Status of the Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment
We review the present status of the hadronic light-by-light contribution to muon g-2 and critically compare recent calculations.
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arXiv subjects
Joaquim Prades
Publications and source records attributed to Joaquim Prades.
|V_us| and m_s from hadronic tau decays
Recent progress in the determination of |V_us| employing strange hadronic tau-decay data are reported. This includes using the recent OPAL update of the strange spectral function, as well as augmenting the dimension-two perturbative contribution with the recently calculated order alpha_s^3 term on the theory side. These updates result in |V_us| = 0.2220 +- 0.0033, with the uncertainty presently being dominated by experiment, and already being competitive with the standard extraction from K_e3 decays and other new proposals to determine |V_us|. In view of the ongoing work to analyse tau-decay data at the B-factories BaBar and Belle, as well as future results from BESIII, the error on |V_us| from tau decays is expected to be much reduced in the near future.
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K -> 3 pi Final State Interactions at NLO in CHPT and Cabibbo's Proposal to Measure a_0-a_2
We present the analytical results for the K -> 3 pi final state interactions at next-to-leading order (NLO) in CHPT. We also study the recent Cabibbo's proposal to measure the pi-pi scattering lenghts combination a_0-a_2 from the cusp effect in the pi^0-pi^0 energy spectrum at threshold for K^+ -> pi^0 pi^0 pi^+ and K_L -> pi^0 pi^0 pi^0$, and give the relevant formulas to describe it at NLO. For that, we use the NLO CHPT expression to fit the real part of K -> 3 pi to data while the pi-pi scattering lenghts are treated non-perturbatively. Using them, we make a quantitative estimate of the theoretical uncertaintity of the a_0-a_2 determination at NLO in our approach and obtain that it is not smaller than 5 % if added quadratically and 7 % if linearly for K^+ -> pi^0 pi^0 pi^+. One gets similar theoretical uncertainties if the neutral K_L -> pi^0 pi^0 pi^0 decay data below threshold are used instead. For this decay, there are very large theoretical uncertainties above threshold due to cancellations and data above threshold cannot be used to get the scattering lenghts. All the numbers we present are in the isospin limit apart of two-pion phase space factors which are physical. We compare our results for the cusp effect with Cabibbo and Isidori's results and discuss the differences and agreements. We also comment on the apperance of the singularity at the K -> 3 pi pseudo-threshold s=(m_K-m_pi)^2 in the discontinuity that defines the cusp.
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Measuring the a0-a2 pion scattering lengths through K to 3 pi decays
We discuss the recent Cabibbo's proposal to measure the pion-pion scattering lengths combination a0-a2 from the cusp effect in the pi0-pi0 energy spectrum at threshold for K+ to (pi0 pi0 pi+) and KL to (pi0 pi0 pi0). We estimate the theoretical uncertainty of the a0-a2 determination at NLO in our approach and obtain that it is not smaller than 5% for K+ to (pi0 pi0 pi+). One gets similar theoretical uncertainties if the neutral KL to (pi0 pi0 pi0) decay data below threshold are used instead. For this decay, there are very large theoretical uncertainties above threshold due to cancellations and data above threshold cannot be used to get the scattering lengths.
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|V_us| from Strange Hadronic Tau Data
We report on recent work to determine the CKM matrix element |V_{us}| using strange hadronic τdecay data. We use the recent OPAL update of the strange spectral function, while on the theory side we update the dimension-two perturbative contribution including the recently calculated α_s^3 terms. Our result |V_{us}|=0.2220 \pm 0.0033 is already competitive with the standard extraction from K_{e3} decays and other new proposals to determine |V_{us}|. The actual uncertainty on |V_{us}| from τdata is dominated largely by experiment and will eventually be much reduced by B-factories and future τ-charm factory data, providing one of the most accurate determinations of this Standard Model parameter.
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Meson-Baryon Effective Chiral Lagrangians to O(q^3)
We construct the complete and minimal O(q^2) and O(q^3) three-flavour Lorentz invariant chiral meson-baryon Lagrangians for the first time in the literature. We compare with previous three-flavour studies reducing the number of independent monomials and adding new ones that were missing.
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The $B_K$ Kaon Parameter in the Chiral Limit
We introduce four-point functions in the hadronic ladder resummation approach to large $N_c$ QCD Green functions. We determine the relevant one to calculate the $B_K$ kaon parameter in the chiral limit. This four-point function contains both the large momenta QCD OPE and the small momenta ChPT at NLO limits, analytically. We get $\hat B_K^χ= 0.38 \pm 0.15$. We also give the ChPT result at NLO for the relevant four-point function to calculate $B_K$ outside the chiral limit, while the leading QCD OPE is the same as the chiral limit one.
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Reply to Comment on "Surprises in threshold antikaon-nucleon physics"
In their Comment, Borasoy et al. [arXiv:hep-ph/0512279], criticize our results [PRL 95 (2005) 172502] that accommodate both scattering data and the new accurate measurement by DEAR of the shift and width of kaonic hydrogen. In our calculations we have employed unitary chiral perturbation theory (UCHPT). We discuss why their arguments are irrelevant or do not hold.
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Charged Kaon K^+ --> 3 pi CP Violating Asymmetries vs epsilon'_K / epsilon_K
We present the next-to-leading order full results in Chiral Perturbation Theory for the charged Kaon K --> 3 pi slope g CP violating asymmetries. We discuss the constraints that a measurement of these asymmetries would impose on the Standard Model results of epsilon_K' and search for new physics. We also study the kind of information that such measurement can provide on Im G_8, Im (e^2 G_E) and higher order weak couplings.
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Surprises in threshold antikaon-nucleon physics
Low energy \bar{K}N interactions are studied within Unitary Chiral Perturbation Theory at next-to-leading order with ten coupled channels. We pay special attention to the recent precise determination of the strong shift and width of the kaonic hydrogen 1s state by the DEAR Collaboration that has challenged our theoretical understanding of this sector of strong interactions. We typically find two classes of solutions, both of them reproducing previous data, that either can or cannot accommodate the DEAR measurements. The former class has not been previously discussed.
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The B_K Kaon Parameter in the 1/N_c Expansion
We present work going on calculating the kaon B_K parameter in the 1/N_c expansion. The goal of this work is to analyze analytically in the presence of chiral corrections this phenomenologically very important parameter. We present the method used and preliminary results for the chiral limit value for which we get the invariant \hat B_K^χ=0.29 \pm 0.15. We also give some analytical indications of why the large N_c prediction of \hat B_K= 3/4 may have small 1/N_c corrections in the real case.
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Extraction of m_s and |V_us| from Hadronic Tau Decays
We review recent work to determine the strange quark mass m_s as well as the proposal to determine |V_{us}| using hadronic tau decay data. The recent update of the strange spectral function by OPAL and their moments of the invariant mass distribution are employed. Our results are |V_us|=0.2208 +- 0.0034 and m_s (2 GeV)=81 +- 22 MeV. Our result is already competitive to the standard extraction of |V_us| from K_e3 decays and to the new proposals to determine it. The error on V_us is dominated by experiment and will be eventually much improved by the B-factories hadronic tau data. Ultimately, a simultaneous fit of both m_s and |V_us| to a set of moments of the hadronic tau decays invariant mass distribution will provide one of the most accurate determinations of these Standard Model parameters.
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Charged Kaon K -> 3 pi CP Violating Asymmetries
First full next-to-leading order analytical results in Chiral Perturbation Theory for the charged Kaon K -> 3 pi slope g and decay rates CP-violating asymmetries are presented. We discuss the constraints that a measurement of these asymmetries would impose on the Standard Model calculations of epsilon_K' and the kind of information it can provide on Im G_8, Im (e^2 G_E) and higher order weak couplings.
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Charged Kaon K \to 3 pi CP Violating Asymmetries at NLO in CHPT
We give the first full next-to-leading order analytical results in Chiral Perturbation Theory for the charged Kaon K \to 3 pi slope g and decay rates CP-violating asymmetries. We have included the dominant Final State Interactions at NLO analytically and discussed the importance of the unknown counterterms. We find that the uncertainty due to them is reasonable just for Δg_C, i.e. the asymmetry in the K^+ \to pi^+ pi^+ pi^- slope g; we get Δg_C = -(2.4 +- 1.2) 10^{-5}. The rest of the asymmetries are very sensitive to the unknown counterterms. In particular, the decay rate asymmetries can change even sign. One can use this large sentivity to get valuable information on those counterterms and on Im(G_8) coupling --very important for the CP-violating parameter epsilon'_K-- from the eventual measurement of these asymmetries. We also provide the one-loop O(e^2 p^2) electroweak octet contributions for the neutral and charged Kaon K \to 3 pi decays.
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Hadronic Matrix Elements for Kaons
We review some work done by us calculating matrix elements for Kaons. Emphasis is put on the matrix elements which are relevant to predict non-leptonic Kaon CP violating observables. In particular, we recall our results for the \hat B_K parameter which governs the \bar{K^0}-K^0 mixing and update our results for epsilon'_K including estimated all-higher-order CHPT corrections and the new results from recent analytical calculations of the ΔI=3/2 component. Some comments on future prospects on calculating matrix elements for Kaons are also added.
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CP-Violating Asymmetries in K^+ -> 3 pi in the Standard Model
We update the CP-violating asymmetries in K^+ -> 3 pi. In particular we study Delta g_C and Delta g_N -the asymmetries in the slope g. We emphasize its complementarity to the direct CP-violation parameter epsilon_K' and the large sensitivity to the size of the imaginary part of the octet coupling Im G_8 at lowest order in CHPT. We also give the prospects of a full calculation at next-to-leading order of this and other CP-violating asymmetries which will be presented elsewhere.
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QCD Short-distance Constraints and Hadronic Approximations
This paper discusses a general class of ladder resummation inspired hadronic approximations. It is found that this approach naturally reproduces many successes of single meson per channel saturation models (e.g. VMD) and NJL based models. In particular the existence of a constituent quark mass and a gap equation follows naturally. We construct an approximation that satisfies a large set of QCD short-distance and large $N_c$ constraints and reproduces many hadronic observables. We show how there exists in general a problem between QCD short-distance constraints for Green Functions and those for form factors and cross-sections following from the quark-counting rule. This problem while expected for Green functions that do not vanish in purely perturbative QCD also persists for many Green functions that are order parameters.
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Matching the Electroweak Penquins Q_7 and Q_8
We report on recent advances on the computation of the matrix elements of the electroweak penguins Q_7 and Q_8 which are relevant for the Delta I=3/2 contribution to epsilon'_K in the chiral limit. The matching of scale and scheme dependences between Wilson coefficients and these matrix elements is done analytically at NLO in alpha_S.
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