1,023 research outputs found
White matter integrity as a predictor of response to treatment in first episode psychosis
The integrity of brain white matter connections is central to a patient's ability to respond to pharmacological interventions. This study tested this hypothesis using a specific measure of white matter integrity, and examining its relationship to treatment response using a prospective design in patients within their first episode of psychosis. Diffusion tensor imaging data were acquired in 63 patients with first episode psychosis and 52 healthy control subjects (baseline). Response was assessed after 12 weeks and patients were classified as responders or non-responders according to treatment outcome. At this second time-point, they also underwent a second diffusion tensor imaging scan. Tract-based spatial statistics were used to assess fractional anisotropy as a marker of white matter integrity. At baseline, non-responders showed lower fractional anisotropy than both responders and healthy control subjects (P < 0.05; family-wise error-corrected), mainly in the uncinate, cingulum and corpus callosum, whereas responders were indistinguishable from healthy control subjects. After 12 weeks, there was an increase in fractional anisotropy in both responders and non-responders, positively correlated with antipsychotic exposure. This represents one of the largest, controlled investigations of white matter integrity and response to antipsychotic treatment early in psychosis. These data, together with earlier findings on cortical grey matter, suggest that grey and white matter integrity at the start of treatment is an important moderator of response to antipsychotics. These findings can inform patient stratification to anticipate care needs, and raise the possibility that antipsychotics may restore white matter integrity as part of the therapeutic response
QCD sum rules for the pseudoscalar decay constants - To constrain the strange quark mass
We study the higher order corrections of quark masses to the
Gell-MannOakesRenner (GOR) relation by constructing QCD sum rules
exclusively for pseudoscalar mesons from the axial-vector correlation function,
. To project out
the pseudoscalar meson contributions, we apply to this
correlation function and construct sum rules for the decay constants of
pseudoscalar mesons, and . The OPE is proportional to
quark masses due to PCAC. To leading order in quark mass, each sum rule
reproduces the corresponding GOR relation. For kaon and , the deviation
from the GOR relation due to higher orders in quark mass is found to be
substantial. But the deviation gives better agreements with the phenomenology.
Our sum rule provides a sensitive relation between and , which
stringently constrain the value for . To reproduce the experimental value
for , is found to be 186 MeV at 1 GeV scale. The sum
rule also supports this finding.Comment: 14 pages including 3 figures. slightly revised. Accepted for
publication in Physical Review
Isospin Breaking in the Pion-Nucleon Coupling from QCD Sum Rules
We use QCD sum rules for the three point function of a pseudoscalar and two
nucleonic currents in order to estimate the charge dependence of the pion
nucleon coupling constant coming from isospin violation in the
strong interaction. The effect can be attributed primarily to the difference of
the quark condensates . For the splitting
we obtain an interval of to , the uncertainties coming mainly from the input
parameters. The charged pion nucleon coupling is found to be the average of
and . Electromagnetic effects are not included.Comment: 18 pages (REVTeX) + 2 figures (as PostScript), to be published in
PRC, replaced with final version: inclusion of pi-eta mixing and N -> N*
transition
Higher Resonance Contamination of pi NN Couplings Obtained Via the Three-Point Function Method in QCD Sum Rules
We investigate the size of potential higher pseudoscalar resonance
contaminations of the estimates of isospin-conserving and isospin-violating
couplings obtained using the 3-point function method in QCD sum rules.
For the isospin-conserving case it is shown that conventional models of the
isovector pseudoscalar spectral function imply resonance decay constants large
enough to create significant contaminations, and that assuming these models are
incorrect, and that the decay constants are actually much smaller, implies
physically implausible values for the flavor-breaking quark condensate ratios.
For the isospin-violating case it is shown explicitly that such resonance
contamination is unavoidably present and precludes using the 3-point function
method as a means of estimating the at present unmeasured isospin-violating
couplings.Comment: 8 page
Low-energy gluon contributions to the vacuum polarization of heavy quarks
We calculate a correction to the electromagnetic current induced by a heavy
quark loop. The contribution of this correction to the vacuum polarization
function appears at the O(alpha_s^3) order of perturbation theory and has a
qualitatively new feature -- its absorptive part starts at zero energy in
contrast to other contributions where the absorptive parts start at the
two-particle threshold. Our result imposes a constraint on the order n of the
moments used in the heavy-quark sum rules, n<4.Comment: 8 pages in LaTeX, 1 PostScript figure included in the tex
Octet Baryons at Finite Temperature: QCD Sum Rules vs. Chiral Symmetry
Correlators of the octet baryons in the hot pion gas are studied in the
framework of the QCD sum rule. The condensates appearing in the OPE side of the
correlators become T-dependent through the interaction with thermal pions. We
present an explicit demonstration that the -dependence of the
condensates is completely compensated by the change of the pole residue and the
scattering effect in the spectral functions. Therefore
the baryon masses are constant to this order, although
, which
is consistent with the chiral symmetry constraint by Leutwyler and Smilga.Comment: 19 pages, MSUNSCL-870, LaTex files, 2 figs. consisting of simple
Feynmann diagrams not included, Phys.Rev.D in pres
Isospin Breaking Effects in the Extraction of Isoscalar and Isovector Spectral Functions From
We investigate the problem of the extraction of the isovector and isoscalar
spectral functions from data on , in the presence of
non-zero isospin breaking. It is shown that the conventional approach to
extracting the isovector spectral function in the resonance region, in
which only the isoscalar contribution associated with is
subtracted, fails to fully remove the effects of the isoscalar component of the
electromagnetic current. The additional subtractions required to extract the
pure isovector and isoscalar spectral functions are estimated using results
from QCD sum rules. It is shown that the corrections are small () in
the isovector case (though relevant to precision tests of CVC), but very large
() in the case of the contribution to the isoscalar spectral
function. The reason such a large effect is natural in the isoscalar channel is
explained, and implications for other applications, such as the extraction of
the sixth order chiral low-energy constant, , are discussed.Comment: minor changes to introduction, section 2. In Press Phys. Rev.
Light-Quark Mesons and Four-Quark Condensates at Finite Temperature
We propose an analog of the familiar gap equation for the case of four-quark
condensates at finite temperature. The condensates of interest correspond to
scalar, vector, psudoscalar, axial vector, and tensor Dirac structures. Working
with correlators at zero chemical potential without factorization, we arrive at
coupled equations for these four-quark condensates and the masses of certain
light-quark mesons. We study the temperature dependence of the four-quark
condensates and masses; in one of our models, factorization of the four-quark
condensates is shown to be increasingly violated as the temperature is
increased toward . The 2 tensor mesons a(1320)-f(1270) are
identified as especially sensitive probes of the four-quark condensates.Comment: Latex file, 6 Fig
Vacuum Condensates in the Global Color Symmetry Model
Based on the quark propagator in the instanton dilute liquid approximation,
we calculate analytically the quark condensate , the mixed quark
gluon condensate $g_{s}$ and the four quark
condensate at the mean field level in the
framework of global color symmetry model. The numerical calculation shows that
the values of these condensates are compatible with the ranges determined by
other nonperturbative approaches. Moreover, we find that for nonlocal four
quark condensate the previous vacuum saturation assumption is not a good
approximation even at the mean field level.Comment: 8 latex pages, no figure, Submitted to Phys. Rev.
Charge and Isospin Fluctuations in High Energy pp-Collisions
Charge and isospin event-by-event fluctuations in high-energy pp-collisions
are predicted within the Unitary Eikonal Model, in particular the fluctuation
patterns of the ratios of charged-to-charged and neutral-to-charged pions.
These fluctuations are found to be sensitive to the presence of unstable
resonances, such as and mesons. We predict that the
charge-fluctuation observable should be restricted to the interval
depending on the production ratio. Also, the
isospin fluctuations of the DCC-type of the ratio of neutral-to-charged pions
are suppressed if pions are produced together with mesons.Comment: Latex, 5 pages, no figures. To appear in the proceedings of 9th
Adriatic Meeting, Dubrovnik, Croatia, 4 - 14 September 2003. Added reference
into reference no.
- …