1,630 research outputs found
Are CP Violating Effects in the Standard Model Really Tiny?
We derive an effective action of the bosonic sector of the Standard Model by
integrating out the fermionic degrees of freedom in the worldline approach. The
CP violation due to the complex phase in the CKM matrix gives rise to
CP-violating operators in the effective action. We calculate the prefactor of
the appropriate next-to-leading order operators and give general estimates of
CP violation in the bosonic sector of the Standard Model. In particular, we
show that the effective CP violation for weak gauge fields is not suppressed by
the Yukawa couplings of the light quarks and is much larger than the bound
given by the Jarlskog determinant.Comment: 4 pages. To appear in the proceedings of the 8th Conference on Strong
and Electroweak Matter (SEWM08), Amsterdam, the Netherlands, 26-29 August
200
Chiral Lagrangian at finite temperature from the Polyakov-Chiral Quark Model
We analyze the consequences of the inclusion of the gluonic Polyakov loop in
chiral quark models at finite temperature. Specifically, the low-energy
effective chiral Lagrangian from two such quark models is computed. The tree
level vacuum energy density, quark condensate, pion decay constant and
Gasser-Leutwyler coefficients are found to acquire a temperature dependence.
This dependence is, however, exponentially small for temperatures below the
mass gap in the full unquenched calculation. The introduction of the Polyakov
loop and its quantum fluctuations is essential to achieve this result and also
the correct large counting for the thermal corrections. We find that new
coefficients are introduced at to account for the Lorentz
breaking at finite temperature. As a byproduct, we obtain the effective
Lagrangian which describes the coupling of the Polyakov loop to the Goldstone
bosons.Comment: 16 pages, no figure
Electromagnetic structure and weak decay of pseudoscalar mesons in a light-front QCD-inspired model
We study the scaling of the meson mass splitting and the
pseudoscalar weak decay constants with the mass of the meson, as seen in the
available experimental data. We use an effective light-front QCD-inspired
dynamical model regulated at short-distances to describe the valence component
of the pseudoscalar mesons. The experimentally known values of the mass
splittings, decay constants (from global lattice-QCD averages) and the pion
charge form factor up to 4 [GeV/c] are reasonably described by the modelComment: 27 Pages, 7 eps figures,use revtex
Weak decay constant of pseudscalar meson in a QCD-inspired model
We show that a linear scaling between the weak decay constants of
pseudoscalar and the vector mesons masses is supported by the available
experimental data. The decay constant scale as (f_m
is decay constant and M_V vector meson ground state mass). This simple form is
justified within a renormalized light-front QCD-inpired model for
quark-antiquark bound states.Comment: 4 pages, use revtex style. To appear "Brazilian Journal of Physics
(2003)
Feynman diagrams with the effective action
A derivation is given of the Feynman rules to be used in the perturbative
computation of the Green's functions of a generic quantum many-body theory when
the action which is being perturbed is not necessarily quadratic. Some
applications are discussed.Comment: Extended revised version. RevTex, 19 pages, 10 figure
Electromagnetic structure and weak decay of meson K in a light-front QCD-inspired
The kaon electromagnetic (e.m.) form factor is reviewed considering a
light-front constituent quark model. In this approach, it is discussed the
relevance of the quark-antiquark pair terms for the full covariance of the e.m.
current. It is also verified, by considering a QCD dynamical model, that a good
agreement with experimental data can be obtained for the kaon weak decay
constant once a probability of about 80% of the valence component is taken into
account.Comment: 4 pages and 1 figure eps. To appear Nucl. Phys. A (2007
Polyakov loop in chiral quark models at finite temperature
We describe how the inclusion of the gluonic Polyakov loop incorporates large
gauge invariance and drastically modifies finite temperature calculations in
chiral quark models after color neutral states are singled out. This generates
an effective theory of quarks and Polyakov loops as basic degrees of freedom.
We find a strong suppression of finite temperature effects in hadronic
observables triggered by approximate triality conservation (Polyakov cooling),
so that while the center symmetry breaking is exponentially small with the
constituent quark mass, chiral symmetry restoration is exponentially small with
the pion mass. To illustrate the point we compute some low energy observables
at finite temperature and show that the finite temperature corrections to the
low energy coefficients are suppressed due to color average of the
Polyakov loop. Our analysis also shows how the phenomenology of chiral quark
models at finite temperature can be made compatible with the expectations of
chiral perturbation theory. The implications for the simultaneous center
symmetry breaking-chiral symmetry restoration phase transition are also
discussed.Comment: 24 pages, 8 ps figures. Figure and appendix added. To appear in
Physical Review
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