12447797
Properties of confining gauge field configurations in the pseudoparticle approach
The pseudoparticle approach is a numerical method to approximate path integrals in SU(2) Yang‐Mills theory. Path integrals are computed by summing over all gauge field configurations, which can be represented by a linear superposition of a small number of pseudoparticles with amplitudes and color orientations as degrees of freedom. By comparing different pseudoparticle ensembles we determine properties of confining gauge field configurations. Our results indicate the importance of long range interactions between pseudoparticles and of non trivial topological properties.
11518347
Static-static-light-light tetraquarks in lattice QCD
I report on a lattice computation of the energy of a system of two light quarks and two static antiquarks as a function of the separation of the static antiquarks. In terms of hadrons such a system corresponds to a pair of B mesons and its energy to the hadronic potential. I present selected results for different isospin, spin and parity combinations of the individual B mesons mainly focusing on those channels relevant to determine, whether two B mesons may form a bound tetraquark state.
43984169
Adjoint string breaking in the pseudoparticle approach
We apply the pseudoparticle approach to SU(2) Yang-Mills theory and perform a detailed study of the potential between two static charges for various representations. Whereas for charges in the fundamental representation we find a linearly rising confining potential, we clearly observe string breaking, when considering charges in the adjoint representation. We also demonstrate Casimir scaling and compute gluelump masses for different spin and parity. Numerical results are in qualitative agreement with lattice results.
38785788
The spectrum of static-light baryons in twisted mass lattice QCD
We compute the static-light baryon spectrum with N_f = 2 flavors of sea quarks using Wilson twisted mass lattice QCD. As light valence quarks we consider quarks, which have the same mass as the sea quarks with corresponding pion masses in the range 340 MeV < m_PS < 525 MeV, as well as partially quenched quarks, which have the mass of the physical s quark. We extract masses of states with isospin I = 0, 1/2, 1, with strangeness S = 0, -1, -2, with angular momentum of the light degrees of freedom j = 0, 1 and with parity P = +, -. We present a preliminary extrapolation in the light u/d and an interpolation in the heavy b quark mass to the physical point and compare with available experimental results.
8900183
Computing K and D meson masses with Nf=2+1+1 twisted mass lattice QCD
We discuss the computation of the mass of the K and D mesons within the framework of N-f = 2 + 1 + 1 twisted mass lattice QCD from a technical point of view. These quantities are essential, already at the level of generating gauge configurations, being obvious candidates to tune the strange and charm quark masses to their physical values. In particular, we address the problems related to the twisted mass flavor and parity symmetry breaking, which arise when considering a non-degenerate (c, s) doublet. We propose and verify the consistency of three methods to extract the K and D meson masses in this framework. (c) 2010 Elsevier By. All rights reserved.
1888088
The pseudoparticle approach for solving path integrals in gauge theories
We present a numerical technique for calculating path integrals in non-compact U(1) and SU(2) gauge theories. The gauge fields are represented by a superposition of pseudoparticles of various types with their amplitudes and color orientations as degrees of freedom. Applied to Maxwell theory this technique results in a potential which is in excellent agreement with the Coulomb potential. For SU(2) Yang-Mills theory the same technique yields clear evidence of confinement. Varying the coupling constant exhibits the same scaling behavior for the string tension, the topological susceptibility and the critical temperature while their dimensionless ratios are similar to those obtained in lattice calculations.
17501397
Low-momentum hyperon-nucleon interactions
We present a first exploratory study for hyperon-nucleon interactions using renormalization group techniques. The effective two-body low-momentum potential ${V}_{\text{low}\phantom{\rule{0.3em}{0ex}}k}$ is obtained by integrating out the high-momentum components from realistic Nijmegen YN potentials. A T-matrix equivalence approach is employed, so that the low-energy phase shifts are reproduced by ${V}_{\text{low}\phantom{\rule{0.3em}{0ex}}k}$ up to a momentum scale $\ensuremath{\Lambda}~500$ MeV. Although the various bare Nijmegen models differ somewhat from each other, the corresponding ${V}_{\text{low}\phantom{\rule{0.3em}{0ex}}k}$ interactions show convergence in some channels, suggesting a possible model-independent YN interaction at low momenta.
119266212
QCD critical region and higher moments for three flavor models
One of the distinctive features of the QCD phase diagram is the possible emergence of a critical endpoint. The critical region around the critical point and the path dependency of the critical exponents are investigated within effective chiral (2 + 1)-flavor models with and without Polyakov loops. Results obtained in no-sea mean-field approximations where a divergent vacuum part in the fermion-loop contribution is neglected are compared to the renormalized ones. Furthermore, the modifications caused by the backreaction of the matter fluctuations on the pure Yang-Mills system are discussed. Higher-order, non-Gaussian moments of event-by-event distributions of various particle multiplicities are enhanced near the critical point and could serve as a probe to determine its location in the phase diagram. By means of a novel derivative technique higher-order generalized quark-number susceptibilities are calculated and their sign structure in the phase diagram is analyzed.
115815562
On the convergence of multi-channel effective interactions
A detailed analysis of convergence properties of the Andreozzi-Lee-Suzuki iteration method, which is used for the calculation of low-momentum effective potentials Vlowk is presented. After summarizing different modifications of the iteration method for one-flavor channel we introduce a simple model in order to study the generalization of the iteration method to multi-flavor channels. The failure of a straightforward generalization is discussed. The introduction of a channel-dependent cutoff cures the conceptual and technical problems. This novel method has already been applied successfully for realistic hyperon-nucleon interactions.
3253782
On the efficient computation of high-order derivatives for implicitly defined functions
Abstract Scientific studies often require the precise calculation of derivatives. In many cases an analytical calculation is not feasible and one resorts to evaluating derivatives numerically. These are error-prone, especially for higher-order derivatives. A technique based on algorithmic differentiation is presented which allows for a precise calculation of higher-order derivatives. The method can be widely applied even for the case of only numerically solvable, implicit dependencies which totally hamper a semi-analytical calculation of the derivatives. As a demonstration the method is applied to a quantum field theoretical physical model. The results are compared with standard numerical derivative methods.
118580235
Higher-order ratios of baryon number cumulants
The relevance of higher order cumulants of net baryon number fluctuations for the analysis of freeze-out and critical conditions in heavy-ion collisions at LHC and RHIC is addressed. The sign structure of the higher order cumulants in the vicinity of the chiral crossover temperature might be a sensitive probe and may allow to elucidate their relation to the QCD phase transition. We calculate ratios of generalized quarknumber susceptibilities to high orders in three flavor QCD-like models and investigate their sign structure close to the chiral crossover line.