arXiv subjects

M. Beneke

Publications and source records attributed to M. Beneke.

At least 37 records · Page 2Linked to original sources

arXiv2015

Unstable-particle effective field theory

Unstable particles are notorious in perturbative quantum field theory for producing singular propagators in scattering amplitudes that require regularization by the finite width. In this review I discuss the construction of an effective field theory for unstable particles, based on the hierarchy of scales between the mass, M, and the width,Gamma, of the unstable particle that allows resonant processes to be systematically expanded in powers of the coupling alpha and Gamma/M, thereby providing gauge-invariant approximations at every order. I illustrate the method with the next-to-leading order line-shape of a scalar resonance in an abelian gauge-Yukawa model, and results on NLO and dominant NNLO corrections to (resonant and non-resonant) pair production of W-bosons and top quarks.

hep-ph↗

arXiv2015

Soft-collinear factorization in B decays

The combination of collinear factorization with effective field theory originally developed for soft interactions of heavy quarks provides the foundations of the theory of exclusive and semi-inclusive B decays. In this article I summarize some of the later conceptual developments of the so-called QCD factorization approach that make use of soft-collinear effective theory. Then I discuss the status and results of the calculation of the hard-scattering functions at the next order, and review very briefly some of the phenomenology, covering aspects of charmless, electroweak penguin and radiative (semi-leptonic) decays.

hep-ph↗

arXiv2014

The bottom-quark mass from non-relativistic sum rules at NNNLO

We determine the mass of the bottom quark from high moments of the bottom production cross section in e+ e- annihilation, which are dominated by the threshold region. On the theory side next-to-next-to-next-to-leading order (NNNLO) calculations both for the resonances and the continuum cross section are used for the first time. We find mb,PS(2 GeV) = 4.532 +0.013 -0.039 GeV for the potential-subtracted mass and mb,MSbar(mb,MSbar) = 4.193 +0.022 -0.035 GeV for the MSbar bottom-quark mass.

hep-ph↗

arXiv2014

Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos III. Computation of the Sommerfeld enhancements

This paper concludes the presentation of the non-relativistic effective field theory formalism designed to calculate the radiative corrections that enhance the pair-annihilation cross sections of slowly moving neutralinos and charginos within the general minimal supersymmetric standard model (MSSM). While papers I and II focused on the computation of the tree-level annihilation rates that feed into the short-distance part, here we describe in detail the method to obtain the Sommerfeld factors that contain the enhanced long-distance corrections. This includes the computation of the potential interactions in the MSSM, which are provided in compact analytic form, and a novel solution of the multi-state Schrödinger equation that is free from the numerical instabilities generated by large mass splittings between the scattering states. Our results allow for a precise computation of the MSSM neutralino dark matter relic abundance and pair-annihilation rates in the present Universe, when Sommerfeld enhancements are important.

hep-ph↗

arXiv2014

Heavy neutralino relic abundance with Sommerfeld enhancements - a study of pMSSM scenarios

We present a detailed discussion of Sommerfeld enhancements in neutralino dark matter relic abundance calculations for several popular benchmark scenarios in the general MSSM. Our analysis is focused on models with heavy wino- and higgsino-like neutralino LSP and models interpolating between these two scenarios. This work is the first phenomenological application of effective field theory methods that we have developed in earlier work and that allow for the consistent study of Sommerfeld enhancements in non-relativistic neutralino and chargino co-annihilation reactions within the general MSSM, away from the pure-wino and pure-higgsino limits.

hep-ph↗

arXiv2014

Muon anomalous magnetic moment and penguin loops in warped extra dimensions

We describe the computation of the one-loop muon anomalous magnetic moment and radiative penguin transitions in the minimal and custodially protected Randall-Sundrum model. A fully five-dimensional (5D) framework is employed to match the 5D theory onto the Standard Model extended by dimension-six operators. The additional contribution to the anomalous magnetic moment from the gauge-boson exchange contributions is Delta a_mu \approx 8.8 (27.2) x 10^(-11) x (1 TeV/T)^2, where the first (second) number refers to the minimal (custodially-protected) model. Here $1/T$ denotes the location of the TeV brane in conformal coordinates, and is related to the mass of the lowest gauge-boson KK excitation by M_KK \approx 2.35 T. We also determine the Higgs-exchange contribution, which depends on the 5D Yukawa structure and the precise interpretation of the localisation of the Higgs field near or at the TeV brane.

hep-ph↗

arXiv2014

Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos I. General framework and S-wave annihilation

We compute analytically the tree-level annihilation rates of a collection of non-relativistic neutralino and chargino two-particle states in the general MSSM, including the previously unknown off-diagonal rates. The results are prerequisites to the calculation of the Sommerfeld enhancement in the MSSM, which will be presented in subsequent work. They can also be used to obtain concise analytic expressions for MSSM dark matter pair annihilation in the present Universe for a large number of exclusive two-particle final states.

hep-ph↗

arXiv2013

P-wave contribution to third-order top-quark pair production near threshold

The next-to-leading order (NLO) P-wave Coulomb Green function contributes at third-order to top-pair production in e+ e- collisions near threshold. In this paper we compute the NLO P-wave Green function in dimensional regularization, as required for a consistent combination with non-resonant production of the W+ W- b\bar{b} final state, and present a phenomenological analysis of the P-wave contribution. We further briefly discuss squark production near threshold and top-pair production in gamma gamma collisions, where no S-wave contribution is present, and the P-wave thus constitutes the dominant production process.

hep-ph↗

arXiv2013

The muon anomalous magnetic moment in the Randall-Sundrum model

We calculate the anomalous magnetic moment of the muon in the minimal Randall-Sundrum model with standard model fields in five-dimensional (5D) warped space and a brane-localized Higgs. We use a fully 5D framework to compute the one-loop matching coefficients of the effective theory at the electroweak scale. The extra contribution to the anomalous magnetic moment from the model-independent gauge-boson exchange contributions Δa_μis approximately 8.8*10^-11 (1TeV/T)^2, where 1/T denotes the location of the TeV brane in conformal coordinates, and is related to the mass of the lowest gauge boson KK excitation, which is roughly 2.5T. The result constitutes the first complete determination of the gauge-boson contribution to g-2 and is robust against the variation of the bulk fermion masses and 5D Yukawa coupling. We also determine the strongly model-parameter dependent effect of Higgs-exchange diagrams.

hep-ph↗

arXiv2012

On "dynamical mass" generation in Euclidean de Sitter space

We consider the perturbative treatment of the minimally coupled, massless, self-interacting scalar field in Euclidean de Sitter space. Generalizing work of Rajaraman, we obtain the dynamical mass m^2 \propto sqrt{lambda} H^2 of the scalar for non-vanishing Lagrangian masses and the first perturbative quantum correction in the massless case. We develop the rules of a systematic perturbative expansion, which treats the zero-mode non-perturbatively, and goes in powers of sqrt{lambda}. The infrared divergences are self-regulated by the zero-mode dynamics. Thus, in Euclidean de Sitter space the interacting, massless scalar field is just as well-defined as the massive field. We then show that the dynamical mass can be recovered from the diagrammatic expansion of the self-energy and a consistent solution of the Schwinger-Dyson equation, but requires the summation of a divergent series of loop diagrams of arbitrarily high order. Finally, we note that the value of the long-wavelength mode two-point function in Euclidean de Sitter space agrees at leading order with the stochastic treatment in Lorentzian de Sitter space, in any number of dimensions.

hep-th↗

arXiv2012

The total top-pair production cross section at NNLL

We present results for the total top-pair production cross section at the Tevatron and the LHC. Our predictions supplement fixed-order results with resummation of soft logarithms and Coulomb singularities to next-to-next-to-leading (NNLL) logarithmic accuracy and include top-antitop bound-state effects. The effects of resummation, the dependence on the PDF set used, the residual sources of theoretical uncertainty and their implication for measurements of the top-quark mass are discussed.

hep-ph↗

arXiv2012

Inclusive top-pair production phenomenology with TOPIXS

We discuss various aspects of inclusive top-quark pair production based on TOPIXS, a new, flexible program that computes the production cross section at the Tevatron and LHC at next-to-next-to-leading logarithmic accuracy in soft and Coulomb resummation, including bound-state effects and the complete next-to-next-to-leading order result in the q-qbar channel, which has recently become available. We present the calculation of the top-pair cross section in pp collisions at 8 TeV centre-of-mass energy, as well as the cross sections for hypothetical heavy quarks in extensions of the standard model. The dependence on the parton distribution input is studied. Further we investigate the impact of LHC top cross section measurements at sqrt(s)=7 TeV on global fits of the gluon distribution using the NNPDF re-weighting method.

hep-ph↗

arXiv2012

NNLL threshold resummation for the total top-pair production cross section

We present predictions for the total top-quark pair production cross section at the Tevatron and the LHC with 7,8 and 14 TeV centre-of-mass energy, including the resummation of threshold logarithms and Coulomb corrections through next-to-next-to-leading logarithmic order, and top-antitop bound-state contributions. The remaining theoretical and PDF uncertainties and prospects for the measurement of the top mass from the total cross section are discussed.

hep-ph↗

arXiv2011

The top-quark pair production cross section at next-to-next-to-leading logarithmic order

We present predictions for the total ttbar production cross section sigma_ttbar at the Tevatron and LHC, which include the resummation of soft logarithms and Coulomb singularities through next-to-next-to-leading logarithmic order, and ttbar bound-state contributions. Resummation effects amount to about 8 % of the next-to-leading order result at Tevatron and about 3 % at LHC with 7 TeV centre-of-mass energy. They lead to a significant reduction of the theoretical uncertainty. With m_t=173.3 GeV, we find sigma_ttbar=7.22^{+0.31+0.71}_{-0.47-0.55} pb at Tevatron and sigma_ttbar=162.6^{+7.4+15.4}_{-7.5-14.7} at the LHC, in good agreement with the latest experimental measurements.

hep-ph↗

arXiv2011

Workshop on Precision Measurements of alphas

These are the proceedings of the "Workshop on Precision Measurements of alphas" held at the Max-Planck-Institute for Physics, Munich, February 9-11, 2011. The workshop explored in depth the determination of alphas(mZ) in the MS-bar scheme from the key categories where high precision measurements are currently being made, including DIS and global PDF fits, tau-decays, electroweak precision observables and Z-decays, event-shapes, and lattice QCD. These proceedings contain a short summary contribution from the speakers, as well as the lists of authors, conveners, participants, and talks.

hep-ph↗

arXiv2011

B meson distribution amplitude from B --> γl ν

We reconsider the utility of the radiative decay $B \to γ\ell ν$ with an energetic photon in the final state for determining parameters of the $B$-meson light-cone distribution amplitude. Including $1/m_b$ power corrections and radiative corrections at next-to-leading logarithmic order, we perform an improved analysis of the existing BABAR data. We find a provisional lower limit on the inverse moment of the $B$ meson distribution amplitude, $λ_B$, which, due to the inclusion of radiative and power corrections, is significantly lower than the previous result. More data with large photon energy is, however, required to obtain reliable results, as should become available in the future from SuperB factories.

hep-ph↗

arXiv2011

Hadronic top-quark pair production with NNLL threshold resummation

We compute the total top-quark pair production cross section at the Tevatron and LHC based on approximate NNLO results, and on the summation of threshold logarithms and Coulomb enhancements to all orders with next-to-next-to-leading logarithmic (NNLL) accuracy, including bound-state effects. We find σ_{t\bar t} = 7.22^{+0.31+0.71}_{-0.47-0.55} pb at Tevatron and σ_{t\bar t} = 162.6^{+7.4+15.4}_{-7.6-14.7} pb at LHC with 7 TeV c.o.m. energy, for m_t=173.3 GeV. The implementation of joint soft and Coulomb resummation, its ambiguities, and the present theoretical uncertainty are discussed in detail. We further obtain new approximate results at N3LO.

hep-ph↗

arXiv2011

Non-local Higgs actions: Tree-level electroweak constraints and high-energy unitarity

We consider electroweak symmetry breaking by a certain class of non-local Higgs sectors. Extending previous studies employing the Mandelstam condition, a straight Wilson line is used to make the Higgs action gauge invariant. We show the unitarization of vector-boson scattering for a wide class of non-local actions, but find that the Wilson-line model leads to tree-level corrections to electroweak precision observables, which restrict the parameter space of the model. We also find that Unhiggs models cannot address the hierarchy problem, once the parameters are expressed in terms of low-energy observables.

hep-ph↗