Alternative to Domain Wall Fermions

An alternative to commonly used domain wall fermions is presented. Some rigorous bounds on the condition number of the associated linear problem are derived. On the basis of these bounds and some experimentation it is argued that domain wall fermions will in general be associated with a condition number that is of the same order of magnitude as the {\it product} of the condition number of the linear problem in the physical dimensions by the inverse bare quark mass. Thus, the computational cost of implementing true domain wall fermions using a single conjugate gradient algorithm is of the same order of magnitude as that of implementing the overlap Dirac operator directly using two nested conjugate gradient algorithms. At a cost of about a factor of two in operation count it is possible to make the memory usage of direct implementations of the overlap Dirac operator independent of the accuracy of the approximation to the sign function and of the same order as that of standard Wilson fermions.Comment: 7 pages, 1 figure, LaTeX, uses espcrc2, reference adde

Tricks to implement the overlap Dirac operator

I present several tricks to help implement the overlap Dirac operator numerically.Comment: 3 pages, latex, espcrc2.st

Lattice Chirality

The external fermion propagator and the internal fermion propagator in the overlap are given by different matrices. A generic problem (formulated by Pelissetto) faced by all chiral, non-local, propagators of Rebbi type is avoided in this manner. Nussinov-Weingarten-Witten mass inequalities are exactly preserved. It is sketched how to obtain simple lattice chiral Yukawa models and simple expressions for covariant currents. Going beyond my oral presentation, I have added to the write-up several comments on Niedermayer's talk. His transparencies are available on the internet.Comment: LATTICE98(chiral

Regularization dependence of the Higgs mass triviality bound

We calculate the triviality bound on the Higgs mass in scalar field theory models whose global symmetry group $SU(2)_L \times SU(2)_{\rm custodial} \approx O(4)$ has been replaced by $O(N)$ and $N$ has been taken to infinity. Limits on observable cutoff effects at four percent in several regularized models with tunable couplings in the bare action yield triviality bounds displaying a large degree of universality. Extrapolating from $N=\infty$ to $N=4$ we conservatively estimate that a Higgs particle with mass up to $0.750~TeV$ and width up to $0.290~TeV$ is realizable without large cutoff effects, indicating that strong scalar self interactions in the standard model are not ruled out. We also present preliminary numerical results of the physical $N=4$ case for the $F_4$ lattice that are in agreement with the large $N$ expectations. Note: The full ps file is also available via anonymous ftp to ftp.scri.fsu.edu. To get the ps file, ftp to this address and use for username "anonymous" and for password your name. The file is in the directory pub/vranas (to go to that directory type: cd pub/vranas) and is called lat92_proc.ps (to get it type: get lat92_proc.ps)Comment: 5 pages with 5 ps figures included. LaTex file. Contribution to the LAT92 proceedings. Preprint, FSU-SCRI-92-150, RU-92-4

A simple derivation of the Overlap Dirac Operator

We derive the vector-like four dimensional overlap Dirac operator starting from a five dimensional Dirac action in the presence of a delta-function space-time defect. The effective operator is obtained by first integrating out all the fermionic modes in the fixed gauge background, and then identifying the contribution from the localized modes as the determinant of an operator in one dimension less. We define physically relevant degrees of freedom on the defect by introducing an auxiliary defect-bound fermion field and integrating out the original five dimensional bulk field.Comment: 9 pages, LaTe

Ginsparg-Wilson relation with R=(a \gamma_5 D)^{2k}

The Ginsparg-Wilson relation $D \gamma_5 + \gamma_5 D = 2 a D R \gamma_5 D$ with $R = (a \gamma_5 D)^{2k}$ is discussed. An explicit realization of D is constructed. It is shown that this sequence of topologically-proper lattice Dirac operators tend to a nonlocal operator in the limit $k \to \infty$. This suggests that the locality of a lattice Dirac operator is irrelevant to its index.Comment: 4 pages, 1 EPS figure, talk presented at Lattice'00 (Chiral Fermion

Chiral fermions on the lattice

Chiral fermions resisted being put on the lattice for twenty years. This raised the suspicion that asymptotically free chiral gauge theories were not renormalizable outside perturbation theory and therefore could not be mathematically extended to infinite energies. During the last several years the situation has reversed itself. Today we believe that all the essential ingredients for a full lattice definition of non-anomalous chiral gauge theories are in place within the overlap construction. This construction is based on earlier work by Callan and Harvey, by Kaplan and by Frolov and Slavnov. It can be reinterpreted as coming from the Ginsparg-Wilson relation, but, at the moment, it is a unique construction and therefore might also be the way by which Nature itself regularizes chiral fermions. This is yet another instance in which lattice field theory makes a potentially important contribution to fundamental particle physics.Comment: 10 pages, latex, espcrc2.st

Truncated Overlap Fermions

In this talk I propose a new computational scheme with overlap fermions and a fast algorithm to invert the corresponding Dirac operator.Comment: LATTICE99(algorithms

Low energy effective action of domain-wall fermion and the Ginsparg-Wilson relation

We derive the effective action of the light fermion field of the domain-wall fermion, which is referred as $q(x)$ by Furman and Shamir. The inverse of the effective Dirac operator turns out to be identical to the inverse of the truncated overlap Dirac operator, except a local contact term which would give the chiral symmetry breaking in the Ginsparg-Wilson relation. This result allows us to relate the light fermion field and the fermion field described by the truncated overlap Dirac operator and to understand the chiral property of the light fermion through the exact chiral symmetry based on the Ginsparg-Wilson relation.Comment: 35 pages, LaTeX2e, references added and updated, minor correction

The overlap lattice Dirac operator and dynamical fermions

I show how to avoid a two level nested conjugate gradient procedure in the context of Hybrid Monte Carlo with the overlap fermionic action. The resulting procedure is quite similar to Hybrid Monte Carlo with domain wall fermions, but is more flexible and therefore has some potential worth exploring.Comment: Further expanded version. 12 pages, plain Te