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Artan Borici

Publications and source records attributed to Artan Borici.

At least 19 recordsLinked to original sources
arXiv2019

Disordered fermions, extra dimensions and a solvable Yang-Mills theory

Generalizing disorder couplings of the SYK model by means of SU(N) matrices we formulate a lattice model of fermions in d+1 dimensions. Integration of fermions yields an effective theory of Yang-Mills fields in d dimensions, the latter approaching the standard Yang-Mills theory in the case of heavy fermions and the classical limit of vanishing coupling constant of the theory. Quantum mechanically, the theory is solved using large N approximation of the dual effective theory of Hermitian matrices in d dimensions. The theory is asymptotically free and confines the color. In case of massless fermions the emerging theory is an asymptotic safe QCD theory. We discuss also the relationship of this theory to the SYK model.

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arXiv2019

Lattice QCD with QCDLAB

QCDLAB is a set of programs, written in GNU Octave, for lattice QCD computations. Version 2.0 includes the generation of configurations for the SU(3) theory, computation of rectangle Wilson loops as well as the low lying meson spectrum with Wilson fermions. Version 2.1 includes also the computation of the low lying meson spectrum using minimally doubled chiral fermions. In this paper, we give a brief tutorial on lattice QCD computations using QCDLAB.

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arXiv2015

Lattice QCD and the Balkan physicists contribution

This is a paper based on the invited talk the author gave at the 9th Balkan Physical Union conference. It contains some of the main achievements of lattice QCD simulations followed by a list of Balkan physicists who have contributed to the project.

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arXiv2010

Weyl and ghost fermions on the lattice

Nielsen-Ninomiya theorem forbids Weyl fermions on the lattice which respect the full hypercubic symmetry. By giving up this assumption in a specific way, it is possible to formulate a lattice theory with a single Weyl fermion in four dimensions and a sextet of Dirac particles in two dimensions. This way, the meaning of the theorem in relation to the doubling problem on the lattice is clarified. Whether the proposal will be suited for future lattice computations will depend on the effects the extra particles will have in the interacting theory.

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arXiv2008

Minimally Doubled Fermion Revival

In this paper, we present the recent progress on minimally doubled lattice actions. In particular, we discuss the proposal of Creutz and its variations on an orthogonal lattice. A preliminary computation of the pion mass on an SU(3) background field shows the expected behaviour as predicted form the chiral perturbation theory.

hep-lat↗
arXiv2008

Creutz Fermions on an Orthogonal Lattice

In a recent paper, Creutz has given a new action describing two species of Dirac fermions with exact chiral symmetry on the lattice. This action depends on a parameter which may be fixed at a certain value in order to get the right continuum limit. In this letter, we elaborate more on this idea and present an action which is free of any other parameter except the fermion mass.

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arXiv2007

A Schur Complement Approach to Chiral Fermions

Lattice chiral fermions are synonymous to the Ginsparg-Wilson relation. Indeed, this relation is satisfied by the overlap, domain wall and perfect action fermion kernel. In a recent work we have shown that it is possible to take a direct RG approach for fermions in the presence of gauge fields. This is due to an algebraically implicit blocking technique which yields a Schur-complementary coarse Dirac operator. Using a Schur complement approximation which is stable and regular, the scheme can be iterated to the fixed point. In this talk, we elaborate more on the direct RG approach and show how to get highly improved chiral fermions on the coarse lattice with the gauge fields remaining on the fine lattice. We give numerical examples in the case of lattice QCD using QCDLAB {\tt http://phys.fshn.edu.al/qcdlab.html}

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arXiv2007

On Gauged Renormalisation Group Transformations of Lattice Fermions

We construct a hierarchy of lattice fermions, where the coarser lattice Dirac operator is the Schur complement of the block UL decomposition of the finer lattice operator. We show that the construction is an exact gauged renormalisation group transformation of the lattice action. In particular, using such a transformation and the QCDLAB tool, it is shown how to implement the Ginsparg-Wilson strategy for chiral fermions in the presence of a dynamical gauge field. The scheme allows, for the first time, a full multigrid algorithm for lattice quarks.

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arXiv2007

Speeding up Domain Wall Fermion Algorithms using QCDLAB

Simulating lattice QCD with chiral fermions and indeed using Domain Wall Fermions continues to be challenging project however large are concurrent computers. One obvious bottleneck is the slow pace of prototyping using the low level coding which prevails in most, if not all, lattice projects. Recently, we came up with a new proposal, namely QCDLAB, a high level language interface, which we believe will boost our endeavours to rapidly code lattice prototype applications in lattice QCD using MATLAB/OCTAVE language and environment. The first version of the software, QCDLAB 1.0 offers the general framework on how to achieve this goal by simulating set of the lattice Schwinger model {\tt http://phys.fshn.edu.al/qcdlab.html}. In this talk we introduce QCDLAB 1.1, which extends QCDLAB 1.0 capabilities for real world lattice computations with Wilson and Domain Wall fermions.

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arXiv2006

QCDLAB: Designing Lattice QCD Algorithms with MATLAB

This paper introduces QCDLAB, a design and research tool for lattice QCD algorithms. The tool, a collection of MATLAB functions, is based on a ``small-code'' and a ``minutes-run-time'' algorithmic design philosophy. The present version uses the Schwinger model on the lattice, a great simplification, which shares many features and algorithms with lattice QCD. A typical computing project using QCDLAB is characterised by short codes, short run times, and the ability to make substantial changes in a few seconds. QCDLAB 1.0 can be downloaded from the QCDLAB project homepage {\tt http://phys.fshn.edu.al/qcdlab.html}.

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arXiv2006

A fast minimal residual solver for overlap fermions

Computing quark propagators with overlap fermions requires the solution of a shifted unitary linear system. Jagels and Reichel have shown that for such systems it is possible to construct a minimal residual algorithm by short recurrences. The Jülich-Wuppertal group have found this algorithm to be the fastest among overlap solvers. In this paper we present a three-term recurrence for the Arnoldi unitary process. Using the new recurrence we construct a minimal residual solver which is the fastest among all Krylov subspace algorithms considered so far for the overlap inversion.

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arXiv2006

Reducing the beta-shift in domain wall fermion simulations

The beta-shift induced from dynamical domain wall quarks leads to increased roughness of the gauge field, thus reversing the effect of smoothing from the gauge action improvement. By exploiting the relation of overlap and domain wall fermions in greater detail,we propose an algorithm which reduces the beta-shift to the level of dynamical overlap fermions.

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arXiv2006

Shifted unitary orthogonal methods for the overlap inversion

In this work we compare the convergence of the shifted unitary orthogonal method (SUOM) and different Krylov subspace solvers for propagator computations with overlap fermions. We show that the SUOM algorithm performs similarly to the shifted unitary minimal residual method (SUMR) with the latter converging slightly faster. When the geometric optimality is applied to SUOM we get e new algorithm which is faster than SUMR.

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arXiv2004

The two-grid algorithm confronts a shifted unitary orthogonal method

In this paper I describe a new optimal Krylov subspace solver for shifted unitary matrices called the Shifted Unitary Orthogonal Method (SUOM). This algorithm is used as a benchmark against any improvement like the two-grid algorithm. I use the latter to show that the overlap operator can be inverted by successive inversions of the truncated overlap operator. This strategy results in large gains compared to SUOM.

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arXiv2004

Computational methods for the fermion determinant and the link between overlap and domain wall fermions

This paper reviews the most popular methods which are used in lattice QCD to compute the determinant of the lattice Dirac operator: Gaussian integral representation and noisy methods. Both of them lead naturally to matrix function problems. We review the most recent development in Krylov subspace evaluation of matrix functions. The second part of the paper reviews the formal relationship and algebraic structure of domain wall and overlap fermions. We review the multigrid algorithm to invert the overlap operator. It is described here as a preconditioned Jacobi iteration where the preconditioner is the Schur complement of a certain block of the truncated overlap matrix.

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arXiv2002

A note on ultraviolet suppressed quasi-optimal domain wall fermions

In a recent work Chiu proposed to modify domain wall fermions that allow in an optimal way fewer number of flavors than in the standard case. This is done using a variant of doamin wall fermions, the so-called truncated overlap fermions. In this note I discuss the possibility to implement his proposal for the original variant of domain wall fermions. I make also some remarks on dynamical simulations with ultraviolet suppressed domain wall fermions.

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