11,759 research outputs found
Form factors of radiative pion decays in nonlocal chiral quark models
We study the radiative pion decay pi+ -> e+ nu_e gamma within nonlocal chiral
quark models that include wave function renormalization. In this framework we
analyze the momentum dependence of the vector form factor F_V(q^2), and the
slope of the axial-vector form factor F_A(q^2) at threshold. Our results are
compared with available experimental information and with the predictions given
by the NJL model. In addition we calculate the low energy constants l_5 and
l_6, comparing our results with the values obtained in chiral perturbation
theory.Comment: 22 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1011.640
Characteristics of the chiral phase transition in nonlocal quark models
The characteristics of the chiral phase transition are analyzed within the
framework of chiral quark models with nonlocal interactions in the mean field
approximation. In the chiral limit, we develop a semi-analytic framework which
allows us to explicitly determine the phase transition curve, the position of
the critical points, some relevant critical exponents, etc. For the case of
finite current quark masses, we show the behavior of various thermodynamical
and chiral response functions across the phase transition.Comment: 19 pages, 5 figures. Figures 1 and 2 modified, references added,
minor changes in the presentation and in the discussion of results. Accepted
for publication in Phys. Rev.
Color neutrality effects in the phase diagram of the PNJL model
The phase diagram of a two-flavor Polyakov loop Nambu-Jona-Lasinio model is
analyzed imposing the constraint of color charge neutrality. Main effects of
this constraint are a shrinking of the chiral symmetry breaking (chiSB) domain
in the T-mu plane, a shift of the critical point to lower temperatures and a
coexistence of chiSB and two-flavor superconducting phases. The effects can be
understood in view of the presence of a nonvanishing color chemical potential
mu_8, which is necessary to compensate the color charge density rho_8 induced
by the nonvanishing Polyakov-loop mean field phi_3.Comment: 8 pages, 4 figures, figures added, minor text modification
Double neutral pion photoproduction at threshold
We consider the chiral expansion of the threshold amplitude for the reaction
to order . We substantiate a
claim that this photoproduction channel is significantly enhanced close to
threshold due to pion loops. A precise measurement of the corresponding cross
sections is called for which allows to test chiral perturbation theory.Comment: 8 pp, LaTe
Exceptional orthogonal polynomials and the Darboux transformation
We adapt the notion of the Darboux transformation to the context of
polynomial Sturm-Liouville problems. As an application, we characterize the
recently described Laguerre polynomials in terms of an isospectral
Darboux transformation. We also show that the shape-invariance of these new
polynomial families is a direct consequence of the permutability property of
the Darboux-Crum transformation.Comment: corrected abstract, added references, minor correction
Cauchy-characteristic Evolution of Einstein-Klein-Gordon Systems
A Cauchy-characteristic initial value problem for the Einstein-Klein-Gordon
system with spherical symmetry is presented. Initial data are specified on the
union of a space-like and null hypersurface. The development of the data is
obtained with the combination of a constrained Cauchy evolution in the interior
domain and a characteristic evolution in the exterior, asymptotically flat
region. The matching interface between the space-like and characteristic
foliations is constructed by imposing continuity conditions on metric,
extrinsic curvature and scalar field variables, ensuring smoothness across the
matching surface. The accuracy of the method is established for all ranges of
, most notably, with a detailed comparison of invariant observables
against reference solutions obtained with a calibrated, global, null algorithm.Comment: Submitted to Phys. Rev. D, 16 pages, revtex, 7 figures available at
http://nr.astro.psu.edu:8080/preprints.htm
Quasi-exact solvability beyond the SL(2) algebraization
We present evidence to suggest that the study of one dimensional
quasi-exactly solvable (QES) models in quantum mechanics should be extended
beyond the usual \sla(2) approach. The motivation is twofold: We first show
that certain quasi-exactly solvable potentials constructed with the \sla(2)
Lie algebraic method allow for a new larger portion of the spectrum to be
obtained algebraically. This is done via another algebraization in which the
algebraic hamiltonian cannot be expressed as a polynomial in the generators of
\sla(2). We then show an example of a new quasi-exactly solvable potential
which cannot be obtained within the Lie-algebraic approach.Comment: Submitted to the proceedings of the 2005 Dubna workshop on
superintegrabilit
- …