Results for "Rainer Sommer"

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Non-perturbative renormalization of HQET and QCDSep 26 2002We discuss the necessity of non-perturbative renormalization in QCD and HQET and explain the general strategy for solving this problem. A few selected topics are discussed in some detail, namely the importance of off-shell improvement in the MOM-scheme ... More
The $Λ$-parameter and $m_s$ of quenched QCDDec 01 1997We explain how scale dependent renormalized quantities can be computed using lattice QCD. Two examples are used: the running coupling and quark masses. A reliable computation of the $\Lambda$-parameter in the quenched approximation is presented.
Non-perturbative Heavy Quark Effective Theory: a test and its matching to QCDDec 15 2004We give an introduction to the special problems encountered in a treatment of HQET beyond perturbation theory in the gauge coupling constant. In particular, we report on a recent test of HQET as an effective theory for QCD and discuss how HQET can be ... More
Determining fundamental parameters of QCD on the latticeJul 08 2006We summarize the status of determinations of fundamental parameters of QCD by the ALPHA Collaboration.
New perspectives for heavy flavour physics from the latticeJun 20 2009In this talk I want to convey an idea about the perspectives for precise lattice QCD computations. Some emphasis is put on the field of flavour physics, where lattice QCD seems to be needed the most in the quantitative interpretation of present and future ... More
Non-perturbative QCD: renormalization, O(a)-improvement and matching to Heavy Quark Effective TheoryNov 20 2006We give an introduction to three topics in lattice gauge theory: I. The Schroedinger Functional and O(a) improvement. O(a) improvement has been reviewed several times. Here we focus on explaining the basic ideas in detail and then proceed directly to ... More
O(a) improved lattice QCDMay 21 1997We review the O(a) improvement of lattice QCD with special emphasis on the motivation for performing the improvement programme non-perturbatively and the general concepts of on-shell improvement. The present status of the calculations of various improvement ... More
Beauty Physics in Lattice Gauge TheoryJan 31 1994We summarize the present status of lattice gauge theory computations of the leptonic decay constants $f_D$ and $f_B$. The various sources of systematic errors are explained in a manner easily understood by the non--expert. The results obtained by the ... More
Scale setting in lattice QCDJan 14 2014The principles of scale setting in lattice QCD as well as the advantages and disadvantages of various commonly used scales are discussed. After listing criteria for good scales, I concentrate on the main presently used ones with an emphasis on scales ... More
Introduction to Non-perturbative Heavy Quark Effective TheoryAug 04 2010Lectures given at the Summer School on "Modern perspectives in lattice QCD", Les Houches, August 3-28, 2009
Non-perturbative renormalization of QCDNov 05 1997In these lectures, we discuss different types of renormalization problems in QCD and their non-perturbative solution in the framework of the lattice formulation. In particular the recursive finite size methods to compute the scale-dependence of renormalized ... More
Non-perturbative Heavy Quark Effective Theory: Introduction and StatusJan 13 2015We give an introduction to Heavy Quark Effective Theory (HQET). Our emphasis is on its formulation non-perturbative in the strong coupling, including the non-perturbative determination of the parameters in the HQET Lagrangian. In a second part we review ... More
New Perspectives for B-Physics from the LatticeSep 29 2003Oct 09 2003We give an introduction to the problems faced on the way to a reliable lattice QCD computation of B-physics matrix elements. In particular various approaches for dealing with the large scale introduced by the heaviness of the b-quark are mentioned and ... More
An explicit example of HQET at one-loop order of perturbation theoryOct 15 2001Oct 23 2001As an explicit example of HQET, we construct correlation functions containing a heavy-light axial current, both in the static approximation and in full QCD. This enables us to investigate the size of finite mass effects. As we use the lattice regularisation, ... More
The running coupling from the QCD Schrödinger functional -- a one-loop analysisAug 09 1995Starting from the Schr\"odinger functional, we give a non-perturbative definition of the running coupling constant in QCD. The spatial boundary conditions for the quark fields are chosen such that the massless Dirac operator in the classical background ... More
String breaking in SU(2) gauge theory with scalar matter fieldsJul 10 1998Mar 30 1999We investigate the static potential in the confinement phase of the SU(2) Higgs model on the lattice, where this model is expected to have properties similar to QCD. We observe that Wilson loops are inadequate to determine the potential at large distances, ... More
On the $N_f$-dependence of gluonic observablesNov 21 2013Apr 17 2014We compute $t_0$, $w_0$ and the topological susceptibility, defined at finite gradient flow time for two-flavour QCD. The use of three lattice spacings and pion masses between 192 and 500 MeV together with a careful error analysis allow to approach the ... More
A one-loop study of matching conditions for static-light flavor currentsNov 05 2012Jan 24 2013Heavy Quark Effective Theory (HQET) computations of semi-leptonic decays, e.g. B -> pi l nu, require the knowledge of the parameters in the effective theory for all components of the heavy-light flavor currents. So far non-perturbative matching conditions ... More
One-loop lattice artifacts of a dynamical charm quarkSep 11 2011For a few observables in O(a) improved lattice QCD, we compute discretization effects arising from the vacuum polarization of a heavy quark at one-loop order. In particular, the force between static quarks, the running coupling in the Schrodinger functional ... More
Non-perturbative Heavy Quark Effective TheoryOct 13 2003Mar 18 2004We explain how to perform non-perturbative computations in HQET on the lattice. In particular the problem of the subtraction of power-law divergences is solved by a non-perturbative matching of HQET and QCD. As examples, we present a full calculation ... More
Renormalization of the static-light axial currentAug 25 1999We discuss the determination of the heavy-light axial current renormalization in the static approximation, using a new method based on the Schr\"odinger Functional (SF). Previous perturbative results for the renormalization constant are confirmed.
The non-perturbative O(a)-improved action for dynamical Wilson fermionsSep 10 1997We compute the improvement coefficient $c_{sw}$ that multiplies the Sheikholeslami-Wohlert term as a function of the bare gauge coupling for two flavour QCD. We discuss several aspects concerning simulations with improved dynamical Wilson fermions.
The Nf=0 heavy quark potential from short to intermediate distancesAug 07 2001We study the potential of a static quark anti-quark pair in the range 0.05fm \leq r \leq 0.8fm, employing a sequence of lattices up to 64^4. Lattice artifacts in potential and force are investigated theoretically as well as numerically and continuum quantities ... More
Fundamental parameters of QCDApr 04 2002The theory of strong interactions, QCD, is described in terms of a few parameters, namely the strong coupling constant alpha_s and the quark masses. We show how these parameters can be determined reliably using computer simulations of QCD on a space-time ... More
O(a) improvement of lattice QCD with two flavors of Wilson quarksMar 23 1998Jul 11 2002We consider O(a) improvement for two flavor lattice QCD. The improvement term in the action is computed non-perturbatively for a large range of the bare coupling. The position of the critical line and higher order lattice artifacts remaining after improvement ... More
Testing perturbation theory on the nf=0 static quark potentialSep 11 2001Sep 28 2001The perturbative expansion of static force and potential is reanalyzed concerning its practical applicability. A well behaved perturbative prediction is given by the integration of the renormalization group equation for the coupling $\alpha_{qq}(\mu=1/r)=(C_f)^{-1} ... More
How perturbative are heavy sea quarks?Sep 10 2018Effects of heavy sea quarks on the low energy physics are described by an effective theory where the expansion parameter is the inverse quark mass, 1/$M$. At leading order in 1/$M$ the dependence of any low energy quantity on $M$ is given in terms of ... More
Non-perturbative computation of the strong coupling constant on the latticeJan 08 2015We review the long term project of the ALPHA collaboration to compute in QCD the running coupling constant and quark masses at high energy scales in terms of low energy hadronic quantities. The adapted techniques required to numerically carry out the ... More
Renormalization and O(a)-improvement of the static-light axial currentJul 03 2000Dec 06 2000A systematic treatment of O(a)-improvement in lattice theories with static quarks is presented. The Schr\"odinger functional is discussed and a renormalization condition for the static axial current in the SF-scheme is introduced. Its relation to other ... More
A strategy to compute the b-quark mass with non-perturbative accuracyOct 06 2001We describe a strategy for a non-perturbative computation of the b-quark mass to leading order in 1/m in the Heavy Quark Effective Theory (HQET). The approach avoids the perturbative subtraction of power law divergencies, and the continuum limit may be ... More
Large $N$ scaling and factorization in SU($N$) Yang-Mills gauge theoryMay 28 2018The large $N$ limit of SU($N$) gauge theories is well understood in perturbation theory. Also non-perturbative lattice studies have yielded important positive evidence that 't Hooft's predictions are valid. We go far beyond the statistical and systematic ... More
Large $N$ scaling and factorization in $\mathrm{SU}(N)$ Yang-Mills theoryOct 17 2017We present results for Wilson loops smoothed with the Yang-Mills gradient flow and matched through the scale $t_0$. They provide renormalized and precise operators allowing to test the $1/N^2$ scaling both at finite lattice spacing and in the continuum ... More
Non-perturbative renormalization of the static axial current in quenched QCDFeb 25 2003Nov 04 2003We non-perturbatively calculate the scale dependence of the static axial current in the Schroedinger functional scheme by means of a recursive finite-size scaling technique, taking the continuum limit in each step. The bare current in the O(a) improved ... More
Precision for B-meson matrix elementsOct 11 2007We demonstrate how HQET and the Step Scaling Method for B-physics, pioneered by the Tor Vergata group, can be combined to reach a further improved precision. The observables considered are the mass of the b-quark and the B_s-meson decay constant. The ... More
Non-perturbative renormalization of the chromo-magnetic operator in Heavy Quark Effective Theory and the B* - B mass splittingMay 14 2007We carry out the non-perturbative renormalization of the chromo-magnetic operator in Heavy Quark Effective Theory. At order 1/m of the expansion, the operator is responsible for the mass splitting between the pseudoscalar and vector B mesons. We obtain ... More
On the computation of hadron-to-hadron transition matrix elements in lattice QCDAug 18 2011We discuss the accurate determination of matrix elements < f| h_w | i > where neither |i> nor |f> is the vacuum state and h_w is some operator. Using solutions of the Generalized Eigenvalue Problem (GEVP) we construct estimators for matrix elements which ... More
Running of the SF-coupling with four massless flavoursNov 10 2010We discuss the status of different determinations of alpha_s, motivating a precise and reliable computation from lattice QCD. In order to suppress perturbative errors, the non-perturbative computation has to reach high energy scales mu. Such results already ... More
On lattice actions for static quarksJun 07 2005We introduce new discretizations of the action for static quarks. They achieve an exponential improvement (compared to the Eichten-Hill regularization) on the signal to noise ratio in static-light correlation functions. This is explicitly checked in a ... More
Non-perturbative improvement of the axial current for dynamical Wilson fermionsMar 03 2005A non-perturbative determination of the axial current improvement coefficient cA is performed with two flavors of dynamical improved Wilson fermions and plaquette gauge action. The improvement condition is formulated with Schroedinger functional boundary ... More
m_b and f_Bs from a combination of HQET and QCDSep 28 2006We compute the mass of the b-quark and the B_s meson decay constant in quenched lattice QCD using a combination of HQET and the standard relativistic QCD Lagrangian. We start from a small volume, where one can directly deal with the b-quark, and compute ... More
Determination of the Wilson ChPT low energy constant c_2Nov 18 2011Following a suggestion by Aoki and B\"ar, c2 can be extracted by analyzing volume effects in 2-pion states. To this end we consider renormalized ratios of four point to two point correlation functions. We present the results from various CLS lattices, ... More
The running coupling of QCD with four flavorsJun 03 2010We have calculated the step scaling function and the running coupling of QCD in the Schroedinger functional scheme with four flavors of O(a) improved Wilson quarks. Comparisons of our non-perturbative results with 2-loop and 3-loop perturbation theory ... More
Topological susceptibility and the sampling of field space in $N_f=2$ lattice QCD simulationsJun 20 2014Jul 04 2014We present a measurement of the topological susceptibility in two flavor QCD. In this observable, large autocorrelations are present and also sizable cutoff effects have to be faced in the continuum extrapolation. Within the statistical accuracy of the ... More
Heavy Quark Effective Theory at one-loop order: An explicit exampleAug 15 2001Oct 23 2001We consider correlation functions containing the axial current of one light and one heavy quark in the static approximation as well as in full QCD, using the lattice regularization. Up to one-loop order of perturbation theory, we study the difference ... More
On cutoff effects in lattice QCD from short to long distancesJul 07 2008Jul 22 2008We discuss kinematical enhancements of cutoff effects at short and intermediate distances. Starting from a pedagogical example with periodic boundary conditions, we switch to the case of the Schroedinger Functional, where the theoretical analysis is checked ... More
The B*Bpi Coupling in the Static LimitNov 19 2010We study an accurate method for the lattice calculation of the B*Bpi Coupling in the static limit, paying particular attention to excited state contamination. As this coupling is a parameter of the heavy meson chiral Lagrangian, it is useful for constraining ... More
Effective Chiral Lagrangians and Lattice QCDJun 27 2000Aug 10 2000We propose a general method to obtain accurate estimates for some of the "low-energy constants" in the one-loop effective chiral Lagrangian by means of simulating lattice QCD. In particular, the method is sensitive to those constants whose values are ... More
Non-perturbative determination of Z_A^{stat} in quenched QCDSep 05 2002We non-perturbatively calculate the renormalization factor of the static axial vector current in O(a) improved quenched lattice QCD. Its scale dependence is mapped out in the Schroedinger functional scheme by means of a recursive finite-size scaling technique, ... More
Symanzik improvement of lattice QCD with four flavors of Wilson quarksNov 20 2009We have determined the non-perturbative O(a)-improvement coefficient c_sw for four flavors of Wilson quarks with the plaquette gauge action in a range of beta >= 5. The data are fitted with several Pade approximation formulae to get an impression of the ... More
Critical slowing down and error analysis in lattice QCD simulationsSep 27 2010We study the critical slowing down towards the continuum limit of lattice QCD simulations with Hybrid Monte Carlo type algorithms. In particular for the squared topological charge we find it to be very severe with an effective dynamical critical exponent ... More
Investigating the critical slowing down of QCD simulationsOct 08 2009Oct 16 2009Simulations of QCD are known to suffer from serious critical slowing down towards the continuum limit. This is particularly prominent in the topological charge. We investigate the severeness of the problem in the range of lattice spacings used in contemporary ... More
Lusztig's Canonical Quotient and Generalized DualityApr 16 2001We present a new characterization of Lusztig's canonical quotient group. We also define a duality map: to a pair consisting of a nilpotent orbit and a conjugacy class in its fundamental group, the map assigns a nilpotent orbit in the Langlands dual Lie ... More
A Precise Determination of the Running Coupling in the SU(3) Yang-Mills TheorySep 13 1993A non-perturbative finite-size scaling technique is used to study the evolution of the running coupling (in a certain adapted scheme) in the SU(3) Yang-Mills theory. At low energies contact is made with the fundamental dynamical scales, such as the string ... More
Non-perturbative O(a) improvement of lattice QCDSep 19 1996Oct 29 1996The coefficients multiplying the counterterms required for O($a$) improvement of the action and the isovector axial current in lattice QCD are computed non-perturbatively, in the quenched approximation and for bare gauge couplings $g_0$ in the range $0 ... More
Determination of the Static Potential with Dynamical FermionsDec 14 2010Apr 13 2011We present in detail a technique to extract the potential between a static quark and anti-quark pair from Wilson loops measured on dynamical configurations. This technique is based on HYP smearing and leads to an exponential improvement of the noise-to-signal ... More
Low energy physics from the QCD Schrödinger functionalSep 13 1999We review recent work by the ALPHA and UKQCD Collaborations where masses and matrix elements were computed in lattice QCD using Schr\"odinger functional boundary conditions and where the strange quark mass was determined in the quenched approximation. ... More
Chiral symmetry breaking in QCD LiteJun 19 2014A distinctive feature of the presence of spontaneous chiral symmetry breaking in QCD is the condensation of low modes of the Dirac operator near the origin. The rate of condensation must be equal to the slope of (Mpi^2 Fpi^2)/2 with respect to the quark ... More
Non-perturbative Heavy Quark Effective Theory: An application to semi-leptonic B-decaysJan 14 2015We review a lattice strategy how to non-perturbatively determine the coefficients in the HQET expansion of all components of the heavy-light axial and vector currents, including 1/m_h-corrections. We also discuss recent preliminary results on the form ... More
Determining the strong coupling: status and challengesNov 28 2018Dec 14 2018The `XIIIth Quark Confinement and the Hadron Spectrum' conference (Confinement 2018) contained a `Round Table Discussion' on the status of the determinations of the strong coupling $\alpha_s(m_Z)$ as well as prospects for future improvements. In this ... More
Non-perturbative determination of the axial current normalization constant in O(a) improved lattice QCDNov 15 1996A finite-size technique is employed to compute the normalization constant $Z_A$ of the isovector axial current in lattice QCD. The calculation is carried out in the quenched approximation for values of the bare gauge coupling $g_0$ ranging from 0 to 1. ... More
Non-perturbative tests of Heavy Quark Effective TheoryJul 20 2004Jan 03 2005We consider QCD with one massless quark and one heavy quark in a finite volume of linear extent L_0 ~ 0.2 fm. In this situation, HQET represents an expansion in terms of 1/z=1/(m L_0), which we test by a non-perturbative computation of quenched current ... More
Spectral density of the Dirac operator in two-flavour QCDNov 24 2014We compute the spectral density of the (Hermitean) Dirac operator in Quantum Chromodynamics with two light degenerate quarks near the origin. We use CLS/ALPHA lattices generated with two flavours of O(a)-improved Wilson fermions corresponding to pseudoscalar ... More
Symanzik Improvement with Dynamical Charm: A 3+1 Scheme for Wilson QuarksMay 04 2018Jun 06 2018We discuss the problem of lattice artefacts in QCD simulations enhanced by the introduction of dynamical charmed quarks. In particular, we advocate the use of a massive renormalization scheme with a close to realistic charm mass. To maintain O(a) improvement ... More
Heavy-light decay constant at the 1/m order of HQETOct 08 2007Following the strategy developed by the ALPHA collaboration, we present a method to compute non-perturbatively the decay constant of a heavy-light meson in HQET including the 1/m corrections. We start by a matching between HQET and QCD in a small volume ... More
HQET at order 1/m: I. Non-perturbative parameters in the quenched approximationJan 26 2010Jun 30 2010We determine non-perturbatively the parameters of the lattice HQET Lagrangian and those of the time component of the heavy-light axial-vector current in the quenched approximation. The HQET expansion includes terms of order 1/m. Our results allow to compute, ... More
Non-perturbative tests of HQET in small-volume quenched QCDSep 15 2004We quantitatively investigate the quark mass dependence of current matrix elements and energies, calculated over a wide range of quark masses in the continuum limit of small-volume quenched lattice QCD. By a precise comparison of these observables as ... More
Determination of c_sw in N_f=3+1 Lattice QCD with massive Wilson fermionsJan 27 2015We develop a strategy for the non-perturbative determination of the O(a)-improvement coefficient c_sw for Wilson fermions with massive sea quarks. The improvement condition is defined via the PCAC relation in the Schr\"odinger functional. It is imposed ... More
SU(3) Yang Mills theory at small distances and fine latticesNov 06 2017We investigate the SU(3) Yang Mills theory at small gradient flow time and at short distances. Lattice spacings down to $a=0.015$ fm are simulated with open boundary conditions to allow topology to flow in and out. We study the behaviour of the action ... More
HQET form factors for $B_s\to K\ellν$ decays beyond leading orderNov 03 2017Nov 25 2017We compute semi-leptonic $B_s$ decay form factors using Heavy Quark Effective Theory on the lattice. To obtain good control of the $1/m_b$ expansion, one has to take into account not only the leading static order but also the terms arising at $O(1/m_b)$: ... More
Heavy Quark Effective Theory computation of the mass of the bottom quarkSep 28 2006Jul 08 2008We present a fully non-perturbative computation of the mass of the b-quark in the quenched approximation. Our strategy starts from the matching of HQET to QCD in a finite volume and finally relates the quark mass to the spin averaged mass of the Bs meson ... More
Hadron masses and matrix elements from the QCD Schr"odinger functionalMar 31 1999We explain how masses and matrix elements can be computed in lattice QCD using Schr"odinger functional boundary conditions. Numerical results in the quenched approximation demonstrate that good precision can be achieved. For a statistical sample of the ... More
Precision computation of the strange quark's mass in quenched QCDJun 17 1999We determine the renormalization group invariant quark mass corresponding to the sum of the strange and the average light quark mass in the quenched approximation of QCD, using as essential input the mass of the K-mesons. In the continuum limit we find ... More
Computation of the Running Coupling in the SU(2) Yang-Mills TheoryJul 09 1992A finite-size scaling technique is applied to the SU(2) gauge theory (without matter fields) to compute a non-perturbatively defined running coupling alpha(q) for a range of momenta q given in units of the string tension K. We find that already at rather ... More
Precision lattice QCD computation of the $B^*Bπ$ couplingApr 28 2014The static $B^{*}B\pi$ coupling, $\hat{g}_\chi$, a low energy constant in the leading order heavy meson chiral Lagrangian, is determined using $N_\mathrm{f} = 2$ lattice QCD. We use CLS ensembles with lattice spacings and pion masses down to $a = 0.05\mathrm{fm}$ ... More
Non-perturbative quark mass renormalization in quenched lattice QCDOct 28 1998Feb 25 2000The renormalization factor relating the bare to the renormalization group invariant quark masses is accurately calculated in quenched lattice QCD using a recursive finite-size technique. The result is presented in the form of a product of a universal ... More
Chiral symmetry and O(a) improvement in lattice QCDMay 29 1996The dominant cutoff effects in lattice QCD with Wilson quarks are proportional to the lattice spacing a. In particular, the isovector axial current satisfies the PCAC relation only up to such effects. Following a suggestion of Symanzik, they can be cancelled ... More
A quenched study of m_b in HQET beyond the leading orderSep 29 2005Oct 14 2005A non perturbative method to compute the mass of the b quark including the 1/m term in HQET has been presented in a companion talk. Following this strategy, we find in the MS bar scheme m_b^{stat}(m_b) = 4.350(64) GeV for the leading term, and m_b^{(1)}(m_b) ... More
A strategy for the computation of m_b including 1/m termsSep 22 2005We consider HQET including the first order correction in 1/m. A strategy for the computation of the b-quark mass is discussed. Only two quantities Phi_1/2 have to be considered in order to match QCD and HQET, since the spin-dependent interaction is easily ... More
The Schroedinger functional coupling in quenched QCD at low energiesOct 25 2001Existing non-perturbative computations of the running coupling of quenched QCD in the Schroedinger functional scheme are extended to scales mu lying much deeper in the low-energy regime. We are able to reach 1/mu ~ 0.9 fm, where a significant deviation ... More
Perturbative versus non-perturbative decoupling of heavy quarksNov 16 2015We simulate a theory with $N_f=2$ heavy quarks of mass $M$. At energies much smaller than $M$ the heavy quarks decouple and the theory can be described by an effective theory which is a pure gauge theory to leading order in $1/M$. We present results for ... More
On the effects of heavy sea quarks at low energiesOct 30 2014We present a factorisation formula for the dependence of light hadron masses and low energy hadronic scales on the mass $M$ of a heavy quark: apart from an overall factor $Q$, ratios such as $r_0(M)/r_0(0)$ are computable in perturbation theory at large ... More
Chiral condensate from the Banks-Casher relationSep 18 2013We report on our ongoing project of determining the chiral condensate of two-flavor QCD from the Banks-Casher relation. We compute the mode number of the O(a)-improved Wilson-Dirac operator for several values of \Lambda, and we discuss different fitting ... More
Strange quark mass and Lambda parameter by the ALPHA collaborationDec 18 2011We determine f_K for lattice QCD in the two flavor approximation with non-perturbatively improved Wilson fermions. The result is used to set the scale for dimensionful quantities in CLS/ALPHA simulations. To control its dependence on the light quark mass, ... More
Non-perturbative quark mass dependence in the heavy-light sector of two-flavour QCDOct 17 2008We present preliminary results of the non-perturbative heavy quark mass dependence of heavy-light meson observables in the continuum limit of finite-volume two-flavour lattice QCD. These observables, which are derived from heavy-light Schroedinger functional ... More
Simulating Galaxies and Galaxy ClustersApr 01 2004The X-ray luminosities of the hot halo gas around simulated, Milky Way like disk galaxies have been determined, as a function of redshift. The X-ray luminosity increases significantly with redshift, in some cases as much as a factor 30 going from z=0 ... More
Are Damped Ly-alpha Systems Large, Galactic Disks ?Jul 26 1999The hypothesis that the Damped Ly-alpha systems (DLAs) are large, galactic disks (Milky Way sized) is tested by confronting predictions of models of the formation and evolution of (large) disk galaxies with observations, in particular the Zinc abundance ... More
Non-perturbative O(a) improvement of the vector currentSep 23 1997We discuss non-perturbative improvement of the vector current, using the Schroedinger Functional formalism. By considering a suitable Ward identity, we compute the improvement coefficient which gives the O(a) mixing of the tensor current with the vector ... More
Weyl group $q$-Kreweras numbers and cyclic sievingMay 30 2016The paper concerns a definition for $q$-Kreweras numbers for finite Weyl groups $W$, refining the $q$-Catalan numbers for $W$, and arising from work of the second author. We give explicit formulas in all types for the $q$-Kreweras numbers. In the classical ... More
Kinematics and Dynamics of the Galactic Stellar HaloDec 18 1998The structure, kinematics and dynamics of the Galactic stellar halo are reviewed including evidence of substructure in the spatial distribution and kinematics of halo stars. Implications for galaxy formation theory are subsequently discussed; in particular ... More
The trace of Hecke operators on the space of classical holomorphic Siegel modular forms of genus twoSep 09 2009We prove multiplicity one for vector valued holomorphic Siegel modular forms of weights greater or equal to 3 and the full Siegel modular group and give a trace formula for the action of the Hecke operators T(p) in the regular cases.
Existence of Whittaker models related to four dimensional symplectic Galois representationsMar 08 2007We show that an irreducible cuspidal automorphic representation of the group GSp(4,A), which is not CAP and whose infinite component belongs to the discrete series, is weakly equivalent to an irreducible generic automorphic cuspidal representation, whose ... More
The Milky Way Nuclear Star Cluster in ContextJan 24 2010Jan 29 2010Nuclear star clusters are located at the dynamical centers of the majority of galaxies. They are usually the densest and most massive star cluster in their host galaxy. In this article, I will give a brief overview of our current knowledge on nuclear ... More
Continuity of symplectically adjoint maps and the algebraic structure of Hadamard vacuum representations for quantum fields on curved spacetimeSep 30 1996Nov 18 1996We derive for a pair of operators on a symplectic space which are adjoints of each other with respect to the symplectic form (that is, they are sympletically adjoint) that, if they are bounded for some scalar product on the symplectic space dominating ... More
Freely falling observersOct 18 2004We show that the field equations of the Schwarzschild geometry are invariant under passive Lorentz transformations to a freely falling system. We decompose the field equations with respect to the accelerated system and find that the force of gravity is ... More
Convergence of depths and depth-trimmed regionsNov 26 2016Depth is a concept that measures the `centrality' of a point in a given data cloud or in a given probability distribution. Every depth defines a family of so-called trimmed regions. For statistical applications it is desirable that with increasing sample ... More
Measuring interstellar magnetic fields by radio synchrotron emissionDec 29 2008Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of interstellar magnetic fields. The total intensity traces the strength and distribution of total magnetic fields. Total fields ... More
The Origin of Magnetic Fields in Galaxies: Observational Tests with the Square Kilometre ArrayDec 20 2005Apr 07 2006The all-sky survey of Faraday rotation, a Key Science Project of the planned Square Kilometre Array, will accumulate tens of millions of rotation measure measurements toward background radio sources and will provide a unique database for characterizing ... More
Testing quantum physics in space using optically trapped nanospheresJul 26 2013Recent developments in space technology like micro-propulsion systems for drag-free control, thermal shielding, ultra-stable laser sources and stable optical cavities set an ideal platform for quantum optomechanical experiments with optically trapped ... More
Invariant functions in Denjoy-Carleman classesNov 20 2007May 09 2008Let $V$ be a real finite dimensional representation of a compact Lie group $G$. It is well-known that the algebra $\mathbb R[V]^G$ of $G$-invariant polynomials on $V$ is finitely generated, say by $\sigma_1,...,\sigma_p$. Schwarz proved that each $G$-invariant ... More
On Well-Posedness for a Piezo-Electromagnetic Coupling Model with Boundary DynamicsApr 06 2017We consider a coupled system of Maxwell's equations and the equations of elasticity, which is commonly used to model piezo-electric material behavior. The boundary influence is encoded as a separate dynamics on the boundary data spaces coupled to the ... More