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R. Rückl

Publications and source records attributed to R. Rückl.

At least 19 recordsLinked to original sources
arXiv2007

Isolated Lepton Events at HERA: SUSY R-Parity Violation?

Events with an isolated high $p_T$ lepton, a hadron jet and missing energy as observed in the H1 experiment at HERA, are potentially associated with R-parity violation in supersymmetric theories. However, stringent kinematic constraints must be fulfilled if the production of supersymmetric particles in R-parity violating scenarios were the correct path for explaining these puzzling events. A reference point \RF is specified for which these constraints are illustrated and implications of the supersymmetric interpretation for new classes of multi-lepton events are indicated.

hep-ph↗
arXiv2007

Constraints on SUSY Seesaw from Leptogenesis and LFV

We study constraints on the fundamental parameters of supersymmetric type I seesaw models imposed by neutrino data, charged lepton flavor violation, thermal leptogenesis and perturbativity of the neutrino Yukawa couplings.

hep-ph↗
arXiv2006

Multi-Higgs boson production in the Standard Model and beyond

We present a calculation of the loop-induced processes gg -> HH and gg -> HHH, and investigate the observability of multi-Higgs boson production at the CERN Large Hadron Collider (LHC) in the Standard Model (SM) and beyond. While the SM cross sections are too small to allow observation at the LHC, we demonstrate that physics beyond the SM can lead to amplified, observable cross sections. Furthermore, the applicability of the heavy top quark approximation in two- and three-Higgs boson production is investigated. We conclude that multi-Higgs boson production at the SuperLHC is an interesting probe of Higgs sectors beyond the SM and warrants further study.

hep-ph↗
arXiv2006

Constraints on SUSY Seesaw Parameters from Leptogenesis and Lepton Flavor Violation

We study the constraints on a minimal supersymmetric seesaw model imposed by neutrino data, charged lepton flavor violation, thermal leptogenesis and perturbativity. We show that it is possible to constrain the three heavy Majorana neutrino masses as well as the complex Yukawa coupling matrix. Our results provide a first step towards a seesaw benchmark model for further phenomenological studies and model building.

hep-ph↗
arXiv2004

Slepton Flavor Violation

If the seesaw mechanism is implemented in supersymmetric theories the heavy neutrinos generate corrections to the slepton mass matrices which enhance the rates of charged lepton flavor violating processes. Here we study lepton flavor violating slepton pair production and decay at a future e+e- linear collider in mSUGRA post-LEP benchmark scenarios. We present the results of a background simulation and investigate the correlations of the collider signals with the corresponding radiative lepton decays.

hep-ph↗
arXiv2004

Lepton flavor violation in the SUSY seesaw model: an update

We present an update of previous work on charged lepton flavor violation (LFV) in the seesaw model. The most recent neutrino data fits and post WMAP mSUGRA benchmark scenarios are used as input. In this framework we compare the sensitivity of rare radiative decays on the right-handed Majorana mass scale M_R with the reach in slepton-pair production at a future linear collider.

hep-ph↗
arXiv2004

The SUSY seesaw model and lepton-flavor violation at a future electron-positron linear collider

We study lepton-flavor violating slepton production and decay at a future e^+e^- linear collider in context with the seesaw mechanism in mSUGRA post-LEP benchmark scenarios. The present knowledge in the neutrino sector as well as improved future measurements are taken into account. We calculate the signal cross-sections σ(e^{+/-}e^- -> l_β^{+/-} l_α^- \tildeχ_b^0 \tildeχ_a^0); l_δ=e, μ, τ; α=|= βand estimate the main background processes. Furthermore, we investigate the correlations of these signals with the corresponding lepton-flavor violating rare decays l_α -> l_β γ. It is shown that these correlations are relatively weakly affected by uncertainties in the neutrino data, but very sensitive to the model parameters. Hence, they are particularly suited for probing the origin of lepton-flavor violation.

hep-ph↗
arXiv2004

Supersymmetric Lepton Flavour Violation at the LHC and LC

In supersymmetric extensions of the Standard Model, the Yukawa and/or mass terms of the heavy neutrinos can generate lepton flavour violating slepton mass terms. These new supersymmetric sources of lepton flavour violation may both enhance the rates of charged lepton flavour violating processes, l_a -> l_b y, and generate distinct final states, like l_b l_a + jets + missing E_T, at future colliders. First, we discuss the sensitivity of future e^+e^- colliders to the SLFV independently of the lepton flavour violating mechanism. Second, we study lepton flavour violating slepton pair production and decay at a future e^+e^- linear collider in the context of the seesaw mechanism in mSUGRA post-LEP benchmark scenarios. We investigate the correlations of these signals with the corresponding lepton flavour violating rare decays l_a -> l_b y, and show that these correlations are particularly suited for probing the origin of lepton flavour violation.

hep-ph↗
arXiv2003

Probing the Majorana mass scale of right-handed neutrinos in mSUGRA

We discuss the perspectives of testing the right-handed Majorana mass scale M_R of the SUSY see-saw model in the mSUGRA framework. Lepton-flavor violating low energy processes are analyzed in recently proposed post-LEP benchmark scenarios, taking into account present uncertainties and future developments in the neutrino sector. Nonobservation of mu -> e gamma in the next-generation PSI experiment will provide upper bounds on M_R of the order of 10^(12-14) GeV, while on the other hand, a positive signal for tau -> mu gamma at SUPERKEKB or the LHC may determine M_R for a given mSUGRA scenario with an accuracy of a factor of 2.

hep-ph↗
arXiv2002

Neutrino Oscillations, SUSY See-Saw Mechanism and Charged Lepton Flavor Violation

Neutrino oscillations give clear evidence for non-vanishing neutrino masses and lepton-flavor violation (LFV) in the neutrino sector. This provides strong motivation to search for signals of LFV also in the charged lepton sector, and to probe the SUSY see-saw mechanism. We compare the sensitivity of rare radiative decays on the right-handed Majorana mass scale M_R with the reach in slepton-pair production at a future linear collider.

hep-ph↗
arXiv2002

LFV Constraints on the Majorana Mass Scale in mSUGRA

We discuss constraints on the right-handed Majorana mass scale M_R of the SUSY see-saw model in the mSUGRA framework. The sensitivity of radiative lepton-flavor violating decays on M_R is compared with the reach in lepton-flavor violating channels at a future linear collider.

hep-ph↗
arXiv2002

Nonfactorizable effects in B -> J/psi K

The method of QCD light-cone sum rules is used to calculate soft nonfactorizable contributions to the decay amplitude for B -> J/psi K. The result confirms expectations that in color-suppressed decays nonfactorizable corrections can be sizable.

hep-ph↗
arXiv2000

Predictions on $B \to π\bar{l} ν_l$, $D \to π\bar{l} ν_l$ and $D\to K \bar{l} ν_l$ from QCD Light-Cone Sum Rules

The $f^+$ form factors of the $B\to π$, $D\to π$ and $D\to K$ transitions are calculated from QCD light-cone sum rules (LCSR) and used to predict the widths and differential distributions of the exclusive semileptonic decays $B\to π\bar{l}ν_l$, $D \toπ\bar{l}ν_l$ and $D \to K \bar{l}ν_l$, where $l=e,μ$. The current theoretical uncertainties are estimated. The LCSR results are found to agree with the results of lattice QCD calculations and with experimental data on exclusive semileptonic D decays. Comparison of the LCSR prediction on $B\to π\bar{l} ν_l$ with the CLEO measurement yields a value of |V_{ub}| in agreement with other determinations.

hep-ph↗
arXiv2000

QCD Sum Rules for Heavy Flavors

We give a short review of QCD sum rule results for B and D mesons and Lambda_Q and Sigma_Q baryons. We focus mainly on recent developments concerning semileptonic B->pion and D->pion transitions, pion couplings to heavy hadrons, decay constants and estimates of the b quark mass from a baryonic sum rule, and the extraction of the pion distribution amplitude from CLEO data.

hep-ph↗
arXiv1999

Perturbative QCD Correction to the Light-Cone Sum Rule for the $B^*Bπ$ and $D^*Dπ$ Couplings

The $B^*Bπ$ and $D^*Dπ$ couplings have previously been derived from a QCD light-cone sum rule in leading order. Here, we describe the calculation of the $O(α_s)$ correction to the twist 2 term of this sum rule. The result is used for a first next-to-leading order analysis. We obtain $g_{B^*Bπ}= 22\pm 7$ and $g_{D^*Dπ}=10.5\pm 3$, where the error indicates the remaining theoretical uncertainty.

hep-ph↗
arXiv1998

High $Q^2$ Physics at HERA and Searches for New Particles

Preliminary results from H1 and ZEUS on Deep Inelastic Scattering (DIS) at high momentum transfer squared $Q^2$ are presented. Used are all available $e^+ p$ data accumulated by the H1 and ZEUS experiments between 1994 and 1997, corresponding to integrated luminosities of $37 {pb}^{-1}$ and $47 {pb}^{-1}$, respectively. The anomalies observed at high $Q^2$ in the 1994 to 1996 data still remain, though with less significance. Since this high $Q^2$ domain represents a new frontier in DIS, the same data are used to search for new particles possessing direct couplings to lepton-quark pairs. Assuming that the slight excess of events observed in Neutral Current DIS is due to a statistical fluctuation, preliminary limits on the production of leptoquarks and of squarks in R-parity violating MSSM are presented.

hep-ph↗