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T. Hurth

Publications and source records attributed to T. Hurth.

72 records · Page 4Linked to original sources
arXiv2003

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.

hep-ph↗
arXiv2003

The CKM Matrix and the Unitarity Triangle

This report contains the results of the Workshop on the CKM Unitarity Triangle, held at CERN on 13-16 February 2002 to study the determination of the CKM matrix from the available data of K, D, and B physics. This is a coherent document with chapters covering the determination of CKM elements from tree level decays and K and B meson mixing and the global fits of the unitarity triangle parameters. The impact of future measurements is also discussed.

hep-ph↗
arXiv2003

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.

hep-th↗
arXiv2002

NNLL QCD Corrections to the Decay $B \to X_s \ell^+ \ell^-$

We briefly discuss the status of the NNLL QCD calculations in the inclusive rare B decay $B \to X_s \ell^+ \ell^-$. Two important ingredients, the two-loop matrix elements of the four quark operator ${\cal O}_2$ and the bremsstrahlung contributions, were quite recently finalised. The new contributions significantly improve the sensitivity of the inclusive decay $B \to X_s l^+ l^-$ decay in testing extensions of the standard model in the sector of flavour dynamics; for instance the two-loop calculation cuts the low- scale uncertainty in half and the bremsstrahlung calculation leads to a 10% shift of the position of the zero of the forward- backward asymmetry.

hep-ph↗
arXiv2002

Forward--Backward Asymmetry in B -> X_s l^+ l^- at the NNLL Level

We report the results of a new calculation of soft-gluon corrections in B -> X_s l^+ l^- decays. In particular, we present the first calculation of bremsstrahlung and corresponding virtual terms to the lepton forward-backward asymmetry, which allows us to systematically include all contributions to this observable beyond the lowest non-trivial order. The new terms are important, for instance the position of the zero of the asymmetry receives corrections of O(10%). Using a different method, we also provide an independent check of recently published results on bremsstrahlung and infrared virtual corrections to the dilepton-invariant mass distribution.

hep-ph↗
arXiv2002

Measurement of the Width Difference of B_d Mesons

We estimate ΔGamma_d/Γ_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 ΔGamma_d/Γ_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 ΔGamma_d seems to be possible. This measurement would be important for an accurate measurement of \sin2ϕ_1 at the LHC. We also derive an upper bound on the value of ΔGamma_d/Γ_d in the presence of new physics.

hep-ph↗
arXiv2001

Measurement of the Lifetime Difference of $B_d$ Mesons: Possible and Worthwhile?

We estimate the decay width difference $ΔGamma_d / Γ_d$ in the $B_d$ system including $1/m_b$ contributions and next-to-leading order QCD corrections, and find it to be around 0.3%. We explicitly show that the time measurements of an untagged $B_d$ decaying to a single final state isotropically can only be sensitive to quadratic terms in $ΔGamma_d / Γ_d$, and hence the use of at least two different final states is desired. We discuss such pairs of candidate decay channels for the final states and explore the feasibility of a $ΔGamma_d / Γ_d$ measurement through them. The measurement of this width difference is essential for an accurate measurement of $\sin(2β)$ at the LHC. The nonzero width difference may also be used to identify new physics effects and to resolve a twofold discrete ambiguity in the $B_d$-$\bar{B}_d$ mixing phase. We also derive an upper bound on the value of $ΔGamma_d / Γ_d$ in the presence of new physics, and point out some differences in the phenomenology of width differences in the $B_s$ and $B_d$ systems.

hep-ph↗
arXiv2001

Kaon physics with a high-intensity proton driver

We study opportunities for future high-precision experiments in kaon physics using a high-intensity proton driver, which could be part of the front-end of a muon storage ring complex. We discuss in particular the rare decays $K_L\toπ^0ν\barν$, $K^+\toπ^+ν\barν$, $K_L\toπ^0e^+e^-$, and lepton-flavour violating modes such as $K_L\toμe$ and $K\toπμe$. The outstanding physics potential and long-term interest of these modes is emphasized. We review status and prospects of current and planned experiments for the processes under consideration, and indicate possible improvements and strategies towards achieving the necessary higher sensitivity. Finally, we outline the machine requirements needed to perform these high-precision kaon experiments in the context of a muon storage ring facility.

hep-ph↗
arXiv2001

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 $b\to sγ$.

hep-ph↗
arXiv2001

On the two-loop electroweak amplitude of the muon decay

We present an analysis of the two-loop amplitude of the muon decay in the Standard Model (SM) using algebraic renormalization techniques. In addition, we discuss a manifestly BRST invariant IR regulator for the photon within the SM.

hep-ph↗
arXiv2000

Non-invariant two-loop counterterms for the three-gauge-boson vertices

Some practical applications of algebraic renormalization are discussed. In particular we consider the two-loop QCD corrections to the three-gauge-boson vertices involving photons, Z and W bosons. For this purpose also the corresponding two-point functions have to be discussed. A recently developed procedure is used to analyze the breaking terms of the functional identities and explicit formulae for the universal counterterms are provided. Special attention is devoted to the treatment of infra-red divergences.

hep-ph↗
arXiv2000

Practical Algebraic Renormalization

A practical approach is presented which allows the use of a non-invariant regularization scheme for the computation of quantum corrections in perturbative quantum field theory. The theoretical control of algebraic renormalization over non-invariant counterterms is translated into a practical computational method. We provide a detailed introduction into the handling of the Slavnov-Taylor and Ward-Takahashi identities in the Standard Model both in the conventional and the background gauge. Explicit examples for their practical derivation are presented. After a brief introduction into the Quantum Action Principle the conventional algebraic method which allows for the restoration of the functional identities is discussed. The main point of our approach is the optimization of this procedure which results in an enormous reduction of the calculational effort. The counterterms which have to be computed are universal in the sense that they are independent of the regularization scheme. The method is explicitly illustrated for two processes of phenomenological interest: QCD corrections to the decay of the Higgs boson into two photons and two-loop electroweak corrections to the process $B \to X_s γ$.

hep-ph↗
arXiv2000

Gluino Contribution to Radiative B Decays: Organization of QCD Corrections and Leading Order Results

The gluino-induced contributions to the decay b-> s gamma are investigated in supersymmetric frameworks with generic sources of flavour violation. It is shown that, when QCD corrections are taken into account, the relevant operator basis of the Standard Model effective Hamiltonian gets enlarged to contain: i) magnetic and chromomagnetic operators with a factor of alpha_s and weighted by a quark mass m_b or m_c; ii) magnetic and chromomagnetic operators of lower dimensionality, also containing alpha_s; iii) four-quark operators weighted by a factor alpha_s^2. Numerical results are given, showing the effects of the leading order QCD corrections on the inclusive branching ratio for b-> s gamma. Constraints on supersymmetric sources of flavour violation are derived.

hep-ph↗
arXiv1998

Radiative corrections in inclusive rare B decays

We report recent theoretical progress in the analysis of radiative corrections in inclusive rare B-decays. In view of the B-factories, currently under construction at SLAC and KEK, and of the upgraded CESR experiment, the experimental status of rare B decays is expected to improve significantly in the near future. We review the complete NLL QCD calculations of the inclusive b -> s gamma and the b -> d gamma decay rates. We also discuss recently computed electroweak corrections and further improvements which lead to the current theoretical prediction of B(B -> X_s gamma) = (3.32 +/- 0.30) * 10^{-4}. We shortly comment on the theoretical uncertainty and on implications to physics beyond the SM. We collect the experimental data already available from CESR and LEP and discuss experimental and theoretical problems regarding the photon energy spectrum.

hep-ph↗
arXiv1997

$B \to X_s gamma$ in the Standard Model

We give a summary about the various contributions which have to be calculated in order to obtain the next-to-leading logarithmic result for the branching ratio $BR(B \to X_s γ)$. Combining all these ingredients, which were obtained by different groups, a complete next-to-leading-logarithmic prediction of the inclusive decay rate was recently presented in the literature. The theoretical uncertainty in the partonic decay rate is now at the 10% level, i.e., less than half of the error in the previous leading-logarithmic result. We also mention the impact of non-perturbative corrections which scale like $1/m_b^2$ and discuss in some more detail the recently discovered corrections which scale like $1/m_c^2$. It turns out that the $1/m_b^2$- and the $1/m_c^2$ terms lead to corrections to the branching ratio $BR(B \to X_s γ)$ well below the 10% level.

hep-ph↗
arXiv1997

Osp(1|8)-Gravity

We analyze a new MacDowell-Mansouri $R^2$-type supergravity action based on the superalgebra Osp(1|8). This contribution summarizes the work of hep-th/9702052.

hep-th↗
arXiv1996

Virtual corrections to the decay $b \to s γ$

We calculate the $O(\a_s)$ virtual corrections to the matrix element for $b \to s γ$, taking into account the contributions of the four-Fermi operator $O_2$ and the electromagnetic and color dipole-type operators. The results are combined with existing $O(\a_s)$ Bremsstrahlung corrections in order to obtain the relevant inclusive rate. The new result drastically reduces the large scale dependence of the leading logarithmic approximation. It implies that a very accurate prediction for the branching ratio for $B \to X_s \g $ will become possible once also the corrections to the Wilson coefficients are available.

hep-ph↗