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G. Isidori

Publications and source records attributed to G. Isidori.

At least 55 records · Page 3Linked to original sources
arXiv2004

The rare decay B --> X_s l^+ l^- to NNLL precision for arbitrary dilepton invariant mass

We present a new phenomenological analysis of the inclusive rare decay $B \to X_s \ell^+\ell^-$. In particular, we present the first calculation of the NNLL contributions due to the leading two-loop matrix elements, evaluated for arbitrary dilepton invariant mass. This allows to obtain the first NNLL estimates of the dilepton mass spectrum and the lepton forward-backward asymmetry in the high $ M^2_{\ell^+ \ell^-}$ region, and to provide an independent check of previously published results in the low $ M^2_{\ell^+ \ell^-}$ region. The numerical impact of these NNLL corrections in the high-mass region ($ M^2_{\ell^+ \ell^-} > 14.4 GeV^2$) amounts to -13% in the integrated rate, and leads to a reduction of the scale uncertainty to $\pm 3%$. The impact of non-perturbative contributions in this region is also discussed in detail.

hep-ph↗
arXiv2003

The CKM Matrix and the Unitarity Triangle

This report contains the results of the Workshop on the CKM Unitarity Triangle, held at CERN on 13-16 February 2002 to study the determination of the CKM matrix from the available data of K, D, and B physics. This is a coherent document with chapters covering the determination of CKM elements from tree level decays and K and B meson mixing and the global fits of the unitarity triangle parameters. The impact of future measurements is also discussed.

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arXiv2002

NNLL QCD Corrections to the Decay $B \to X_s \ell^+ \ell^-$

We briefly discuss the status of the NNLL QCD calculations in the inclusive rare B decay $B \to X_s \ell^+ \ell^-$. Two important ingredients, the two-loop matrix elements of the four quark operator ${\cal O}_2$ and the bremsstrahlung contributions, were quite recently finalised. The new contributions significantly improve the sensitivity of the inclusive decay $B \to X_s l^+ l^-$ decay in testing extensions of the standard model in the sector of flavour dynamics; for instance the two-loop calculation cuts the low- scale uncertainty in half and the bremsstrahlung calculation leads to a 10% shift of the position of the zero of the forward- backward asymmetry.

hep-ph↗
arXiv2002

Forward--Backward Asymmetry in B -> X_s l^+ l^- at the NNLL Level

We report the results of a new calculation of soft-gluon corrections in B -> X_s l^+ l^- decays. In particular, we present the first calculation of bremsstrahlung and corresponding virtual terms to the lepton forward-backward asymmetry, which allows us to systematically include all contributions to this observable beyond the lowest non-trivial order. The new terms are important, for instance the position of the zero of the asymmetry receives corrections of O(10%). Using a different method, we also provide an independent check of recently published results on bremsstrahlung and infrared virtual corrections to the dilepton-invariant mass distribution.

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arXiv2002

Minimal Flavour Violation: an effective field theory approach

We present a general analysis of extensions of the Standard Model which satisfy the criterion of Minimal Flavour Violation (MFV). We define this general framework by constructing a low-energy effective theory containing the Standard Model fields, with one or two Higgs doublets and, as the only source of SU(3)^5 flavour symmetry breaking, the background values of fields transforming under the flavour group as the ordinary Yukawa couplings. We analyse present bounds on the effective scale of dimension-six operators, which range between 1 and 10 TeV, with the most stringent constraints imposed by B -> X_s gamma. In this class of theories, it is possible to relate predictions for FCNC processes in B physics to those in K physics. We compare the sensitivity of various experimental searches in probing the hypothesis of MFV. Within the two-Higgs-doublet scenario, we develop a general procedure to obtain all tan(beta)-enhanced Higgs-mediated FCNC amplitudes, discussing in particular their impact in B -> l^+l^-, Delta M_B and B -> X_s gamma. As a byproduct, we derive some two-loop tan(beta)-enhanced supersymmetric contributions to B -> X_s gamma previously unknown.

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arXiv2001

Kaon physics with a high-intensity proton driver

We study opportunities for future high-precision experiments in kaon physics using a high-intensity proton driver, which could be part of the front-end of a muon storage ring complex. We discuss in particular the rare decays $K_L\toπ^0ν\barν$, $K^+\toπ^+ν\barν$, $K_L\toπ^0e^+e^-$, and lepton-flavour violating modes such as $K_L\toμe$ and $K\toπμe$. The outstanding physics potential and long-term interest of these modes is emphasized. We review status and prospects of current and planned experiments for the processes under consideration, and indicate possible improvements and strategies towards achieving the necessary higher sensitivity. Finally, we outline the machine requirements needed to perform these high-precision kaon experiments in the context of a muon storage ring facility.

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arXiv2000

Phenomenology of non-standard Z couplings in exclusive semileptonic b -> s transitions

The rare decays $B\to K^{(*)}\ell^+\ell^-$, $B\to K^{(*)}ν\barν$ and $B_s\toμ^+μ^-$ are analyzed in a generic scenario where New Physics effects enter predominantly via $Z$ penguin contributions. We show that this possibility is well motivated on theoretical grounds, as the $\bar sbZ$ vertex is particularly susceptible to non-standard dynamics. In addition, such a framework is also interesting phenomenologically since the $\bar sbZ$ coupling is rather poorly constrained by present data. The characteristic features of this scenario for the relevant decay rates and distributions are investigated. We emphasize that both sign and magnitude of the forward-backward asymmetry of the decay leptons in $\bar B\to \bar K^*\ell^+\ell^-$, ${\cal A}^{(\bar B)}_{FB}$, carry sensitive information on New Physics. The observable ${\cal A}^{(\bar B)}_{FB}+{\cal A}^{(B)}_{FB}$ is proposed as a useful probe of non-standard CP violation in $\bar sbZ$ couplings.

hep-ph↗
arXiv2000

Electromagnetism in nonleptonic weak interactions

We construct a low-energy effective field theory that permits the complete treatment of isospin-breaking effects in nonleptonic weak interactions to next-to-leading order. To this end, we enlarge the chiral Lagrangian describing strong and Delta S=1 weak interactions by including electromagnetic terms with the photon as additional dynamical degree of freedom. The complete and minimal list of local terms at next-to-leading order is given. We perform the one-loop renormalization at the level of the generating functional and specialize to K -> pi pi decays.

hep-ph↗
arXiv2000

Final State Interactions and epsilon'/epsilon: A Critical Look

We critically analyze recent attempts to include final state interaction (FSI) effects in the calculation of the CP violating ratio epsilon'/epsilon. In particular the approach of using the Muskhelishvili-Omnes equation for the decay amplitudes is examined. We find that the values of the dispersive correction factors are very sensitive to initial conditions which are, at present, out of control, and demonstrate that the claimed large enhancement of epsilon'/epsilon through FSI is questionable. We propose, instead, a different implementation of this approach which may be useful to lattice determinations of weak amplitudes.

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arXiv1999

Direct CP violation in K->3pi decays induced by SUSY chromomagnetic penguins

An analysis of the CP violating asymmetry in $K^\pm \to (3π)^\pm$ decays in the Standard Model and, by means of the mass insertion approximation, in a wide class of possible supersymmetric extensions, is presented. We find that the natural order of magnitude for this asymmetry is $\cO(10^{-5})$ in both cases. Within supersymmetric models effects as large as $\cO(10^{-4})$ are possible, but only in a restricted range of the relevant parameters.

hep-ph↗
arXiv1999

Supersymmetric contributions to direct CP violation in K -> pi pi gamma decays

We analyze the supersymmetric contributions to direct-CP-violating observables in $K \to ππγ$ decays induced by gluino-mediated magnetic-penguin operators. We find that $\epsp_{+-γ}$ and the differential width asymmetry of $K^\pm \to π^\pm π^0 γ$ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where $\epsp/\eps$ is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in $|ΔS|=1$ transitions, complementary to $\epsp/\eps$ and rare decays.

hep-ph↗
arXiv1999

Connections between epsilon'/epsilon and Rare Kaon Decays in Supersymmetry

We analyze the rare kaon decays $K_L \to π^0 ν\bar ν$, $K^+ \to π^+ ν\bar ν$, $K_L \to π^0 e^+ e^-$ and $K_L \to μ^+ μ^-$ in conjunction with the CP violating ratio $ε'/ε$ in a general class of supersymmetric models in which $Z$- and magnetic-penguin contributions can be substantially larger than in the Standard Model. We point out that radiative effects relate the double left-right mass insertion to the single left-left one, and that the phenomenological constraints on the latter reflect into a stringent bound on the supersymmetric contribution to the $Z$ penguin. Using this bound, and those coming from recent data on $ε'/ε$ we find ${\rm BR}(K_L \to π^0 ν\bar ν)\lsim 1.2\cdot 10^{-10}$, ${\rm BR}(K^+ \to π^+ ν\bar ν)\lsim 1.7\cdot 10^{-10}$, ${\rm BR}(K_L \to π^0 e^+ e^-)_{\rm dir}\lsim 2.0\cdot 10^{-11}$, assuming the usual determination of the CKM parameters and neglecting the possibility of cancellations among different supersymmetric effects in $ε'/ε$. Larger values are possible, in principle, but rather unlikely. We stress the importance of a measurement of these three branching ratios, together with improved data and improved theory of $ε'/ε$, in order to shed light on the realization of various supersymmetric scenarios. We reemphasize that the most natural enhancement of $ε'/ε$, within supersymmetric models, comes from chromomagnetic penguins and show that in this case sizable enhancements of $BR(K_L \to π^0 e^+ e^-)_{\rm dir}$ can also be expected.

hep-ph↗
arXiv1999

eta -> pi^+ pi^- pi^0 gamma in Chiral Perturbation Theory

We analyse the radiative decay $η\to π^+π^- π^0γ$ in the low--energy expansion of the Standard Model. We employ the notion of ``generalized bremsstrahlung'' to take full advantage of the theoretical and experimental information on the corresponding non-radiative $η\to 3 π$ decay. The direct emission amplitude of ${\cal O}(p^4)$ is due to one-loop diagrams with intermediate pions (isospin violating) and kaons (isospin conserving). The isospin conserving contributions to direct emission, including vector meson exchange appearing at ${\cal O}(p^6)$, are suppressed.

hep-ph↗
arXiv1998

The Decays $K \to π\ell^+ \ell^-$ beyond Leading Order in the Chiral Expansion

We present a model-independent analysis of $K^+\toπ^+\ell^+\ell^-$ and $K_S\toπ^0\ell^+\ell^-$ decays, including $K\to 3 π$ unitarity corrections and a general decomposition of the dispersive amplitude. From the existing data on $K^+\toπ^+ e^+ e^-$ we predict the ratio $R= B(K^+\toπ^+μ^+μ^-)/B(K^+\toπ^+ e^+ e^-)$ to be larger than 0.23, in slight disagreement with the recent measurement $R = 0.167 \pm 0.036$. Consequences for the $K^\pm \toπ^\pm e^+ e^-$ charge asymmetries and for the $K_L\toπ^0 e^+ e^-$ mode are also discussed.

hep-ph↗
arXiv1998

Searching for K_L -> pi^0 nu nubar at a Phi-factory

The perspectives of a search for the rare decay $K_L\toπ^0ν\barν$ at a Phi-factory are discussed. After a general analysis, we focus on the realistic case of KLOE and DAFNE, showing that limits of the order of $10^{-9}$ on BR($K_L\toπ^0ν\barν$) are achievable in the next few years. We also discuss the theoretical implications of this kind of measurements.

hep-ph↗
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

Can we extract short-distance information from B(K_L -> mu^+ mu^-)?

A new analysis of the long-distance two-photon dispersive amplitude of K_L -> mu^+ mu^- is presented. We introduce a phenomenological parameterization of the K_L -> gamma^* gamma^* form factor, constrained at low energies by K_L -> gamma l^+ l^- (l = e,mu) data and at high energies by perturbative QCD. Using this form factor we provide a reliable estimate of magnitude and relative uncertainty of the two-photon dispersive contribution to K_L -> mu^+ mu^-. We finally discuss the implications of this analysis for the extraction of short-distance information from B(K_L -> mu^+ mu^-).

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