6,742 research outputs found
Staggered Chiral Perturbation Theory and the Fourth-Root Trick
Staggered chiral perturbation theory (schpt) takes into account the
"fourth-root trick" for reducing unwanted (taste) degrees of freedom with
staggered quarks by multiplying the contribution of each sea quark loop by a
factor of 1/4. In the special case of four staggered fields (four flavors,
nF=4), I show here that certain assumptions about analyticity and phase
structure imply the validity of this procedure for representing the rooting
trick in the chiral sector. I start from the observation that, when the four
flavors are degenerate, the fourth root simply reduces nF=4 to nF=1. One can
then treat nondegenerate quark masses by expanding around the degenerate limit.
With additional assumptions on decoupling, the result can be extended to the
more interesting cases of nF=3, 2, or 1. A apparent paradox associated with the
one-flavor case is resolved. Coupled with some expected features of unrooted
staggered quarks in the continuum limit, in particular the restoration of taste
symmetry, schpt then implies that the fourth-root trick induces no problems
(for example, a violation of unitarity that persists in the continuum limit) in
the lowest energy sector of staggered lattice QCD. It also says that the theory
with staggered valence quarks and rooted staggered sea quarks behaves like a
simple, partially-quenched theory, not like a "mixed" theory in which sea and
valence quarks have different lattice actions. In most cases, the assumptions
made in this paper are not only sufficient but also necessary for the validity
of schpt, so that a variety of possible new routes for testing this validity
are opened.Comment: 39 pages, 3 figures. v3: minor changes: improved explanations and
less tentative discussion in several places; corresponds to published versio
Baryon Electromagnetic Properties in Partially Quenched Heavy Hadron Chiral Perturbation Theory
The electromagnetic properties of baryons containing a heavy quark are
calculated at next-to-leading order in partially quenched heavy hadron chiral
perturbation theory. Calculations are performed for three light flavors in the
isospin limit and additionally for two light non-degenerate flavors. We use
partially-quenched charge matrices that are easy to implement on the lattice.
The results presented are necessary for the light quark mass extrapolation and
zero-momentum extrapolation of lattice QCD and partially quenched lattice QCD
calculations of heavy hadron electromagnetic properties. Additionally relations
between the sextet electromagnetic form factors and transition form factors are
derived.Comment: 29 pages, 3 figures, RevTex
What are the barriers affecting the use of earth as a modern construction material in the context of circular economy?
Surface mixing and biological activity in the four Eastern Boundary Upwelling Systems
Eastern Boundary Upwelling Systems (EBUS) are characterized by a high
productivity of plankton associated with large commercial fisheries, thus
playing key biological and socio-economical roles. The aim of this work is to
make a comparative study of these four upwelling systems focussing on their
surface stirring, using the Finite Size Lyapunov Exponents (FSLEs), and their
biological activity, based on satellite data. First, the spatial distribution
of horizontal mixing is analysed from time averages and from probability
density functions of FSLEs. Then we studied the temporal variability of surface
stirring focussing on the annual and seasonal cycle. There is a global negative
correlation between surface horizontal mixing and chlorophyll standing stocks
over the four areas. To try to better understand this inverse relationship, we
consider the vertical dimension by looking at the Ekman-transport and vertical
velocities. We suggest the possibility of a changing response of the
phytoplankton to sub/mesoscale turbulence, from a negative effect in the very
productive coastal areas to a positive one in the open ocean.Comment: 12 pages. NPG Special Issue on "Nonlinear processes in oceanic and
atmospheric flows". Open Access paper, available also at the publisher site:
http://www.nonlin-processes-geophys.net/16/557/2009
Extrapolations of Lattice Meson Form Factors
We use chiral perturbation theory to study the extrapolations necessary to
make physical predictions from lattice QCD data for the electromagnetic form
factors of pseudoscalar mesons. We focus on the quark mass, momentum, lattice
spacing, and volume dependence and apply our results to simulations employing
mixed actions of Ginsparg-Wilson valence quarks and staggered sea quarks. To
determine charge radii at quark masses on the lattices currently used, we find
that all extrapolations except the one to infinite volume make significant
contributions to the systematic error.Comment: 14pp, discussion and Ref. added for disconnected diagram
The role of rotation on Petersen Diagrams. II The influence of near-degeneracy
In the present work, the effect of near-degeneracy on rotational Petersen
diagrams (RPD) is analysed. Seismic models are computed considering rotation
effects on both equilibrium models and adiabatic oscillation frequencies
(including second-order near-degeneracy effects). Contamination of coupled
modes and coupling strength on the first radial modes are studied in detail.
Analysis of relative intrinsic amplitudes of near-degenerate modes reveals that
the identity of the fundamental radial mode and its coupled quadrupole pair are
almost unaltered once near-degeneracy effects are considered. However, for the
first overtone, a mixed radial/quadrupole identity is always predicted. The
effect of near-degeneracy on the oscillation frequencies becomes critical for
rotational velocities larger than 15-20 km/s, for which large wriggles in the
evolution of the period ratios are obtained (up ). Such wriggles imply
uncertainties, in terms of metallicity determinations using RPD, reaching up to
0.50 dex, which can be critical for Pop. I HADS (High Amplitude \dss). In terms
of mass determinations, uncertainties reaching up to 0.5 M_sun are predicted.
The location of such wriggles is found to be independent of metallicity and
rotational velocity, and governed mainly by the avoided-crossing phenomenon.Comment: 8 pages, 7 figures, 1 table. (accepted for publication in A&A
Weathering the storm:A framework to assess the resistance of earthen structures to water damage
Lie Superalgebras and the Multiplet Structure of the Genetic Code II: Branching Schemes
Continuing our attempt to explain the degeneracy of the genetic code using
basic classical Lie superalgebras, we present the branching schemes for the
typical codon representations (typical 64-dimensional irreducible
representations) of basic classical Lie superalgebras and find three schemes
that do reproduce the degeneracies of the standard code, based on the
orthosymplectic algebra osp(5|2) and differing only in details of the symmetry
breaking pattern during the last step.Comment: 34 pages, 9 tables, LaTe
Spectroscopic determination of the fundamental parameters of 66 B-type stars in the field-of-view of the CoRoT satellite
We aim to determine the fundamental parameters of a sample of B stars with
apparent visual magnitudes below 8 in the field-of-view of the CoRoT space
mission, from high-resolution spectroscopy. We developed an automatic procedure
for the spectroscopic analysis of B-type stars with winds, based on an
extensive grid of FASTWIND model atmospheres. We use the equivalent widths
and/or the line profile shapes of continuum normalized hydrogen, helium and
silicon line profiles to determine the fundamental properties of these stars in
an automated way. After thorough tests, both on synthetic datasets and on very
high-quality, high-resolution spectra of B stars for which we already had
accurate values of their physical properties from alternative analyses, we
applied our method to 66 B-type stars contained in the ground-based archive of
the CoRoT space mission. We discuss the statistical properties of the sample
and compare them with those predicted by evolutionary models of B stars. Our
spectroscopic results provide a valuable starting point for any future seismic
modelling of the stars, should they be observed by CoRoT.Comment: 31 pages (including 14 pages online material), 32 figure
Analytic estimates for penguin operators in quenched QCD
Strong penguin operators are singlets under the right-handed flavor symmetry
group SU(3)_R. However, they do not remain singlets when the operator is
embedded in (partially) quenched QCD, but instead they become linear
combinations of two operators with different transformation properties under
the (partially) quenched symmetry group. This is an artifact of the quenched
approximation. Each of these two operators is represented by a different set of
low-energy constants in the chiral effective theory. In this paper, we give
analytic estimates for the leading low-energy constants, in quenched and
partially quenched QCD. We conclude that the effects of quenching on Q_6 are
large.Comment: 6 pages. Typo fixed and an explanatory footnote adde
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