Nonabelian Gauge Symmetry in the Causal Epstein-Glaser Approach

We present some generalizations of a recently proposed alternative approach to nonabelian gauge theories based on the causal Epstein-Glaser method in perturbative quantum field theory. Nonabelian gauge invariance is defined by a simple commutator relation in every order of perturbation theory separately using only the linear (abelian) BRS-transformations of the asymptotic fields. This condition is sufficient for the unitarity of the S-matrix in the physical subspace. We derive the most general specific coupling compatible with the conditions of nonabelian gauge invariance and normalizability. We explicitly show that the quadrilinear terms, the four-gluon-coupling and the four-ghost-coupling, are generated by our linear condition of nonabelian gauge invariance. Moreover, we work out the required generalizations for linear gauges.Comment: 32 pages, latex-file, no figure

Flavour data constraints on new physics and SuperIso

We discuss the implications of B_s -> mu+mu- and B -> K*mu+mu- decays in the context of indirect searches for new physics, emphasising the new LHCb results. In particular, we derive the consequences of the MFV hypothesis and discuss the importance of the MFV predictions. The impact of the recent LHCb measurements in the context of the MSSM will also be addressed, and the SuperIso program will be briefly described.Comment: 7 pages, 4 figures, contribution to the ICHEP 2012 Conference proceedings, 4-11 July 2012, Melbourne, Australi

Signs for new physics in the recent LHCb data?

We comment on some tensions with the Standard Model predictions in the recent LHCb data.Comment: 6 pages, 6 figures. Based on talks given at the Fifth Workshop on Theory, Phenomenology and Experiments in Flavour Physics, Capri, 23-25 May 2014 and at the FPCP 2014 conference on Flavor Physics and CP Violation, Marseille, 25-30 May 201

Indirect search for supersymmetry in rare B decays

QCD corrections to the gluino induced contribution to b --> s gamma are shown to be important in order to extract reliable bounds on the off-diagonal elements of the squark mass matrices.Comment: 4 pages including 2 postscript figure

Non-diagonal flavour observables in B and Collider Physics

Until now the focus within the direct search for supersymmetry has mainly been on flavour diagonal observables. Recently lepton flavour violating signals at future electron positron colliders have been studied. There is now an opportunity to analyse the relations between collider observables and low-energy observables in the hadronic sector. In a first work in this direction, we study flavour violation in the squark decays of the second and third generations taking into account results from B physics, in particular from the rare decay b ->s gamma. Correlations between various squark decay modes can be used to get more precise information on various flavour violating parameters.Comment: 3 pages, latex, Contribution to the International Europhysics Conference on High Energy Physics EPS03, 17-23 July 2003, Aachen, German

Measurement of the Width Difference of B_d Mesons

We estimate \Delta Gamma_d/\Gamma_d, including 1/m_b contributions and part of the next-to-leading order QCD corrections, and find it to be around 0.3%. We show the methods to measure \Delta Gamma_d/\Gamma_d by using at least two different final states on the untagged B_d decay. The nonzero width difference can also be used to identify new physics effects and to resolve a twofold discrete ambiguity in the B_d-\bar{B}_d mixing phase. With the high statistics and accurate time resolution of the upcoming LHC experiment, the measurement of \Delta Gamma_d seems to be possible. This measurement would be important for an accurate measurement of \sin2\phi_1 at the LHC. We also derive an upper bound on the value of \Delta Gamma_d/\Gamma_d in the presence of new physics.Comment: 3 pages, LaTeX, Presented at the 5th KEK Topical Conference(KEKTC5

The Algebraic Method

Combining the effect of an intermediate renormalization prescription (zero momentum subtraction) and the background field method (BFM), we show that the algebraic renormalization procedure needed for the computation of radiative corrections within non-invariant regularization schemes is drastically simplified. The present technique is suitable for gauge models and, here, is applied to the Standard Model. The use of the BFM allows a powerful organization of the counterterms and avoids complicated Slavnov-Taylor identities. Furthermore, the Becchi-Rouet-Stora-Tyutin (BRST) variation of background fields plays a special role in disentangling Ward-Takahashi identities (WTI) and Slavnov-Taylor identities (STI). Finally, the strategy to be applied to physical processes is exemplified for the process $b\to s\gamma$.Comment: Latex, 38 page

Super Background Field Method for N=2 SYM

The implementation of the Background Field Method (BFM) for quantum field theories is analysed within the Batalin-Vilkovisky (BV) formalism. We provide a systematic way of constructing general splittings of the fields into classical and quantum parts, such that the background transformations of the quantum fields are linear in the quantum variables. This leads to linear Ward-Takahashi identities for the background invariance and to great simplifications in multiloop computations. In addition, the gauge fixing is obtained by means of (anti)canonical transformations generated by the gauge-fixing fermion. Within this framework we derive the BFM for the N=2 Super-Yang-Mills theory in the Wess-Zumino gauge viewed as the twisted version of Donaldson-Witten topological gauge theory. We obtain the background transformations for the full BRST differential of N=2 Super-Yang-Mills (including gauge transformations, SUSY transformations and translations). The BFM permits all observables of the supersymmetric theory to be identified easily by computing the equivariant cohomology of the topological theory. These results should be regarded as a step towards the construction of a super BFM for the Minimal Supersymmetric Standard Model.Comment: 34 pages, Latex, JHEP3.cl

On the LHCb anomaly in B -> K* l+ l-

The latest LHCb angular analysis of the rare decay B -> K* mu+ mu- shows some discrepancies from the SM up to the 3.7 sigma level. There is a consistent new physics explanation of these anomalies, while it is also reasonable that these anomalies are just statistical fluctuations and/or a direct consequence of underestimated hadronic uncertainties. We briefly discuss possible cross-checks of the various hypotheses with an analysis of the inclusive B -> Xs l+ l- based on the data collected by the B factories Babar and Belle and also based on future opportunities at SuperBelle. We also present a global analysis of the latest LHCb data under the hypothesis of Minimal Flavour Violation. The latter is an important benchmark scenario for new physics models. Any measurements beyond the MFV bounds and relations unambiguously indicate the existence of new flavour structures next to the Yukawa couplings of the Standard Model. However, if new physics is responsible for these discrepancies, we show it is compatible with the MFV hypothesis, so no new flavour structures are needed. Moreover, we analyse the impact of the correlations between the observables based on a Monte Carlo study.Comment: 23 pages, 9 figure

Updated NLL Results for B -> (Xs,Xd) gamma in and beyond the SM

We present general model-independent formulae for the branching ratios and the direct tagged CP asymmetries for the inclusive B -> Xd gamma and B -> Xs gamma modes. We also update the corresponding SM predictions.Comment: 3 pages, Contribution to the International Europhysics Conference on High Energy Physics EPS03, 17-23 July 2003, Aachen, Germany, minor change