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  • 1. Agarwalla, S. K.
    et al.
    Ghosh, M.
    Raut, Sushant
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. Institute for Basic Science (IBS), South Korea.
    A hybrid setup for fundamental unknowns in neutrino oscillations using T2HK (ν) and μ-DAR (ν¯)2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2017, no 5, article id 115Article in journal (Refereed)
    Abstract [en]

    Neutrino mass hierarchy, CP-violation, and octant of θ23 are the fundamental unknowns in neutrino oscillations. In order to address all these three unknowns, we study the physics reach of a setup, where we replace the antineutrino run of T2HK with antineutrinos from muon decay at rest (μ-DAR). This approach has the advantages of having higher statistics in both neutrino and antineutrino modes, and lower beam-on backgrounds for antineutrino run with reduced systematics. We find that a hybrid setup consisting of T2HK (ν) and μ-DAR (ν¯) in conjunction with full exposure from T2K and NOνA can resolve the issue of mass hierarchy at greater than 3σ C.L. irrespective of the choices of hierarchy, δCP, and θ23. This hybrid setup can also establish the CP-violation at 5σ C.L. for ∼ 55% choices of δCP, whereas the same for conventional T2HK (ν+ν¯) setup along with T2K and NOνA is around 30%. As far as the octant of θ23 is concerned, this hybrid setup can exclude the wrong octant at 5σ C.L. if θ23 is at least 3° away from maximal mixing for any δCP.

  • 2.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Clementz, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Self-interacting inelastic dark matter: A viable solution to the small scale structure problems2017In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, Vol. 2017, no 3, article id 048Article in journal (Refereed)
    Abstract [en]

    Self-interacting dark matter has been proposed as a solution to the small-scale structure problems, such as the observed flat cores in dwarf and low surface brightness galaxies. If scattering takes place through light mediators, the scattering cross section relevant to solve these problems may fall into the non-perturbative regime leading to a non-trivial velocity dependence, which allows compatibility with limits stemming from cluster-size objects. However, these models are strongly constrained by different observations, in particular from the requirements that the decay of the light mediator is sufficiently rapid (before Big Bang Nucleosynthesis) and from direct detection. A natural solution to reconcile both requirements are inelastic endothermic interactions, such that scatterings in direct detection experiments are suppressed or even kinematically forbidden if the mass splitting between the two-states is sufficiently large. Using an exact solution when numerically solving the Schrödinger equation, we study such scenarios and find regions in the parameter space of dark matter and mediator masses, and the mass splitting of the states, where the small scale structure problems can be solved, the dark matter has the correct relic abundance and direct detection limits can be evaded.

  • 3.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Clementz, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Herrero-Garcia, Juan
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. University of Adelaide, Australia.
    Self-interacting inelastic dark matter: A viable solution to the small scale structure problemsManuscript (preprint) (Other academic)
    Abstract [en]

    Self-interacting dark matter has been proposed as a solution to the small-scale structure problems, such as the observed flat cores in dwarf and low surface brightness galaxies. If scattering takes place through light mediators, the scattering cross section relevant to solve these problems may fall into the non-perturbative regime leading to a non-trivial velocity dependence, which allows compatibility with limits stemming from cluster-size objects. However, these models are strongly constrained by different observations, in particular from the requirements that the decay of the light mediator is sufficiently rapid (before Big Bang Nucleosynthesis) and from direct detection. A natural solution to reconcile both requirements are inelastic endothermic interactions, such that scatterings in direct detection experiments are suppressed or even kinematically forbidden if the mass splitting between the two-states is sufficiently large. Using an exact solution when numerically solving the Schr\"odinger equation, we study such scenarios and find regions in the parameter space of dark matter and mediator masses, and the mass splitting of the states, where the small scale structure problems can be solved, the dark matter has the correct relic abundance and direct detection limits can be evaded.

  • 4.
    Clementz, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Effects of Dark Matter in Astrophysical Systems2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    When studying astrophysical structures with sizes ranging from dwarf galaxies to galaxy clusters, it becomes clear that there are vast amounts of unobservable gravitating mass. A compelling hypothesis is that this missing mass, which we call dark matter, consists of elementary particles that can be described in the same manner as those of the standard model of particle physics. This thesis is dedicated to the study of particle dark matter in astrophysical systems.

    The solar composition problem refers to the current mismatch between theoretical predictions and observations of the solar convection zone depth and sound speed profile. It has been shown that heat transfer by dark matter in the Sun may cool the solar core and alleviate the problem. We discuss solar capture of a self-interacting Dirac fermion dark matter candidate and show that, even though particles and antiparticles annihilate, the abundance of such a particle may be large enough to influence solar physics.

    Currently, direct and indirect methods are employed in searches for dark matter. In this context, we study inelastic dark matter, where a small mass splitting separates two dark matter particles and scattering takes one into the other. This affects the scattering kinematics, which in turn affects direct detection and solar capture rates. We also discuss the information contained in a direct detection signal and how it can be used to infer a minimal solar capture rate of dark matter.

    When comparing simulated dark matter halos with collisionless dark matter with dark matter halos inferred from observations, problems appear in the smallest structures. A proposed solution is self-interacting dark matter with long range forces. As the simplest models are under severe constraints, we study self-interactions in a model of inelastic dark matter.

  • 5.
    Herrero-Garcia, Juan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Riad, Stella
    KTH, School of Engineering Sciences (SCI), Physics.
    Wirén, Jens
    KTH, School of Engineering Sciences (SCI), Physics.
    Full parameter scan of the Zee model: exploring Higgs lepton flavor violation2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, article id 130Article in journal (Refereed)
    Abstract [en]

    We study the general Zee model, which includes an extra Higgs scalar doublet and a new singly-charged scalar singlet. Neutrino masses are generated at one-loop level, and in order to describe leptonic mixing, both the Standard Model and the extra Higgs scalar doublets need to couple to leptons (in a type-III two-Higgs doublet model), which necessarily generates large lepton flavor violating signals, also in Higgs decays. Imposing all relevant phenomenological constraints and performing a full numerical scan of the parameter space, we find that both normal and inverted neutrino mass orderings can be fitted, although the latter is disfavored with respect to the former. In fact, inverted ordering can only be accommodated if theta(23) turns out to be in the first octant. A branching ratio for h -> tau mu of up to 10(-2) is allowed, but it could be as low as 10(-6). In addition, if future expected sensitivities of tau -> mu gamma are achieved, normal ordering can be almost completely tested. Also, mu e conversion is expected to probe large parts of the parameter space, excluding completely inverted ordering if no signal is observed. Furthermore, non-standard neutrino interactions are found to be smaller than 10(-6), which is well below future experimental sensitivity. Finally, the results of our scan indicate that the masses of the additional scalars have to be below 2.5 TeV, and typically they are lower than that and therefore within the reach of the LHC and future colliders.

  • 6.
    Huang, Guo-yuan
    et al.
    Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China.;Univ Chinese Acad Sci, Sch Phys Sci, Beijing 100049, Peoples R China..
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. Univ Iceland, Sci Inst, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Zhou, Shun
    Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China.;Univ Chinese Acad Sci, Sch Phys Sci, Beijing 100049, Peoples R China.;Peking Univ, Ctr High Energy Phys, Beijing 100871, Peoples R China..
    Observational constraints on secret neutrino interactions from big bang nucleosynthesis2018In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 97, no 7, article id 075009Article in journal (Refereed)
    Abstract [en]

    We investigate possible interactions between neutrinos and massive scalar bosons via g(phi)(nu) over bar nu phi (or massive vector bosons via g(V)(nu) over bar gamma(mu)nu V-mu) and explore the allowed parameter space of the coupling constant g phi (or g(V)) and the scalar (or vector) boson mass m(phi) (or m(V)) by requiring that these secret neutrino interactions (SNIs) should not spoil the success of big bang nucleosynthesis (BBN). Incorporating the SNIs into the evolution of the early Universe in the BBN era, we numerically solve the Boltzmann equations and compare the predictions for the abundances of light elements with observations. It turns out that the constraint on g(phi) and m(phi) in the scalar-boson case is rather weak, due to a small number of degrees of freedom (d.o.f.). However, in the vector-boson case, the most stringent bound on the coupling g(V) less than or similar to 6 x 10(-10) at 95% confidence level is obtained for m(V) similar or equal to 1 MeV, while the bound becomes much weaker g(V) less than or similar to 8 x 10(-6) for smaller masses m(V) less than or similar to 10(-4) MeV. Moreover, we discuss in some detail how the SNIs affect the cosmological evolution and the abundances of the lightest elements.

  • 7.
    Kuhnel, Florian
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. Stockholm Univ, Sweden.
    Freese, Katherine
    Constraints on primordial black holes with extended mass functions2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 8, article id 083508Article in journal (Refereed)
    Abstract [en]

    Constraints on primordial black holes in the range 10(-18) M circle dot to 10(3) M circle dot are reevaluated for a general class of extended mass functions. Whereas previous work has assumed that PBHs are produced with one single mass, instead there is expected to be a range of masses even in the case of production from a single mechanism; constraints therefore change from previous literature. Although tightly constrained in the majority of cases, it is shown that, even under conservative assumptions, primordial black holes in the mass range 10(-10) M circle dot to 10(-8) M circle dot could still constitute the entirety of the dark matter. This stresses both the importance for a comprehensive reevaluation of all respective constraints that have previously been evaluated only for a monochromatic mass function and the need to obtain more constraints in the allowed mass range.

  • 8.
    Kuhnel, Florian
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. AlbaNova University Center, Sweden.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. AlbaNova University Center, Sweden; University of Iceland, Iceland.
    Signatures of compact halos of sterile-neutrino dark matter2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 96, no 10, article id 103020Article in journal (Refereed)
    Abstract [en]

    We investigate compact halos of sterile-neutrino dark matter and examine observable signatures with respect to neutrino and photon emission. Primarily, we consider two cases: primordial black-hole halos and ultracompact minihalos. In both cases, we find that there exists a broad range of possible parameter choices such that detection in the near future with x-ray and gamma-ray telescopes might be well possible. In fact, for energies above 10 TeV, the neutrino telescope IceCube would be a splendid detection machine for such macroscopic dark-matter candidates.

  • 9. Meloni, Davide
    et al.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Riad, Stella
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Renormalization group running of fermion observables in an extended non-supersymmetric SO(10) model2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, article id 045Article in journal (Refereed)
    Abstract [en]

    We investigate the renormalization group evolution of fermion masses, mixings and quartic scalar Higgs self-couplings in an extended non-supersymmetric SO(10) model, where the Higgs sector contains the 10(H), 120(H), and 126(H) representations. The group SO(10) is spontaneously broken at the GUT scale to the Pati-Salam group and subsequently to the Standard Model (SM) at an intermediate scale MI. We explicitly take into account the effects of the change of gauge groups in the evolution. In particular, we derive the renormalization group equations for the different Yukawa couplings. We find that the computed physical fermion observables can be successfully matched to the experimental measured values at the electroweak scale. Using the same Yukawa couplings at the GUT scale, the measured values of the fermion observables cannot be reproduced with a SM-like evolution, leading to differences in the numerical values up to around 80%. Furthermore, a similar evolution can be performed for a minimal SO(10) model, where the Higgs sector consists of the 10(H) and 126(H) representations only, showing an equally good potential to describe the low-energy fermion observables. Finally, for both the extended and the minimal SO(10) models, we present predictions for the three Dirac and Majorana CP-violating phases as well as three effective neutrino mass parameters.

  • 10.
    Riad, Stella
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Phenomenology of neutrino properties, unification, and Higgs couplings beyond the Standard Model2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The vast majority of experiments in particle physics can be described by the Standard Model of particle physics (SM). However, there are indications for physics beyond it. The only experimentally demonstrated problem of the model is the difficulty to describe neutrino masses and leptonic mixing. There is a plethora of models that try to describe these phenomena and this thesis investigates several possibilities for new models, both full theories and effective frameworks.

     

    The values of the parameters in a model are dependent on the energy scale and we say that the parameters run. The exact behavior of the running depends on the model and it provides a signature of the model. For a model defined at high energies it is necessary to run the parameters down to the electroweak scale in order to perform a comparison to the known values of observed quantities. In this thesis, we discuss renormalization group running in the context of extra dimensions and we provide an upper limit on the cutoff scale. We perform renormalization group running in two versions of a non-supersymmetric SO(10) model and we show that the SM parameters can be accommodated in both versions. In addition, we perform the running for the gauge couplings in a large set of radiative neutrino mass models and conclude that unification is possible in some of them.

     

    The Higgs boson provides new possibilities to study physics beyond the SM. Its properties have to be tested with extremely high precision before it could be established whether the particle is truly the SM Higgs boson or not. In this thesis, we perform Bayesian parameter inference and model comparison. For models where the magnitude of the Higgs couplings is varied, we show that the SM is favored in comparison to all other models. Furthermore, we discuss lepton flavor violating processes in the context of the Zee model. We find that these can be sizeable and close to the experimental limits.

  • 11.
    Riad, Stella
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Herrero-Garcia, Juan
    Wirén, Jens
    KTH, Superseded Departments, Physics.
    Full parameter scan of the Zee model: exploring Higgs lepton flavor violationManuscript (preprint) (Other academic)
    Abstract [en]

    We study the general Zee model, which includes an extra Higgs scalar doublet and a new singly-charged scalar singlet. Neutrino masses are generated at one-loop level, and in order to describe leptonic mixing, both the Standard Model and the extra Higgs scalar doublets need to couple to leptons (in a type-III two-Higgs doublet model), which necessarily generates large lepton flavor violating signals, also in Higgs decays. Imposing all relevant phenomenological constraints and performing a full numerical scan of the parameter space, we find that both normal and inverted neutrino mass orderings can be fitted, although the latter is disfavored with respect to the former. In fact, inverted ordering can only be accommodated if θ23 turns out to be in the first octant. A branching ratio for h→τμ of up to 10−2 is allowed, but it could be as low as 10−6. In addition, if future expected sensitivities of τ→μγ are achieved, normal ordering can be completely tested. Also, μeconversion is expected to strongly reduce the allowed parameter space, excluding completely inverted ordering. Furthermore, non-standard neutrino interactions are found to be smaller than 10−6, which is well below future experimental sensitivity. Finally, the results of our scan indicate that the masses of the additional scalars have to be below 2.5 TeV, and typically they are lower than that and therefore within the reach of the LHC and future colliders.

  • 12.
    Riad, Stella
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics.
    Meloni, Davide
    Renormalization Group Running of Fermion Observables in an Extended Non-Supersymmetric SO(10) ModelManuscript (preprint) (Other academic)
    Abstract [en]

    We investigate the renormalization group evolution of fermion masses, mixings and quartic scalar Higgs self-couplings in an extended non-supersymmetric SO(10) model, where the Higgs sector contains the 10H, 120H, and 126H representations. The group SO(10) is spontaneously broken at the GUT scale to the Pati-Salam group and subsequently to the Standard Model (SM) at an intermediate scale MI. We explicitly take into account the effects of the change of gauge groups in the evolution. In particular, we derive the renormalization group equations for the different Yukawa couplings. We find that the computed physical fermion observables can be successfully matched to the experimental measured values at the electroweak scale. Using the same Yukawa couplings at the GUT scale, the measured values of the fermion observables cannot be reproduced with a SM-like evolution, leading to differences in the numerical values up to around 80 %. Furthermore, a similar evolution can be performed for a minimal SO(10) model, where the Higgs sector consists of the 10H and 126H representations only, showing an equally good potential to describe the low-energy fermion observables. Finally, for both the extended and the minimal SO(10) models, we present predictions for the three Dirac and Majorana CP-violating phases as well as three effective neutrino mass parameters.

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