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Tobias Hurth

Publications and source records attributed to Tobias Hurth.

At least 73 records · Page 4Linked to original sources
arXiv2004

Non-factorizable Contributions to $B \to ππ$ Decays

We investigate to what extent the experimental information on $B \to ππ$ branching fractions and CP asymmetries can be used to better understand the QCD dynamics in these decays. For this purpose we decompose the independent isospin amplitudes into factorizable and non-factorizable contributions. The former can be estimated within the framework of QCD factorization for exclusive $B$ decays. The latter vanish in the heavy-quark limit, $m_b \to \infty$, and are treated as unknown hadronic parameters. We discuss at some length in which way the non-factorizable contributions are treated in different theoretical and phenomenological frameworks. We point out the potential differences between the phenomenological treatment of power-corrections in the ``BBNS approach'', and the appearance of power -suppressed operators in soft-collinear effective theory (SCET). On that basis we define a handful of different (but generic) scenarios where the non-factorizable part of isospin amplitudes is parametrized in terms of three or four unknowns, which can be constrained by data. We also give some short discussion on the implications of our analysis for $B \to πK$ decays. In particular, since non-factorizable QCD effects in $B \to ππ$ may be large, we cannot exclude sizeable non-factorizable effects, which violate $SU(3)_F$ flavour symmetry, or even isospin symmetry (via long-distance QED effects). This may help to explain certain puzzles in connection with isospin-violating observables in $B \to πK$ decays.

hep-ph↗
arXiv2004

Comments on the Gauge Fixed BRST Cohomology and the Quantum Noether Method

We discuss in detail the relation between the gauge fixed and gauge invariant BRST cohomology. We showed previously that in certain gauges some cohomology classes of the gauge-fixed BRST differential do not correspond to gauge invariant observables. We now show that in addition ``accidental'' conserved currents may appear. These correspond one-to-one to observables that become trivial in this gauge. We explicitly show how the gauge-fixed BRST cohomology appears in the context of the Quantum Noether Method.

hep-th↗
arXiv2003

On Exclusive and Inclusive Rare B Decays: CKM Phenomenology and New Physics Reach

We report recent results in rare B decays. Our focus will be on b -> d gamma and b -> s l^+ l^- transitions. We discuss their impact on the CKM phenomenology and their role within our search for new physics. In particular, we analyse the impact of a recent lattice QCD estimate of the B -> K* form factor at zero recoil. We also briefly discuss the presently available optimal theoretical tools for the inclusive and exclusive modes.

hep-ph↗
arXiv2003

Present Status of Inclusive Rare B Decays

We give a status report on inclusive rare B decays, highlighting recent developments and open problems. We focus on the decay modes $B \to X_{s,d} γ$, $ B \to X_s \ell^+\ell^-$ and $B \to X_s ν\bar ν$ and on their role in the search for new physics. Most of the inclusive rare B decays are important modes of flavour physics due to the small hadronic uncertainties. They can be regarded as laboratories to search for new physics. We collect the experimental data already available from CLEO and the $B$ factories BABAR and BELLE. We review the NLL and NNLL QCD calculations of the inclusive decay rates that were recently completed, and discuss future prospects, especially the issue of the charm mass scheme ambiguity. Finally, we analyse the phenomenological impact of these decay modes, in particular on the CKM phenomenology and on the indirect search for supersymmetry. We also briefly discuss direct CP violation in inclusive rare B decays, as well as the rare kaon decays $K^+\to π^+ν\barν$ and $K_L \to π^0 ν\barν$, which offer complementary theoretically clean information.

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arXiv2001

The Width Difference of $B_d$ Mesons

We estimate $\dg/Γ_d$, including $1/m_b$ contributions and part of the next-to-leading order QCD corrections. We find that adding the latter corrections decreases the value of $\dg/Γ_d$ computed at the leading order by a factor of almost 2. We also show that under certain conditions an upper bound on the value of $\dg/Γ_d$ in the presence of new physics can be derived. With the high statistics and accurate time resolution of the upcoming LHC experiment, the measurement of $\dg$ seems to be possible. This measurement would be important for an accurate measurement of $\sin(2β)$ at the LHC. In addition, we point out the possibility that the measurement of the width difference leads to a clear signal for new physics.

hep-ph↗
arXiv2001

A New Model-Independent Analysis of $B \to X_s γ$ in Supersymmetry

Using the example of the rare decay $B \to X_s γ$, we analyse the importance of interference effects for the bounds on the parameters in the squark mass matrices within the unconstrained MSSM. In former model-independent analyses no correlations between the different sources of flavour violation were taken into account. In our new analysis we include the contributions from charged Higgs bosons, charginos and neutralinos and their interference effects and, even more important, the effects that appear when several flavour violating parameters, i.e. several off-diagonal elements in the squark mass matrices, are switched on simultaneously. We derive new bounds on certain off-diagonal elements of the squark-mass matrix which are in general one order of magnitude weaker than the previous bounds.

hep-ph↗
arXiv2001

Direct CP Violation In Radiative B Decays

We discuss the role of the radiative B decays $B \to X_{s/d} γ$ in our search for new physics focusing on the issue of direct CP violation. We discuss in some detail a SM prediction for the CP asymmetries in inclusive $b \to s/d$ transitions, namely $\mid Δ{\cal B}(B \to X_s γ) + Δ{\cal B}(B \to X_d γ) \mid \sim 1 \cdot 10^{-9}$. Any measured value in significant deviation of this estimate would indicate new sources of CP violation beyond the CKM phase.

hep-ph↗
arXiv2001

Inclusive Rare B Decays

We review the present status of rare B decays, focusing on inclusive decay modes and their role in our search for new physics. We also briefly discuss direct CP violation in rare B decays and the rare kaon decays $K^+\to π^+ν\barν$ and $K_L \to π^0 ν\barν$, which offer complementary opportunities for precision flavour physics.

hep-ph↗
arXiv2001

Bounds on flavour violating parameters in supersymmetry

We investigate the constraints on the flavour violating parameters from the decay B --> X_s gamma, taking into account the interplay of the various sources of flavour violation in the unconstrained MSSM. We present a systematic leading logarithmic QCD analysis of these model-independent constraints, including contributions from gluinos, neutralinos, charginos, charged Higgs bosons and interferences between them. We show that two simple combinations of elements of the down squark mass matrix are stringently bounded over large parts of the parameter space where only weak assumptions on the hierarchical structure of the squark mass matrices are made. We also briefly analyse up to which values SUSY contributions, compatible with B --> X_s gamma, can enhance the Wilson coefficient C_8(m_W), which plays an important role in the phenomenology of charmless hadronic B decays.

hep-ph↗
arXiv2001

CP Asymmetries in $b \to (s/d)$ Transitions as a Test of CKM CP Violation

We point out that a simple test of the mechanism of CP violation can be performed by a measurement of the CP asymmetries in exclusive and inclusive radiative rare decays. We show that the rate asymmetries $ΔΓ= Γ(B^- \to f γ) - Γ(B^+ \to \bar{f} γ)$} for certain final states $f$ can be predicted in a theoretically clean way. Some implications for $b \to s \ell^+ \ell^-$ decays are discussed.

hep-ph↗
arXiv2001

Present and Future CP Measurements

We review theoretical and experimental results on CP violation summarizing the discussions in the working group on CP violation at the UK phenomenology workshop 2000 in Durham.

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arXiv1999

Gluino-Mediated Rare B Decays

We discuss the gluino-induced contribution to rare B decays in supersymmetric frameworks with generic sources of flavour change.

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arXiv1999

The Quantum Noether Condition in terms of interacting fields

We review our recent work, hep-th/9803030, on the constraints imposed by global or local symmetries on perturbative quantum field theories. The analysis is performed in the Bogoliubov-Shirkov-Epstein-Glaser formulation of perturbative quantum field theory. In this formalism the S-matrix is constructed directly in the asymptotic Fock space with only input causality and Poincare invariance. We reformulate the symmetry condition proposed in our earlier work in terms of interacting Noether currents.

hep-th↗
arXiv1999

Cohomological analysis of gauged-fixed gauge theories

The relation between the gauge-invariant local BRST cohomology involving the antifields and the gauge-fixed BRST cohomology is clarified. It is shown in particular that the cocycle conditions become equivalent once it is imposed, on the gauge-fixed side, that the BRST cocycles should yield deformations that preserve the nilpotency of the (gauge-fixed) BRST differential. This shows that the restrictions imposed on local counterterms by the Quantum Noether condition in the Epstein--Glaser construction of gauge theories are equivalent to the restrictions imposed by BRST invariance on local counterterms in the standard Lagrangian approach.

hep-th↗
arXiv1999

The $c \to u γ$ Contribution to Weak Radiative Charm Decay

The $c \to u γ$ transition does not occur at the tree level in the Standard Model and is strongly GIM-suppressed at one loop. The leading QCD logarithms are known to enhance the amplitude by two orders of magnitude. We point out that the amplitude increases further by two orders of magnitude after including the complete 2-loop QCD contributions. Nevertheless, $ΔS =0$ radiative decays of charmed hadrons remain dominated by the $c \to d \bar{d} u γ$ and $c \to s \bar{s} u γ$ quark subprocesses.

hep-ph↗
arXiv1998

Quantum Noether Method

We present a general method for constructing consistent quantum field theories with global symmetries. We start from a free non-interacting quantum field theory with given global symmetries and we determine all consistent perturbative quantum deformations assuming the construction is not obstructed by anomalies. The method is established within the causal Bogoliubov-Shirkov-Epstein-Glaser approach to perturbative quantum field theory (which leads directly to a finite perturbative series and does not rely on an intermediary regularization). Our construction can be regarded as a direct implementation of Noether's method at the quantum level. We illustrate the method by constructing the pure Yang-Mills theory (where the relevant global symmetry is BRST symmetry), and the N=1 supersymmetric model of Wess and Zumino. The whole construction is done before the so-called adiabatic limit is taken. Thus, all considerations regarding symmetry, unitarity and anomalies are well-defined even for massless theories.

hep-th↗
arXiv1997

Next-To-Leading Logarithmic Results in $ B \to X_s γ$

We give a brief review of the next-to-leading logarithmic results in $B \to X_s γ$. Combining the results of different groups, a practically complete next-to-leading-logarithmic prediction of the inclusive decay rate was recently presented. The theoretical uncertainty in the decay rate in now less than half of the error in the previously leading-logarithmic result. Therefore, the inclusive $B \to X_s γ$ mode will provide important tests of the SM and its extensions when more precise experimental data is available.

hep-ph↗