82,788 research outputs found
Orbitally excited and hybrid mesons from the lattice
We discuss in general the construction of gauge-invariant non-local meson
operators on the lattice. We use such operators to study the - and -wave
mesons as well as hybrid mesons in quenched QCD, with quark masses near the
strange quark mass. The resulting spectra are compared with experiment for the
orbital excitations. For the states produced by gluonic excitations (hybrid
mesons) we find evidence of mixing for non-exotic quantum numbers. We give
predictions for masses of the spin-exotic hybrid mesons with $J^{PC}=1^{-+},\
0^{+-}2^{+-}$.Comment: 31 pages, LATEX, 8 postscript figures. Reference adde
On the Predictiveness of Single-Field Inflationary Models
We re-examine the predictiveness of single-field inflationary models and
discuss how an unknown UV completion can complicate determining inflationary
model parameters from observations, even from precision measurements. Besides
the usual naturalness issues associated with having a shallow inflationary
potential, we describe another issue for inflation, namely, unknown UV physics
modifies the running of Standard Model (SM) parameters and thereby introduces
uncertainty into the potential inflationary predictions. We illustrate this
point using the minimal Higgs Inflationary scenario, which is arguably the most
predictive single-field model on the market, because its predictions for ,
and are made using only one new free parameter beyond those measured
in particle physics experiments, and run up to the inflationary regime. We find
that this issue can already have observable effects. At the same time, this
UV-parameter dependence in the Renormalization Group allows Higgs Inflation to
occur (in principle) for a slightly larger range of Higgs masses. We comment on
the origin of the various UV scales that arise at large field values for the SM
Higgs, clarifying cut off scale arguments by further developing the formalism
of a non-linear realization of in curved space. We
discuss the interesting fact that, outside of Higgs Inflation, the effect of a
non-minimal coupling to gravity, even in the SM, results in a non-linear EFT
for the Higgs sector. Finally, we briefly comment on post BICEP2 attempts to
modify the Higgs Inflation scenario.Comment: 31 pp, 4 figures v4: Minor correction to section 3.1. Main arguments
and conclusions unchange
Regularity Theory and Superalgebraic Solvers for Wire Antenna Problems
We consider the problem of evaluating the current distribution that is induced on a straight wire antenna by a time-harmonic incident electromagnetic field. The scope of this paper is twofold. One of its main contributions is a regularity proof for a straight wire occupying the interval . In particular, for a smooth time-harmonic incident field this theorem implies that , where is an infinitely differentiable function—the previous state of the art in this regard placed in the Sobolev space , . The second focus of this work is on numerics: we present three superalgebraically convergent algorithms for the solution of wire problems, two based on Hallén's integral equation and one based on the Pocklington integrodifferential equation. Both our proof and our algorithms are based on two main elements: (1) a new decomposition of the kernel of the form , where and are analytic functions on the real line; and (2) removal of the end-point square root singularities by means of a coordinate transformation. The Hallén- and Pocklington-based algorithms we propose converge superalgebraically: faster than and for any positive integer , where and are the numbers of unknowns and the number of integration points required for construction of the discretized operator, respectively. In previous studies, at most the leading-order contribution to the logarithmic singular term was extracted from the kernel and treated analytically, the higher-order singular derivatives were left untreated, and the resulting integration methods for the kernel exhibit convergence at best. A rather comprehensive set of tests we consider shows that, in many cases, to achieve a given accuracy, the numbers of unknowns required by our codes are up to a factor of five times smaller than those required by the best solvers previously available; the required number of integration points, in turn, can be several orders of magnitude smaller than those required in previous methods. In particular, four-digit solutions were found in computational times of the order of four seconds and, in most cases, of the order of a fraction of a second on a contemporary personal computer; much higher accuracies result in very small additional computing times
The radial distributions of a heavy-light meson on a lattice
In an earlier work, the charge (vector) and matter (scalar) radial
distributions of heavy-light mesons were measured in the quenched approximation
on a 16^3 times 24 lattice with a quark-gluon coupling of 5.7, a lattice
spacing of 0.17 fm, and a hopping parameter corresponding to a light quark mass
about that of the strange quark.
Several improvements are now made: 1) The configurations are generated using
dynamical fermions with a quark-gluon coupling of 5.2 (a lattice spacing of
0.14 fm); 2) Many more gauge configurations are included (78 compared with the
earlier 20); 3) The distributions at many off-axis, in addition to on-axis,
points are measured; 4) The data-analysis is much more complete. In particular,
distributions involving excited states are extracted.
The exponential decay of the charge and matter distributions can be described
by mesons of mass 0.9+-0.1 and 1.5+-0.1 GeV respectively - values that are
consistent with those of vector and scalar qqbar-states calculated directly
with the same lattice parameters.Comment: 3 pages, 4 figures, Lattice2002(heavyquark
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