417 research outputs found

### 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

### 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

### 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

### 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

### 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

### On the anomalies in the latest LHCb data

Depending on the assumptions on the power corrections to the exclusive b -> s
l+ l- decays, the latest data of the LHCb collaboration - based on the 3 fb^-1
data set and on two different experimental analysis methods - still shows some
tensions with the SM predictions. We present a detailed analysis of the
theoretical inputs and various global fits to all the available b -> s l+ l-
data. This constitutes the first global analysis of the new data of the LHCb
collaboration based on the hypothesis that these tensions can be at least
partially explained by new physics contributions. In our model-independent
analysis we present one-, two-, four-, and also five-dimensional global fits in
the space of Wilson coefficients to all available b -> s l+ l- data. We also
compare the two different experimental LHCb analyses of the angular observables
in B -> K* mu+ mu-. We explicitly analyse the dependence of our results on the
assumptions about power corrections, but also on the errors present in the form
factor calculations. Moreover, based on our new global fits we present
predictions for ratios of observables which may show a sign of lepton
non-universality. Their measurements would crosscheck the LHCb result on the
ratio R_K = BR(B+ -> K+ mu+ mu-) / BR(B+ -> K+ e+ e-) in the low-q^2 region
which deviates from the SM prediction by 2.6 sigma.Comment: 41 pages, 24 figures. v2: references and comment on 1006.4945
[hep-ph] adde

### Global fits to b -> s ll data and signs for lepton non-universality

There are some slight tensions with the SM predictions within the latest LHCb
measurements. Besides the known anomaly in one angular observable of the rare
decay B -> K* mu+ mu-, another small discrepancy recently occurred. The ratio
R_K = BR(B+ -> K+ mu+ mu-) / BR(B+ -> K+ e+ e-) in the low-q^2 region has been
measured by LHCb showing a 2.6 sigma deviation from the SM prediction. In
contrast to the anomaly in the rare decay B -> K* mu+ mu- which is affected by
power corrections, the ratio R_K is theoretically rather clean. We analyse all
the b -> s ll data with global fits and in particular explore the possibility
of breaking of lepton universality. Possible cross-checks with an analysis of
the inclusive B -> X_s l+ l- decay are also explored.Comment: 15 pages, 11 figures. v2: references added, to appear in JHE

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