Balint C. Toth

Comprehensive search for the {theta}{sup +} pentaquark on the lattice

We study spin 1/2 isoscalar and isovector, even and odd parity candidates for the

Lattice QCD on nonorientable manifolds

\Theta^+(1540)

Recursive approach to determine correlation functions in multibaryon systems

pentaquark particle using large scale lattice QCD simulations. Previous lattice works led to inconclusive results because so far it has not been possible to unambiguously identify the known scattering spectrum and tell whether additionally a genuine pentaquark state also exists. Here we carry out this analysis using several possible wave functions (operators). Linear combinations of those have a good chance of spanning both the scattering and pentaquark states. Our operator basis is the largest in the literature, and it also includes spatially non-trivial ones with unit orbital angular momentum. The cross correlator we compute is 14

Hadron spectroscopy from canonical partition functions

\times

Overlapping Modularity at the Critical Point of k-Clique Percolation

14 with 60 non-vanishing elements. We can clearly distinguish the lowest scattering state(s) in both parity channels up to above the expected location of the pentaquark, but we find no trace of the latter. Based on that we conclude that there are most probably no pentaquark bound states at our quark masses, corresponding to

QCD thermodynamics with Wilson fermions

m_\pi

Spectral functions of charmonium with 2+1 flavours of dynamical quarks

=400--630 MeV. However, we cannot rule out the existence of a pentaquark state at the physical quark mass corresponding to

Correlation functions of atomic nuclei in Lattice QCD

m_\pi

Comprehensive search for the Θ+ pentaquark on the lattice

=135 MeV or pentaquarks with a more exotic wave function.

Comprehensive search for theΘ+pentaquark on the lattice

A common problem in lattice QCD simulations on the torus is the extremely long autocorrelation time of the topological charge, when one approaches the continuum limit. The reason is the suppressed tunneling between topological sectors. The problem can be circumvented by replacing the torus with a different manifold, so that the field configuration space becomes connected. This can be achieved by using open boundary conditions on the fields, as proposed earlier. It has the side effect of breaking translational invariance completely. Here we propose to use a non-orientable manifold, and show how to define and simulate lattice QCD on it. We demonstrate in quenched simulations that this leads to a drastic reduction of the autocorrelation time. A feature of the new proposal is, that translational invariance is preserved up to exponentially small corrections. A Dirac-fermion on a non-orientable manifold poses a challenge to numerical simulations: the fermion determinant becomes complex. We propose two approaches to circumvent this problem, one of which we tested numerically.