4,616 research outputs found
Quark condensate for various heavy flavors
The quark condensate is calculated within the world-line effective-action
formalism, by using for the Wilson loop an ansatz provided by the stochastic
vacuum model. Starting with the relation between the quark and the gluon
condensates in the heavy-quark limit, we diminish the current quark mass down
to the value of the inverse vacuum correlation length, finding in this way a
64%-decrease in the absolute value of the quark condensate. In particular, we
find that the conventional formula for the heavy-quark condensate cannot be
applied to the c-quark, and that the corrections to this formula can reach 23%
even in the case of the b-quark. We also demonstrate that, for an exponential
parametrization of the two-point correlation function of gluonic field
strengths, the quark condensate does not depend on the non-confining
non-perturbative interactions of the stochastic background Yang-Mills fields.Comment: 12 pages, 2 figures, to appear in Eur. Phys. J.
A multiplicative potential approach to solutions for cooperative TU-games
Concerning the solution theory for cooperative games with transferable utility, it is well-known that the Shapley value is the most appealing representative of the family of (not necessarily efficient) game-theoretic solutions with an additive potential representation. This paper introduces a new solution concept, called Multiplicativily Proportional () value, that can be regarded as the counterpart of the Shapley value if the additive potential approach to the solution theory is replaced by a multiplicative potential approach in that the difference of two potential evaluations is replaced by its quotient. One out of two main equivalence theorems states that every solution with a multiplicative potential representation is equivalent to this specifically chosen efficient value in that the solution of the initial game coincides with the value of an auxiliary game. The associated potential function turns out to be of a multiplicative form (instead of an additive form) with reference to the worth of all the coalitions. The second equivalence theorem presents four additional characterizations of solutions that admit a multiplicative potential representation, e.g., preservation of discrete ratios or path independence
A model for fermion masses and lepton mixing in SO(10) x A4
The discrete flavor symmetry A4 explains very well neutrino data at low
energy, but it seems difficult to extend it to grand unified models since in
general left-handed and right-handed fields belong to different A4
representations. Recently it has been proposed a model where all the fermions
equally transform under A4. We study here a concrete SO(10) realization of such
a model providing small neutrino masses through the seesaw mechanism. We fit at
tree level the charged fermion masses run up to the unification scale. Some
fermion masses properties come from the SO(10) symmetry while lepton mixing
angles are consequence of the A4 properties. Moreover, our model predicts the
absolute value of the neutrino masses, these ones are in the range .Comment: 15 pages. V2: Final version to appear in the journa
Uloga kiralne simetrije u hadronskim procesima
The role of chiral symmetry in hadronic processes is discussed. Emphasis is given to the cancellation of diagrams in π −π scattering induced by chiral symmetry and its consequences in the scalar sector.Raspravljamo ulogu kiralne simetrije u hadronskim procesima. Naglašavamo poništenje dijagrama u ππ raspršenju uzrokovano kiralnom simetrijom i njene posljedice u skalarnom sektoru
Uloga kiralne simetrije u hadronskim procesima
The role of chiral symmetry in hadronic processes is discussed. Emphasis is given to the cancellation of diagrams in π −π scattering induced by chiral symmetry and its consequences in the scalar sector.Raspravljamo ulogu kiralne simetrije u hadronskim procesima. Naglašavamo poništenje dijagrama u ππ raspršenju uzrokovano kiralnom simetrijom i njene posljedice u skalarnom sektoru
Rapid and MR-Independent IK1 activation by aldosterone during ischemia-reperfusion
In ST elevation myocardial infarction (STEMI) context, clinical studies have shown the deleterious
effect of high aldosterone levels on ventricular arrhythmia occurrence and cardiac
mortality. Previous in vitro reports showed that during ischemia-reperfusion, aldosterone
modulates K+ currents involved in the holding of the resting membrane potential (RMP).
The aim of this study was to assess the electrophysiological impact of aldosterone on IK1
current during myocardial ischemia-reperfusion. We used an in vitro model of “border zone”
using right rabbit ventricle and standard microelectrode technique followed by cell-attached
recordings from freshly isolated rabbit ventricular cardiomyocytes. In microelectrode experiments,
aldosterone (10 and 100 nmol/L, n=7 respectively) increased the action potential
duration (APD) dispersion at 90% between ischemic and normoxic zones (from 95±4ms to
116±6 ms and 127±5 ms respectively, P<0.05) and reperfusion-induced sustained premature
ventricular contractions occurrence (from 2/12 to 5/7 preparations, P<0.05). Conversely,
potassium canrenoate 100 nmol/L and RU 28318 1 μmol/l alone did not affect AP
parameters and premature ventricular contractions occurrence (except Vmax which was
decreased by potassium canrenoate during simulated-ischemia). Furthermore, aldosterone
induced a RMP hyperpolarization, evoking an implication of a K+ current involved in the
holding of the RMP. Cell-attached recordings showed that aldosterone 10 nmol/L quickly
activated (within 6.2±0.4 min) a 30 pS K+-selective current, inward rectifier, with pharmacological
and biophysical properties consistent with the IK1 current (NPo =1.9±0.4 in control vs
NPo=3.0±0.4, n=10, P<0.05). These deleterious effects persisted in presence of RU 28318,
a specific MR antagonist, and were successfully prevented by potassium canrenoate, a non
specific MR antagonist, in both microelectrode and patch-clamp recordings, thus indicating
a MR-independent IK1 activation. In this ischemia-reperfusion context, aldosterone induced
rapid and MR-independent deleterious effects including an arrhythmia substrate (increased
APD90 dispersion) and triggered activities (increased premature ventricular contractions
occurrence on reperfusion) possibly related to direct IK1 activation
High-harmonic generation: taking control of polarization
The ability to control the polarization of short-wavelength radiation generated by high-harmonic generation is useful not only for applications but also for testing conservation laws in physics
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