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Elisabetta Pallante

Publications and source records attributed to Elisabetta Pallante.

At least 55 records · Page 3Linked to original sources
arXiv2002

Panel discussion on chiral extrapolation of physical observables

This is an approximate reconstruction of the panel discussion on chiral extrapolation of physical observables. The session consisted of brief presentations from panelists, followed by responses from the panel, and concluded with questions and comments from the floor with answers from panelists. In the following, the panelists have summarized their statements, and the ensuing discussion has been approximately reconstructed from notes.

hep-lat↗
arXiv2002

On systematic errors due to quenching in epsilon-prime over epsilon

Recently, we pointed out that chiral transformation properties of penguin operators change in the transition from unquenched to (partially) quenched QCD. As a consequence, new operators appear in (partially) quenched QCD penguins, introducing ambiguities which should be considered a quenching artifact. Here we discuss more specifically the effects of this phenomenon on the quenched Delta I=1/2 K to pi pi amplitude, and in particular, its potential numerical effect on recent lattice estimates for epsilon-prime over epsilon.

hep-lat↗
arXiv2001

Effects of Quenching and Partial Quenching on QCD Penguin Matrix Elements

We point out that chiral transformation properties of penguin operators change in the transition from unquenched to (partially) quenched QCD. The way in which this affects the lattice determination of weak matrix elements can be understood in the framework of (partially) quenched chiral perturbation theory.

hep-lat↗
arXiv2001

Effects of Quenching and Partial Quenching on Penguin Matrix Elements

In the calculation of non-leptonic weak decay rates, a "mismatch" arises when the QCD evolution of the relevant weak hamiltonian down to hadronic scales is performed in unquenched QCD, but the hadronic matrix elements are then computed in (partially) quenched lattice QCD. This mismatch arises because the transformation properties of penguin operators under chiral symmetry change in the transition from unquenched to (partially) quenched QCD. Here we discuss QCD-penguin contributions to $ΔS=1$ matrix elements, and show that new low-energy constants contribute at leading order in chiral perturbation theory in this case. In the partially quenched case (in which sea quarks are present), these low-energy constants are related to electro-magnetic penguins, while in the quenched case (with no sea quarks) no such relation exists. As a simple example, we give explicit results for $K^+\toπ^+$ and $K^0\to vacuum$ matrix elements, and discuss the implications for lattice determinations of $K\toππ$ amplitudes from these matrix elements.

hep-lat↗
arXiv2001

Using Lattice QCD and ChPT to obtain non-leptonic K-decay amplitudes

We summarize some of the difficulties that confront lattice calculations of non-leptonic kaon decay matrix elements. We review some of the methods that have been proposed to overcome these difficulties, and discuss the importance of one-loop ChPT in this respect, including the role of O(p^4) operators.

hep-lat↗
arXiv2000

Final State Interactions and eps'/eps

I discuss the role of strong final state interactions (FSI) in K \to 2πdecays. In this case strong FSI effects can be resummed [1,2] by solving the Omnès problem for K\to 2πamplitudes. Implications for the CP conserving Delta I=1/2 ratio and the direct CP violation parameter eps'/eps are also discussed.

hep-ph↗
arXiv2000

Final State Interactions in Kaon Decays

We quantify the important effect of strong final state interactions in the weak $K\to 2π$ amplitudes, using the measured $π$-$π$ phase shifts with J=0 and $I=0,2$. The main results of this analysis, with their implications for $ε'/ε$ and the $ΔI =1/2$ rule, have been already presented in a previous paper [1]. Here we provide a detailed formal derivation of those results and further discuss the Standard Model prediction of $ε'/ε$.

hep-ph↗
arXiv2000

Final State Interactions in $ε'/ε$

Strong final state interaction (FSI) effects can play a central role in the Standard Model prediction of weak $K\to 2π$ matrix elements. Here, I discuss how FSI's affect the direct CP violation parameter $\vepp / \vep$ by solving the Omnès problem for the necessary $K\to 2π$ amplitudes. The main results of this analysis have been reported in a previous paper [1] and are further discussed in Refs. [2,3]. The resulting Standard Model prediction ${Re} (\vepp / \vep) = (15\pm 5)\times 10^{-4}$ is in good agreement with the present experimental world average.

hep-ph↗
arXiv2000

On the Determination of Nonleptonic Kaon Decays from $K\toπ$ Matrix Elements

The coupling constants of the order $p^2$ low-energy weak effective lagrangian can be determined from the $K\toπ$ and $K\to 0$ weak matrix elements, choosing degenerate quark masses for the first of these. However, for typical values of quark masses in Lattice QCD computations, next-to-leading $O(p^4)$ corrections are too large to be ignored, and will need to be included in future analyses. Here we provide the complete $O(p^4)$ expressions for these matrix elements obtained from Chiral Perturbation Theory, valid for partially quenched QCD with $N$ degenerate sea quarks. Quenched QCD corresponds to the special case N=0. We also discuss the role of the $η'$ meson in some detail, and we give numerical examples of the size of chiral logarithms.

hep-lat↗
arXiv1999

Strong Enhancement of $ε'/ε$ Through Final State Interactions

We quantify the important effect of strong final state interactions in the weak $K\to2π$ amplitudes, using the measured $π$--$π$ phase shifts with J=0 and $I=0,2$. The final rescattering of the two pions provides a strong enhancement of the $ΔI =1/2$ amplitude, which so far has been neglected in the theoretical predictions of $ε'/ε$. This correction increases the Standard Model prediction of $ε'/ε$ to values in good agreement with the experimental measurements.

hep-ph↗
arXiv1999

On $K\toππ$ Decays in Quenched and Unquenched Chiral Perturbation Theory

We calculate the logarithmic corrections to the matrix elements for $K^+\toπ^+$ and $K\to$vacuum (which are used on the lattice to determine $K\toππ$ amplitudes), in one-loop quenched and unquenched Chiral Perturbation Theory. We find that these corrections can be large. We also discuss, and present some results for, the direct determination of $K\toππ$ amplitudes. In particular, we address effects from choosing $m_s=m_d$ and vanishing external spatial momenta, finite volume and quenching. In the quenched octet case, we find enhanced finite-volume contributions which may make numerical estimates of this matrix element unreliable for large volumes.

hep-lat↗
arXiv1998

Quenched Chiral Perturbation Theory to one loop

We calculate the divergences of the generating functional of quenched Chiral Perturbation Theory at one loop, and renormalize the theory by an appropriate definition of the counterterms. We show that the quenched chiral logarithms can be reabsorbed in the renormalization of the B_0 parameter which, at lowest order, is proportional to the vacuum expectation value of the scalar quark density. Finally, we calculate several quantities at one loop to analyze the modifications induced by quenching in the finite part of the one-loop corrections. We point out that some of the finite loop corrections may diverge in the chiral limit.

hep-lat↗
arXiv1998

Obtaining K to pi pi from Off-Shell K to pi Amplitudes

We properly define off-shell $K\toπ$ transition amplitudes and use them to extract information for on-shell $K\toππ$ amplitudes within Chiral Perturbation Theory. At order $p^2$ in the chiral expansion all three parameters of weak interaction can be determined. At order $p^4$ we are able to fix eleven additional constants out of thirteen contributing to off-shell $K\toπ$ transitions, which leaves four undetermined constants in the on-shell $K\toππ$ amplitudes. All ${\cal O}(p^4)$ contributions have been exactly derived with $m_π^2\ne 0$. We finally discuss the weak mass term issue and find contributions to on-shell $ΔS=\pm 1$ Kaon decays, in particular to transitions like $K_L \to γγ$, $K_L \to μ^+ μ^-$ and $K_S \to π^0 γγ$ at the lowest non-zero order.

hep-ph↗
arXiv1997

Pion loops in quenched Quantum Chromodynamics

We calculate the divergences of the generating functional of quenched Chiral Perturbation Theory to one loop for a generic number of flavours. The flavour number dependence of our result enlightens the mechanism of quark loop cancellation in the quenched effective theory for any Green function or S matrix element. We also apply our results to $ππ$ scattering and evaluate the coefficient of the chiral log in the S-wave scattering lengths for the quenched case.

hep-lat↗
arXiv1996

The mass of the scalar boson beyond the large-N_c limit

Within the framework of the $1/N_c$ expansion of four-fermion interaction models, we analyse the next to leading $1/N_c$ corrections to the well known large-$N_c$ result $M_S=2M_Q$ where $M_S$ is the mass of the scalar boson and $M_Q$ is the constituent quark mass. The calculation is performed in the Extended Nambu-Jona Lasinio (ENJL) model which is suitable for describing low energy hadron properties. We treat the model as fully non renormalizable and discuss the comparison with approaches based on the equivalence with renormalizable Yukawa type models. We consider both the $G_V=0$ and the $G_V\neq 0$ cases with $n_f=2$ flavours and study the dependence upon the regularization scheme. We find that pure next-to-leading $1/N_c$ corrections are large and negative, while a partially resummed treatment can induce positive and smaller corrections. A triplet-singlet states' splitting is observed.

hep-ph↗
arXiv1996

Weak long distance contributions to the neutron and proton electric dipole moments

We evaluate the long distance weak contribution to the neutron and proton electric dipole moments using an effective Lagrangian framework. We estimate the coefficients needed by a factorization hypothesis and additional assumptions on $γ_5$ terms in the baryon lagrangian. We obtain $|d_e^n|\approx 5\times 10^{-32}$ e$\cdot$cm and $|d_e^p|\approx 4\times 10^{-32}$ e$\cdot$cm. The former estimate is similar to the quark model estimates done previously.

hep-ph↗
arXiv1996

Analysis of the Hadronic Light-by-Light Contributions to the Muon $g-2$

We calculate the hadronic light-by-light contributions to the muon $g-2$. We use both $1/N_c$ and chiral counting to organize the calculation. Then we calculate the leading and next-to-leading order in the $1/N_c$ expansion low energy contributions using the Extended Nambu--Jona-Lasinio model as hadronic model. We do that to all orders in the external momenta and quark masses expansion. Although the hadronic light-by-light contributions to muon $g-2$ are not saturated by these low energy contributions we estimate them conservatively. A detailed analysis of the different hadronic light-by-light contributions to muon $g-2$ is done. The dominant contribution is the twice anomalous pseudoscalar exchange diagram. The final result we get is $a_μ^{\rm light-by-light}= (-9.2\pm3.2 ) \cdot 10^{-10}$. This is between two and three times the expected experimental uncertainty at the forthcoming BNL muon $g-2$ experiment.

hep-ph↗