arXiv subjects

Antonio Pich

Publications and source records attributed to Antonio Pich.

At least 109 records · Page 6Linked to original sources

arXiv2010

Flavour constraints on multi-Higgs-doublet models: Yukawa alignment

In multi-Higgs-doublet models, the alignment in flavour space of all Yukawa matrices coupling to a given right-handed fermion guarantees the absence of tree-level flavour-changing neutral couplings, while introducing new sources of CP violation. With N Higgs doublets (and no right-handed neutrinos) the Yukawa Lagrangian is characterized by the fermion masses, the CKM quark mixing matrix and 3(N-1) complex couplings. Quantum corrections break the alignment, generating a minimal-flavour-violation structure with flavour-blind phases. The aligned multi-Higgs-doublet models lead to a rich and viable phenomenology with an interesting hierarchy of flavour-changing neutral current effects, suppressing them in light-quark systems while allowing potentially relevant signals in heavy-quark transitions.

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arXiv2010

Duality violation in QCD Sum Rules with the LR correlator

We analyse the so-called violations of quark-hadron duality in Finite Energy Sum Rules with the LR correlator, through the study of the possible high-energy behavior of the LR spectral function, taking into account all known short-distance constraints and the experimental tau-decay data. In particular we show that the use of pinched weights allows to determine with high accuracy the dimension six and eight contributions in the Operator-Product Expansion, O_6 = (-4.3^{+0.9}_{-0.7}) 10^{-3} GeV^6 and O_8 = (-7.2^{+4.2}_{-5.3}) 10^{-3} GeV^8.

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arXiv2010

Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model

The alignment in flavour space of the Yukawa matrices of a general two-Higgs-doublet model results in the absence of tree-level flavour-changing neutral currents. In addition to the usual fermion masses and mixings, the aligned Yukawa structure only contains three complex parameters, which are potential new sources of CP violation. For particular values of these three parameters all known specific implementations of the model based on discrete Z_2 symmetries are recovered. One of the most distinctive features of the two-Higgs-doublet model is the presence of a charged scalar. In this work, we discuss its main phenomenological consequences in flavour-changing processes at low energies and derive the corresponding constraints on the parameters of the aligned two-Higgs-doublet model.

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arXiv2010

Pinched weights and Duality Violation in QCD Sum Rules: a critical analysis

We analyze the so-called pinched weights, that are generally thought to reduce the violation of quark-hadron duality in Finite-Energy Sum Rules. After showing how this is not true in general, we explain how to address this question for the LR correlator and any particular pinched weight taking advantage of our previous work [1], where the possible high-energy behavior of the LR spectral function was studied. In particular we show that the use of pinched weights allows to determine with high accuracy the dimension six and eight contributions in the operator product expansion, O6=(-4.3^[+0.9}_{-0.7})*10^-3 GeV^6 and O8=(-7.2^{+4.2}_{-5.3})*10^-3 GeV^8.

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arXiv2010

Violation of Quark-Hadron Duality and Spectral Chiral Moments in QCD

We analyze the spectral moments of the V-A two-point correlation function. Using all known short-distance constraints and the most recent experimental data from tau decays, we determine the lowest spectral moments, trying to assess the uncertainties associated with the so-called violations of quark-hadron duality. We have generated a large number of "acceptable" spectral functions, satisfying all conditions, and have used them to extract the wanted hadronic parameters through a careful statistical analysis. We obtain accurate values for the ChPT couplings L10 and C87, and a realistic determination of the dimension six and eight contributions in the operator product expansion, O6=(-5.4^{+3.6}_{-1.6})*10^-3 GeV^6 and O8=(-8.9^{+12.6}_{-7.4})*10^-3 GeV^8, showing that the duality-violation effects have been usually underestimated in previous literature.

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arXiv2010

The Aligned two-Higgs Doublet model

In the two-Higgs-Doublet model the alignment of the Yukawa flavour matrices of the two scalar doublets guarantees the absence of tree-level flavour-changing neutral couplings. The resulting fermion-scalar interactions are parameterized in terms of three complex parameters, leading to a generic Yukawa structure which contains as particular cases all known specific implementations of the model based on Z2 symmetries. These three complex parameters are potential new sources of CP violation.

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arXiv2010

Alpha_s Determination from Tau Decays: Theoretical Status

The total tau hadronic width can be accurately calculated using analyticity and the operator product expansion. The result turns out to be very sensitive to the value of alpha_s(m_tau^2), providing a precise determination of the strong coupling constant. The theoretical description of this observable is updated, including the recently computed O(alpha_s^4) contributions. The experimental determination of alpha_s(m_tau^2) and its actual uncertainties are discussed.

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arXiv2009

Yukawa Alignment in the Two-Higgs-Doublet Model

In multi-Higgs-doublet models the alignment in flavour space of the relevant Yukawa matrices guarantees the absence of tree-level flavour-changing couplings of the neutral scalar fields. We analyze the consequences of this condition within the two-Higgs-doublet model and show that it leads to a generic Yukawa structure which contains as particular cases all known specific implementations of the model based on Z_2 symmetries. All possible freedom in the Yukawa sector gets parametrized in terms of three complex couplings. In spite of having flavour conservation in the neutral scalar couplings, the phases of these three parameters represent potential new sources of CP violation.

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arXiv2008

Low-Energy Constants from Resonance Chiral Theory

I discuss the recent attempts to build an effective chiral Lagrangian incorporating massive resonance states. A useful approximation scheme to organize the resonance Lagrangian is provided by the large-Nc limit of QCD. Integrating out the resonance fields, one recovers the usual chiral perturbation theory Lagrangian with explicit values for the low-energy constants, parameterized in terms of resonance masses and couplings. The resonance chiral theory generates Green functions that interpolate between QCD and chiral perturbation theory. Analyzing these Green functions, both for large and small momenta, one gets QCD constraints on the resonance couplings and, therefore, information on the low-energy constants governing the Goldstone interactions.

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arXiv2008

Determination of the Chiral Couplings L_10 and C_87 from Semileptonic Tau Decays

Using recent precise hadronic tau-decay data on the V-A spectral function, and general properties of QCD such as analyticity, the operator product expansion and chiral perturbation theory, we get accurate values for the QCD chiral order parameters L_10^r(M_rho) and C_87^r(M_rho). These two low-energy constants appear at order p^4 and p^6, respectively, in the chiral perturbation theory expansion of the V-A correlator. At order p^4 we obtain L_10^r(M_rho) = -(5.22\pm 0.06)10^{-3}. Including in the analysis the two-loop (order p^6) contributions, we get L_10^r(M_rho) = -(4.06\pm 0.39)10^{-3} and C_87^r(M_rho) = (4.89\pm 0.19)10^{-3}GeV^{-2}. In the SU(2) chiral effective theory, the corresponding low-energy coupling takes the value \overline l_5 = 13.30 \pm 0.11 at order p^4, and \overline l_5 = 12.24 \pm 0.21 at order p^6.

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arXiv2008

Chiral low-energy constants L_10 and C_87 from hadronic tau decays

Using recent precise hadronic tau-decay data on the V-A spectral function and general properties of QCD such as analyticity, the operator product expansion and chiral perturbation theory, we get accurate values for the QCD chiral order parameters L_10 and C_87. At order p^4 we obtain L_10^r(M_rho)=-(5.22+-0.06)10^-3, whereas at order p^6 we get L_10^r(M_rho)=-(4.06+-0.39)10^-3 and C_87^r(M_rho) = (4.89+-0.19)10^-3 GeV^-2.

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arXiv2008

What can be learned from the Belle spectrum for the decay tau- -> nu_tau K_S pi-

A theoretical description of the differential decay spectrum for the decay tau- -> nu_tau K_S pi-, which is based on the contributing K pi vector and scalar form factors F_+^{K pi}(s) and F_0^{K pi}(s) being calculated in the framework of resonance chiral theory (R$χ$T), additionally imposing constraints from dispersion relations as well as short distance QCD, provides a good representation of a recent measurement of the spectrum by the Belle collaboration. Our fit allows to deduce the total branching fraction B[tau- -> nu_tau K_S pi-] = 0.427 +- 0.024 % by integrating the spectrum, as well as the K^* resonance parameters M_{K^*} = 895.3 +- 0.2 MeV and Gamma_{K^*} = 47.5 +- 0.4 MeV, where the last two errors are statistical only. From our fits, we confirm that the scalar form factor F_0^{K pi}(s) is required to provide a good description, but we were unable to further constrain this contribution. Finally, from our results for the vector form factor F_+^{K pi}(s), we update the corresponding slope and curvature parameters lambda'_+ = (25.2 +- 0.3)*10^{-3} and lambda''_+ = (12.9 +- 0.3)*10^{-4}, respectively.

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arXiv2007

Selected topics on tau physics

The B Factories have generated a large amount of new results on the tau lepton. The present status of some selected topics on tau physics is presented: charged-current universality tests, bounds on lepton-flavour violation, the determination of alpha_s from the inclusive tau hadronic width, and the measurement of |V_{us}| through the Cabibbo-suppressed decays of the tau lepton.

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arXiv2007

Theoretical progress on the V_us determination from tau decays

A very precise determination of V_us can be obtained from the semi-inclusive hadronic decay width of the tau lepton into final states with strangeness. The ratio of the Cabibbo-suppressed and Cabibbo-allowed tau decay widths directly measures (V_us/V_ud)^2, up to very small SU(3)-breaking corrections which can be theoretically estimated with the needed accuracy. Together with previous LEP and CLEO data, the recent measurements by Babar and Belle of some Cabibbo-suppressed tau decays imply V_us= 0.2165 +- 0.0026_exp +- 0.0005_th, which is already competitive with the standard extraction from K_l3 decays. The uncertainty is largely dominated by experimental errors and should be easily reduced with the high statistics of the B factories, providing the most accurate determination of this parameter. A 1% experimental precision on the Cabibbo-suppressed tau decay width would translate into a 0.6% uncertainty on V_us.

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arXiv2007

The Standard Model of Electroweak Interactions

Gauge invariance is a powerful tool to determine the dynamics of the electroweak and strong forces. The particle content, structure and symmetries of the Standard Model Lagrangian are discussed. Special emphasis is given to the many phenomenological tests which have established this theoretical framework as the Standard Theory of electroweak interactions.

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arXiv2007

Tau Physics 2006: Summary & Outlook

A large amount of new results have been presented at TAU2006. The highlights of the workshop, the present status of a few selected topics on lepton physics (universality, QCD tests, V_{us} determination from tau decay, g-2, neutrino oscillations, lepton-flavour violation) and the prospects for future improvements are briefly summarized.

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arXiv2006

|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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arXiv2006

|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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