We discuss a preliminary study of the impact of duality violations on extractions from τ decay da... more We discuss a preliminary study of the impact of duality violations on extractions from τ decay data of the D = 6 VEVs which determine chiral limit Standard Model K → ππ matrix elements of the electroweak penguin operators.
It is shown that the usual large-N c counting of the coupling constant L 7 of the O(p 4) low-ener... more It is shown that the usual large-N c counting of the coupling constant L 7 of the O(p 4) low-energy chiral SU(3) Lagrangian [3] is in conict with general properties of QCD in the large-N c limit. The solution of this conict within the framework of a chiral U(3) Lagrangian is explained.
We study contributions to the ∆S = 2 weak Chiral Lagrangian producing K 0 − K 0 mixing which are ... more We study contributions to the ∆S = 2 weak Chiral Lagrangian producing K 0 − K 0 mixing which are not enhanced by the charm mass. For the real part, these contributions turn out to be related to the box diagram with up quarks but, unlike in perturbation theory, they do not vanish in the limit m u → 0. They increase the leading contribution to the K L −K S mass difference by ∼ 10%. This means that short distances amount to (90 ± 15)% of this mass difference. For the imaginary part, we find a correction to the λ * 2 c m 2 c term of −5% from the integration of charm, which is a small contribution to ǫ K. The calculation is done in the large-N c limit and we show explicitly how to match short and long distances.
I review some progress made on the problem of calculating electroweak processes of mesons at low ... more I review some progress made on the problem of calculating electroweak processes of mesons at low energy with the use of an approximation to large-Nc QCD which we call the Minimal Hadronic Approximation.
Nonrenormalization theorems for the transverse, i.e. non anomalous, part of the V V A correlator ... more Nonrenormalization theorems for the transverse, i.e. non anomalous, part of the V V A correlator in perturbative QCD are proven. Some of their consequences and questions they raise are discussed.
Starting from a very general lagrangian for the self interactions of weak bosons we show that, to... more Starting from a very general lagrangian for the self interactions of weak bosons we show that, to leading order in the (hypothesised) compositeness scale A, low-energy neutrino scattering is only sensitive to "anomalous magnetic moment type" effects of the ZWW interaction. We use experimental data on neutrino scattering to restrict the deviations from the standard ZWW coupling to the percent level.
We study the production of E6 scalar leptoquarks in electron-proton scattering. We focus on three... more We study the production of E6 scalar leptoquarks in electron-proton scattering. We focus on three issues: (i) eR p-~vX, (ii) e-p-,e-X, and (iii) A= [tr(eff)-tr(eff)]/[tr(eff) +a(eff)]. An incredible amount of work and hope has been invested in the study of (super)strings and their physical applications [ 1 ]. In particular, on the phenomenological front, searches for extra gauge bosons and/or exotic isosinglet quarks have been proposed and the cross sections, backgrounds and discovery limits carefully assessed at e+e-machines (LEP, SLC), e-p machines (HERA) and hadron-hadron (SSC) colliders [2-6]. While it is not at all clear that there is an actual connection between the so-called superstring inspired models and string theory, it is certainly worth to survey such scenarios as the E 6 scenario, since they provide a convenient frame within which one can explore the physics beyond the standard model in a well defined way. Hence, they may provide a guide into uncharted domains of physics even though their ultimate relationship to a true theory does remain obscure. In this sense it might prove fruitful to further explore their consequences for future experimental collider physics. HERA is, of course, a best suited ground for the production of objects with combined lepton and quark quantum numbers, i.e. leptoquarks. Their production and decay in e-p machines has been discussed in different theoretical contexts and by different groups. Recent work on the subject has been performed by the authors in refs. [ 4-6 ]. Buchmiiller et al. explored leptoquark production in a general setting without referring to a specific underlying model. Angelopoulos et al. have carried a thorough analysis of production of new quarks in the context of E6 in e-p and hadron-hadron colliders. Finally, Gunion and Ma have also discussed scalar leptoquark production in e-p collisions. Their work is very complete when they come to the discussion of backgrounds. Although these investigations certainly overlap to some extent, they differ in the approach in the particular subjects covered and in the depth of the various issues considered. Here, we would like to present still another paper on the subject. Some of it, section (ii) below, is repetitive (although it has been carried out independently). However, we include some other issues which are not treated in the literature commented before. To set the frame, let us briefly introduce the model. Each matter multiplet sits in a 27 representation of E 6. The 27 particles in it are the usual 15 quarks and leptons in the standard model plus a right-handed neutrino, an additional singlet neutrino N, extra isosinglet quark color triplets D and D c and the usual Higgs doublets H and 17/. The extra color quark states-those we are interested in-have Yukawa interactions to ordinary quarks and leptons. In general, these interactions are, as derived from the most general superpotential, 21D c LQ + 2z De c u c + 23 Dv c d c. (1) Actually we have made a choice here. In fact, D and D ~ could have also interactions of the type ~, DQQ+~zDCuCd c. (2) ¢r Work partially supported by research project CAICYT and "Acci6n Integrada entre Espafia y la R.F.A." n ° 1/51 Tipo A.
The vacuum polarization of a quark, when considered in terms of the external momentum q 2 , is a ... more The vacuum polarization of a quark, when considered in terms of the external momentum q 2 , is a function of the Stieltjes type. Consequently, the mathematical theory of Pade Approximants assures that the full function, at any finite value of q 2 away from the physical cut, can be reconstructed from its low-energy power expansion around q 2 = 0. We illustrate this point by applying this theory to the vacuum polarization of a heavy quark and obtain the value of the constant K (2) governing the threshold expansion at order O(α 2 s).
The data on v.e ~ v~e and ~.e + hue from the CHARM Collaboration are used to set new and interest... more The data on v.e ~ v~e and ~.e + hue from the CHARM Collaboration are used to set new and interesting bounds on the masses of hypothetical excited electrons and muons. In particular, it turns out that excited electrons cannot exist with masses below a couple of hundred GeV.
The counterterm combination that describes the decay of pseudoscalar mesons into charged lepton p... more The counterterm combination that describes the decay of pseudoscalar mesons into charged lepton pairs at lowest order in chiral perturbation theory is considered within the framework of QCD in the limit of a large number of colours NC. When further restricted to the lowest meson dominance approximation to large-NC QCD , our results agree well with the available experimental data.
Using a method previously developed, based on the Mellin-Barnes transform, we reconstruct the two... more Using a method previously developed, based on the Mellin-Barnes transform, we reconstruct the two-point correlators in the vector, axial, scalar and pseudoscalar channels from the Taylor expansion at q 2 = 0, the threshold expansion at q 2 = 4m 2 and the OPE at q 2 → −∞, where m is the heavy quark mass. The reconstruction is analytic and systematic and is controlled by an error function which becomes smaller as more terms in those expansions are known.
Following a recent suggestion by Weinberg, we use the large-N expansion in QCD to discuss the dec... more Following a recent suggestion by Weinberg, we use the large-N expansion in QCD to discuss the decay amplitudes of tetraquarks into ordinary mesons as well as their mixing properties. We find that the flavor structure of the tetraquark is a crucial ingredient to determine both this mixing as well as the decays. Although in some cases tetraquarks should be expected to be as narrow as ordinary mesons, they may get to be even narrower, depending on this flavor structure.
Being a determination at low energies, the analysis of hadronic τ decay data provides a rather pr... more Being a determination at low energies, the analysis of hadronic τ decay data provides a rather precise determination of the strong coupling α s after evolving the result to M Z. At such a level of precision, even small non-perturbative effects become relevant for the central value and error. While those effects had been taken into account in the framework of the operator product expansion, contributions going beyond it, so-called duality violations, have previously been neglected. The following investigation fills this gap through a finite-energy sum rule analysis of τ decay spectra from the OPAL experiment, including duality violations and performing a consistent fit of all appearing QCD parameters. The resulting values for α s (M τ) are 0.307(19) in fixed-order perturbation theory and 0.322(26) in contour-improved perturbation theory, which translates to the n f = 5 values 0.1169(25) and 0.1187(32) at M Z , respectively.
We discuss some key issues associated with duality-violating and non-perturbative OPE contributio... more We discuss some key issues associated with duality-violating and non-perturbative OPE contributions to the theoretical representations of light quark current-current two-point functions and relevant to precision determinations of α s from hadronic τ decay and electroproduction cross-section data. We demonstrate that analyses with an explicit representation of duality-violating effects are required to bring theoretical errors in such extractions under control, motivating the accompanying paper in these proceedings, which presents the results of such an analysis.
I report on a recent calculation done in collaboration with E. de Rafael [7] of the invariantBK f... more I report on a recent calculation done in collaboration with E. de Rafael [7] of the invariantBK factor of K 0-K 0 mixing in the chiral limit and to next-to-leading order in the 1/Nc expansion. This calculation is, to the best of our knowledge, the first example of a calculation ofBK in which there is an explicit analytic cancellation of the µ renormalization scale and the scheme dependence between the Wilson coefficient and the corresponding kaon matrix element. I try to emphasize the ideas involved in the approach and how the method could be applied to other physical situations, rather than the details of the numerical analysis for which I refer the reader to ref. [7].
We discuss a preliminary study of the impact of duality violations on extractions from τ decay da... more We discuss a preliminary study of the impact of duality violations on extractions from τ decay data of the D = 6 VEVs which determine chiral limit Standard Model K → ππ matrix elements of the electroweak penguin operators.
It is shown that the usual large-N c counting of the coupling constant L 7 of the O(p 4) low-ener... more It is shown that the usual large-N c counting of the coupling constant L 7 of the O(p 4) low-energy chiral SU(3) Lagrangian [3] is in conict with general properties of QCD in the large-N c limit. The solution of this conict within the framework of a chiral U(3) Lagrangian is explained.
We study contributions to the ∆S = 2 weak Chiral Lagrangian producing K 0 − K 0 mixing which are ... more We study contributions to the ∆S = 2 weak Chiral Lagrangian producing K 0 − K 0 mixing which are not enhanced by the charm mass. For the real part, these contributions turn out to be related to the box diagram with up quarks but, unlike in perturbation theory, they do not vanish in the limit m u → 0. They increase the leading contribution to the K L −K S mass difference by ∼ 10%. This means that short distances amount to (90 ± 15)% of this mass difference. For the imaginary part, we find a correction to the λ * 2 c m 2 c term of −5% from the integration of charm, which is a small contribution to ǫ K. The calculation is done in the large-N c limit and we show explicitly how to match short and long distances.
I review some progress made on the problem of calculating electroweak processes of mesons at low ... more I review some progress made on the problem of calculating electroweak processes of mesons at low energy with the use of an approximation to large-Nc QCD which we call the Minimal Hadronic Approximation.
Nonrenormalization theorems for the transverse, i.e. non anomalous, part of the V V A correlator ... more Nonrenormalization theorems for the transverse, i.e. non anomalous, part of the V V A correlator in perturbative QCD are proven. Some of their consequences and questions they raise are discussed.
Starting from a very general lagrangian for the self interactions of weak bosons we show that, to... more Starting from a very general lagrangian for the self interactions of weak bosons we show that, to leading order in the (hypothesised) compositeness scale A, low-energy neutrino scattering is only sensitive to "anomalous magnetic moment type" effects of the ZWW interaction. We use experimental data on neutrino scattering to restrict the deviations from the standard ZWW coupling to the percent level.
We study the production of E6 scalar leptoquarks in electron-proton scattering. We focus on three... more We study the production of E6 scalar leptoquarks in electron-proton scattering. We focus on three issues: (i) eR p-~vX, (ii) e-p-,e-X, and (iii) A= [tr(eff)-tr(eff)]/[tr(eff) +a(eff)]. An incredible amount of work and hope has been invested in the study of (super)strings and their physical applications [ 1 ]. In particular, on the phenomenological front, searches for extra gauge bosons and/or exotic isosinglet quarks have been proposed and the cross sections, backgrounds and discovery limits carefully assessed at e+e-machines (LEP, SLC), e-p machines (HERA) and hadron-hadron (SSC) colliders [2-6]. While it is not at all clear that there is an actual connection between the so-called superstring inspired models and string theory, it is certainly worth to survey such scenarios as the E 6 scenario, since they provide a convenient frame within which one can explore the physics beyond the standard model in a well defined way. Hence, they may provide a guide into uncharted domains of physics even though their ultimate relationship to a true theory does remain obscure. In this sense it might prove fruitful to further explore their consequences for future experimental collider physics. HERA is, of course, a best suited ground for the production of objects with combined lepton and quark quantum numbers, i.e. leptoquarks. Their production and decay in e-p machines has been discussed in different theoretical contexts and by different groups. Recent work on the subject has been performed by the authors in refs. [ 4-6 ]. Buchmiiller et al. explored leptoquark production in a general setting without referring to a specific underlying model. Angelopoulos et al. have carried a thorough analysis of production of new quarks in the context of E6 in e-p and hadron-hadron colliders. Finally, Gunion and Ma have also discussed scalar leptoquark production in e-p collisions. Their work is very complete when they come to the discussion of backgrounds. Although these investigations certainly overlap to some extent, they differ in the approach in the particular subjects covered and in the depth of the various issues considered. Here, we would like to present still another paper on the subject. Some of it, section (ii) below, is repetitive (although it has been carried out independently). However, we include some other issues which are not treated in the literature commented before. To set the frame, let us briefly introduce the model. Each matter multiplet sits in a 27 representation of E 6. The 27 particles in it are the usual 15 quarks and leptons in the standard model plus a right-handed neutrino, an additional singlet neutrino N, extra isosinglet quark color triplets D and D c and the usual Higgs doublets H and 17/. The extra color quark states-those we are interested in-have Yukawa interactions to ordinary quarks and leptons. In general, these interactions are, as derived from the most general superpotential, 21D c LQ + 2z De c u c + 23 Dv c d c. (1) Actually we have made a choice here. In fact, D and D ~ could have also interactions of the type ~, DQQ+~zDCuCd c. (2) ¢r Work partially supported by research project CAICYT and "Acci6n Integrada entre Espafia y la R.F.A." n ° 1/51 Tipo A.
The vacuum polarization of a quark, when considered in terms of the external momentum q 2 , is a ... more The vacuum polarization of a quark, when considered in terms of the external momentum q 2 , is a function of the Stieltjes type. Consequently, the mathematical theory of Pade Approximants assures that the full function, at any finite value of q 2 away from the physical cut, can be reconstructed from its low-energy power expansion around q 2 = 0. We illustrate this point by applying this theory to the vacuum polarization of a heavy quark and obtain the value of the constant K (2) governing the threshold expansion at order O(α 2 s).
The data on v.e ~ v~e and ~.e + hue from the CHARM Collaboration are used to set new and interest... more The data on v.e ~ v~e and ~.e + hue from the CHARM Collaboration are used to set new and interesting bounds on the masses of hypothetical excited electrons and muons. In particular, it turns out that excited electrons cannot exist with masses below a couple of hundred GeV.
The counterterm combination that describes the decay of pseudoscalar mesons into charged lepton p... more The counterterm combination that describes the decay of pseudoscalar mesons into charged lepton pairs at lowest order in chiral perturbation theory is considered within the framework of QCD in the limit of a large number of colours NC. When further restricted to the lowest meson dominance approximation to large-NC QCD , our results agree well with the available experimental data.
Using a method previously developed, based on the Mellin-Barnes transform, we reconstruct the two... more Using a method previously developed, based on the Mellin-Barnes transform, we reconstruct the two-point correlators in the vector, axial, scalar and pseudoscalar channels from the Taylor expansion at q 2 = 0, the threshold expansion at q 2 = 4m 2 and the OPE at q 2 → −∞, where m is the heavy quark mass. The reconstruction is analytic and systematic and is controlled by an error function which becomes smaller as more terms in those expansions are known.
Following a recent suggestion by Weinberg, we use the large-N expansion in QCD to discuss the dec... more Following a recent suggestion by Weinberg, we use the large-N expansion in QCD to discuss the decay amplitudes of tetraquarks into ordinary mesons as well as their mixing properties. We find that the flavor structure of the tetraquark is a crucial ingredient to determine both this mixing as well as the decays. Although in some cases tetraquarks should be expected to be as narrow as ordinary mesons, they may get to be even narrower, depending on this flavor structure.
Being a determination at low energies, the analysis of hadronic τ decay data provides a rather pr... more Being a determination at low energies, the analysis of hadronic τ decay data provides a rather precise determination of the strong coupling α s after evolving the result to M Z. At such a level of precision, even small non-perturbative effects become relevant for the central value and error. While those effects had been taken into account in the framework of the operator product expansion, contributions going beyond it, so-called duality violations, have previously been neglected. The following investigation fills this gap through a finite-energy sum rule analysis of τ decay spectra from the OPAL experiment, including duality violations and performing a consistent fit of all appearing QCD parameters. The resulting values for α s (M τ) are 0.307(19) in fixed-order perturbation theory and 0.322(26) in contour-improved perturbation theory, which translates to the n f = 5 values 0.1169(25) and 0.1187(32) at M Z , respectively.
We discuss some key issues associated with duality-violating and non-perturbative OPE contributio... more We discuss some key issues associated with duality-violating and non-perturbative OPE contributions to the theoretical representations of light quark current-current two-point functions and relevant to precision determinations of α s from hadronic τ decay and electroproduction cross-section data. We demonstrate that analyses with an explicit representation of duality-violating effects are required to bring theoretical errors in such extractions under control, motivating the accompanying paper in these proceedings, which presents the results of such an analysis.
I report on a recent calculation done in collaboration with E. de Rafael [7] of the invariantBK f... more I report on a recent calculation done in collaboration with E. de Rafael [7] of the invariantBK factor of K 0-K 0 mixing in the chiral limit and to next-to-leading order in the 1/Nc expansion. This calculation is, to the best of our knowledge, the first example of a calculation ofBK in which there is an explicit analytic cancellation of the µ renormalization scale and the scheme dependence between the Wilson coefficient and the corresponding kaon matrix element. I try to emphasize the ideas involved in the approach and how the method could be applied to other physical situations, rather than the details of the numerical analysis for which I refer the reader to ref. [7].
Uploads
Papers by S. Peris