arXiv subjects

Herbi K. Dreiner

Publications and source records attributed to Herbi K. Dreiner.

52 records · Page 3Linked to original sources

arXiv2011

Neutrino masses and mixings in the baryon triality constrained minimal supersymmetric standard model

We discuss how the experimental neutrino oscillation data can be realized in the framework of the baryon triality ($B_3$) constrained supersymmetric Standard Model (cSSM). We show how to obtain phenomenologically viable solutions, which are compatible with the recent WMAP observations. We present results for the hierarchical, inverted and degenerate cases which illustrate the possible size and structure of the lepton number violating couplings. We work with a new, as yet unpublished version of SOFTSUSY, where we implemented full one--loop neutrino masses. Finally, we shortly discuss some phenomenological implications at the LHC.

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arXiv2011

What if the LHC does not find supersymmetry in the sqrt(s)=7 TeV run?

We investigate the implications for supersymmetry from an assumed absence of any signal in the first period of LHC data taking at 7 TeV center-of-mass energy and with 1 to 7 fb^(-1) of integrated luminosity. We consider the zero-lepton plus four jets and missing transverse energy signature, and perform a combined fit of low-energy measurements, the dark matter relic density constraint and potential LHC exclusions within a minimal supergravity model. A non-observation of supersymmetry in the first period of LHC data taking would still allow for an acceptable description of low-energy data and the dark matter relic density in terms of minimal supergravity models, but would exclude squarks and gluinos with masses below 1 TeV.

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arXiv2010

SUSY parameter determination at the LHC using cross sections and kinematic edges

We study the determination of supersymmetric parameters at the LHC from a global fit including cross sections and edges of kinematic distributions. For illustration, we focus on a minimal supergravity scenario and discuss how well it can be constrained at the LHC operating at 7 and 14 TeV collision energy, respectively. We find that the inclusion of cross sections greatly improves the accuracy of the SUSY parameter determination, and allows to reliably extract model parameters even in the initial phase of LHC data taking with 7 TeV collision energy and 1/fb integrated luminosity. Moreover, cross section information may be essential to study more general scenarios, such as those with non-universal gaugino masses, and distinguish them from minimal, universal, models.

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arXiv2010

Normal tau polarisation as a sensitive probe of CP violation in chargino decay

CP violation in the spin-spin correlations in chargino production and subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC. From the normal polarisation of the tau, an asymmetry is defined to test the CP-violating phase of the higgsino mass parameter μ. Asymmetries of more than \pm70% are obtained, also in scenarios with heavy first and second generation sfermions. Bounds on the statistical significances of the CP asymmetries are estimated. As a result, the normal tau polarisation in the chargino decay is one of the most sensitive probes to constrain or measure the phase ϕ_μat the ILC, motivating further detailed experimental studies.

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arXiv2008

Sneutrino LSPs in R-parity violating minimal supergravity models

We consider the minimal supergravity model (mSUGRA) with one additional R-parity violating operator at the GUT scale. The superparticles mass spectra at the weak scale are generally altered due to the presence of the R-parity violating coupling in the renormalization group equations. We show that a lepton number violating coupling at the GUT scale can lead to a sneutrino as the lightest supersymmetric particle (LSP) in a large region of parameter space consistent with the muon anomalous magnetic moment and other precision measurements. We also give characteristic collider signatures at the LHC.

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arXiv2008

Disentangling CP phases in nearly degenerate resonances: neutralino production via Higgs at a muon collider

In the CP-violating Minimal Supersymmetric Standard Model, we study the pair production of neutralinos at center-of-mass energies around the heavy neutral Higgs boson resonances. For longitudinally polarized muon beams, we analyze CP asymmetries which are sensitive to the interference of the two heavy neutral Higgs bosons. Due to radiatively induced scalar-pseudoscalar transitions, the CP asymmetries can be strongly enhanced when the resonances are nearly degenerate, as in the Higgs decoupling limit. The Higgs couplings to the neutralino sector can then be analyzed in the presence of CP violating phases. We present a detailed numerical analysis of the cross sections, neutralino branching ratios, and the CP observables. We find that radiatively induced CP violation in the Higgs sector leads to sizable CP-asymmetries, which are accessible in future measurements at a muon collider. However, we expect that our proposed method should be applicable to other processes with nearly degenerate scalar resonances, even at hadron colliders.

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arXiv2007

Proton Hexality from an Anomalous Flavor U(1) and Neutrino Masses - Linking to the String Scale

We devise minimalistic gauged U(1)_X Froggatt-Nielsen models which at low-energy give rise to the recently suggested discrete gauge Z_6 symmetry, proton hexality, thus stabilizing the proton. Assuming three generations of right-handed neutrinos, with the proper choice of X-charges, we obtain viable neutrino masses. Furthermore, we find scenarios such that no X-charged hidden sector superfields are needed, which from a bottom-up perspective allows the calculation of g_string, g_X and G_SM's Kac-Moody levels. The only mass scale apart from M_grav is m_soft.

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arXiv2007

A Simple Baryon Triality Model for Neutrino Masses

We make a simple ansatz for the supersymmetric lepton-number violating Yukawa couplings, by relating them to the corresponding Higgs Yukawa couplings. This reduces the free B$_3$ parameters from 36 to 6. We fit these parameters to solve the solar and atmospheric neutrino anomalies in terms of neutrino oscillations. The resulting couplings are consistent with the stringent low-energy bounds. We investigate the resulting LHC collider signals for a stau LSP scenario.

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arXiv2007

Electroweak Contributions to Squark Pair Production

We compute electroweak contributions to the production of squark pairs at hadron colliders. These include the exchange of electroweak gauge bosons in the $s-$channel as well as electroweak gaugino exchange in the $t-$ and/or $u-$channel. In many cases these can interfere with the dominant QCD contributions. As a result, we find sizable contributions to the production of two SU(2) doublet squarks. At the LHC, they amount to 10 to 20% for typical mSUGRA (or CMSSM) scenarios, but in more general scenarios they can vary between -40 and $+55%$, depending on size and sign of the SU(2) gaugino mass. The electroweak contribution to the total squark pair production rate at the LHC is about 3.5 times smaller.

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arXiv2007

Electroweak Contributions to Squark Pair Production at the LHC

In this paper we compute electroweak contributions to the production of squark pairs at hadron colliders. These include the exchange of electroweak gauge bosons in the s-channel as well as electroweak gaugino exchange in the t- and/or u-channel. In many cases these can interfere with the dominant QCD contributions. As a result, we find sizable contributions to the production of two SU(2) doublet squarks. At the LHC, they amount to 10 to 20% for typical mSUGRA (or CMSSM) scenarios, but in more general scenarios they can vary between -40 and +55%, depending on size and sign of the SU(2) gaugino mass. The electroweak contribution to the total squark pair production rate at the LHC is about 3.5 times smaller.

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arXiv2007

Baryon Triality and Neutrino Masses from an Anomalous Flavor U(1)

We construct a concise U(1)_X Froggatt-Nielsen model in which baryon triality, a discrete gauge Z_3 symmetry, arises from U(1)_X breaking. The proton is thus stable, however, R-parity is violated. With the proper choice of U(1)_X charges we can obtain neutrino masses and mixings consistent with an explanation of the atmospheric and solar neutrino anomalies in terms of neutrino oscillations, with no right-handed neutrinos required. The only mass scale apart from M_grav is m_3/2 ~ m_soft.

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arXiv2007

Supersymmetric Jarlskog Invariants: the Neutrino Sector

We generalize the notion of the Jarlskog invariant to supersymmetric models with right--handed neutrinos. This allows us to formulate basis--independent necessary and sufficient conditions for CP conservation in such models.

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arXiv2006

Discovery potential of radiative neutralino production at the ILC

We study radiative neutralino production e^+e^- \to \tildeχ^0_1 \tildeχ^0_1γat the linear collider with longitudinally polarised beams. We consider the Standard Model background from radiative neutrino production e^+e^- \to ν\barνγ, and the supersymmetric radiative production of sneutrinos e^+e^- \to \tildeν\tildeν^\ast γ, which can be a background for invisible sneutrino decays. We give the complete tree-level formulas for the amplitudes and matrix elements squared. In the Minimal Supersymmetric Standard Model, we study the dependence of the cross sections on the beam polarisations, on the parameters of the neutralino sector, and on the selectron masses. We show that for bino-like neutralinos longitudinal polarised beams enhance the signal and simultaneously reduce the background, such that statistics is significantly enhanced. We point out that there are parameter regions where radiative neutralino production is the only channel to study SUSY particles, since heavier neutralinos, charginos and sleptons are too heavy to be pair-produced in the first stage of the linear collider with \sqrt{s}=500 GeV.

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arXiv2006

Anomalous Flavor U(1)_X for Everything

We present an ambitious model of flavor, based on an anomalous U(1)_X gauge symmetry with one flavon, only two right-handed neutrinos and only two mass scales: M_{grav} and m_{3/2}. In particular, there are no new scales introduced for right-handed neutrino masses. The X-charges of the matter fields are such that R-parity is conserved exactly, higher-dimensional operators are sufficiently suppressed to guarantee a proton lifetime in agreement with experiment, and the phenomenology is viable for quarks, charged leptons, as well as neutrinos. In our model one of the three light neutrinos automatically is massless. The price we have to pay for this very successful model are highly fractional X-charges which can likely be improved with less restrictive phenomenological ansatze for mass matrices.

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arXiv2006

What is the Discrete Gauge Symmetry of the MSSM?

We systematically study the extension of the Supersymmetric Standard Model (SSM) by an anomaly-free discrete gauge symmetry Z_N. We extend the work of Ibanez and Ross with N=2,3 to arbitrary values of N. As new fundamental symmetries, we find four Z_6, nine Z_9 and nine Z_18. We then place three phenomenological demands upon the low-energy effective SSM: (i) the presence of the mu-term in the superpotential, (ii) baryon-number conservation upto dimension-five operators, and (iii) the presence of the see-saw neutrino mass term LHLH. We are then left with only two anomaly-free discrete gauge symmetries: baryon-triality, B_3, and a new Z_6, which we call proton-hexality, P_6. Unlike B_3, P_6 prohibits the dimension-four lepton-number violating operators. This we propose as the discrete gauge symmetry of the Minimal SSM, instead of R-parity.

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arXiv2004

Supersymmetric Froggatt-Nielsen Models with Baryon- and Lepton-Number Violation

We systematically investigate the embedding of U(1)_X Froggatt-Nielsen models in (four-dimensional) local supersymmetry. We restrict ourselves to models with a single flavon field. We do not impose a discrete symmetry by hand, e.g. R-parity, baryon-parity or lepton-parity. Thus we determine the order of magnitude of the baryon- and/or lepton violating coupling constants through the Froggatt-Nielsen mechanism. We then scrutinize whether the predicted coupling constants are in accord with weak or GUT scale constraints. Many models turn out to be incompatible.

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