Sum rules in the oscillator radiation processes

We consider the problem of a harmonic oscillator coupled to a scalar field in the framework of recently introduced dressed coordinates. We compute all the probabilities associated with the decay process of an excited level of the oscillator. Instead of doing direct quantum mechanical calculations we establish some sum rules from which we infer the probabilities associated to the different decay processes of the oscillator. Thus, the sum rules allows to show that the transition probabilities between excited levels follow a binomial distribution. (c) 2005 Published by Elsevier B.V.

The bottom-quark mass from non-relativistic sum rules at NNNLO

We determine the mass of the bottom quark from high moments of the bbproduction cross section in e+e−annihilation, which are dominated by the threshold region. On the theory side next-to-next-to-next-to-leading order (NNNLO) calculations both for the resonances and the continuum cross section are used for the first time. We find mPSb(2GeV) =4.532+0.013−0.039GeVfor the potential-subtracted mass and mMSb(mMSb) =4.193+0.022−0.035GeVfor the MSbottom-quark mass.

A QCD sum rule calculation for the Y(4140) narrow structure

We use the QCD sum rules to evaluate the mass of a possible scalar mesonic state that couples to a molecular D(s)*(D) over bar (s)* current. We find a mass m(Ds)*(Ds)* = (4.14 +/- 0.09) GeV, which is in an excellent agreement with the recently observed Y(4140) charmonium state. We consider the contributions of condensates up to dimension-eight, we work at leading order in alpha(s) and we keep terms which are linear in the strange quark mass m(s). We also consider a molecular D*(D) over bar* current and we obtain m m(D)*(D)* = (4.13 +/- 0.10), around 200 MeV above the mass of the Y(3930) charmonium state. We conclude that it is possible to describe the Y(4140) structure as a D(s)*(D) over bar (s)* molecular state or even as a mixture of D(s)*(D) over bar (s)* and D*(D) over bar* molecular states. (C) 2009 Elsevier B.V. All rights reserved.

QCD sum rule calculation for the charmonium-like structures in the J/psi phi and J/psi omega invariant mass spectra

Using the QCD sum rules we test if the charmonium-like structure Y(4274), observed in the J/psi phi invariant mass spectrum, can be described with a D(s)(D) over bar (s0)(2317)+ h.c. molecular current with J(PC) = 0(-+). We consider the contributions of condensates up to dimension ten and we work at leading order in alpha(s). We keep terms which are linear in the strange quark mass m(s). The mass obtained for such state is mD(s)D(s0) = (4.78 +/- 0.54) GeV. We also consider a molecular 0(-+) D (D) over bar (0)(2400)+ h.c. current and we obtain m(DD0) = (4.55 +/- 0.49) GeV. Our study shows that the newly observed Y(4274) in the J/psi phi invariant mass spectrum can be, considering the uncertainties, described using a molecular charmonium current. (C) 2011 Elsevier B.V. All rights reserved.

QCD sum rule study for a possible charmed pentaquark Θ c(3250)

We use QCD sum rules to study the possible existence of a Θc(3250) charmed pentaquark. We consider the contributions of condensates up to dimension 12 and work at leading order in αs. We obtain mΘc=(3.29±0.13) GeV, compatible with the mass of the structure seen by BABAR Collaboration in the decay channel B-→p̄Σc++π-π-. The proposed state is compatible with a previous proposed pentaquark state in the anticharmed sector. © 2013 American Physical Society.

Heavy λ semileptonic decay: A QCD sum rule approach

In this work we calculate the form factors of the Lambda(c) and Lambda(b) semileptonic decay using the QCD sum rules approach. We found that the form factors sum rules are more stable than the respective mass sum rules, and we get a decay rate for Lambda(c) compatible with experiment.

QCD sum rule approach to the s->d gamma contribution to the Omega(-)->Xi(-)gamma radiative decay

QCD sum rules are used to calculate the contribution of the short-distance single-quark transition s-->d gamma to the amplitudes of the hyperon radiative decay Omega(-)-->Xi(-) gamma. We reevaluate the Wilson coefficient of the effective operator responsible for this transition. We obtain a branching ratio which is comparable to the unitarity limit.

Renormalization of the axial-vector current in QCD

Following the method of Ioffe and Smilga, the propagation of the baryon current in an external constant axial-vector field is considered. The close similarity of the operator-product expansion with and without an external field is shown to arise from the chiral invariance of gauge interactions in perturbation theory. Several sum rules corresponding to various invariants both for the nucleon and the hyperons are derived. The analysis of the sum rules is carried out by two independent methods, one called the ratio method and the other called the continuum method, paying special attention to the nondiagonal transitions induced by the external field between the ground state and excited states. Up to operators of dimension six, two new external-field-induced vacuum expectation values enter the calculations. Previous work determining these expectation values from PCAC (partial conservation of axial-vector current) are utilized. Our determination from the sum rules of the nucleon axial-vector renormalization constant GA, as well as the Cabibbo coupling constants in the SU3-symmetric limit (ms=0), is in reasonable accord with the experimental values. Uncertainties in the analysis are pointed out. The case of broken flavor SU3 symmetry is also considered. While in the ratio method, the results are stable for variation of the fiducial interval of the Borel mass parameter over which the left-hand side and the right-hand side of the sum rules are matched, in the continuum method the results are less stable. Another set of sum rules determines the value of the linear combination 7F-5D to be ≊0, or D/(F+D)≊(7/12). .AE

Constantes de acoplamento de vértices com mésons estranhos e charmosos usando as regras de soma da QCD

Neste trabalho, foram calculados os fatores de forma e as constantes de acoplamento dos vértices mesônicos J/ψ DsDs, J/ψ Ds*Ds e J/ψ Ds*Ds*usando a técnica das regras de soma da QCD (RSQCD) até a ordem 5 da OPE. Estes três vértices estão envolvidos em algumas das numerosas hipóteses que tentam explicar a estrutura interna de alguns mésons charmosos exóticos que começaram a ser observados a partir de 2003. Tais mésons não se encaixam no espectro do charmonium e/ou apresentam números quânticos exóticos dentro do modelo CQM (constituent quark model). Um exemplo é o méson Y(4140), cujo decaimento observado é no par J/ψφ enquanto o esperado seria que tivesse decaimento predominante em mésons com open charm, devido à sua massa. Uma das propostas para se entender este méson consiste em estudá-lo como um estado molecular Ds*ar{D}s*, de modo que seu decaimento seria Y(4140) → Ds* ar{D}s* → J/ψφ. Neste processo, aparecerão os vértices de interação estudados neste trabalho, de maneira que o conhecimento mais preciso de seus fatores de forma e de suas constantes de acoplamento pode beneficiar a compreensão sobre a constituição fundamental do Y(4140) assim como a de outros novos estados como o X(4350), Y(4274) e Y(4660) por exemplo. Foram considerados neste trabalho, todos os casos off-shell possíveis para cada um dos três vértices, obtendo assim dois fatores de forma distintos para o vértice J/ψ DsDs, três para o vértice J/ψ Ds*Ds e dois para o vértice J/ψ Ds* Ds*. Nestes três vértices, os fatores de forma para o caso J/ψ off-shell foram bem ajustados por curvas monopolares enquanto os casos Ds e Ds* foram ajustados por curvas exponenciais, o que está de acordo com o comportamento encontrado em trabalhos anteriores do grupo. Os cálculos das constantes de acoplamento tiveram como resultados: g_{J/ψ Ds Ds} = 5.98^{+0.67}_{ -0.58}, g_{J/ψ D*s Ds} = 4.30_{+0.41}^{-0.35}GeV^{-1} e g_{J/ψ Ds* Ds*} = 7.47^{+1.04}_{-0.71}, resultados estes que estão compatíveis com os trabalhos anteriores que utilizaram as RSQCD para o cálculo das constantes de acoplamento dos vértices J/ψ D(*)D(*).

The omega DD vertex in a sum rule approach

The study of charmonium dissociation in heavy ion collisions is generally performed in the framework of effective Lagrangians with meson exchange. Some studies are also developed with the intention of calculate form factors and coupling constants related with charmed and light mesons. These quantifies are important in the evaluation of charmonium cross sections. In this Letter we present a calculation of the omega DD vertex that is a possible interaction vertex in some meson-exchange models spread in the literature. We used the standard method of QCD sum rules in order to obtain the vertex form factor as a function of the transferred momentum. Our results are compatible with the value of this vertex form factor (at zero momentum transfer) obtained in the vector-meson dominance model. (c) 2006 Elsevier B.V. All rights reserved.

Uses of QCD sumrules (QCDSR) from different points of view

We support the idea that the baryon, B with mass MB, couples to its current with a coupling λ2 B ∼ 0.71 M6 B from an analysis of magnetic moment sum rules. And we find a sum rule among the experimental magnetic moments which is independent of the parameters of QCDSR. © 1998 Elsevier Science B.V. All rights reserved.

Relating the quark and gluon condensâtes through the QCD vacuum energy

Using the Cornwall-Jackiw-Tomboulis effective potential for composite operators we compute the QCD vacuum energy as a function of the dynamical quark and gluon propagators, which are related to their respective condensâtes as predicted by the operator product expansion. The identification of this result to the vacuum energy obtained from the trace of the energy-momentum tensor allows us to study the gluon self-energy, verifying that it is fairly represented in the ultraviolet by the asymptotic behavior predicted by the operator product expansion, and in the infrared it is frozen at its asymptotic value at one scale of the order of the dynamical gluon mass. We also discuss the implications of this identity for heavy and light quarks. For heavy quarks we recover, through the vacuum energy calculation, the relation nij{filif)-îi(asl'n)GlivGllv obtained many years ago with QCD sum rules. ©2000 The American Physical Society.

Um estudo sobre o fator de forma 'gkk*'pi'(q POT. 2)' usando regras de soma da QCD

Pós-graduação em Física - IFT

Deep inelastic electroproduction structure functions for polarized and unpolarized proton targets

Following Ioffe's method of QCD sum rules the structure functions F2(x) for deep inelastic ep and en scattering are calculated. Valence u-quark and d-quark distributions are obtained in the range 0.1 less, approximate x <0.4 and compared with data. In the case of polarized targets the structure function g1(x) and the asymmetry Image Full-size image are calculated. The latter is in satisfactory agreement in sign and magnitude with experiments for x in the range 0.1< x < 0.4.

Axial and pseudoscalar current correlators and their couplings to eta and eta(') mesons

Correlators of singlet and octet axial currents, as well as anomaly and pseudoscalar densities have been studied using QCD sum rules. Several of these sum rules are used to determine the couplings f(eta)(8),f(eta)(0), f(eta)('8) and f(eta)('0). We find mutually consistent values which are also in agreement with phenomenological values obtained from data on various decay and production rates. While most of the sum rules studied by us are independent of the contributions of direct instantons and screening correction, the singlet-singlet current correlator and the anomaly-anomaly correlator improve by their inclusion.