arXiv subjects

Irinel Caprini

Publications and source records attributed to Irinel Caprini.

59 records · Page 4Linked to original sources

arXiv1999

Dispersive and chiral symmetry constraints on the light meson form factors

The form factors of the light pseudoscalar mesons are investigated in a dispersive formalism based on hadronic unitarity, analyticity and the OPE expansion of the QCD Green functions. We propose generalizations of the original mathematical techniques, suitable for including additional low energy information provided by experiment or Chiral Perturbation Theory (CHPT). The simultaneous treatment of the electroweak form factors of the $π$ and $K$ mesons allows us to test the consistency with QCD of a low energy CHPT theorem. By applying the formalism to the pion electromagnetic form factor, we derive quite strong constraints on the higher Taylor coefficients at zero momentum, using information about the phase and the modulus of the form factor along a part of the unitarity cut.

hep-ph↗

arXiv1999

Borel summation and momentum-plane analyticity in perturbative QCD

We derive a compact expression for the Borel sum of a QCD amplitude in terms of the inverse Mellin transform of the corresponding Borel function. The result allows us to investigate the momentum-plane analyticity properties of the Borel-summed Green functions in perturbative QCD. An interesting connection between the asymptotic behaviour of the Borel transform and the Landau singularities in the momentum plane is established. We consider for illustration the polarization function of massless quarks and the resummation of one-loop renormalon chains in the large-$β_0$ limit, but our conclusions have a more general validity.

hep-ph↗

arXiv1998

Accelerated convergence of perturbative QCD by optimal conformal mapping of the Borel plane

The technique of conformal mappings is applied to enlarge the convergence of the Borel series and to accelerate the convergence of Borel-summed Green functions in perturbative QCD. We use the optimal mapping, which takes into account the location of all the singularities of the Borel transform as well as the present knowledge about its behaviour near the first branch points. The determination of α_{s}(m_τ) from the hadronic decay rate of the τ-lepton is discussed as an illustration of the method.

hep-ph↗

arXiv1996

Improved Bounds for the Slope and Curvature of $\bar B\to D^{(*)}\ell\barν$ Form Factors

We derive a theoretically allowed domain for the slope $\widehat\varrho^2$ and curvature $\widehat c$ of the physical form factor appearing in the decay $\bar B\to D^*\ell\barν$. Using heavy-quark symmetry, we relate this function to a particular $\bar B \to D$ form factor free of ground-state $B_c$ poles below the threshold for $B D$ production, for which almost model-independent constraints are derived from QCD using unitarity and analyticity. Our results are of interest for the extraction of $|V_{cb}|$ from the recoil spectrum in exclusive semileptonic $B$ decays. Making conservative estimates of the theoretical uncertainties, we find (up to $1/m_Q$ corrections) $\widehat\varrho^2<1.11$ and $\widehat c\simeq 0.66\widehat\varrho^2-0.11$. We also derive the corresponding bounds for the form factor in the decay $\bar B\to D\ell\barν$.

hep-ph↗

arXiv1994

Slope of the Isgur-Wise Function from a QSSR Constraint on the $ΥB\bar{B}$ Couplings

We derive optimal upper and lower bounds on the slope of the Isgur-Wise function at the zero recoil point in terms of the sum of the $ΥB\bar{B}$ couplings, estimated recently from a $QCD$ Spectral Sum Rule ($QSSR$). The problem is solved by means of a duality theorem in functional optimization. Optimal correlations between the slope and the convexity parameters of the Isgur-Wise function with the same input are also obtained.

hep-ph↗