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Andreas S. Kronfeld

Publications and source records attributed to Andreas S. Kronfeld.

At least 91 records · Page 5Linked to original sources
arXiv2002

Remark on the Theoretical Uncertainty in $B^0$-$\bar{B}^0$ Mixing

We re-examine the theoretical uncertainty in the Standard Model expression for $B^0$-$\bar{B}^0$ mixing. We focus on lattice calculations of the ratio $ξ$, needed to relate the oscillation frequency of $B^0_s$-$\bar{B}^0_s$ mixing to $V_{td}$. We replace the usual linear chiral extrapolation with one that includes the logarithm that appears in chiral perturbation theory. We find a significant shift in the ratio $ξ$, from the conventional $1.15\pm0.05$ to $ξ=1.32\pm0.10$.

hep-lat↗
arXiv2002

Perturbative calculation of O(a) improvement coefficients

We compute several coefficients needed for O(a) improvement of currents in perturbation theory, using the Brodsky-Lepage-Mackenzie prescription for choosing an optimal scale q*. We then compare the results to non-perturbative calculations. Normalization factors of the vector and axial vector currents show good agreement, especially when allowing for small two-loop effects. On the other hand, there are large discrepancies in the coefficients of O(a) improvement terms. We suspect that they arise primarily from power corrections inherent in the non-perturbative methods.

hep-lat↗
arXiv2002

F(1) for B -> D^*lνfrom Lattice QCD

Short description of our calculation of the form factor needed to determine CKM element |V_{cb}| from the exclusive decay B -> D^*lν. For full details, see hep-ph/0110253. Also, here we recommend distribution for CKM fits.

hep-ph↗
arXiv2002

Remark on the Theoretical Uncertainty in B^0-\bar{B}^0 Mixing

We re-examine the theoretical uncertainty in the Standard Model expression for $B^0$-$\bar{B}^0$ mixing. We focus on lattice calculations of the ratio $ξ$, needed to relate the oscillation frequency of $B^0_s$-$\bar{B}^0_s$ mixing to the poorly known CKM element $V_{td}$. We replace the usual linear chiral extrapolation with one that includes the logarithm that appears in chiral perturbation theory. We find a significant shift in the ratio $ξ$, from the conventional $1.15\pm0.05$ to $ξ=1.32\pm0.10$.

hep-ph↗
arXiv2001

Application of heavy-quark effective theory to lattice QCD: III. Radiative corrections to heavy-heavy currents

We apply heavy-quark effective theory (HQET) to separate long- and short-distance effects of heavy quarks in lattice gauge theory. In this paper we focus on flavor-changing currents that mediate transitions from one heavy flavor to another. We stress differences in the formalism for heavy-light currents, which are discussed in a companion paper, showing how HQET provides a systematic matching procedure. We obtain one-loop results for the matching factors of lattice currents, needed for heavy-quark phenomenology, such as the calculation of zero-recoil form factors for the semileptonic decays $B\to D^{(*)}lν$. Results for the Brodsky-Lepage-Mackenzie scale $q^*$ are also given.

hep-lat↗
arXiv2001

Lattice QCD and the Unitarity Triangle

Theoretical and computational advances in lattice calculations are reviewed, with focus on examples relevant to the unitarity triangle of the CKM matrix. Recent progress in semi-leptonic form factors for B -> pi l nu and B -> D* l nu, as well as the parameter ξin B-Bbar mixing, are highlighted.

hep-ph↗
arXiv2001

Lattice calculation of the zero-recoil form factor of anti-B --> D* lepton anti-neutrino: toward a model independent determination of |V(cb)|

We develop a new method in lattice QCD to calculate the form factor F(1) at zero recoil. This is the main theoretical ingredient needed to determine |V(cb)| from the exclusive decay anti-B --> D* lepton anti-neutrino. We introduce three ratios, in which most of statistical and systematic error cancels, making a precise calculation possible. We fit the heavy-quark mass dependence directly, and extract the 1/m_Q^2 and three of the four 1/m_Q^3 corrections in the heavy-quark expansion. In this paper we show how the method works in the quenched approximation, obtaining F(1) = 0.913 (+0.024-0.017)(+/-0.016)(+0.003-0.014)(+0.000-0.016)(+0.006-0.014) where the uncertainties come, respectively, from statistics and fitting, matching lattice gauge theory to QCD, lattice spacing dependence, light quark mass effects, and the quenched approximation. We also discuss how to reduce these uncertainties and, thus, to obtain a model-independent determination of |V(cb)|.

hep-ph↗
arXiv2001

Linear Collider Physics

We report on a study of the physics potential of linear $e^+e^-$ colliders. Although a linear collider (LC) would support a broad physics program, we focus on the contributions that could help elucidate the origin of electroweak symmetry breaking. Many extensions of the standard model have a decoupling limit, with a Higgs boson similar to the standard one and other, higher-mass states. Mindful of such possibilities, we survey the physics of a (nearly) standard Higgs boson, as a function of its mass. We also review how measurements from an LC could help verify several well-motivated extensions of the standard model. For supersymmetry, we compare the strengths of an LC with the LHC. Also, assuming the lightest superpartner explains the missing dark matter in the universe, we examine other places to search for a signal of supersymmetry. We compare the signatures of several scenarios with extra spatial dimensions. We also explore the possibility that the Higgs is a composite, concentrating on models that (unlike technicolor) have a Higgs boson with mass of a few hundred GeV or less. Where appropriate, we mention the importance of high luminosity, for example to measure branching ratios of the Higgs, and the importance of multi-TeV energies, for example to explore the full spectrum of superpartners.

hep-ex↗
arXiv2001

O(a)-improved quark action on anisotropic lattices and perturbative renormalization of heavy-light currents

We investigate the Symanzik improvement of the Wilson quark action on anisotropic lattices. Taking first a general action with nearest-neighbor and clover interactions, we study the mass dependence of the ratio of the hopping parameters, the clover coefficients, and an improvement coefficient for heavy-light vector and axial vector currents. We show how tree-level improvement can be achieved. For a particular choice of the spatial Wilson coupling, the results simplify, and $O(m_0a_τ)$ improvement is possible. (Here $m_0$ is the bare quark mass and $a_τ$ the temporal lattice spacing.) With this choice we calculate the renormalization factors of heavy-light bilinear operators at one-loop order of perturbation theory employing the standard plaquette gauge action.

hep-lat↗
arXiv2001

The Semileptonic Decays $B\toπlν$ and $D\toπlν$ from Lattice QCD

We present a lattice QCD calculation of the form factors and differential decay rates for semileptonic decays of the heavy-light mesons $B$ and $D$ to the final state $πlν$. The results are obtained with three methodological improvements over previous lattice calculations: a matching procedure that reduces heavy-quark lattice artifacts, the first study of lattice-spacing dependence, and the introduction of kinematic cuts to reduce model dependence. We show that the main systematics are controllable (within the quenched approximation) and outline how the calculations could be improved to aid current experiments in the determination of~$|V_{ub}|$ and~$|V_{cd}|$.

hep-ph↗
arXiv2000

B and D Mesons in Lattice QCD

Computational and theoretical developments in lattice QCD calculations of B and D mesons are surveyed. Several topical examples are given: new ideas for calculating the HQET parameters \barΛ and λ_1; form factors needed to determine |V_{cb}| and |V_{ub}|; bag parameters for the mass differences of the B mesons; and decay constants. Prospects for removing the quenched approximation are discussed.

hep-ph↗
arXiv2000

Computation of $\barΛ$ and $λ_1$ with Lattice QCD

We pursue a new method, based on lattice QCD, for determining the quantities $\barΛ$, $λ_1$, and $λ_2$ of heavy-quark effective theory. We combine Monte Carlo data for the meson mass spectrum with perturbative calculations of the short-distance behavior, to extract $\barΛ$ and $λ_1$ from a formula from HQET. Taking into account uncertainties from fitting the mass dependence and from taking the continuum limit, we find $\barΛ = 0.68{+0.02}_{-0.12} \text{GeV}$ and $λ_1 = -(0.45 \pm 0.12) \text{GeV}^2$ in the quenched approximation.

hep-ph↗
arXiv2000

Application of heavy-quark effective theory to lattice QCD: I. Power Corrections

Heavy-quark effective theory (HQET) is applied to lattice QCD with Wilson fermions at fixed lattice spacing a. This description is possible because heavy-quark symmetries are respected. It is desirable because the ultraviolet cutoff $1/a$ in current numerical work and the heavy-quark mass $m_Q$ are comparable. Effects of both short distances, a and $1/m_Q$, are captured fully into coefficient functions, which multiply the operators of the usual HQET. Standard tools of HQET are used to develop heavy-quark expansions of lattice observables and, thus, to propagate heavy-quark discretization errors. Three explicit examples are given: namely, the mass, decay constant, and semileptonic form factors of heavy-light mesons.

hep-lat↗
arXiv1999

Lattice QCD calculation of $\bar{B}\to Dl\barν$ decay form factors at zero recoil

A lattice QCD calculation of the $\bar{B}\to Dl\barν$ decay form factors is presented. We obtain the value of the form factor $h_+(w)$ at the zero-recoil limit $w=1$ with high precision by considering a ratio of correlation functions in which the bulk of the uncertainties cancels. The other form factor $h_-(w)$ is calculated, for small recoil momenta, from a similar ratio. In both cases, the heavy quark mass dependence is observed through direct calculations with several combinations of initial and final heavy quark masses. Our results are $h_+(1) = 1.007(6)(2)(3)$ and $h_-(1)=-0.107(28)(04)(^{10}_{30})$. For both the first error is statistical, the second stems from the uncertainty in adjusting the heavy quark masses, and the last from omitted radiative corrections. Combining these results, we obtain a precise determination of the physical combination $F_{B\to D}(1)=1.058(^{20}_{17})$, where the mentioned systematic errors are added in quadrature. The dependence on lattice spacing and the effect of quenching are not yet included, but with our method they should be a fraction of $F_{B\to D}-1$.

hep-ph↗
arXiv1999

B and D semileptonic decays to light mesons

We present an update of our calculation of the form factors and partial widths of semileptonic heavy-to-light meson decays, in the quenched approximation. Our complete data set has now been analysed and our results include chiral extrapolations and a study of the lattice spacing dependence.

hep-lat↗
arXiv1998

Lattice QCD Calculations of Leptonic and Semileptonic Decays

In lattice QCD, obtaining properties of heavy-light mesons has been easier said than done. Focusing on the $B$ meson's decay constant, it is argued that towards the end of 1997 the last obstacles were removed, at least in the quenched approximation. These developments, which resulted from a fuller understanding and implementation of ideas in effective field theory, bode well for current studies of neutral meson mixing and of semileptonic decays.

hep-ph↗
arXiv1998

Three Electroweak Results from Lattice QCD

Quantum chromodynamics is needed to understand quarks and, hence, to determine the quarks' Yukawa couplings from experimental measurements. As a short illustration, the results of three lattice calculations are given.

hep-ph↗