arXiv subjects

Stephan Narison

Publications and source records attributed to Stephan Narison.

At least 37 records · Page 2Linked to original sources

arXiv2018

Updating m_c,b(m_c,b) from SVZ-Moments and their Ratios

Using recent values of α_s, the gluon condensates <α_s G^2> and and the new data on the ψ/Υ-families, we update our determinations of the MS-bar running quark masses m_c,b(m_c,b) from the SVZ-Moments M_n(Q^2) and their ratios by including higher order perturbative (PT) corrections, non-perturbative (NPT) terms up to dimension d=8 and using the degree n-stability criteria of the (ratios of) moments. Optimal results from different (ratios of) moments converge to the accurate mean values: m_c(m_c)=1264(6) MeV} and m_b(m_b)=4188(8) MeV in Table 4, which improve and confirm our previous findings [1,2] and the recent ones from Laplace sum rules [3]. Comments on some other determinations of m_c(m_c) and <α_s G^2> from the SVZ-(ratios of) moments in the vector channel are given in Section 5.

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arXiv2015

Decay Constants of Heavy-Light Mesons from QCD

We summarize recently improved results for the pseudoscalar [1,2] and vector [3] meson decay constants and their ratios from QCD spectral sum rules where N2LO + estimate of the N3LO PT and power corrections up to d< 6 dimensions have been included in the SVZ expansion. The "optimal results" based on stability criteria with respect to the variations of the Laplace/Moments sum rule variables, QCD continuum threshold and subtraction constant μare compared with recent sum rules and lattice calculations. To understand the "apparent tension" between some recent results for f_B*/f_B, we present in Section 8 "a novel extraction" of this ratio from heavy quark effective theory (HQET) sum rules by including the normalization factor (M_b/M_B)^2 relating the pseudoscalar to the universal HQET correlators for finite b-quark and B-meson masses. We obtain f_B*/f_B=1.025(16) in good agreement with the one 1.016(16) from (pseudo)scalar sum rules in full QCD [3]. We complete the paper by including new improved estimates of the scalar, axial-vector and B^*_c meson decays constants (Sections 11-13). For further phenomenological uses, we attempt to extract a Global Average of different sum rules and lattice determinations of the decay constants which are summarized in Tables 2-6. We do not found any deviation of these SM results from the present data.

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arXiv2015

Improved f_{D_(s)}, f_{B_(s)} and f_{B_c} from QCD Laplace sum rules

Anticipating future precise measurements of the D- and B-like (semi-)leptonic and hadronic decays for alternative determinations of the CKM mixing angles, we pursue our program on the D- and B-like mesons by improving the estimates of f_{D*_(s)} and f_{B*_(s)} (analogue to f_π) by using the well-established (inverse) Laplace sum rules (LSR) and / or their suitable ratios less affected by the systematics, which are known to N2LO pQCD and where the complete d = 6 non-perturbative condensate contributions are included. The convergence of the PT series is analyzed by an estimate of the N3LO terms based on geometric growth of the coefficients. In addition to the standard LSR variable τ and the QCD continuum threshold t_c stability criteria, we extract our optimal results by also requiring stability on the variation of the arbitrary QCD subtraction point μ. We complete the analysis by a direct estimate of f_{B_c}. Our results summarized in Tables III and IV are compared with some other recent estimates.

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arXiv2014

Mini-review on QCD spectral sum rules

Taking the example of the most popular and well-established Borel / Laplace / Exponential sum rule (LSR), I shortly review some of its recent applications in hadron physics namely the estimates of non-perturbative condensates, the determination of the light and heavy quark masses, the extraction of the heavy-light decay constants, the estimates of charmonium and bottomium molecule masses and the properties of scalar gluonium. In addition to the standard τ(sum rule variable) and t_c (QCD continuum threshold) stablity criteria, I introduce a new stability criterion versus the arbitrary QCD subtraction point μfor extracting the optimal results when radiative QCD corrections are included. Future improvements on further uses of QCD spectral sum rules (QSSR) are commented.

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arXiv2014

Improved light quark masses from pseudoscalar sum rules

Using ratios of the inverse Laplace transform sum rules within stability criteria for the subtraction point μin addition to the ones of the usual tau spectral sum rule variable and continuum threshold t_c, we extract the π(1300) and K(1460) decay constants to order α_s^4 of perturbative QCD by including power corrections up to dimension-six condensates, tachyonic gluon mass, instanton and finite width corrections. Using these inputs with enlarged generous errors, we extract, in a model-independent and conservative ways, the sum of the scale-independent renormalization group invariant (RGI) quark masses (m_u+ m_q):q\equiv d,s and the corresponding running masses (m_u+m_q) evaluated at 2 GeV. By giving the value of the ratio m_u/m_d, we deduce the running quark masses m_{u,d,s} and condensate <\bar uu> and the scale-independent mass ratios : 2m_s/(m_u+m_d) and m_s/m_d. Using the positivity of the QCD continuum contribution to the spectral function, we also deduce, from the inverse Laplace transform sum rules, for the first time to order α_s^4, new lower bounds on the RGI masses which are translated into the running masses at 2 GeV and into upper bounds on the running quark condensate <\bar uu>. Our results summarized in Table 2 and compared with our previous results and with recent lattice averages suggest that precise phenomenological determinations of the sum of light quark masses require improved experimental measurements of the π(1.3) and K(1.46) hadronic widths and/or decay constants which are the dominant sources of errors in the analysis.

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arXiv2013

Revisiting f_B and m_b(m_b) from HQET spectral sum rules

Using recent values of the QCD (non-) perturbative parameters given in Table 1, we reconsider the extraction of f_B and the on-shell mass M_b from HQET Laplace spectral sum rules known to N2LO PT series and including dimension 7 condensates in the OPE. We especially study the convergence of the PT series, the effects on "different spectral sum rules data" of the continuum threshold and subtraction point varied in a larger range than in the existing literature and include in the error an estimate of the N3LO PT series based on a geometric growth of the PT series. We obtain the Renormalization Group Invariant (RGI) universal coupling : \hat f_B^\infty=0.416(60) GeV^{3/2} in the static limit M_b \to \infty and the physical decay constant including 1/M_b corrections: f_B^{hqet}=199(29) MeV. Using the ratio of sum rules, we obtain, to order α_s^2, the running mass m_b(m_b)=4213(59) MeV. The previous results are in good agreement with the ones from QCD spectral sum rules (QSSR) in full QCD to the same order from the same channel [1]: f_B^{qcd}=206(7) MeV and m_b(m_b)^{qcd}=4236(69) MeV.

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arXiv2012

A fresh look into m_{c,b} and precise f_{D_(s),B_(s)} from heavy-light QCD spectral sum rules

Using recent values of the QCD (non-) perturbative parameters given in Table 1 and an estimate of the N3LO QCD perturbative contributions based on the geometric growth of the PT series, we re-use QCD spectral sum rules (QSSR) known to N2LO PT series and including all dimension-six NP condensate contributions in the full QCD theory, for improving the existing estimates of {m}_{c,b} and f_{D_(s)}, f_{B_(s)} from the open charm and beauty systems. We especially study the effects of the subtraction point on "different QSSR data" and use (for the first time) the Renormalization Group Invariant (RGI) scale independent quark masses in the analysis. The estimates [rigourous model-independent upper bounds within the SVZ framework] reported in Table 8: f_D/f_π=1.56(5)[< 1.68(1)], f_B/f_π=1.58(5)[< 1.80(3)] and f_{D_s}/f_K= 1.58(4) [< 1.63(1)], f_{B_s}/f_K=1.50(3)[< 1.61(3.5)], which improve previous QSSR estimates, are in perfect agreement (in values and precisions) with some of the experimental data on f_{D,D_s} and on recent lattice simulations within dynamical quarks. These remarkable agreements confirm both the success of the QSSR semi-approximate approach based on the OPE in terms of the quark and gluon condensates and of the Minimal Duality Ansatz (MDA) for parametrizing the hadronic spectral function which we have tested from the complete data of the J/ψand Υsystems. The values of the running quark masses m_c(m_c)=1286(66) MeV and m_b(m_b)= 4236(69) MeV from M_{D,B} are in good agreement though less accurate than the ones from recent J/ψand Υsum rules.

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arXiv2012

Summary on m_{c,b}(m_{c,b}) and precise f_{D_(s),B_(s)} from heavy-light QCD spectral sum rules

We summarize recent results obtained in [1] on the running m_{c,b}(m_{c,b}) in the MS scheme and f_{D_(s), B_(s)} using QCD spectral sum rules (QSSR) known to N2LO PT series, including all dimension-six NP condensate contributions in the full QCD theory, an estimate of the N3LO terms based on the geomteric growth of the PT series and using the most recent values of the QCD input parameters given in Table [1]. The study of the effects of the subtraction scale μon "different QSSR data" and the use (for the first time) of the Renormalization Group Invariant (RGI) scale independent quark masses in the analysis are emphasized. The estimates [rigourous model-independent upper bounds] reported in Table 2: f_D/f_π=1.56(5)[< 1.68(1)], f_B/f_π=1.58(5)[< 1.80(3)] and f_{D_s}/f_K= 1.58(4) [< 1.63(1)], f_{B_s}/f_K=1.50(3)[< 1.61(3.5)], improve previous QSSR estimates. The remarkable agreements with some of the experimental data on f_{D,D_s} and with lattice simulations within dynamical quarks confirm both the success of the QSSR semi-approximate approach based on the OPE in terms of the quark and gluon condensates and of the Minimal Duality Ansatz (MDA) for parametrizing the hadronic spectral function which we have tested from the complete data of the J/ψand Υsystems. The running quark masses m_c({m_c})=1286(66) MeV and m_b({m_b})= 4236(69) MeV from M_{D,B} are in good agreement though less accurate than the ones from recent J/ψand Υsum rules.

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arXiv2012

Isospin violating decay of $ψ(3770)\rightarrow J/ψ+ π^0$

The strong-isospin violation in $ψ(3770)\rightarrow J/ψ+ π^0$ via intermediate $D$ meson loops is investigated in an effective Lagrangian approach. In this process, there is only one $D$-meson loop contributing to the absorptive part, and the uncertainties due to the introduction of form factors can be minimized. With the help of QCD spectral sum rules (QSSR), we extract the $J/ψDD^*$ form factor as an implement from the first principle of QCD. The $DD^*π^0$ form factor can be well determined from the experimental data for $D\rightarrowπlν$. The exploration of the dispersion relation suggests the dominance of the dispersive part via the intermediate $D$ meson loops even below the open charm threshold. This investigation could provide further insights into the puzzling question on the mechanisms for $ψ(3770)\to$ non-$D\bar{D}$ transitions.

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arXiv2011

Gluon Condensates and m_b(m_b) from QCD-Exponential Moments at Higher Orders

We test the convergence of the QCD exponential moments by including PT corrections to order α_s^3 and the NP contributions up to D=8 condensates. Then, using the ratio of exponential sum rules where the QCD PT series is more convergent, we study the correlation between the gluon condensates <α_s G^2> and < g^3f_{abc} G^3>. From charmonium systems and using the charm quark mass as input, we deduce:< g^3f_{abc} G^3> =(8.2+-1.0)GeV^2 <α_s G^2> corresponding to < α_s G^2>=(7.5+- 2.0) 10^{-2} GeV^4. Using these results for the bottomium systems, we obtain: m_b(m_b)= 4212(32) MeV, which is slightly higher but consistent within the errrors with the ones from Q^2-moments and their ratios: m_b(m_b)= 4172(12) MeV. We are tempted to consider as a final result from the sum rules approaches, the average m_b(m_b)= 4177(11) MeV of the two previous determinations.

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arXiv2011

Gluon Condensates and m_{c,b} from QCD-Moments and their ratios to Order alpha_s^3 and

We reconsider the extraction of the gluon condensates , and the MS running quark masses m_{c,b} from different M_n(Q^2) Moments and their Ratios by including PT corrections to order alpha_s^3, NPT terms up to and using stability criteria of the results versus the degree n (number of Q^2-derivative). We explicitly show that the spectral part of the lowest moment M_1(0) depends strongly (as expected) on its high-energy (continuum) contribution, which is minimized for M_{n> 3-4}(0). Using higher moments and the correlations of with and < G^4>, we obtain =(7.0+- 1.3)10^{-2} GeV^4 and =(8.8+- 5.5) GeV^2 , while our analysis favours a modified factorisation for . Using the previous results, we re-determine m_c(m_c) and find that the commonly used M_1(0) lowest moment tends to overestimate its value compared to the ones from higher moments where stable values of m_c(m_c) versus the variations of n and the continuum models are reached. These features can indicate that the quoted errors of m_{c,b} from M_1(0) may have been underestimated. Optimal results from different high-n moments converge to the accurate (artithmetic) mean values: m_c(m_c)=1261(16) MeV and m_b(m_b)=4171(14) MeV, in excellent agreement with results obtained in [1] using some judicious choices of ratios of moments.

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arXiv2011

Gluon condensates and c, b quark masses from quarkonia ratios of moments

We extract (for the first time) the ratio of the gluon condensate < g^3f_{abc}G^3 >/< alpha_s G^2 > expressed in terms of the liquid instanton radius rho_c from charmonium moments sum rules by examining the effects of < alpha_s G^2 > in the determinations of both rho_c and the running MS mass m_c(m_c). Using a global analysis of selected ratios of moments at different Q^2=0, 4m_c^2 and 8m_c^2 and taking < alpha_s G^2 > from 0.06 GeV^4, where the estimate of rho_c is almost independent of < alpha_s G^2 >, we deduce: rho_c=0.98(21) GeV^{-1} which corresponds to < g^3f_{abc}G^3 > = (31+- 13) GeV^2 < alpha_s G^2 >. The value of m_c(m_c) is less affected (within the errors) by the variation of < alpha_s G^2 >, where a common solution from different moments are reached for < alpha_s G^2 > greater than 0.02 GeV^4. Using the values of < alpha_s G^2 >=0.06(2) GeV^4 from some other channels and the previous value of < g^3f_{abc}G^3 >, we deduce: m_c(m_c)=1260(18) MeV and m_b(m_b)=4173(10) MeV, where an estimate of the 4-loops contribution has been included. Our analysis indicates that the errors in the determinations of the charm quark mass without taking into account the ones of the gluon condensates have been underestimated. To that accuracy, one can deduce the running light and heavy quark masses and their ratios evaluated at M_Z, where it is remarkable to notice the approximate equalities: m_s/m_u= m_b/m_s= m_t/m_b= 51(4), which might reveal some eventual underlying novel symmetry of the quark mass matrix in some Grand Unified Theories.

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arXiv2010

SVZ sum rules : 30 + 1 years later

For this exceptional 25th anniversary of the QCD-Montpellier series of conferences initiated in 85 with the name "Non-perturbative methods", we take the opportunuity to celebrate the 30 + 1 years of the discovery of the SVZ (also called ITEP, QCD or QCD spectral) sum rules by M.A. Shifman, A.I. Vainshtein and V.I. Zakahrov in 79 [1]. In this talk, I have the duty to present the status of the method. I shall (can) not enumerate the vast area of successful applications of sum rules in hadron physics but I shall focus on the historical evolution of field and its new developments. More detailed related discussions and more complete references can be found in the textbooks [2,3].

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arXiv2010

Investigating different structures for the $X(3872)$

Using the QCD spectral sum rule approach we investigate different currents with $J^{PC}=1^{++}$, which could be associated with the $X(3872)$ meson. Our results indicate that, with a four-quark or molecular structure, it is very difficult to explain the narrow width of the state unless the quarks have a special color configuration.

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arXiv2009

1^{-+} light exotic mesons in QCD

We systematically re-examine the extraction of the masses and couplings of the 1^{-+} hybrid, four-quark and molecule mesons from QCD spectral sum rules (QSSR). To NLO for the perturbative and power corrections, the hybrid mass is M_H=1.81(6) GeV and M_H < 2.2(2) GeV from the positivity of the spectral function. In the same way, but to LO, the four-quark state mass is M_{4q}= 1.70(4) GeV and M_{4q} < 2.4(1) GeV, while the molecule mass is about 1.3(1) GeV. The observed π_1(1400) and π_1(1600) might be explained by a two-component mixing with the set of input masses (1.2-1.3 ; 1.70-1.74) GeV and with a mixing angle θ= -(11.7+- 2.2)^0, which slightly favours a molecule/four-quark mixing, and which eventually suggests that the π_1(2015) is mostly an hybrid meson. Isospin and non-exotic partners of the previous states and some of their radial excitations are also expected to be found in the energy region around 2 GeV. Further tests of this phenomenological scenario are required.

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arXiv2009

Tribute to Francisco (Paco) Yndurain

This part of the talk aims to present briefly the biodata and the exceptional career of Paco Yndurain who left us suddenly in June 2008. The scientific part: Light Scalar Mesons in QCD is published in the proceedings of QCD 08 (Montpellier 7-12th july 2008: arXiv:0811.0563 [hep-ph]).

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arXiv2009

Power corrections to alpha_s(M_τ),|V_{us}| and m_s

We re-examine recent determinations of power corrections from tau-decay and confront the results with the existing ones from QCD spectral sum rules (QSSR). We conclude that contrary to the QSSR analysis, which lead to =(6.8+-1.3)10^{-2} GeV^4, tau-decay is not a good place for extracting the gluon condensate due to its extra alpha_s^2 coefficient which suppresses its contribution in this process. Results from e^+e^- sum rules and tau-decay: rho alpha_s ^2= (4.5+-0.3)10^{-4}GeV^6, where rho=3.0+-0.2 confirm the deviation from the vacuum saturation estimate of the four-quark condensate."Non-standard" power corrections (direct instantons, duality violation and tachyonic gluon mass) beyond the SVZ-expansion, partially cancel out in the V+A hadronic tau-decay channel, which gives at order alpha_s^4: alpha_s(M_tau)=0.3249(29)_{ex}(75)_{th} leading to als(M_Z)|_tau=0.1192 (4)_{ex}(9)_{th},in remarkable agreement with (but more accurate than) alpha_s(M_Z)|_Z=0.1191(27)obtained at the same alpha_s^4 order from the Z-width and the global fit of electroweak data. Finally, the role of the tachyonic gluon mass in the determinations of |V_{us}|from tau-decay and of m_s from tau-decay, e^+e^- and (pseudo)scalar channels is emphasized.

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arXiv2008

Light scalar mesons in QCD

I present a mini-review of the masses and couplings of the bare (unmixed) light scalar mesons : $\bar qq, (\overline{qq})(qq), (\bar qq)(\bar qq), gg$ from QCD spectral sum rules (QSSR) and low-energy theorems (LET) which we compare with recent lattice calculations when available. Some unbiased comments on the different scenarios are given. The possiblity for the $σ(0.6)$ to be mostly a gluonium/glueball with a huge violation of the OZI rule in its decay is discussed. This review complements and updates the ones presented earlier [1]. Despite some progresses, the internal structure of the light scalar mesons remain puzzling, and some further efforts are required. It will be more fun at LHC if the Higgs of the Standard Model is a $σ$-like resonance.

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