arXiv subjects

F. Jugeau

Publications and source records attributed to F. Jugeau.

At least 19 recordsLinked to original sources

arXiv2013

Anomalous dimensions and scalar glueball spectroscopy in AdS/QCD

An extended version of the AdS/QCD Soft-Wall model that incorporates QCD-like anomalous contributions to the dimensions of gauge theory operators is proposed. This exploratory approach leads to a relation between scalar glueball masses and beta functions. Using this relation, properties of the glueball mass spectroscopy that emerge from phenomenological beta functions proposed in the literature are investigated. The reverse problem is also considered: starting from a linear Regge trajectory which fits the lattice glueball masses, beta functions with different asymptotic infrared behaviours are found. Remarkably, some of them present a fixed point at finite coupling.

hep-th↗

arXiv2013

SVZ + 1/q2 expansion versus some QCD holographic Models

Considering the classical two-point correlators built from (axial)-vector, scalar \bar qq and gluonium currents, we confront results obtained using the SVZ + 1/q^2 expansion to the ones from some QCD holographic models in the Euclidian region and with negative dilaton Φ_i(z)=- |c_i^2| z^2. We conclude that the presence of the 1/q^2-term in the SVZ-expansion due to a tachyonic gluon mass appears naturally in the Minimum Soft Wall (MSW) and the Gauge/String Dual (GSD) models which can also reproduce semi-quantitatively some of the higher dimension condensate contributions appearing in the OPE. The Hard-Wall model shows a large departure from the SVZ + 1/q^2 expansion in the vector, scalar and gluonium channels due to the absence of any power corrections. The equivalence of the MSW and GSD models is manifest in the vector channel through the relation of the dilaton parameter with the tachyonic gluon mass. For approximately reproducing the phenomenological values of the dimension d=4,6 condensates, the holographic models require a tachyonic gluon mass (α_s/π)λ^2= -(0.12- 0.14) GeV^2, which is about twice the fitted phenomenological value from e^+e^- data. The relation of the inverse length parameter c_i to the tachyonic gluon mass also shows that c_i is channel dependent but not universal for a given holographic model. Using the MSW model and M_ρ=0.78 GeV as input, we predict a scalar \bar qq mass M_S=(0.95-1.10) GeV and a scalar gluonium mass M_G= (1.1- 1.3) GeV.

hep-ph↗

arXiv2012

New results on the baryon decay Lambda_b -> Lambda_c ell nu in Heavy Quark Effective Theory

The baryon differential spectrum of the baryon decay $Λ_b \to Λ_c \ell \barν_\ell$ will be measured in detail at LHCb. We obtain new results on the form factors in the heavy quark expansion of Heavy Quark Effective Theory that can be useful in the interpretation of the data. We formulate a sum rule for the elastic subleading form factor $A(w)$ at order $1/m_Q$, that originates from the Lagrangian perturbation $\mathcal{L}_{kin}$. In the sum rule appear only the intermediate states $(j^P, J^P) = (0^+, {1 \over 2}^+)$, entering also in the $1/{m_Q^2}$ correction to the axial form factor $G_1(w)$, that contributes to the differential rate at zero recoil $w = 1$. This result, together with another sum rule in the forward direction for $|G_1(1)|^2$, allows us to obtain a lower bound for the correction at zero recoil $- δ_{1/{m_Q^2}}^{(G_1)}$ in terms of the derivative $A'_1(1)$ and the slope $ρ^2_Λ$ and curvature $σ^2_Λ$ of the elastic Isgur-Wise function $ξ_Λ(w)$. Another theoretical implication is that $A'(1)$ must vanish for some relation between $ρ^2_Λ$ and $σ^2_Λ$, as well as for $ρ^2_Λ\to 0$, establishing a non-trivial correlation between the leading IW function $ξ_Λ(w)$ and the subleading one $A(w)$. A phenomenological estimation of these two functions allows to obtain a lower bound on $- δ_{1/{m_Q^2}}^{(G_1)}$.

hep-ph↗

arXiv2009

The Holographic Models of the scalar sector of QCD

We investigate the AdS/QCD duality for the two-point correlation functions of the lowest dimension scalar meson and scalar glueball operators, in the case of the Soft Wall holographic model of QCD. Masses and decay constants as well as gluon condensates are compared to their QCD estimates. In particular, the role of the boundary conditions for the bulk-to-boundary propagators is emphasized.

hep-ph↗

arXiv2009

Investigating AdS/QCD duality through scalar glueball correlators

We investigate AdS/QCD duality for the two-point correlation function of the lowest dimension scalar glueball operator, in the case of the IR soft wall model. We point out the role of the boundary conditions for the bulk-to-boundary propagator in determining the gluon condensates. We show that a low energy QCD theorem can be obtained within the AdS approach, together with a gluon condensate close to the commonly accepted value and robust against perturbation of the background dilaton field.

hep-ph↗

arXiv2008

Light scalar mesons in the soft-wall model of AdS/QCD

We study light scalar mesons in the AdS/QCD soft-wall model with a background dilaton field. The masses and decay constants are compatible with experiment and QCD determinations if $a_0(980)$ and $f_0(980)$ are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Comparing the two-point correlation function of scalar operators in AdS and QCD, information about the condensates can be derived. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD estimates: this discrepancy is related to the description of chiral symmetry breaking in this model.

hep-ph↗

arXiv2007

On the light glueball spectrum in a holographic description of QCD

We investigate the spectra of light scalar and vector glueballs in a holografic description of QCD with a dilaton background bulk field. In particular, we study how the glueball masses depend on the conditions on the dilaton background and on the geometry of the bulk.

hep-ph↗

arXiv2006

The Isgur-Wise function in the BPS limit

From sum rules in the heavy quark limit of QCD, using the non-forward amplitude, we demonstrate that if the slope rho^2 = -xsi'(1) of the Isgur-Wise function xsi(w) attains its lower bound 3/4 (as happens in the BPS limit proposed by Uraltsev), the IW function is completely determined, given by the function xsi(w) = [2/(w+1)]^(3/2).

hep-ph↗

arXiv2006

Explicit form of the Isgur-Wise function in the BPS limit

Using previously formulated sum rules in the heavy quark limit of QCD, we demonstrate that if the slope rho^2 = -xi'(1) of the Isgur-Wise function xi(w) attains its lower bound 3/4, then all the derivatives (-1)^L xi^(L)(1) attain their lower bounds (2L+1)!!/2^(2L), obtained by Le Yaouanc et al. This implies that the IW function is completely determined, given by the function xi(w) = [2/(w+1)]^(3/2). Since the so-called BPS condition proposed by Uraltsev implies rho^2 = 3/4, it implies also that the IW function is given by the preceding expression.

hep-ph↗

arXiv2006

The tensor force in Heavy Quark Effective Theory

We extend the formalism of Leibovich, Ligeti, Stewart and Wise in the 1/m_Q expansion of Heavy Quark Effective Theory for the B semileptonic decays into excited D[(3/2)^+] mesons to the opposite parity states D[(3/2)^-]. For D[(3/2)^+] the 1/m_Q current perturbation dominates over the leading term at zero recoil, while for D[(3/2)^-] the 1/m_Q perturbation due to L_mag dominates also at zero recoil. We show that the corresponding 1/m_Q magnetic coupling is proportional to the mixing between the states D[(3/2)^-] and D[(1/2)^-] induced by the tensor force. We point out some subtleties that appear in this respect in HQET.

hep-ph↗

arXiv2005

Sum rules for leading and subleading form factors in Heavy Quark Effective Theory using the non-forward amplitude

Within the OPE, we the new sum rules in Heavy Quark Effective Theory in the heavy quark limit and at order 1/m_Q, using the non-forward amplitude. In particular, we obtain new sum rules involving the elastic subleading form factors chi_i(w) (i = 1,2, 3) at order 1/m_Q that originate from the L_kin and L_mag perturbations of the Lagrangian. To the sum rules contribute only the same intermediate states (j^P, J^P) = ((1/2)^-, 1^-), ((3/2)^-, 1^-) that enter in the 1/m_Q^2 corrections of the axial form factor h_(A_1)(w) at zero recoil. This allows to obtain a lower bound on -delta_(1/m^2)^(A_1) in terms of the chi_i(w) and the shape of the elastic IW function xi(w). An important theoretical implication is that chi'_1(1), chi_2(1) and chi'_3(1) (chi_1(1) = chi_3(1) = 0 from Luke theorem) must vanish when the slope and the curvature attain their lowest values rho^2->3/4, sigma^2->15/16. These constraints should be taken into account in the exclusive determination of |V_(cb)|.

hep-ph↗

arXiv2005

Lagrangian perturbations at order 1/m$_{\bf Q}$ and the non-forward amplitude in Heavy Quark Effective Theory

We pursue the program of the study of the non-forward amplitude in HQET. We obtain new sum rules involving the elastic subleading form factors $χ_i(w)$ $(i = 1,2, 3)$ at order $1/m_Q$ that originate from the ${\cal L}_{kin}$ and ${\cal L}_{mag}$ perturbations of the Lagrangian. To obtain these sum rules we use two methods. On the one hand we start simply from the definition of these subleading form factors and, on the other hand, we use the Operator Product Expansion. To the sum rules contribute only the same intermediate states $ (j^P, J^P) = ({1 \over 2}^-, 1^-), ({3\over 2}^-, 1^-)$ that enter in the $1/m_Q^2$ corrections of the axial form factor $h_{A_1}(w)$ at zero recoil. This allows to obtain a lower bound on $- δ_{1/m^2}^{(A_1)}$ in terms of the $χ_i(w)$ and the shape of the elastic IW function $ξ(w)$. We find also lower bounds on the $1/m_Q^2$ correction to the form factors $h_+(w)$ and $h_1(w)$ at zero recoil. An important theoretical implication is that $χ'_1(1)$, $χ_2(1)$ and $χ'_3(1)$ ($χ_1(1) = χ_3(1) = 0$ from Luke theorem) must vanish when the slope and the curvature attain their lowest values $ρ^2 \to {3 \over 4}$, $σ^2 \to {15 \over 16}$. We discuss possible implications on the precise determination of $|V_{cb}|$.

hep-ph↗

arXiv2005

Quark-antiquark bound state equation in the Wilson loop approach with minimal surfaces

The quark-antiquark gauge invariant Green function is studied through its dependence on Wilson loops. The latter are saturated, in the large Nc limit and for large contours, by minimal surfaces. A covariant bound state equation is derived which in the center-of-mass frame and at equal-times takes the form of a Breit-Salpeter type equation. The large-distance interaction potentials reduce in the static case to a confining linear vector potential. In general, the interaction potentials involve contributions having the structure of flux tube like terms.

hep-ph↗

arXiv2005

The decays $\bar{B} \to D^{**}π$ and the Isgur-Wise functions $τ_{1/2}(w)$, $τ_{3/2}(w)$

We perform a phenomenological analysis of the decays $B \to D^{**}π$, where $D^{**}$ is a $P$-wave excited meson with total angular momentum $j = {1 \over 2}$ or ${3 \over 2}$ for the light cloud, recently measured by the Belle Collaboration in the modes $\bar{B}^0\to D^{**+}π^-$ (Class I) and $B^- \to D^{**0}π^-$ (Class III). Making the reasonable assumption of naive factorization, that we test in $B \to D(D^*)π$ decays, Class I decays allow to extract the Isgur-Wise form factors $τ_{1/2}(w)$, $τ_{3/2}(w)$ at $w \cong w_{max}$ ($q^2 \cong 0$). We obtain $τ_{1/2}(w_{max}) < 0.20$, $τ_{3/2}(w_{max}) = 0.31 \pm 0.12$. We discuss the question of the $w$ dependence of these IW functions. We find agreement with the Bakamjian-Thomas quark model of form factors and, extrapolating at $w=1$, with Bjorken and Uraltsev sum rules. We discuss also Class III decays, where the $D^{**0}$ $(j = {1 \over 2})$ emission diagram contributes. We extract the corresponding $f_{D_{1/2}}$ decay constant, that is in agreement with theoretical estimates at finite mass. Finally, we must warn that $1/m_Q$ corrections could be large and upset the results of the present stage of this analysis. On the other hand, we confront present data on the semileptonic rate of $B$ mesons to excited states with theoretical expectations.

hep-ph↗

arXiv2005

B mesons and form factors

In order to extract some information on the CKM matrix element |Vcb|, we have to determine form factors in B decays. For this, we show that it is relevant to consider the non-forward amplitude between the heavy-light B and D mesons within the Heavy Quark Effective Theory. This method provides us bounds on the shape of the elastic Isgur-Wise function. These bounds should be taken into account in the parametrizations of the Isgur-Wise function used to extract |Vcb|. Besides, we have also obtain new information on subleading functions at the order O(1/mQ) where mQ is the heavy quark mass.

hep-ph↗

arXiv2005

Subleading form factors at order 1/m_Q in terms of leading quantities using the non-forward amplitude in HQET

We consider the non-forward amplitude within the Heavy Quark Effective theory. We show that one can obtain new information on the subleading corrections in 1/m_Q. We illustrate the method by deriving new simple relations between the functions Xsi_3(w) and Lambdabar Xsi(w) and the sums Sum_n DeltaE^(n)_j tau^(n)_j(1) tau^(n)_j(w) (j=1/2,3/2), that involve leading quantities, namely the Isgur-Wise functions tau^(n)_j(w) and the level spacings DeltaE^(n)_j. The simplicity of our results follows from the fact that, for the non-forward amplitude B(v_i)->D^(n)(v')->B(v_f), there are three variables (w_i,w_f,w_if)=(v_i.v',v_f.v',v_i.v_f) independent in a certain domain, and we consider the zero recoil frontier (w,1,w) where only a finite number of j^P states contribute (1/2^+,3/2^+). These sum rules reduce to known results at w=1, for Lambdabar obtainted by Voloshin, and for Xsi_3(1) obtained by Le Yaouanc et al. and by Uraltsev, and generalizes them to all values of w. We discuss phenomenological applications of these results, in particular the check of Bakamjian-Thomas quark models and the comparison with the QCD Sum Rules approach.

hep-ph↗

arXiv2004

Quarkonium bound state equation in the Wilson loop approach with minimal surfaces

Wilson loop averages are evaluated for large contours and in the large N limit by means of minimal surfaces. This allows the study of the quark-antiquark gauge invariant Green function through its dependence on Wilson loops. A covariant bound state equation is derived which in the center-of-mass frame and at equal-times takes the form of a Breit-Salpeter type equation. The interaction potentials reduce in the static case to a confining linear vector potential. For moving quarks, flux tube like contributions are present. The nonrelativistic limit is considered.

hep-ph↗

arXiv2004

Sum rules in the heavy quark limit of QCD and Isgur-Wise functions

Using the OPE, we formulate new sum rules in the heavy quark limit of QCD. These sum rules imply that the elastic Isgur-Wise function $ξ(w)$ is an alternate series in powers of $(w-1)$. Moreover, one gets that the $n$-th derivative of $ξ(w)$ at $ w=1$ can be bounded by the $(n-1)$-th one, and an absolute lower bound for the $n$-th derivative $(-1)^n ξ^{(n)}(1) \geq {(2n+1)!! \over 2^{2n}}$. Moreover, for the curvature we find $ξ''(1) \geq {1 \over 5} [4 ρ^2 + 3(ρ^2)^2]$ where $ρ^2 = - ξ'(1)$. We show that the quadratic term ${3 \over 5} (ρ^2)^2$ has a transparent physical interpretation, as it is leading in a non-relativistic expansion in the mass of the light quark. These bounds should be taken into account in the parametrizations of $ξ(w)$ used to extract $|V_{cb}|$. These results are consistent with the dispersive bounds, and they strongly reduce the allowed region of the latter for $ξ(w)$. The method is extended to the subleading quantities in $1/m_Q$, namely $ξ_3(w)$ and $\barΛξ(w)$.}]

hep-ph↗