 5.62 Impact Factor
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    Johan Bijnens, Jie Lu, Johan Rathsman
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    ABSTRACT: We analysis the constraints of the general two Higgs doublet models via evolving the Yukawa coupling constants to high energy under renormalization group. We consider the appearance of a Landau pole or large off-diagonal Yukawa couplings which cause tree level flavour changing neutral currents. Our study shows the latter condition can be used to answer that how much $Z_2$ symmetry breaking can be allowed in a given 2HDM model.
    01/2013;
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    ABSTRACT: We revisit diffractive and exclusive W production at hadron colliders in different models for soft colour exchanges. The process pp to p[WX]p, and in particular a W charge asymmetry, has been suggested as a way to discriminate diffractive processes as being due to pomeron exchange in Regge phenomenology or QCD-based colour reconnection models. Our detailed analysis of the latter models at LHC energies shows, however, that they give similar results as pomeron models for very leading protons and central W production, including a vanishing W charge asymmetry. We demonstrate that soft colour exchange models provide a continuous transition from diffractive to inelastic processes and thereby include the intrinsic asymmetry of inelastic interactions while being at the same time sensitive to the underlying hadronisation models. Such sensitivity also concerns the differential distributions in proton momentum and W transverse momentum which opens possibilities to discriminate between different colour reconnection models.
    Physical review D: Particles and fields 10/2012; 87(9).
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    Johan Rathsman, Thomas Rössler
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    ABSTRACT: In the Next-to-Minimal SuperSymmetric Model (NMSSM) the lightest CP-odd Higgs bosons (a1) can be very light. As a consequence, in addition to the standard charged Higgs boson (h+) decays considered in the MSSM for a light charged Higgs (m_h+ < m_t), the branching fraction for h+ to a1 W can be dominant. We investigate how this signal can be searched for in t tbar production at the Large Hadron Collider (LHC) in the case that m_a1 \gtrsim 2m_B with the a1 giving rise to a single b bbar-jet and discuss to what extent the LHC experiments are able to discover such a scenario with an integrated luminosity \sim 20 fb-1. We also discuss the implications of the possible Higgs-signal observed at the LHC.
    Advances in High Energy Physics 06/2012; 2012. · 3.50 Impact Factor
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    Johan Bijnens, Jie Lu, Johan Rathsman
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    ABSTRACT: We study how general two Higgs doublet models can be constrained by considering their properties under renormalization group evolution of the Yukawa couplings. We take into account both the appearance of a Landau pole as well as off-diagonal Yukawa couplings leading to flavour changing neutral currents in violation with experimental constraints at the electroweak scale. We find that the latter condition can be used to limit the amount of Z2 symmetry breaking allowed in a given model.
    Journal of High Energy Physics 11/2011; 2012(5). · 5.62 Impact Factor
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    Johan Rathsman, Oscar Stål
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    ABSTRACT: We present the program 2HDMC and how it can be used to explore the physics of general CP conserving two Higgs doublet models.
    04/2011;
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    Lisa Carloni, Johan Rathsman, Torbjorn Sjostrand
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    ABSTRACT: New fundamental particles, charged under new gauge groups and only weakly coupled to the standard sector, could exist at fairly low energy scales. In this article we study a selection of such models, where the secluded group either contains a softly broken U(1) or an unbroken SU(N). In the Abelian case new {\gamma}v gauge bosons can be radiated off and decay back into visible particles. In the non-Abelian case there will not only be a cascade in the hidden sector, but also hadronization into new {\pi}v and {\rho}v mesons that can decay back. This framework is developed to be applicable both for e+e- and pp collisions, but for these first studies we concentrate on the former process type. For each Abelian and non-Abelian group we study three different scenarios for the communication between the standard sector and the secluded one. We illustrate how to distinguish the various characteristics of the models and especially study to what extent the underlying gauge structure can be determined experimentally.
    Journal of High Energy Physics 02/2011; 2011(4). · 5.62 Impact Factor
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    ABSTRACT: The Jewel 1.0 Monte Carlo simulates jet evolution in a medium with a microscopic description of splitting and scattering processes. In the framework of this model we investigate the transverse momentum broadening due to medium effects in different scenarios. Depending on assumptions about hadronisation, we observe either a small increase or even a slight decrease of the mean transverse momentum, but no sizeable broadening. This appears to be a natural consequence of a model formulation which conserves energy and momentum microscopically at each splitting and at each scattering. KeywordsJet quenching–dihadron correlations
    Indian Journal of Physics 01/2011; 85(7):1033-1038. · 1.79 Impact Factor
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    F. Mahmoudi, J. Rathsman, O. Stål, L. Zeune
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    ABSTRACT: We consider scenarios in the next-to-minimal supersymmetric model (NMSSM) where the CP-odd and charged Higgs bosons are very light. As we demonstrate, these can be obtained as simple deformations of existing phenomenological MSSM benchmarks scenarios with parameters defined at the weak scale. This offers a direct and meaningful comparison to the MSSM case. Applying a wide set of up-to-date constraints from both high-energy collider and flavour physics, the Higgs boson masses and couplings are studied in viable parts of parameter space. The LHC phenomenology of the light Higgs scenario for neutral and charged Higgs boson searches is discussed.
    European Physical Journal C 12/2010; · 5.25 Impact Factor
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    ABSTRACT: At the Large Hadron Collider, we prove the feasibility to detect pair production of the lightest CP-even Higgs boson h of a Type II 2-Higgs Doublet Model through the process q \bar q' --> Vhh (Higgs-strahlung, V=W+-,Z), in presence of two h --> b \bar b decays. We also show that, through such production and decay channels, one has direct access to the following Higgs self-couplings, thus enabling one to distinguish between a standard and the Supersymmetric version of the above model: lambda_(Hhh) -- which constrains the form of the Higgs potential -- as well as lambda_(W+- H+- h) and lambda_(Z A h) -- which are required by gauge invariance. Unfortunately, such claims cannot be extended to the Minimal Supersymmetric Standard Model, where the extraction of the same signals is impossible. Comment: Added one figure, few references and minor corrections to the text. Results unchanged
    Journal of High Energy Physics 08/2010; · 5.62 Impact Factor
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    David Eriksson, Johan Rathsman, Oscar Stål
    Computer Physics Communications 04/2010; 181:985-985. · 2.41 Impact Factor
  • David Eriksson, Johan Rathsman, Oscar Stål
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    ABSTRACT: On page 196 in the original 2HDMC publication [the authors, “2HDMC – two-Higgs-doublet model calculator”, ibid. 181, No. 1, 189–205 (2010; Zbl 1205.82016)], the normalization factors in the expressions for the oblique parameters were reported correctly. The correct expressions should read S=1 24π{⋯},T=1 16πsin 2 θ w m w 2 {⋯},U=1 24π{⋯}, in order to correspond to what is calculated by the code. The contents of the large parentheses are left unchanged from the expressions in [the authors, loc. cit.].
    Computer Physics Communications 01/2010; 181(5). · 2.41 Impact Factor
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    David Eriksson, Johan Rathsman, Oscar Stål
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    ABSTRACT: This manual describes the public code 2HDMC which can be used to perform calculations in a general, CP-conserving, two-Higgs-doublet model (2HDM). The program features simple conversion between different parametrizations of the 2HDM potential, a flexible Yukawa sector specification with choices of different Z_2-symmetries or more general couplings, a tree-level decay library including all two-body - and some three-body - decay modes for the Higgs bosons, and the possibility to calculate observables of interest for constraining the 2HDM parameter space, as well as theoretical constraints from positivity and unitarity. The latest version of the 2HDMC code and full documentation is available from: http://www.isv.uu.se/thep/MC/2HDMC Comment: 28 pages, no figures. Minor changes to the text, new interface to HiggsBounds described. Agrees with published version
    Computer Physics Communications 02/2009; · 2.41 Impact Factor
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    David Eriksson, Gunnar Ingelman, Johan Rathsman
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    ABSTRACT: We present a new model, based on color rearrangements, which at the same time can describe both hidden and open charm production in B-meson decays. The model is successfully compared to both inclusive decays, such as B→J/ψX and B→DsX, as well as exclusive ones, such as B→J/ψK(*) and B→D(*)D(*)K. It also gives a good description of the momentum distribution of direct J/ψ’s, especially in the low-momentum region, which earlier has been claimed as a possible signal for new exotic states.
    Physical review D: Particles and fields 01/2009; 79(1).
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    D Eriksson, S Hesselbach, J Rathsman
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    ABSTRACT: We investigate the viability of observing charged Higgs bosons (H±) produced in association with W bosons at the CERN Large Hadron Collider, using the leptonic decay H+ → and hadronic W decay, within the Minimal Supersymmetric Standard Model. Performing a parton level study we show how the irreducible Standard Model background from W + 2 jets can be controlled by applying appropriate cuts. In the standard mmaxh scenario we find a viable signal for large tan β and intermediate H± mmasses (~ mt).
    Journal of Physics Conference Series 06/2008; 110(7):072008.
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    ABSTRACT: We have developed the Monte Carlo simulation program JEWEL 1.0 (Jet Evolution With Energy Loss), which interfaces a perturbative final state parton shower with medium effects occurring in ultra-relativistic heavy ion collisions. This is done by comparing for each jet fragment the probability of further perturbative splitting with the density-dependent probability of scattering with the medium. A simple hadronisation mechanism is included. In the absence of medium effects, we validate JEWEL against a set of benchmark jet measurements. For elastic interactions with the medium, we characterise not only the medium-induced modification of the jet, but also the jet-induced modification of the medium. Our main physics result is the observation that collisional and radiative medium modifications lead to characteristic differences in the jet fragmentation pattern, which persist above a soft background cut. We argue that this should allow to disentangle collisional and radiative parton energy loss mechanisms by measuring the n-jet fraction or a class of jet shape observables.
    European Physical Journal C 05/2008; · 5.25 Impact Factor
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    ABSTRACT: Report of the Working Group on Higgs Bosons for the Workshop, ``Physics at TeV Colliders'', Les Houches, France, 11-29 June, 2007.
    03/2008;
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    ABSTRACT: The quark–gluon plasma (QGP) can be explored in relativistic heavy ion collisions by the jet quenching signature, i.e., by the energy loss of a high energy quark or gluon traversing the plasma. We introduce a novel QCD evolution formalism in the leading logarithm approximation, where normal parton radiation is interleaved with scattering on the plasma gluons occuring at a similar time scale. The idea is elaborated in two approaches. One extends the DGLAP evolution equations for fragmentation functions to include scatterings in the medium, which facilitates numerical solutions for comparison with data and provides a basis for a Monte Carlo implementation. The other approach is more general by including also the transverse momentum dependence of the jet evolution, which allows a separation of the scales also for the scattering term and provides a basis for analytical investigations. The two approaches are shown to be related and give the same characteristic softening of the jet depending on the temperature of the plasma. A substantial effect is found at the RHIC energy and is further enhanced at LHC. Systematic studies of data on the energy loss could, therefore, demonstrate the existence of the QGP and probe its properties.
    Nuclear Physics A 02/2008; · 2.50 Impact Factor

Publication Stats

1k Citations
163.64 Total Impact Points

Institutions

  • 2011–2013
    • Lund University
      • Department of Astronomy and Theoretical Physics
      Lund, Skåne, Sweden
  • 1993–2011
    • Uppsala University
      • • Department of Physics and Astronomy
      • • Department of Radiology, Oncology and Radiation Science
      Uppsala, Uppsala, Sweden
  • 2007
    • University of Wuerzburg
      • Department of Theoretical and Astrophysics
      Würzburg, Bavaria, Germany
  • 2000–2002
    • CERN
      Genève, Geneva, Switzerland
    • University of Santiago de Compostela
      • Department of Particle Physics
      Santiago de Compostela, Galicia, Spain
  • 1999
    • Autonomous University of Barcelona
      Cerdanyola del Vallès, Catalonia, Spain
  • 1997–1998
    • Stanford University
      • Stanford Linear Accelerator Center
      Palo Alto, CA, United States
  • 1993–1996
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany