86 research outputs found
New fermion discretizations and their applications
We review the recent progress in new lattice fermion formulations. We focus
on the following three types which have possibility of improving lattice
simulations. (1) Flavored-mass fermions are a generalization of Wilson fermions
with species-splitting mass terms. In particular, staggered-Wilson fermions
initiated by Adams have possibilities of reducing numerical costs in overlap
fermions and the influence of taste-breaking in staggered fermions. (2)
Central-branch Wilson fermions, in which additive mass renormalization is
forbidden by extra axial symmetry, could enable us to perform Wilson-fermion
lattice QCD without fine-tuning. (3) Minimally doubled fermions, which reduce
the number of species by species-dependent chemical potential terms, realizes a
ultra-local chiral fermion at the price of hypercubic symmetry. These setups
reveal unknown aspects of lattice fermions, and we obtain a deeper
understanding of lattice field theory.Comment: 15 pages, 9 figures, plenary talk presented at the 30th International
Symposium on Lattice Field Theory - Lattice 2012, June 24-29, 2012 Cairns,
Australi
Characters of Lattice Fermions Based on the Hyperdiamond Lattice
We study minimal-doubling fermion actions on hyperdiamond and deformed
hyperdiamond lattices, with emphasis on the real-space construction of them and
Lorentz covariance of excitations from fermion poles. We propose the improved
spatial construction of Creutz fermion action on a deformed hyperdiamond
lattice, and discuss conditions for a hyperdiamond-lattice action to produce
Lorentz-covariant excitations from poles of fermion propagators. It is pointed
out that the non-nearest-site hoppings are essential for the correct
excitations. We propose a class of minimal-doubling actions defined on a
deformed hypercubic lattice as a generalization of Creutz-type actions. In
addition we introduce a two-parameter class of Wilczek-type minimal-doubling
actions.Comment: 22 pages, 3 figures. v2:Discussion clarified and extended, the order
of sections changed. v3:final version accepted for publicatio
Lattice Fermions Based on Higher-Dimensional Hyperdiamond Lattices
In this paper we generalize to higher dimensions several types of fermion
actions on the hyperdiamond lattice including a two-parameter class of
minimal-doubling fermions "Creutz fermion" and a simple fermion with sufficient
discrete symmetry "BBTW fermion". Then it is shown that they possess some
properties in common with the four-dimensional case: BBTW fermions in higher
even dimensions inevitably yield unphysical degrees of freedom. Creutz fermions
are defined on the distorted lattices, and they lose the high discrete symmetry
of the original lattices. We also find properties specific to the
higher-dimensional cases. The parameter range for Creutz action to yield
minimal-doubling and physical fermions becomes narrower with the dimension
getting higher, thus it becomes more and more difficult to realize
minimal-doubling. In addition, we generalize the subspecies of Creutz and BBTW
actions including a new class of minimal-doubling actions "Appended Creutz
action".Comment: 18 pages, 2 figures. To appear in Prog. Theo. Phy
Circle compactification and 't Hooft anomaly
Anomaly matching constrains low-energy physics of strongly-coupled field
theories, but it is not useful at finite temperature due to contamination from
high-energy states. The known exception is an 't Hooft anomaly involving
one-form symmetries as in pure Yang-Mills theory at .
Recent development about large- volume independence, however, gives us a
circumstantial evidence that 't Hooft anomalies can also remain under circle
compactifications in some theories without one-form symmetries. We develop a
systematic procedure for deriving an 't Hooft anomaly of the
circle-compactified theory starting from the anomaly of the original
uncompactified theory without one-form symmetries, where the twisted boundary
condition for the compactified direction plays a pivotal role. As an
application, we consider -twisted sigma model
and massless -QCD, and compute their anomalies explicitly.Comment: 22 pages; (v2) references updated, minor change
Lattice study on QCD-like theory with exact center symmetry
We investigate QCD-like theory with exact center symmetry, with emphasis on
the finite-temperature phase transition concerning center and chiral
symmetries. On the lattice, we formulate center symmetric gauge theory
with three fundamental Wilson quarks by twisting quark boundary conditions in a
compact direction (-QCD model). We calculate the expectation value of
Polyakov loop and the chiral condensate as a function of temperature on 16^3 x
4 and 20^3 x 4 lattices along the line of constant physics realizing
. We find out the first-order center phase transition, where
the hysteresis of the magnitude of Polyakov loop exists depending on
thermalization processes. We show that chiral condensate decreases around the
critical temperature in a similar way to that of the standard three-flavor QCD,
as it has the hysteresis in the same range as that of Polyakov loop. We also
show that the flavor symmetry breaking due to the twisted boundary condition
gets qualitatively manifest in the high-temperature phase. These results are
consistent with the predictions based on the chiral effective model in the
literature. Our approach could provide novel insights to the nonperturbative
connection between the center and chiral properties.Comment: 25 pages, 6 figures, to apper in JHE
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