Searcharxiv⌕ Search

arXiv subjects

J. G. Körner

Publications and source records attributed to J. G. Körner.

At least 55 records · Page 3Linked to original sources
arXiv2004

Laurent series expansion of sunrise-type diagrams using configuration space techniques

We show that configuration space techniques can be used to efficiently calculate the complete Laurent series \eps-expansion of sunrise-type diagrams to any loop order in D-dimensional space-time for any external momentum and for arbitrary mass configurations. For negative powers of \eps the results are obtained in analytical form. For positive powers of \eps including the finite \eps^0 contribution the result is obtained numerically in terms of low-dimensional integrals. We present general features of the calculation and provide exemplary results up to five loop order which are compared to available results in the literature.

hep-ph↗
arXiv2003

QCD improved determination of the hadronic contribution to the anomalous magnetic moment of the muon

We present the results of a new evaluation of the anomalous magnetic moment a_mu=(g_mu-2)/2 of the muon where the role of input data needed in the evaluation is lowered in the interval between 1.2 and 3.0 GeV below charm threshold. This is achieved by decreasing the size of the weight function in the dispersion integral over the experimental ratio R(s) by subtracting a polynomial from the weight function which mimics its energy dependence in that given energy interval. In order to compensate for this subtraction, the same polynomial weight integral is added again but is now evaluated on a circular contour in the complex plane using QCD and global duality. For the hadronic contribution to the shift in the anomalous magnetic moment of the muon we obtain a_mu^had(LO) = (701.3 +/- 6.4) x 10^-10 at leading order in the electromagnetic coupling. In addition, using the same procedure, we recalculate the next-to-leading contribution a_mu^had(NLO) = (-10.3 +/- 0.2) x 10^-10. Including QED, electroweak, and light-by-light contribution, we obtain a value a_mu = (11 659 185.6 +/- 6.4_had +/- 3.5_LBL +/- 0.4_QED+EW) x 10^-10.

hep-ph↗
arXiv2003

Leptonic $ μ$- and $ τ$-decays: mass effects, polarization effects and $ O(α) $ radiative corrections

We calculate the radiative corrections to the unpolarized and the four polarized spectrum and rate functions in the leptonic decay of a polarized $ μ$ into a polarized electron. The new feature of our calculation is that we keep the mass of the final state electron finite which is mandatory if one wants to investigate the threshold region of the decay. Analytical results are given for the energy spectrum and the polar angle distribution of the final state electron whose longitudinal and transverse polarization is calculated. We also provide analytical results on the integrated spectrum functions. We analyze the $ m_e \to 0 $ limit of our general results and investigate the quality of the $ m_e \to 0 $ approximation. In the $ m_e \to 0 $ case we discuss in some detail the role of the $ O(α) $ anomalous helicity flip contribution of the final electron which survives the $ m_e \to 0 $ limit. The results presented in this 0203048 also apply to the leptonic decays of polarized $ τ$-leptons for which we provide numerical results.

hep-ph↗
arXiv2003

A Supersymmetric Model with the Gauge Symmetry SU(3)_1 X SU(2)_1 X U(1)_1 X SU(3)_2 X SU(2)_2 X U(1)_2

A supersymmetric model with two copies of the Standard Model gauge groups is constructed in the gauge mediated supersymmetry breaking scenario. The supersymmetry breaking messengers are in a simple form. The Standard Model is obtained after first step gauge symmetry breaking. In the case of one copy of the gauge interactions being strong, a scenario of electroweak symmetry breaking is discussed, and the gauginos are generally predicted to be heavier than the sfermions.

hep-ph↗
arXiv2002

$ SU(3) $ Classification of $ p $-Wave $ ηπ$ and $ η'π$ Systems

An exotic meson, the $π_1(1400)$ with $J^{PC}=1^{-+}$, has been seen to decay into a p-wave $ηπ$ system. If this decay conserves flavor SU(3), then it can be shown that this exotic meson must be a four-quark state ($q\bar q+q\bar q$) belonging to a flavor ${\bf10}\oplus{\bf\bar{10}}$ representation of SU(3). In contrast, the $π_1(1600)$ with a substantial decay mode into $η'π$ is likely to be a member of a flavor octet.

hep-ph↗
arXiv2002

Heavy Quarks on the Lattice

I review the basic ideas behind lattice QCD calculations that involve charm and bottom quarks. I report on the progress in getting the correct hyperfine splitting in charmonium from lattice QCD. Some of the basic technology behind numerical lattice QCD calculations is explained by studying some specific examples: computation of the charm quark mass, and the calculation of fB.

hep-lat↗
arXiv2002

Electroweak and finite width corrections to top quark decays into transverse and longitudinal $ W $-bosons

We calculate the electroweak and finite width corrections to the decay of an unpolarized top quark into a bottom quark and a $ W $-gauge boson where the helicities of the $ W $ are specified as longitudinal, transverse-plus and transverse-minus. Together with the $ O(α_s) $ corrections these corrections may become relevant for the determination of the mass of the top quark through angular decay measurements.

hep-ph↗
arXiv2002

An interpolation of the vacuum polarization function for the evaluation of hadronic contributions to the muon anomalous magnetic moment

We propose a simple parameterization of the two-point correlator of hadronic electromagnetic currents for the evaluation of the hadronic contributions to the muon anomalous magnetic moment. The parameterization is explicitly done in the Euclidean domain. The model function contains a phenomenological parameter which provides an infrared cutoff to guarantee the smooth behavior of the correlator at the origin in accordance with experimental data in e+ e- annihilation. After fixing a numerical value for this parameter from the leading order hadronic contribution to the muon anomalous magnetic moment the next-to-leading order results related to the vacuum polarization function are accurately reproduced. The properties of the four-point correlator of hadronic electromagnetic currents as for instance the so-called light-by-light scattering amplitude relevant for the calculation of the muon anomalous magnetic moment are briefly discussed.

hep-ph↗
arXiv2001

Complete angular analysis of polarized top decay at O(alpha_s)

We calculate the O(alpha_s) radiative corrections to the three spin independent and five spin dependent structure functions that describe the angular decay distribution in the decay of a polarized top quark into a W-boson (followed by the decay W^{+} -> l^{+} + nu_l or by W^{+} -> anti-q + q and a bottom quark. The angular decay distribution is described in cascade fashion, i.e. the decay t(uparrow) -> W^{+} + X_b is analyzed in the top rest system while the subsequent decay W^{+} -> l^{+} + nu_l (or W^{+} -> anti-q + q) is analyzed in the W rest frame. We present our results for the eight O(alpha_s) integrated structure functions in analytical form keeping the mass of the bottom quark finite. In the limit m_b -> 0 the structure function expressions reduce to rather compact forms.

hep-ph↗
arXiv2001

Spectral moments of two-point correlators in perturbation theory and beyond

We discuss the choice of weight functions for the moments of the spectral density for two-point correlators of hadronic currents over a finite energy interval. Of phenomenological relevance is an analysis of the spectra of tau lepton decay on the energy interval [0,M_tau] and the low-energy hadron production in e+ e- annihilation. General arguments are given for the calculability of such moments in perturbation theory using both a finite-order analysis and infinite resummation on the contour. Nonperturbative contributions emerging from the operator product expansion for two-point correlators are discussed within explicit models for the physical spectra. The quantitative analysis strongly disfavours weight functions that suppress the high-energy contribution to theoretical moments. This is in agreement with expectations from qualitative considerations in perturbative QCD with asymptotic freedom. We discuss the implication of our results for the ultimate accuracy that can be reached in tau decays and low-energy e+ e- annihilation into hadrons with present experimental data.

hep-ph↗
arXiv2001

QCD Sum Rule for Heavy Baryons

We construct the heavy baryonic currents by using the Bethe-Salpeter wave functions in the heavy quark limit. We discuss the one-loop renormalization of these heavy baryonic currents as well as their two-point correlators up to the order $1/M_h$. For a special case, we do the QCD sum rule for masses of the doublet (3/2,5/2).

hep-ph↗
arXiv2001

QCD Sum Rule Determination of $α(M_Z)$ with Minimal Data Input

We present the results of a new evaluation of the running fine structure constant $α$ at the scale of the $Z$ mass in which the role of the $e^+e^-$ annihilation input data needed in this evaluation is minimized. This is achieved by reducing the weight function $M_Z^2/(s(M_Z^2-s))$ in the dispersion integral over the $e^+e^-$ annihilation data by subtracting a polynomial function from the weight function which mimics its energy dependence in given energy intervals. In order to compensate for this subtraction the same polynomial weight integral is added again but is now evaluated on a circular contour in the complex plane using QCD and global duality. For the hadronic contribution to the shift in the fine structure constant we obtain $Δα^{(5)}_{\rm had}=(277.6\pm 4.1)\cdot 10^{-4}$. Adding in the leptonic and top contributions our final result is $α(M_Z)^{-1}=128.925\pm 0.056$.

hep-ph↗
arXiv2000

Longitudinal, transverse-plus and transverse-minus W-bosons in unpolarized top quark decays at O(alpha_s)

We consider the O(alpha_s) radiative corrections to the decay of an unpolarized top quark into a bottom quark and a W-gauge boson where the helicities of the W are specified as longitudinal, transverse-plus and transverse-minus. The O(alpha_s) radiative corrections lower the normalized longitudinal rate Gamma_L/Gamma by 1.06% and increase the the normalized transverse-minus rate Gamma_-/Gamma by 2.17%. We find that the normalized transverse-plus rate Gamma_+/Gamma, which vanishes at the Born term level for m_b->0, receives radiative correction contributions at the sub-percent level. We discuss m_b!=0 effects for the Born term and the alpha_s-contributions but find these to be small. Our results are discussed in the light of recent measurements of the helicity content of the W in top quark decays by the CDF Collaboration.

hep-ph↗
arXiv2000

O(alpha_s) corrections to longitudinal and transverse W-bosons in top quark decays

In this talk we consider the O(alpha_s) radiative corrections to the decay of an unpolarized top quark into a bottom quark and a W gauge boson where the helicities of the W are specified as transverse-plus, transverse-minus and longitudinal. The O(alpha_s) radiative corrections lower the normalized longitudinal rate Gamma_L/Gamma by 0.8%. We find that the normalized transverse-plus rate Gamma_+/Gamma, which vanishes at the Born term level for m_b->0, receives radiative correction contributions at the sub-percent level. Our results are discussed in the light of recent measurements of the helicity content of the W in top quark decays by the CDF Collaboration.

hep-ph↗
arXiv2000

Analytical calculation of heavy baryon correlators in NLO of perturbative QCD

We present analytical next-to-leading order results for the correlator of baryonic currents at the three-loop level with one finite mass quark. We obtain the massless and the HQET limits of the correlator as particular cases from the general formula, we also give explicit expressions for the moments of the spectral density. Calculations have been performed with an extensive use of the symbolic manipulation programs MATHEMATICA and REDUCE.

hep-ph↗
arXiv2000

Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function

Starting from the known one-loop result for the $e^{+}e^{-}$-annihilation process $e^{+}e^{-}\stackrel{γ,Z} {\longrightarrow} q\bar{q}g$ with massless quarks we employ analyticity and crossing to determine the absorptive parts of the corresponding one-loop contributions in Deep Inelastic Scattering (DIS) and in the Drell-Yan process (DY). Whereas the ${\cal O}(α_s^2)$ absorptive parts generate a non-measurable phase factor in the $e^{+}e^{-}$-annihilation channel one obtains measurable phase effects from the one-loop contributions in the deep inelastic and in the Drell-Yan case. We compare our results with the results of previous calculations where the absorptive parts in DIS and in the DY process were calculated directly in the respective channels. We also present some new results on the dispersive and absorptive contributions of the triangle anomaly graph to the DIS process.

hep-ph↗
arXiv2000

Configuration Space Based Recurrence Relations for Sunset-Type Diagrams

We derive recurrence relations for the calculation of multiloop sunset-type diagrams with large powers of massive propagators. The technique is formulated in configuration space and exploits the explicit form of the massive propagator raised to a given power. We write down and evaluate a convenient set of basis integrals. The method is well suited for a numerical evaluation of this class of diagrams. We give explicit analytical formulae for the basis integrals in the asymptotic regime.

hep-ph↗