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Laurent Lellouch

Publications and source records attributed to Laurent Lellouch.

At least 37 records · Page 2Linked to original sources
arXiv2009

Kaon physics: a lattice perspective

I critically review recent lattice QCD results relevant for kaon phenomenology, as well as the methods that are used to obtain them. The focus is on calculations with N_f=2 and N_f=2+1 flavors of sea quarks. Concerning methodology, the subjects covered include a discussion of how best to extrapolate and/or interpolate results to the physical quark-mass point, a scheme for assessing the extent to which a lattice QCD calculation includes the various effects required to compute a given quantity reliably and a procedure for averaging lattice results. The phenomenological topics that I review comprise leptonic and semileptonic kaon decays, as well as neutral kaon mixing and CP violation in K->ππdecays.

hep-lat↗
arXiv2007

Diquark correlations in baryons on the lattice with overlap quarks

We evaluate baryon wave functions in both the Coulomb and Landau gauge in lattice QCD. These are constructed from quark propagators calculated with the overlap Dirac operator on quenched gauge configurations at beta = 6. By comparing baryon states that differ in their diquark content, we find evidence for enhanced correlation in the scalar diquark channel, as favored by quark models. We also summarize earlier results for diquark masses in the Landau gauge, casting them in a form more easily compared with subsequent studies.

hep-lat↗
arXiv2006

Light hadron and diquark spectroscopy in quenched QCD with overlap quarks on a large lattice

A simulation of quenched QCD with the overlap Dirac operator has been completed using 100 Wilson gauge configurations at beta = 6 on an 18^3 x 64 lattice and at beta = 5.85 on a 14^3 x 48 lattice, both in Landau gauge. We present results for light meson and baryon masses, meson final state "wave functions," and other observables, as well as some details on the numerical techniques that were used. Our results indicate that scaling violations, if any, are small. We also present an analysis of diquark correlations using the quark propagators generated in our simulation.

hep-lat↗
arXiv2006

K^0-\bar K^0 mixing beyond the standard model and CP-violating electroweak penguins in quenched QCD with exact chiral symmetry

We present results for the ΔS=2 matrix elements which are required to study neutral kaon mixing in the standard model (SM) and beyond (BSM). We also provide leading chiral order results for the matrix elements of the electroweak penguin operators which give the dominant ΔI=3/2 contribution to direct CP violation in K->ππdecays. Our calculations were performed with Neuberger fermions on two sets of quenched Wilson gauge configurations at inverse lattice spacings of approximately 2.2 GeV and 1.5 GeV. All renormalizations were implemented non-perturbatively in the RI/MOM scheme, where we accounted for sub-leading operator product expansion corrections and discretization errors. We find ratios of non-SM to SM matrix elements which are roughly twice as large as in the only other dedicated lattice study of these amplitudes. On the other hand, our results for the electroweak penguin matrix elements are in good agreement with two recent domain-wall fermion calculations. As a by-product of our study, we determine the strange quark mass. Our main results are summarized and discussed in Sec. VII. Within our statistics, we find no evidence for scaling violations.

hep-lat↗
arXiv2005

Light hadron spectroscopy in quenched QCD with overlap fermions

A simulation of quenched QCD with the overlap Dirac operator has been carried out using 100 Wilson gauge configurations at beta = 6 on an 18^3 x 64 lattice and at beta = 5.85 on a 14^3 x 48 lattice. Here we present results for meson masses, meson final state "wave functions," decay constants, and other observables, as well as details on our algorithmic and data analysis techniques. We also summarize results for baryon masses and quark and diquark propagators in the Landau gauge.

hep-lat↗
arXiv2004

Electroweak penguins and SUSY K^0-\bar K^0 mixing with Neuberger quarks

We present results for Delta I=3/2 and Delta S=2 matrix elements relevant for CP violation in K->Pi Pi decays and for the K_S-K_L mass difference in the standard model and beyond. They were obtained with Neuberger fermions on quenched gauge configurations generated with the Wilson plaquette action at beta=6.0 on an 18^3x64 lattice.

hep-lat↗
arXiv2003

CKM matrix elements from tree-level decays and b-hadron lifetimes

We give an updated summary of the topics covered in Working Group I of the 2nd Workshop on the CKM Unitarity Triangle, with emphasis on the results obtained since the 1st CKM Workshop. The topics covered include the measurement of |V_{ub}|, of |V_{cb}| and of non-perturbative Heavy Quark Expansion parameters, and the determination of b-hadron lifetimes and lifetime differences.

hep-ph↗
arXiv2003

B_K from quenched QCD with exact chiral symmetry

We present a calculation of the standard model ΔS=2 matrix element relevant to indirect CP violation in K->ππdecays which uses Neuberger's chiral formulation of lattice fermions. The computation is performed in the quenched approximation on a 16^3x32 lattice that has a lattice spacing a\sim 0.1 fm. The resulting bare matrix element is renormalized non-perturbatively. Our main result is B_K^{RGI}=0.87(8)^{+2+14}_{-1-14}, where the first error is statistical, the second is systematic and the third is an estimate of the uncertainty associated with the quenched approximation and with the fact that our kaons are composed of degenerate s and d quarks with masses \sim m_s/2.

hep-ph↗
arXiv2002

Phenomenology from lattice QCD

After a short presentation of lattice QCD and some of its current practical limitations, I review recent progress in applications to phenomenology. Emphasis is placed on heavy-quark masses and on hadronic weak matrix elements relevant for constraining the CKM unitarity triangle. The main numerical results are highlighted in boxes.

hep-ph↗
arXiv2002

From enemies to friends: chiral symmetry on the lattice

The physics of strong interactions is invariant under the exchange of left-handed and right-handed quarks, at least in the massless limit. This invariance is reflected in the chiral symmetry of quantum chromodynamics. Surprisingly, it has become clear only recently how to implement this important symmetry in lattice formulations of quantum field theories. We will discuss realizations of exact lattice chiral symmetry and give an example of the computation of a physical observable in quantum chromodynamics where chiral symmetry is important. This calculation is performed by relying on finite size scaling methods as predicted by chiral perturbation theory.

hep-lat↗
arXiv2002

Standard Model Matrix Elements for Neutral B-Meson Mixing and Associated Decay Constants

We present results of quenched lattice calculations of the matrix elements relevant for B_d-\bar B_d and B_s-\bar B_s mixing in the Standard Model. Results for the corresponding SU(3)-breaking ratios, which can be used to constrain or determine |V_{td}|, are also given. The calculations are performed at two values of the lattice spacing, corresponding to β= 6.0 and β= 6.2, with quarks described by a mean-field-improved Sheikholeslami-Wohlert action. As a by-product, we obtain the leptonic decay constants of B and D mesons. We also present matrix elements relevant for D^0-\bar D^0 mixing. Our results are summarized in the Introduction.

hep-ph↗
arXiv2001

Scalar condensate and light quark masses from overlap fermions

We have studied pseudoscalar correlation functions computed using the overlap operator. Within the accuracy of our calculation we find that the quark mass dependence agrees with the prediction of lowest-order Chiral Perturbation Theory (ChPT) for quark masses in the range of m ~ m_s/2-2m_s. We present the results of an analysis which assumes lowest-order ChPT to be valid to extract the low-energy constants Sigma and f_P, as well as the strange quark mass. Non-perturbative renormalization is implemented via a matching procedure with data obtained using Wilson fermions in the Schroedinger functional set-up. We find that the scalar condensate computed here agrees with the one obtained previously through a finite-size scaling analysis.

hep-lat↗
arXiv2001

Non-perturbative renormalization of the quark condensate in Ginsparg-Wilson regularizations

We present a method to compute non-perturbatively the renormalization constant of the scalar density for Ginsparg-Wilson fermions. It relies on chiral symmetry and is based on a matching of renormalization group invariant masses at fixed pseudoscalar meson mass, making use of results previously obtained by the ALPHA Collaboration for O(a)-improved Wilson fermions. Our approach is quite general and enables the renormalization of scalar and pseudoscalar densities in lattice regularizations that preserve chiral symmetry and of fermion masses in any regularization. As an application we compute the non-perturbative factor which relates the renormalization group invariant quark condensate to its bare counterpart, obtained with overlap fermions at beta=5.85 in the quenched approximation.

hep-lat↗
arXiv2000

Light Hadron Weak Matrix Elements

I review this year's developments in the study of weak matrix elements of light hadrons on the lattice, with emphasis on K^0-\bar K^0 mixing and K -> pi pi decays.

hep-lat↗