469 research outputs found
Group-theoretical construction of extended baryon operators
The design and implementation of large sets of spatially extended baryon
operators for use in lattice simulations are described. The operators are
constructed to maximize overlaps with the low-lying states of interest, while
minimizing the number of sources needed in computing the required quark
propagators.Comment: 3 pages, 3 tables, talk presented at Lattice2004(spectrum), Fermilab,
June 21-26, 200
Impact of Acute Ethanol Injections on Medial Prefrontal Cortex Neural Activity
Indiana University-Purdue University Indianapolis (IUPUI)The medial prefrontal cortex (mPFC) is a cortical brain region involved in the evaluation
and selection of motivationally relevant outcomes. mPFC-mediated cognitive functions
are impaired following acute alcohol exposure. In rodent models, ethanol (EtOH) doses
as low as 0.75 g/kg yield deficits in cognitive functions. These deficits following acute
EtOH are thought to be mediated, at least in part, by decreases in mPFC firing rates.
However, these data have been generated exclusively in anesthetized rodents. To
eliminate the potentially confounding role of anesthesia on EtOH modulated mPFC
activity, the present study investigated the effects of acute EtOH injections on mPFC
neural activity in awake-behaving rodents. We utilized three groups: the first group
received 2 saline injections during the recording. The second group received a saline
injection followed 30 minutes later by a 1.0 g/kg EtOH injection. The last group received
a saline injection followed 30 minutes later by a 2.0 g/kg EtOH injection. One week
following the awake-behaving recording, an anesthetized recording was performed using
one dose of saline followed 30 minutes later by one dose of 1.0 g/kg EtOH in order to
replicate previous studies. Firing rates were normalized to a baseline period that occurred
5 minutes prior to each injection. A 5-minute time period 30 minutes following the
injection was used to compare across groups. There were no significant differences
across the awake-behaving saline-saline group, indicating no major effect on mPFC
neural activity as a result of repeated injections. There was a significant main effect
across treatment & behavioral groups in the saline-EtOH 1.0 g/kg group with reductions
in the EtOH & Sleep condition. In the saline-EtOH 2.0 g/kg, mPFC neural activity was
only reduced in lowered states of vigilance. This suggests that EtOH only causes gross
changes on neural activity when the animal is not active and behaving. Ultimately this
means that EtOH’s impact on decision making is not due to gross changes in mPFC
neural activity and future work should investigate its mechanism
Quarks, Gluons and Frustrated Antiferromagnets
The Contractor Renormalization Group method (CORE) is used to establish the
equivalence of various Hamiltonian free fermion theories and a class of
generalized frustrated antiferromagnets. In particular, after a detailed
discussion of a simple example, it is argued that a generalized frustrated
SU(3) antiferromagnet whose single-site states have the quantum numbers of
mesons and baryons is equivalent to a theory of free massless quarks.
Furthermore, it is argued that for slight modification of the couplings which
define the frustrated antiferromagnet Hamiltonian, the theory becomes a theory
of quarks interacting with color gauge-fields.Comment: 21 pages, Late
Baryonic sources using irreducible representations of the double-covered octahedral group
Irreducible representations (IRs) of the double-covered octahedral group are
used to construct lattice source and sink operators for three-quark baryons.
The goal is to achieve a good coupling to higher spin states as well as ground
states. Complete sets of local and nonlocal straight-link operators are
explicitly shown for isospin 1/2 and 3/2 baryons. The orthogonality relations
of the IR operators are confirmed in a quenched lattice simulation.Comment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26, 2004, 3
page
Nucleon, and excited states in lattice QCD
The energies of the excited states of the Nucleon, and are
computed in lattice QCD, using two light quarks and one strange quark on
anisotropic lattices. The calculation is performed at three values of the light
quark mass, corresponding to pion masses = 392(4), 438(3) and 521(3)
MeV. We employ the variational method with a large basis of interpolating
operators enabling six energies in each irreducible representation of the
lattice to be distinguished clearly. We compare our calculation with the
low-lying experimental spectrum, with which we find reasonable agreement in the
pattern of states. The need to include operators that couple to the expected
multi-hadron states in the spectrum is clearly identified.Comment: Revised for publication. References added, Table VI expanded to add
strange baryon multiparticle thresholds and multiparticle thresholds added to
Figs. 4, 5 and 6. 15 pages, 6 figure
Perturbative coefficients for improved actions by Monte Carlo at large
Perturbative estimates of operator coefficients for improved lattice actions
are becoming increasingly important for precision simulations of many hadronic
observables. Following previous work by Dimm, Lepage, and Mackenzie, we
consider the feasibility of computing operator coefficients from numerical
simulations deep in the perturbative region of lattice theories. Here we
introduce a background field technique that may allow for the computation of
the coefficients of clover-field operators in a variety of theories. This
method is tested by calculations of the renormalized quark mass in lattice
NRQCD, and of the clover coefficient for Sheikholeslami-Wohlert
fermions. First results for the coefficient of the magnetic moment operator in
NRQCD are also presented.Comment: 3 Pages, LaTeX (espcrc2.sty, uses \psfig), 3 Postscript figures, Talk
presented at LATTICE'97, Edinburg
Ab Initio Study of Hybrid b-bar-gb Mesons
Hybrid b-bar-gb molecules in which the heavy b-bar-b pair is bound together
by the excited gluon field g are studied using the Born-Oppenheimer expansion
and numerical simulations. The consistency of results from the two approaches
reveals a simple and compelling physical picture for heavy hybrid states.Comment: 4 pages, 3 figures, uses REVTeX and epsf, final published versio
Continuum Limit of Scalar Masses and Mixing Energies
We evaluate the continuum limit of the valence approximation to the mass of
scalar quarkonium and to the scalar quarkonium-glueball mixing energy for a
range of different quark masses. Our results answer several questions raised by
the proposed identification of as composed primarily of the
lightest scalar glueball.Comment: 3 pages, 2 PostScript figures, LATTICE98(spectrum), one reference
correcte
Scalar Quarkonium Masses and Mixing with the Lightest Scalar Glueball
We evaluate the continuum limit of the valence (quenched) approximation to
the mass of the lightest scalar quarkonium state, for a range of different
quark masses, and to the mixing energy between these states and the lightest
scalar glueball. Our results support the interpretation of as
composed mainly of the lightest scalar glueball.Comment: 14 pages of Latex, 5 PostScript figure
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