arXiv subjects
Publications and source records attributed to Kim Maltman.
We explore the phenomenology of, and models for, the Z^* resonances, the lowest of which is now well established, and called the Theta. We provide an overview of three models which have been proposed to explain its existence and/or its small width, and point out other relevant predictions, and potential problems, for each. The relation to what is known about KN scattering, including possible resonance signals in other channels, is also discussed.
Expectations and predictions for pentaquark exotics based on the quark model perspective are presented. Recent quark model scenarios, and calculations performed in different realizations of the quark model approach, up to the end of March 2004, are also reviewed and discussed.
We perform a finite energy sum rule analysis of the flavor ud two-point V-A current correlator, Delta Pi (Q^2). The analysis, which is performed using both the ALEPH and OPAL databases for the V-A spectral function, Delta rho, allows us to extract the dimension six V-A OPE coefficient, a_6, which is related to the matrix element of the electroweak penguin operator, Q_8, by chiral symmetry. The result for a_6 leads directly to the improved (chiral limit) determination epsilon'/epsilon = (- 15.0 +- 2.7) 10^{-4}. Determination of higher dimension OPE contributions also allows us to perform an independent test using a low-scale constrained dispersive analysis, which provides a highly nontrivial consistency check of the results.
Hadronic tau decay data provides access to the light quark vector (V) and axial vector (A) spectral functions. This makes possible investigations of the dynamics of QCD at intermediate scales and improved determinations of certain QCD/Standard Model parameters. We discuss three such applications: (1) the investigation of the nature of duality violation in QCD at intermediate scales (and its relation to the determination of alpha_s); (2) the extraction of m_s from flavor-breaking differences of flavor 'ud' and 'us' data; and (3) the determination of the dimension D=6 term in the OPE for the flavor 'ud' V-A correlator difference. The latter is relevant to the evaluation of the chiral limit values of the K-->pi pi electroweak penguin matrix elements, and hence to our understanding of expectations for epsilon'/epsilon in the Standard Model.
We reconsider the dispersive evaluation of the weak matrix elements <2pi_{I=2}|Q_{7,8}|K0> in the chiral limit. The perturbative matching is accomplished fully within the scheme dependence used in the two loop weak OPE calculations. The effects of dimension eight (and higher dimension) operators are fully accounted for. We perform a numerical determination of the weak matrix elements using our dispersive sum rules fortified by constraints from the classical chiral sum rules. A careful assessment of the attendant uncertainties is given.
The flavor $ud$ and $us$ pseudoscalar correlators are investigated using families of finite energy sum rules (FESR's) known to be very accurately satisfied in the isovector vector channel. It is shown that the combination of constraints provided by the full set of these sum rules is sufficiently strong to allow determination of both the light quark mass combinations $m_u+m_d$, $m_s+m_u$ and the decay constants of the first excited pseudoscalar mesons in these channels. The resulting masses and decay constants are also shown to produce well-satisfied Borel transformed sum rules, thus providing non-trivial constraints on the treatment of direct instanton effects in the FESR analysis. The values of $m_u+m_d$ and $m_s+m_u$ obtained are in good agreement with the values implied by recent hadronic $τ$ decay analyses and the ratios obtained from ChPT. New light quark mass bounds based on FESR's involving weight functions which strongly suppress spectral contributions from the excited resonance region are also presented.
A number of recent determinations of $m_s$ using hadronic $τ$ decay data involve inclusive analyses based on the so-called $(k,0)$ spectral weights. We show here that the OPE representations of the longitudinal contributions appearing in these analyses, which are already known to be poorly converging, have in addition an unphysical $k$ dependence which produces a significant unphysical decrease in $m_s$ with increasing $k$. We also show how, using additional sum rule constraints, the decay constants of the excited resonances in the strange scalar and pseudoscalar channels may be determined, allowing one to evaluate the longitudinal spectral contributions to the $(k,0)$ sum rules. Taking into account the very-accurately known $π$ and $K$ pole contributions, we find that longitudinal contributions can be determined with an accuracy at the few % level, and hence reliably subtracted, leaving an analysis for $m_s$ involving the sum of longitudinal and transverse contributions, for which the OPE representation is much better converged.
We revisit the isovector pseudoscalar sum rule determination of m_u+m_d, using families of finite energy sum rules known to be very accurately satisfied in the isovector vector channel. The sum rule constraints are sufficiently strong to allow a determination of both m_u+m_d and the excited resonance decay constants. The corresponding Borel transformed sum rules are also very well satisfied, providing a non-trivial consistency check on the treatment of direct instanton contributions. We obtain [m_u+m_d](2 GeV)=7.8\pm 1.1 MeV (in the MS bar scheme), only marginally compatible with the most recent sum rule determinations, but in good agreement with recent unquenched lattice extractions.
A summary of the extraction of light quark masses from both QCD sumrules and lattice QCD simulations is presented. The focus is on providing a careful statement of the potential weaknesses in each calculation, and on integrating the work of different collaborations to provide a coherent picture.
Strong isospin-breaking (IB) contributions to both the octet and 27-plet weak K-->2 pi transitions are evaluated at next-to-leading order (NLO) in the chiral expansion. NLO contributions are shown to significantly reduce the leading order result for the potentially large contribution to the $ΔI=3/2$ amplitude resulting from strong isospin-breaking modifications to the weak Delta I=1/2 amplitude. The ratio of strong IB 27-plet to strong IB octet contributions is found to be small for all decay amplitudes. Combined with recent results on the corresponding electromagnetic contributions, we find that the ratio of the intrinsic strengths of octet and 27-plet effective weak operators can be taken to be that obtained from experimental data, analyzed ignoring isospin breaking, to an accuracy better than of order 10 percent.
We re-examine the use of sum rules in the extraction of light quark masses and discuss a number of potential problems with existing analyses. The most important issue is that of the overall normalization of the hadronic spectral functions should not be fixed by assuming complete resonance dominance of the continuum threshold region as it can overestimate the resonance contributions to spectral integrals by factors as large as $\sim 5$. The second important uncertainty comes from the assumed location, $s_0$, of the onset of duality with perturbative QCD, as the extracted quark masses depend very sensitively on this parameter. The assumption of duality and the requirement of positivity of $ρ_5(s)$ imposes very severe constraints on the shape of the relevant spectral function in the dual region, and leads to rigorous lower bounds for $m_u+m_d$ as a function of $s_0$. In the extractions of $m_s$ we find that the conventional choice of the value of $s_0$ is not physical. For a more reasonable choice of $s_0$ we are not able to find a solution that is stable with respect to variations of the Borel transform parameter. This problem can be overcome only if the hadronic spectral function is determined up to significantly larger values of $s$ than is currently possible. Finally, we also estimate the error associated with the convergence of perturbative QCD expressions used in the sum rule analyses. Our conclusion is that, taking all of these issues into account, the resulting sum rule estimates for both $m_u+m_d$ and $m_s$ could easily have uncertainties as large as a factor of 2.
The isospin-breaking vector meson decay constants are determined from a QCD sum rule analysis of the vector current correlator $ $, using a recently proposed implementation of the finite energy sum rule approach. The analysis employs the three-loop version of the OPE, and two different families of weight functions. It is shown that the requirement of consistency between results obtained using these two different weight families leads to a rather good determination of the parameter describing the deviation of the D=6 condensate term in the OPE from its vacuum saturation value, and that the ability to determine this value has non-trivial numerical consequences to the analysis. The phenomenological relevance of the results to the extraction of the strange quark mass and the determination of the $6^{th}$ order chiral low energy constant, $Q$, is also briefly discussed.
Narison's $τ$-decay-like sum rule for determining the strange quark mass is re-investigated, taking into account isospin-breaking corrections in the extraction of the input spectral functions from $e^+e^-\to hadrons$ data. The corrections, estimated using experimental data on vector meson electromagnetic decay constants and a QCD sum rule analysis of the 38 vector current correlator, are shown to be especially large for the isoscalar case. The reason such large corrections are natural is also explained. Due to the high degree of cancellation in the original sum rule, the effect of these corrections on the determination of $m_s$ is significant. A new central value $m_s=113-138 MeV$ is found, in the $\bar{MS}$ scheme at 1 GeV$^2$, with significant (asymmetric) errors associated with errors in the input experimental data.
A numerical error is pointed out in the existing expression for the order $α_s^2$ longitudinal component of the squared-mass (D=2) contribution to the hadronic $τ$ decay rate. The corrected version is found to be such that, to order $α_s^2$, each term in the resulting series is larger than the previous one, ruling out the direct use of flavor breaking in hadronic $τ$ decays as a means of extracting the strange quark mass. An alternate approach, using model spectral functions previously developed for the strangeness-changing scalar channel (and employed in alternate sum rule analyses of $m_s$) as input to the $τ$ decay analysis, is shown to provide mutual consistency checks for the two different methods. The results for $m_s$ implied by $τ$ decay data, and the existing model spectral function are also presented.
We investigate the problem of the extraction of the isovector and isoscalar spectral functions from data on $e^+e^-\to hadrons$, in the presence of non-zero isospin breaking. It is shown that the conventional approach to extracting the isovector spectral function in the $ρ$ resonance region, in which only the isoscalar contribution associated with $ω\to ππ$ is subtracted, fails to fully remove the effects of the isoscalar component of the electromagnetic current. The additional subtractions required to extract the pure isovector and isoscalar spectral functions are estimated using results from QCD sum rules. It is shown that the corrections are small ($\sim 2%$) in the isovector case (though relevant to precision tests of CVC), but very large ($\sim 20%$) in the case of the $ω$ contribution to the isoscalar spectral function. The reason such a large effect is natural in the isoscalar channel is explained, and implications for other applications, such as the extraction of the sixth order chiral low-energy constant, $Q$, are discussed.
We investigate the size of potential higher pseudoscalar resonance contaminations of the estimates of isospin-conserving and isospin-violating $πNN$ couplings obtained using the 3-point function method in QCD sum rules. For the isospin-conserving case it is shown that conventional models of the isovector pseudoscalar spectral function imply resonance decay constants large enough to create significant contaminations, and that assuming these models are incorrect, and that the decay constants are actually much smaller, implies physically implausible values for the flavor-breaking quark condensate ratios. For the isospin-violating case it is shown explicitly that such resonance contamination is unavoidably present and precludes using the 3-point function method as a means of estimating the at present unmeasured isospin-violating $πNN$ couplings.
We employ Chiral Perturbation Theory (ChPT) to evaluate the complete set of pseudoscalar matrix elements, <0|P_f|pi^0,eta>, with P_f any of the flavor-diagonal pseudoscalar currents (f=u,d,s), to order (m_d-m_u), and to next-to-leading order in the chiral expansion. These matrix elements represent the basic input to a QCD sum rule analysis of isospin breaking in the pi NN couplings using the three-point-function method. We discuss also how one could use the results to construct a one parameter family of interpolating fields for the $π^0$, all of whose members have zero vacuum-to-$η$ matrix element, and explain how this could in principle be used to provide non-trivial tests of the reliability of the assumptions underlying the use of the three-point-function method. It is shown that the isospin-breaking mixing parameters required for this construction receive significant corrections beyond leading order in the chiral expansion.
We revisit the QCD sum-rule treatment of the isospin-breaking axial correlator in light of the recent claim that a previous treatment produced results incompatible with known chiral constraints. The source of the error in the previous analysis is identified, and a corrected version of the sum-rule treatment obtained. It is then shown that, using input from chiral perturbation theory, one may use the resulting sum rule to extract information on the leading chiral behavior of isospin-breaking parameters associated with the coupling of excited pseudoscalar resonances to the axial currents. A rather accurate extraction is possible for the case of the eta'. Demanding stability of the sum-rule analysis also allows us to improve the upper bound on the fourth-order low-energy constant, L_7.