arXiv subjects

Stephan Narison

Publications and source records attributed to Stephan Narison.

At least 55 records · Page 3Linked to original sources

arXiv2008

|V_{cd}|, |V_{cs}| and f_{D_s} from (semi) leptonic $D_{(s)}$-decays : signals of New Physics ?

We confront the recent improved measurements of the D_{(s)} (semi) leptonic decays with lattice QCD (LQCD) with n_f=3 flavours and QCD spectral sum rules (QSSR) predictions. D\toμν_μleptonic width data compared with theoretical determinations of f_D, leads to the value of the CKM mixing angle : |V_cd|= 0.230 (10)_exp (9)_th. Measured ratio of the D semi-leptonic widths combined with LQCD and QSSR predictions leads to the average |V_cd|/|V_cs|= 0.2175(88), and then to |V_cs|= 1.068(47). We consider the previous determinations as improvements of the existing estimates. Using the average data of the D_s\to μν_μ(resp. D_s\to τν_τ) branching ratios, one obtains : |V_cs|f_{D_s}^μ= (259 +- 12) {MeV} (resp) |V_cs|f_{D_s}^τ= (274 +- 13) {MeV}, which can be compared with the average of the Standard Model (SM) values from LQCD and QSSR f_{D_s}=(240 +- 7) MeV. If one uses the present determination of |V_cs|, there is an agreement with the SM prediction within 1σ. If instead, we impose the unitarity constraint |V_cs|< 1, or assume (as frequently done) |V_cs|=|V_ud|, we would obtain a deviation from the SM expectations ranging from 1.5 to 3 σ, eventually signaling some New Physics beyond the SM.

hep-ph↗

arXiv2008

A Fresh Look into the Neutron EDM and Magnetic Susceptibility

We reexamine the estimate of the neutron Electric Dipole Moment (NEDM) from chiral and QCD spectral sum rules (QSSR) approaches. In the former, we evaluate the pion mass corrections which are about 5% of the leading Log. results. However, the chiral estimate can be affected by the unknown value of the renormalizaton scale nu. For QSSR, we analyze the effect of the nucleon interpolating currents on the existing predictions. We conclude that previous QSSR results are not obtained within the optimal choice of these operators, which lead to an overestimate of these results by about a factor 4. The weakest upper bound |theta|< 2 10^-9 for the strong CP-violating angle is obtained from QSSR, while the strongest upper bound |theta|< 1.3 10^-10 comes from the chiral approach evaluated at the scale ν=M_N. We also re-estimate the proton magnetic susceptibility, which is an important input in the QSSR estimate of the NEDM.

hep-ph↗

arXiv2006

Strange quark mass from e+e- revisited and present status of light quark masses

We reconsider the determinations of the strange quark mass m_s from e+e- into hadrons data using a new combination of FESR and revisiting the existing tau-like sum rules by including non-resonant contributions to the spectral functions. To order alpha_s^3 and including the tachyonic gluon mass lambda^2 contribution, which phenomenologically parametrizes the UV renormalon effect into the PT series, we obtain the invariant mass m_s=(119 +- 17)MeV leading to: m_s(2 GeV)=(104+- 15)MeV. Combining this value with the recent and independent phenomenological determinations from some other channels, to order alpha_s^3 and including lambda^2, we deduce the weighted average: m_s (2 GeV)=(96.1 +- 4.8)MeV . The positivity of the spectral functions in the (pseudo)scalar [resp. vector] channels leads to the lower [resp. upper] bounds of m_s(2 GeV): (71 +- 4) MeV < m_s(2 GeV) < (151 +- 14) MeV, to order alpha_s^3. Using the ChPT mass ratio r_3 = 2m_s/(m_u+m_d)=24.2 +- 1.5, and the average value of m_s, we deduce: (m_u+m_d)(2 GeV)=(7.9 +- 0.6) MeV, consistent with the pion sum rule result, which, combined with the ChPT value for m_u/m_d, gives: m_d(2 GeV)=(5.1 +- 0.4)MeV and m_u(2 GeV)=(2.8 +- 0.2)MeV. Finally, using (m_u+m_d) from the pion sum rule and the average value of m_s (without the pion sum rule), the method gives: r_3= 23.5 +- 5.8 in perfect agreement with the ChPT ratio, indicating the self-consistency of the sum rule results. Using the value: m_b(m_b)=(4.23 +- 0.06) GeV, we also obtain the model-building useful scale-independent mass ratio: m_b/m_s=50 +- 3.

hep-ph↗

arXiv2006

QCD Tests of the Puzzling Scalar Mesons

Motivated by several recent data, we test the QCD spectral sum rules (QSSR) predictions based on different proposals (\bar qq, \bar q\bar q qq, and gluonium) for the nature of scalar mesons. In the I=1 and 1/2 channels, the unusual (wrong) splitting between the a_0(980) and κ(900) and the a_0(980) width can be understood from QSSR within a \bar qq assignement. However, none of the \bar qq and \bar q\bar q qq results can explain the large κwidth, which may suggest that it can result from a strong interference with non-resonant backgrounds. In the I=0 channel, QSSR and some low-energy theorems (LET) require the existence of a low mass gluonium σ_B(1 GeV) coupled strongly to Goldstone boson pairs which plays in the U(1)_V channel, a similar role than the η' for the value of the U(1)_A topological charge. The observed σ(600) and f_0(980) mesons result from a maximal mixing between the gluonium σ_B and \bar qq(1 GeV) mesons, a mixing scheme which passes several experimental tests. OZI violating J/ψ--> ϕπ^+π^-, D_s--> 3πdecays and J/ψ--> γS glueball filter processes may indicate that most of the I=0 mesons above 1 GeV have important gluonium in their wave functions. We expect that the f_0(1500), f_0(1710) and f_0(1790) have significant gluonium component in their wave functions, while the f_0(1370) is mostly \bar qq. Tests of these results can be provided by the measurements of the pure gluonium η'ηand 4πspecific U(1)_A decay channels.

hep-ph↗

arXiv2006

U(1)_A Topological Susceptibility and its Slope, Pseudoscalar Gluonium and the Spin of the Proton

We review the determinations of the pseudoscalar glueball and eventual radial excitation of the η' masses and decay constants from QCD spectral sum rules (QSSR). The glueball mass is (2.05+-0.19) which one can compare with the eventual experimental candidate X(1835), while the η(1400) is likely a radial excitation of the η'-meson. Their effects on the estimates of U(1)_A topological susceptibility and its slope as well as the impact of the latter in the estimate of the spin of the proton is discussed. We predict the singlet polarized parton distributions to be a^0(Q^2=4 GeV^2)=0.32+-0.02, which is about a factor two smaller than the OZI value, but comparable with the COMPASS measurement of 0.24+-0.02.

hep-ph↗

arXiv2005

The SVZ-Expansion and Beyond

I discuss the standard SVZ-expansion of the QCD two-point correlators in terms of the QCD vacuum condensates and beyond it due to a new unflavoured 1/Q^2-term (tachyonic gluon mass squared λ^2) which modelizes the effects of uncalculated higher order perturbative terms. The approach is confronted with low-energy and lattice data. One can notice that, in the different examples studied here, high-dimension condensates are expected to deviate largely from their vacuum saturation (large N_c) values, while the new 1/Q^2-term due to λ^2 solves the hadronic mass scale hierarchy-puzzle encountered in the early SVZ-sum rule analysis and improves the low-energy phenomenology. From tau-decay data, one can extract the running strange quark mass m_s(2 GeV)=(93^{+29}_{-32}) MeV and a more accurate value of the QCD coupling α_s(M_Z)=0.117+- 0.002.

hep-ph↗

arXiv2005

V-A hadronic tau decays : a laboratory for the QCD vacuum

ALEPH/OPAL data on the V-A spectral functions from hadronic tau decays are used in connection with a set of Laplace transform sum rules (LSR) for fixing the size of the QCD vacuum condensates up to dimension 18. Our results favour the ones from large-N_c QCD within the Minimal Hadronic Approximation (MHA) and show a violation of about a factor 2-5 of the vacuum saturation estimate of the dimension-six to -ten condensates. We scrutinize the different determinations of the QCD vacuum condensates using tau-decays data. After revisiting some of the existing results, we present coherent values of the condensates from different methods.

hep-ph↗

arXiv2005

Strange Quark, Tachyonic Gluon Masses and V_{us} from Hadronic Tau Decays

We apply, to the new OPAL data on V+A strange spectral functions, a suitable combination of QCD spectral sum rules directly sensitive to the combination of strange quark (m_s) and tachyonic gluon (λ^2) masses . Using the mean value of λ^2 from a sum rule analysis of different channels, we deduce the invariant strange quark mass m_s= (106 +33 -37) MeV to order α_s^3, which leads to the running mass m_s(2 GeV)= (93 +29 -32) MeV. We also obtain an interesting though less competitive estimate of the CKM angle: |V_{us}|=0.217\pm 0.019.

hep-ph↗

arXiv2004

Heavy-light mesons in QCD

This talk summarizes the study of the dynamics of the heavy-light \bar Qq open charm and beauty mesons obtained in [1] using QCD spectral sum rules (QSSR) and motivated by the recent experimental discovery of the D{sJ}(2317) and D{sJ}(2457) mesons. The important rôle of the chiral condensate <\barψψ> in the mass-splittings between the scalar-pseudoscalar mesons is emphasized. The emerging value of the running charm quark mass for reproducing the well-known D(0-) and Ds(0-) masses is: mc(mc)=1.13^{+0.08}_{-0.04} GeV, which confirms previous estimates from this channel [2]. Using this value, the sum rules give: M{Ds(0+)}= (2297+- 113) MeV, and a small SU(3) breaking: M{Ds{(0+)}}-M{D{(0+)}}= 25 MeV. Extending the analysis to the B-system, we find M{B(0+)}- M{B(0-)}= (422+- 196) MeV = M{Ds(0^+)}-M{Ds(0^-)}. Assuming an approximate (heavy and light) flavour and spin symmetries of the mass-splittings as indicated by the previous results, one also deduces M{D*s(1+)}= (2440+- 113) MeV. Finally, one also gets: f{D(0+)}= (217+- 25) MeV much bigger than fπ=130.6 MeV, suggesting a large violation of the 1/sqrt{M_D} scaling, while the size of the SU(3) breaking ratio f{Ds(0+)}/f{D(0+)}= 0.93+- 0.02 is opposite to the one of the 0^- channel of about 1.14.

hep-ph↗

arXiv2004

Are the pentaquark sum rules reliable?

We rewiew and scrutinize the existing mass determinations of the pentaquarks from the exponential Laplace Sum Rules (LSR). We do not find any sum rule window for extracting optimal and reliable results from the LSR, due to the unusual slow convergence of the OPE and to the exceptional important role of the QCD continuum into the spectral function in this channel. Instead, we use in this channel,for the first time, Finite Energy Sum Rules (FESR), which exhibit a nice stability in the QCD continuum threshold t_c, at which one can extract, with a good accuracy, the mass of the lowest resonance. Including the D=7, 9 condensate contributions in the OPE, we obtain M_Theta=(1513+- 114) MeV, and the corresponding residue lambda_Theta^2= -(0.14-- 0.49)x 10^{-9} GeV^{12}, which favours the I=0, J=1/2, and negative parity S-wave interpretation of the Theta (1540). However, our analysis indicates a degeneracy between the unmixed I=0 and I=1 S-wave states. In the I=0, J=1/2, P-wave channel, we obtain, for the P-resonance, M_P = (1.99+- 0.19) GeV and lambda_P= -(0.7--7.1)x 10^{-9} GeV^{14}, which we expect to be discovered experimentally. Our results also suggest that some intuitive choices of the continuum threshold used in the LSR literature are inconsistent with the FESR results. Finally, a study of the Theta-K-N coupling using a vertex sum rule shows that, for the I=0, S-wave channel, the leading OPE contributions only start to order alpha_s^2 in the chiral limit m_s=0, indicating that the Theta is very narrow.

hep-ph↗

arXiv2004

Open Charm and Beauty Chiral Multiplets in QCD

We study the dynamics of the the spin zero open charm and beauty mesons using QCD spectral sum rules (QSSR), where we observe the important rôle of the chiral condensate <\bar ψψ> in the mass-splittings between the scalar-pseudoscalar mesons. Fixing the sum rule parameters for reproducing the well-known D(0-) and Ds(0-) masses, we re-obtain the running charm quark mass: mc(mc)=1.13^{+0.08}_{-0.04} GeV, which confirms our recent estimate from this channel [1]. Therefore, using sum rules, with no-free parameters, we deduce M_{Ds(0+)}= (2297+- 113) MeV, which is consistent with the observed Ds(2317) meson, while a small SU(3) breaking of about 25 MeV for the Ds(0+)-D(0+) mass-difference has been obtained. We extend our analysis to the B-system and find M{B(0+)}- M{B(0-)}= (422+- 196) MeV confirming our old result from moment sum rules [2]. Assuming an approximate (heavy and light) flavour and spin symmetries of the mass-splittings as indicated by our results, we also deduce M_{D*s(1+)}= (2440+-113) MeV in agreement with the observed D{sJ}(2457). We also get: f{D(0+)}= (217+- 25) MeV much bigger than fpi=130.6 MeV, while the size of the SU(3) breaking ratio f{Ds(0+)}/f{D(0+)}= 0.93+- 0.02 is opposite to the one of the 0- channel of about 1.14.

hep-ph↗

arXiv2003

Scalar mesons and the muon anomaly

We evaluate systematically some new contributions of the QCD scalar mesons, including radiative decay-productions, not considered with a better attention until now in the evaluation of the hadronic contributions to the muon anomaly. The sum of the scalar contributions to be added to the existing Standard Model predictions a_mu^{SM} are estimated in units 10^{-10} to be a^{S}_mu= 1.0(0.6) [TH based]} and 13(11) [ PDG based], where the errors are dominated by the ones from the experimental widths of these scalar mesons. PDG based results suggest that the value of a_mu^{SM} and its errors might have been underestimated in previous works. The inclusion of these new effects leads to a perfect agreement (< 1.1σ) of the measured value a^{exp}_mu and a_mu^{SM} from tau-decay and implies a (1.5 ~ 3.3) sigma discrepancy between a^{exp}_mu and a_mu^{SM} from e^+e^- into hadrons data. More refined unbiased estimates of a_mu^{SM} require improved measurements of the scalar meson masses and widths. The impact of our results to a_mu^{SM} is summarized in the conclusions.

hep-ph↗

arXiv2002

Fundamental Research and Developing Countries

In the first part of this report, I discuss the sociological role of fundamental research in Developing Countries (DC) and how to realize this program. In the second part, I give a brief and elementary introduction to the field of high-energy physics (HEP), accessible to a large audience not necessary physicists. The aim of this report is to make politicians and financial backers aware on the long-term usefulness of fundamental research in DC and on the possible globalisation of HEP and, in general, of science.

physics.soc-ph↗

arXiv2002

UV and IR divergences within Dimensional Regularization in Non-Commutative theories and Phenomenological Implications

Using Dimensional Regularization (DR) for some two-point functions of a prototype Non-Comutative (NC) ϕ^4 scalar theory in 4-dimensions, we explictly analyze, to one-loop, the IR and UV divergences of non-planar diagrams having quadratic divergences and compare to the case of the Pauli-Villars cut-off regularization (PVR). We also note that the IR structure 1/p0p obtained from DR is reproduced by PVR in the limit where the UV cut-off Λis set to infinity. We study the phenomenological implications of this result by rederiving bounds from low-energy data on the violation of Lorentz invariance based on the existence of the quadratic divergence. The most stringent (and regularization independent) bound on Lorentz violation from low-energy data is 1/\sqrtθ\approx ν\geq 10^{15} GeV for NCQCD and 10^{10} GeV for NCQED, which comes from the absence of sidereal variations between the Cs and Hg atomic clocks.

hep-ph↗

arXiv2002

Scalar mesons in QCD and tests of the gluon content of the sigma

We summarize the different features of the scalar mesons from QCD spectral sum rule analyses of the two- and three-point functions. The results do not favour the u-bar u + d-bar d interpretation of the broad and low mass sigma (0.6), and the u-bar s resonance nature of the eventually observed kappa(0.9) meson. We also discuss some OZI-violating and classic semileptonic and radiative decay processes which can reveal in a model-independent way the eventual gluon component sigma_B of the sigma. In a meson-gluonium mixing scenario, one also expects an observation of the K K-bar final states from the sigma_B which may compete (if phase space allowed) with the one from a low mass s-bar s state assumed in the literature to be the SU(3) partner of the $σ(0.6)$ if this latter is a u-bar u + d-bar d state

hep-ph↗

arXiv2002

B^0_{d,s} - \bar{B}^0_{d,s} mass-differences from QCD spectral sum rules

We present the first QCD spectral sum rules analysis of the SU(3) breaking parameter ξand an improved estimate of the renormalization group invariant (RGI) bag constant \hat{B}_{B_q} both entering into the B^0_{d,s} - \bar{B}^0_{d,s} mass-differences. The averages of the results from the Laplace and moment sum rules to order α_s are f_B\sqrt{\hat B_B} \simeq (247 \pm 59) MeV and ξ\equiv f_{B_s} \sqrt{\hat B_{B_s}} / f_{B} \sqrt{\hat B_{B}} \simeq (1.18\pm 0.03), in units where f_π=130.7 MeV. Combined with the experimental data on the mass-differences ΔM_{d,s}, one obtains the constraint on the CKM weak mixing angle |V_{ts}/V_{td}|^2 > 20.0 (1.1). Alternatively, using the weak mixing angle from the analysis of the unitarity triangle and the data on ΔM_d, one predicts ΔM_s=18.6 (2.2) ps^{-1} in agreement with the present experimental lower bound and within the reach of Tevatron 2.

hep-ph↗

arXiv2002

QCD as a theory of hadrons (from partons to confinement)

This submission is withdrawn by arXiv administrators. arXiv does not accept book advertisements.

hep-ph↗

arXiv2002

Status of the B^0_{(s)}-\bar B^0_{(s)}} mixing from QCD spectral sum Rules

In this talk, I present new results [1] obtained from QCD spectral sum rules (QSSR), on the bag constant parameters entering in the analysis of the B^0_{(s)}-\bar B^0_{(s)} mass-differences. Taking the average of the results from the Laplace and moment sum rules, one obtains to order α_s: f_B\sqrt{\hat B_B}= (228 +- 61) MeV, f_{B_s}\sqrt{B_{B_s}}/{f_{B}\sqrt{B_{B}}= 1.18 +- 0.03, in units where f_π=130.7 MeV. Combined with the experimental data on the mass-differences ΔM_{d,s}, one obtains the constraint on the CKM weak mixing angle: |V_{ts}/V_{td}|^2 > 20.2(1.3). Alternatively, using the weak mixing angle from the analysis of the unitarity triangle and the data on ΔM_d, one predicts ΔM_s=18.3(2.1) ps^{-1} in agreement with the present experimental lower bound and within the reach of Tevatron 2.

hep-ph↗