arXiv subjects

Oliver Bär

Publications and source records attributed to Oliver Bär.

3 recordsLinked to original sources

arXiv2022

Estimating excited states contamination of $B \to π$ form factors using heavy meson chiral perturbation theory

Using Heavy Meson Chiral Perturbation Theory (HMChPT), the $B^* π$ excited states contamination of the $B \to π$ vector form factors is computed to NLO in the chiral expansion and in the static limit. The results suggest that the excited states for $h_\parallel$ are of the order of a few percent whereas $h_\perp$ receives large negative contributions and thus might be significantly underestimated in lattice simulations.

hep-lat↗

arXiv2009

Anomalous discrete chiral symmetry in the Gross-Neveu model and loop gas simulations

We investigate the discrete chiral transformation of a Majorana fermion on a torus. Depending on the boundary conditions the integration measure can change sign. Taking this anomalous behavior into account we define a chiral order parameter as a ratio of partition functions with differing boundary conditions. Then the lattice realization of the Gross-Neveu model with Wilson fermions is simulated using the recent `worm' technique on the loop gas or all-order hopping representation of the fermions. An algorithm is formulated that includes the Gross-Neveu interaction for N fermion species. The critical line m_c(g) is constructed for a range of couplings at N = 6 and for N = 2, the Thirring model, as examples.

hep-lat↗

arXiv2006

Automatic O$(a)$ improvement for twisted-mass QCD

We present a condition for automatic O$(a)$ improvement in twisted mass lattice QCD, using symmetries of the Symanzik effective theory. If the continuum part of the Symanzik effective theory is invariant under a particular transformation, named $T_1$ in this report, scaling violations of all quantities invariant under $T_1$ transformation are even in the lattice spacing $a$. On the other hand, quantities non-invariant under $T_1$ vanish in the continuum limit with odd powers in $a$. We prove this statement even for the massive case without using the equation of motion. We also consider a few different criteria for the $T_1$ invariant condition in lattice theories and discuss ambiguities of the lattice condition for O$(a)$ improvement.

hep-lat↗