arXiv subjects

S. Sint

Publications and source records attributed to S. Sint.

25 records · Page 2Linked to original sources

arXiv2002

Twisted mass QCD and the $ΔI=1/2$ rule

We show that the application of twisted mass QCD (tmQCD) with four (Wilson) quark flavours to the computation of lattice weak matrix elements relevant to $ΔI=1/2$ transitions has important advantages: the renormalisation of $K \to π$ matrix elements does not require the subtraction of other dimension six operators, the divergence arising from the subtraction of lower dimensional operators is softened by one power of the lattice spacing and quenched simulations do not suffer from exceptional configurations at small pion mass. This last feature is also retained in the tmQCD computation of $K \to ππ$ matrix elements, which, as far as renormalisation and power subtractions are concerned, has properties analogous to the standard Wilson case.

hep-lat↗

arXiv2002

Non-perturbative scale evolution of four-fermion operators

We apply the Schroedinger Functional (SF) formalism to determine the renormalisation group running of four-fermion operators which appear in the effective weak Hamiltonian of the Standard Model. Our calculations are done using Wilson fermions and the parity-odd components of the operators. Preliminary results are presented for the operator $O_{VA}=(\bar s γ_μd)(\bar s γ_μγ_5 d)$.

hep-lat↗

arXiv2001

Cutoff effects in twisted mass lattice QCD

We present a first numerical study of lattice QCD with O(a) improved Wilson quarks and a chirally twisted mass term. Renormalized correlation functions are derived from the Schroedinger functional and evaluated in an intermediate space-time volume of size 0.75^3 x 1.5 fm^4. In the quenched approximation precise results are then obtained with a moderate computational effort, allowing for a detailed study of the continuum approach. The latter is discussed in terms of observables which converge to meson masses and decay constants in the limit of large space-time volume. In the O(a) improved theory we find residual cutoff effects to be at the level of a few percent for lattice spacings of about 0.1 fm.

hep-lat↗

arXiv2001

K0-K0bar mixing from the Schroedinger functional and twisted mass QCD

We describe how the Schroedinger functional and twisted mass QCD can be used to compute the kaon B-parameter B_K on the lattice with Wilson fermions. This new approach is expected to reduce the systematic uncertainties on B_K through a better control of its (nonperturbative) renormalisation. Preliminary results for the bare matrix element in a physical volume of (1.5^3 x 4.5) fm^4 are presented. The renormalisation of the matrix element in a Schroedinger functional scheme is also discussed.

hep-lat↗

arXiv2001

Non-perturbative scaling tests of twisted mass QCD

We present a scaling study of lattice QCD with O(a) improved Wilson fermions and a chirally twisted mass term. In order to get precise results with a moderate computational effort, we have considered a system of physical size of 0.75^3 * 1.5 fm^4 with Schroedinger functional boundary conditions in the quenched approximation. Looking at meson observables in the pseudoscalar and vector channels, we find that O(a) improvement is effective and residual cutoff effects are fairly small.

hep-lat↗

arXiv1997

Non-perturbative quark mass renormalization

We show that the renormalization factor relating the renormalization group invariant quark masses to the bare quark masses computed in lattice QCD can be determined non-perturbatively. The calculation is based on an extension of a finite-size technique previously employed to compute the running coupling in quenched QCD. As a by-product we obtain the $Λ$--parameter in this theory with completely controlled errors.

hep-lat↗

arXiv1996

Some new results in O(a) improved lattice QCD

It is shown how on-shell O(a) improvement can be implemented non-perturbatively in lattice QCD with Wilson quarks. Improvement conditions are obtained by requiring the PCAC relation to hold exactly in certain matrix elements. These are derived from the QCD Schrödinger functional which enables us to simulate directly at vanishing quark masses. In the quenched approximation and for bare couplings in the range $0\leq g_0\leq 1$, we determine the improved action, the improved axial current, the additive renormalization of the quark mass and the isospin current normalization constants Z_A and Z_V.

hep-lat↗