Searcharxiv⌕ Search

arXiv subjects

A. M. Weber

Publications and source records attributed to A. M. Weber.

13 recordsLinked to original sources
arXiv2009

Mass Bounds on a Very Light Neutralino

Within the Minimal Supersymmetric Standard Model (MSSM) we systematically investigate the bounds on the mass of the lightest neutralino. We allow for non-universal gaugino masses and thus even consider massless neutralinos, while assuming in general that R-parity is conserved. Our main focus are laboratory constraints. We consider collider data, precision observables, and also rare meson decays to very light neutralinos. We then discuss the astrophysical and cosmological implications. We find that a massless neutralino is allowed by all existing experimental data and astrophysical and cosmological observations.

hep-ph↗
arXiv2008

Bayesian Selection of sign(mu) within mSUGRA in Global Fits Including WMAP5 Results

We study the properties of the constrained minimal supersymmetric standard model (mSUGRA) by performing fits to updated indirect data, including the relic density of dark matter inferred from WMAP5. In order to find the extent to which mu < 0 is disfavoured compared to mu > 0, we compare the Bayesian evidence values for these models, which we obtain straightforwardly and with good precision from the recently developed multi-modal nested sampling ('MultiNest') technique. We find weak to moderate evidence for the mu > 0 branch of mSUGRA over mu < 0 and estimate the ratio of probabilities to be P(mu > 0)/P(mu < 0) = 6-61 depending on the prior measure and range used. There is thus positive (but not overwhelming) evidence that mu > 0 in mSUGRA. The MultiNest technique also delivers probability distributions of parameters and other relevant quantities such as superpartner masses. We explore the dependence of our results on the choice of the prior measure used. We also use the Bayesian evidence to quantify the consistency between the mSUGRA parameter inferences coming from the constraints that have the largest effects: (g-2)_mu, BR(b -> s gamma) and cold dark matter (DM) relic density Omega_{DM}h^2.

hep-ph↗
arXiv2008

Global Fits of the Large Volume String Scenario to WMAP5 and Other Indirect Constraints Using Markov Chain Monte Carlo

We present global fits to the Large Volume Scenario (LVS) of string models using current indirect data. We use WMAP5 constraints on dark matter relic density, b-physics and electroweak observables as well as direct search constraints. Such data can be adequately fit by LVS, with the best-fit point for mu>0 having chi^2=13.6 for 8 degrees of freedom. The resulting constraints on parameter space are robust in that they do not depend much upon the prior, or upon whether one uses Bayesian or frequentist interpretations of the data. Sparticle masses are constrained to be well below the 1 TeV level, predicting early SUSY discovery at the LHC. We devise a method of quantifying which are the most important constraints. We find that the LEP2 Higgs mass constraint, the relic density of dark matter and the anomalous magnetic moment of the muon affect the fits to the strongest degree.

hep-ph↗
arXiv2008

Z Pole Observables in the MSSM

We present the currently most accurate prediction of Z pole observables such as sin^2 theta_eff, Gamma_Z, R_b, R_l, and sigma^0_had in the Minimal Supersymmetric Standard Model (MSSM). We take into account the complete one-loop results including the full complex phase dependence, all available MSSM two-loop corrections as well as the full SM results. We furthermore include higher-order corrections in the MSSM Higgs boson sector, entering via virtual Higgs boson contributions. For Gamma(Z -> neutralino{1} neutralino{1}) we present a full one-loop calculation. We analyse the impact of the different sectors of the MSSM with particular emphasis on the effects of the complex phases. The predictions for the Z boson observables and M_W are compared with the current experimental values. Furthermore we provide an estimate of the remaining higher-order uncertainties in the prediction of sin^2 theta_eff.

hep-ph↗
arXiv2008

Physics Beyond the Standard Model: Supersymmetry

This collection of studies on new physics at the LHC constitutes the report of the supersymmetry working group at the Workshop `Physics at TeV Colliders', Les Houches, France, 2007. They cover the wide spectrum of phenomenology in the LHC era, from alternative models and signatures to the extraction of relevant observables, the study of the MSSM parameter space and finally to the interplay of LHC observations with additional data expected on a similar time scale. The special feature of this collection is that while not each of the studies is explicitely performed together by theoretical and experimental LHC physicists, all of them were inspired by and discussed in this particular environment.

hep-ph↗
arXiv2007

Prediction for the Lightest Higgs Boson Mass in the CMSSM using Indirect Experimental Constraints

Measurements at low energies provide interesting indirect information about masses of particles that are (so far) too heavy to be produced directly. Motivated by recent progress in consistently and rigorously calculating electroweak precision observables and flavour related observables, we derive the preferred value for m_h in the Constrained Minimal Supersymmetric Standard Model (CMSSM), obtained from a fit taking into account electroweak precision data, flavour physics observables and the abundance of Cold Dark Matter. No restriction is imposed on m_h itself: the experimental bound from direct Higgs boson search at LEP is not included in the fit. A multi-parameter chi^2 is minimized with respect to the free parameters of the CMSSM, M_0, M_1/2, A_0, tan(beta). A statistical comparison with the Standard Model fit to the electroweak precision data is made. The preferred value for the lightest Higgs boson mass in the CMSSM is found to be m_h^CMSSM = 110+8-10(exp.)+-3(theo.) GeV/c^2, where the first uncertainty is experimental and the second uncertainty is theoretical. This value is in agreement with the limit from direct Higgs boson search at LEP.

hep-ph↗
arXiv2007

High-Precision Tests of the MSSM with GigaZ

We review the physics potential of the GigaZ option of the International Linear Collider (ILC) for probing the Minimal Supersymmetric Standard Model (MSSM) via the sensitivity of the electroweak precision observables measured at the ILC to quantum corrections. A particular focus is put on the effective leptonic weak mixing angle, sin^2_theta_eff. The MSSM predictions take into account the complete one-loop results including the full complex phase dependence, all available MSSM two-loop corrections as well as the full Standard Model (SM) results. We find that the anticipated experimental accuracy at the ILC with GigaZ option may resolve the virtual effects of SUSY particles even in scenarios where the SUSY particles are so heavy that they escape direct detection at the LHC and the first phase of the ILC.

hep-ph↗
arXiv2007

MSSM precision physics at the Z resonance

LEP and SLC provide accurate data on the process (e^+e^- -> f bar f) at the Z resonance. The GigaZ option at a future linear e^+e^- collider (ILC) will further improve these measurements. As a consequence, theory predictions with sufficiently smaller errors are necessary in order to fully exploit the experimental accuracies and to derive indirect bounds on the scales of new physics. Here we review the currently most accurate predictions of the Z pole observables (e.g. sin^2 theta_eff, Gamma_Z, sigma^0_had) in the context of the Minimal Supersymmetric Standard Model (MSSM). These predictions contain the complete one-loop results including the full complex phase dependence, all available MSSM two-loop corrections, as well as all relevant Standard Model contributions.

hep-ph↗
arXiv2007

How light can the lightest neutralino be?

We show that in the Minimal Supersymmetric Standard Model, the mass of the lightest neutralino is experimentally unconstrained if the GUT relation between the gaugino mass parameters M_1 and M_2 is dropped. We discuss what the impact of light or massless neutralinos would be on their production at LEP, as well as on electroweak precision data and rare decays.

hep-ph↗
arXiv2007

The Supersymmetric Parameter Space in Light of B-physics Observables and Electroweak Precision Data

Indirect information about the possible scale of supersymmetry (SUSY) breaking is provided by B-physics observables (BPO) as well as electroweak precision observables (EWPO). We combine the constraints imposed by recent measurements of the BPO BR(b -> s gamma), BR(B_s -> mu^+ mu^-), BR(B_u -> tau nu_tau) and Delta M_{B_s} with those obtained from the experimental measurements of the EWPO M_W, sin^2 theta_eff, Gamma_Z, (g-2)_mu and M_h, incorporating the latest theoretical calculations of these observables within the Standard Model and supersymmetric extensions. We perform a chi^2 fit to the parameters of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the SUSY-breaking parameters are universal at the GUT scale, and the non-universal Higgs model (NUHM), in which this constraint is relaxed for the soft SUSY-breaking contributions to the Higgs masses. Assuming that the lightest supersymmetric particle (LSP) provides the cold dark matter density preferred by WMAP and other cosmological data, we scan over the remaining parameter space. Within the CMSSM, we confirm the preference found previously for a relatively low SUSY-breaking scale, though there is some slight tension between the EWPO and the BPO. In studies of some specific NUHM scenarios compatible with the cold dark matter constraint we investigate M_A-tan_beta planes and find preferred regions that have values of chi^2 somewhat lower than in the CMSSM.

hep-ph↗
arXiv2006

Testing the MSSM with the Mass of the W Boson

We review the currently most accurate evaluation of the W boson mass, M_W, in the Minimal Supersymmetric Standard Model (MSSM). It consists of a full one-loop calculation, including the complex phase dependence, all available MSSM two-loop corrections as well as the full Standard Model result. We analyse the impact of the phases in the scalar quark sector on M_W and compare the prediction for M_W based on all known higher-order contributions with the experimental results.

hep-ph↗
arXiv2006

Precise Prediction for M_W in the MSSM

We present the currently most accurate evaluation of the W boson mass, M_W, in the Minimal Supersymmetric Standard Model (MSSM). The full complex phase dependence at the one-loop level, all available MSSM two-loop corrections as well as the full Standard Model result have been included. We analyse the impact of the different sectors of the MSSM at the one-loop level with a particular emphasis on the effect of the complex phases. We discuss the prediction for M_W based on all known higher-order contributions in representative MSSM scenarios. Furthermore we obtain an estimate of the remaining theoretical uncertainty from unknown higher-order corrections.

hep-ph↗