Searcharxiv⌕ Search

arXiv subjects

E. Pallante

Publications and source records attributed to E. Pallante.

33 records · Page 2Linked to original sources
arXiv2003

Finite-Volume Two-Pion Amplitudes in the I=0 Channel

We perform a calculation in one-loop chiral perturbation theory of the two-pion matrix elements and correlation functions of an I=0 scalar operator, in finite and infinite volumes for both full and quenched QCD. We show that major difficulties arise in the quenched theory due to the lack of unitarity. Similar problems are expected for quenched lattice calculations of $K \to ππ$ amplitudes with $ΔI=1/2$. Our results raise the important question of whether it is consistent to study $K\toππ$ amplitudes beyond leading order in chiral perturbation theory in quenched or partially quenched QCD.

hep-lat↗
arXiv2002

K^+ -> pi^+ pi^0 Decays on Finite Volumes and at Next-to-Leading Order in the Chiral Expansion

We present the ingredients necessary for the determination of physical K->pi pi decay amplitudes for Delta I=3/2 transitions, from lattice simulations at unphysical kinematics and the use of chiral perturbation theory at next-to-leading order. In particular we derive the expressions for the matrix elements , where O_W is one of the operators appearing in the Delta S=1 weak Hamiltonian, in terms of low-energy constants at next-to-leading order in the chiral expansion. The one-loop chiral corrections are evaluated for arbitrary masses and momenta, both in full QCD and in the quenched approximation. We also investigate the finite-volume effects in this procedure.

hep-lat↗
arXiv2002

Effects of Quenching in ΔI=1/2 Kaon Decays

We present the inconsistencies which arise in quenched QCD in $ΔI=1/2$ non-leptonic kaon decays using chiral perturbation theory (ChPT) to one loop. In particular we discuss how the lack of unitarity of the quenched theory invalidates the usual methods for the extraction of matrix elements from correlation functions.

hep-lat↗
arXiv2002

$K^{+}\toπ^{+}π^{0}$ decays at next-to-leading order in the chiral expansion on finite volumes

We present the ingredients for determining $K^{+}\toπ^{+}π^{0}$ matrix elements via the combination of lattice QCD and chiral perturbation theory ($χ$PT). By simulating these matrix elements at unphysical kinematics, it is possible to determine all the low-energy constants (LECs) for constructing the physical $K^{+}\toπ^{+}π^{0}$ amplitudes at next-to-leading order (NLO) in the chiral expansion. In this work, the one-loop chiral corrections are calculated for arbitrary meson four-momenta, in both $χ$PT and quenched $χ$PT (q$χ$PT), and the finite-volume effects are studied.

hep-lat↗
arXiv2001

epsilon'/eps in the Standard Model

We overview the detailed analysis of epsilon'/epsilon within the Standard Model, presented in ref. 1. When all sources of large logarithms are considered, both at short and long distances, it is possible to perform a reliable Standard Model estimate of epsilon'/epsilon. The strong S-wave rescattering of the final pions has an important impact on this observable. The Standard Model prediction is found to be Re(epsilon'/epsilon) =(1.7 +- 0.9)*10^{-3}, in good agreement with the most recent experimental measurements. A better estimate of the strange quark mass would reduce the uncertainty to about 30%.

hep-ph↗
arXiv2001

The Standard Model Prediction for epsilon'/epsilon

We present a detailed analysis of epsilon'/epsilon within the Standard Model, taking into account the strong enhancement through final-state interactions identified in refs. [1] and [2]. The relevant hadronic matrix elements are fixed at leading order in the 1/N_C expansion, through a matching procedure between the effective short-distance Lagrangian and its corresponding low-energy description in Chiral Perturbation Theory. All large logarithms are summed up, both at short and long distances. Two different numerical analyses are performed, using either the experimental or the theoretical value for epsilon, with compatible results. We obtain Re(epsilon'/epsilon) = (1.7 +- 0.9)*10^{-3}. The error is dominated by the uncertainty in the value of the strange quark mass and the estimated corrections from unknown 1/N_C-suppressed local contributions. A better estimate of the strange quark mass would reduce the uncertainty to about 30%. The Standard Model prediction agrees with the present experimental world average Re(epsilon'/epsilon) =(1.93 +- 0.24)*10^{-3}.

hep-ph↗
arXiv2000

The role of final state interactions in epsilon'/epsilon

The Standard Model prediction for epsilon'/epsilon is updated, taking into account the chiral loop corrections induced by final state interactions. The resulting value, epsilon'/epsilon = (17\pm 6)\times 10^{-4}, is in good agreement with present measurements.

hep-ph↗
arXiv1999

The generating functional for hadronic weak interactions and its quenched approximation

We derive the generating functional of $|ΔS| =1, 2$ hadronic weak interactions at one loop for a generic number of flavours and its counterpart in the quenched approximation. A systematic analysis of the ultraviolet divergences in the full theory (with and without a singlet dynamical field) and in the quenched case is performed. We show that the quenched chiral logarithms in the presence of weak interactions amount to a redefinition of the weak mass term in the $ΔS=\pm 1$ weak effective Lagrangian at leading order. Finally, we apply the results to $B_K$ and $K\toππ$ matrix elements with $ΔI=1/2,3/2$ to analyze the modifications induced by quenching on the coefficients of chiral logarithms in the one-loop corrections.

hep-lat↗
arXiv1998

The quenched generating functional for hadronic weak interactions

The ultraviolet behaviour of the generating functional for hadronic weak interactions with $|ΔS| =1, 2$ is investigated to one loop for a generic number of flavours and in the quenched approximation. New quenched chiral logarithms generated by the weak interactions can be accounted for via a redefinition of the weak mass term in the $ΔS=\pm 1$ weak effective Lagrangian at leading order. Finally, we illustrate how chiral logarithms are modified by the quenched approximation in $K\toππ$ matrix elements with $ΔI=1/2$ and 3/2.

hep-lat↗
arXiv1997

Report of the Working Group on Goldstone Boson Production and Decay

This is the summary of the working group on Goldstone Boson Production and Decay of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997. For the production aspects we discuss $π^0$ and $η$ production in nucleon-nucleon collisions and the behaviour of hadrons in various sum rules. For the decays we present a discussion on various $K$, $η$ and $π$ decay channels. Other aspects discussed are a new treatment of meson-meson scattering, the light-by-light contribution to the muon anomalous magnetic moment and progress in various aspects of the $p^6$ generating functional in the mesonic sector.

hep-ph↗
arXiv1997

Quenched Chiral Perturbation Theory to one loop

The divergences of the generating functional of quenched Chiral Perturbation theory (qCHPT) to one loop are computed in closed form. We show how the quenched chiral logarithms can be reabsorbed in the renormalization of the $B_0$ parameter of the leading order Lagrangian. Finally, we do the chiral power counting for the quenched case and show that also finite loop corrections may diverge in the chiral limit.

hep-lat↗
arXiv1994

The S parameter in a technicolour model with explicit chiral symmetry breaking

We derive the S parameter of the electroweak radiative corrections in a scaled-QCD technicolour and using a Nambu-Jona Lasinio model for hadronic low energy interactions. In this framework deviations from low energy QCD can be quantitatively deduced. We induce explicit chiral symmetry breaking in the NJL model through the current-quarks mass term. It is shown that the prediction for the S parameter can be sensitively reduced respect to the chiral prediction.

hep-ph↗
arXiv1994

The hadronic vacuum polarization contribution to the muon g-2 in the quark-resonance model

The hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is parametrized by using the quark-resonance model formulated in \cite{QR}. In this context a recent prediction obtained within the ENJL model \cite{RAF} can be affected by two additional contributions: the next to leading corrections in the inverse cutoff expansion and the gluonic corrections. Motivated by the necessity of reaching a highly accurate theoretical prediction of the hadronic contribution to the muon g-2, we study in detail both the effects.

hep-ph↗
arXiv1994

Quark-Resonance model

We construct an effective Lagrangian for low energy hadronic interactions through an infinite expansion in inverse powers of the low energy cutoff $Λ_χ$ of all possible chiral invariant non-renormalizable interactions between quarks and mesons degrees of freedom. We restrict our analysis to the leading terms in the $1/N_c$ expansion. The effective expansion is in $(μ^2/\cutoff^2 )^P \ln (\cutoff^2/μ^2 )^Q$. Concerning the next-to-leading order, we show that, while the pure $μ^2/\cutoff^2 $ corrections cannot be traced back to a finite number of non renormalizable interactions, those of order $(μ^2/\cutoff^2 ) \ln (\cutoff^2/μ^2 )$ receive contributions from a finite set of $1/\cutoff^2$ terms. Their presence modifies the behaviour of observable quantities in the intermediate $Q^2$ region. We explicitely discuss their relevance for the two point vector currents Green's function.

hep-ph↗