We develop a general theoretical framework for the description of higher-twist baryon operators which makes maximal use of the conformal symmetry of the QCD Lagrangian. The conformal operator basis is constructed for all twists. The complete analysis of the one-loop renormalization of twist-4 operators is given. The evolution equation for three-quark operators of the same chirality turns out to be completely integrable. The spectrum of anomalous dimensions coincides in this case with the energy spectrum of the twist-4 subsector of the SU(2,2) Heisenberg spin chain. The results are applied to give a general classification and calculate the scale dependence of subleading twist-4 nucleon distribution amplitudes that are relevant for hard exclusive reactions involving a helicity flip. In particular we find an all-order expression (in conformal spin) for the contributions of geometric twist-3 operators to the (light-cone) twist-4 nucleon distribution amplitudes, which are usually referred to as Wandzura-Wilczek terms.
Families of $J^P=1/2+$ nucleons (N(939), N(1440), N(1710), N(1880), N(2100), N(2300)) and $J^P=3/2-$ nucleons (N(1520), N(1700), N(1875) and N(2120)) are scrutinized from the point of view of the configurational entropy (CE). The mass spectra of higher $J^P$ resonances in each one of these families are then obtained when configurational-entropic Regge trajectories, that relate the CE of nucleon families to both their $J^P$ spin and also to their experimental mass spectra, are interpolated. The mass spectra of the next generation of nucleon resonances are then compared to already established ba…
I review the recent progress in understanding the complete gauge invariant decomposition of the nucleon spin with particular emphasis on its twist structure.
We derive the higher twist (four and five) nucleon distribution amplitudes in the Wandzura-Wilczek approximation. Our method is based on an analysis of the conformal expansion of nonlocal operators in the spinor formalism.
This is a short review of the theory and phenomenology of baryon distribution amplitudes, including recent applications to the studies of nucleon form factors at intermediate momentum transfers using the light-cone sum rule approach.
The twist-four quark and gluon distributions in a transversely polarized nucleon are identified and relations among them are discussed by using QCD equations of motion. Their contribution, at the order of ${\cal O} \left( 1/Q^2 \right)$, to the Drell-Yan cross section in transversely polarized nucleon-nucleon collisions is calculated.
An extended chiral constituent quark approach, which embodies higher Fock five-quark components in the baryons wave-functions, is employed to study the sea quark content of the octet baryons. We report on the probabilities of $\bar{u}$, $\bar{d}$ and $\bar{s}$ in the nucleon, $Λ$, $Σ$ and $Ξ$ baryons, arising from the intrinsic five-quark states in the baryons wave functions. Based on those probabilities, results for meson-nucleon $σ$-terms; namely $σ_{πN}, σ_{K N}$ and $σ_{ηN}$, are presented.
The amplitude of the deeply virtual Compton scattering off nucleon is computed to the twist-3 accuracy in the Wandzura-Wilczek (WW) approximation. The result is presented in the form which can be easily used for the analysis of DVCS observables.
In this paper we present an analytic result for the evolution in $Q^2$ of the structure functions for the neutrino-nucleon interaction, valid at twist-2 in the region of small values of the Bjorken $x$ variable and for soft non-perturbative input. In the special case of flat initial conditions, we include in the calculation also the contribution of the twist-4 gluon recombination corrections, whose effect in the evolution is explicitly determined. Finally, we estimate the resulting charged-current neutrino-nucleon total cross section and discuss its behavior at ultra-high energies.
The pion nucleon sigma-term is extracted on the basis of the soliton picture of the nucleon from the mass spectrum of usual and the recently observed exotic baryons, assuming that they have positive parity. The value found is consistent with that inferred by means of conventional methods from pion nucleon scattering data. The study can also be considered as a phenomenological consistency check of the soliton picture of baryons.
We estimate the size of the twist-3 effects on deeply virtual Compton scattering (DVCS) observables, in the Wandzura-Wilczek approximation. We present results in the valence region for the DVCS cross sections, charge asymmetries and single spin asymmetries, to twist-3 accuracy.
The Nachtmann moment is employed to study the contribution of twist-3 operator to the nucleon spin structure functions. Target mass corrections to the Cornwall-Norton moments of the spin structure functions $g_{1,2}$ are discussed. It is found that the corrections play a sizeable role to the contribution of the twist-3 $\tilde d_2$ extracted from the Cornwall-Norton moments.
We present the first heavy baryon chiral perturbation theory calculation at ${\mathcal O}(p^4)$ for the spin-dependent amplitudes for virtual Compton scattering off the nucleon, and extract the ${\cal O}(p^4)$ order results for the generalized spin polarizabilities of the nucleon.
We derive exact relations among the polarized gluon and three-gluon distributions in the transversely polarized nucleon which are relevant to single and double spin asymmetries in various hard processes. We also discuss the partonic decomposition of the transverse nucleon spin and point out a potential problem with frame-independence.
We study twist-three effects in deeply virtual Compton scattering on an unpolarized spin-1/2 target. A careful definition of observables as Fourier moments w.r.t. the azimuthal angle allows for a clear separation of twist-two and -three effects. Although the latter are power suppressed, they give leading contributions to the twist-three asymmetries and do not affect the twist-two observables.
We present the first systematic study of higher-twist light-cone distribution amplitudes of the nucleon in QCD. We find that the valence three-quark state is described at small transverse separations by eight independent distribution amplitudes. One of them is leading twist-3, three distributions are twist-4 and twist-5, respectively, and one is twist-6. A complete set of distribution amplitudes is constructed, which satisfies equations of motion and constraints that follow from conformal expansion. Nonperturbative input parameters are estimated from QCD sum rules.
We present a detailed analysis of resonance contributions in the context of higher twist effects in the moments of the proton spin structure function g_1. For each of these moments, it is found that there exists a characteristic Q^2 region in which (perturbative) higher twist corrections coexist with (non-perturbative) resonance contribution of comparable magnitude.
The $O(p^4)$ calculation on pion-nucleon elastic scattering amplitude in EOMS scheme within covariant baryon chiral perturbation theory is reviewed. Numerical fits to partial wave amplitudes up to $\sqrt{s}=1.13$ GeV and 1.20 GeV are performed and the results are compared with previous studies.
The nucleon mass corrections are calculated to all polarized structure functions for neutral and charged current deep inelastic scattering in lowest order in the coupling constant. The impact of the target mass corrections on the general relations between the twist--2 and twist--3 parts of the structure functions is studied and three new relations between the twist--3 contributions are derived. The size of nucleon mass corrections for the $g_1$ and $g_2$ structure functions are estimated.
The phenomenological sum-rule-based approach is used to discuss the quark composition dependence of some static electroweak characteristics of baryons.The role of nonvalence degrees of freedom (the sea partons and/or peripheral meson currents) is shown to be important to select and make use of the relevant symmetry parametrization of baryon observables.The implications of the baryon magnetic moment analysis for estimation of the $Δ$q values of the spin-dependent DIS on nucleons, the contribution of hidden strangeness to the nucleon magnetic moment and to the quark-line-rule violating $ϕπ$ - pr…
These proceedings contain the 'physical' derivation of the Wandzura-Wilczek relations for the spin-dependent structure function g2 (amounting to keeping the intrinsic transverse momentum of quarks, and neglecting the physical transverse components of the gluon fields), recently generalized for the case of non-forward processes (hep-ph/0102209). The simple numerical model for the twist-3 contribution to g2 was also suggested.
Vertex operators for photo- and electro-production of baryon states with arbitrary spin-parity, $ γ+ N\to B(J^P)$, are constructed. The operators obey gauge invariance and analyticity constraints. Analyticity is realized as a requirement of the generalized Siegert theorem for vertex form factors.
Higher twist effects in the deeply inelastic scattering are studied. We start with a short review of the theoretical results on higher twists in QCD. Within the saturation model we perform a twist analysis of the nucleon structure functions FT and FL at small value of the Bjorken variable x. The parameters of the model are fitted to the HERA F2 data, and we derive a prediction for the longitudinal structure function FL. We conclude that for FL the higher twist corrections are sizable whereas for F2 = FT + FL there is a nearly complete cancellation of twist-4 corrections in FT and FL. We discus…
We discuss the masses of the ground state baryon octet and the nucleon sigma terms in the framework of manifestly Lorentz-invariant baryon chiral perturbation theory. In order to obtain a consistent power counting for renormalized diagrams the extended on-mass-shell renormalization scheme is applied.
We present a model of baryonic matter which contains free constituent quarks in addition to bound constituent quarks in nucleons. In addition to the common linear sigma-model we include the exchange of vector-mesons. The percentage of free quarks increases with baryon density but the nucleons resist a restoration of chiral symmetry.
We construct a holographic model for baryons in the context of AdS/QCD and study the spin-1/2 nucleon spectra and its couplings to mesons, taking fully account of the effects from the chiral symmetry breaking. A pair of 5D spinors is introduced to represent both left and right chiralities. Our model contains two adjustable parameters, the infrared cutoff and the Yukawa coupling of bulk spinors to bulk scalars, corresponding to the order parameter of chiral symmetry. Taking the lowest-lying nucleon mass as an input, we calculate the mass spectrum of excited nucleons and the nucleon couplings to…
The strong coupling form factors related to the strong vertices of the positive and negative parity nucleons with the heavy $Λ_{b[c]}[Σ_{b[c]}]$ baryons and heavy $B^*[D^*]$ vector mesons are calculated using a three-point correlation function. Using the values of the form factors at $Q^2=-m^2_{meson}$ we compute the strong coupling constants among the participating particles.
We computed the NLO corrections to twist-3, $L \to T$, flavor non-singlet amplitude in DVCS on a nucleon in the Wandzura-Wilczek approximation. Explicit calculation shows that factorization holds for NLO contribution to this amplitude, although the structure of the factorized amplitude at the NLO is more complicated than in the leading-order formula. Next-to-leading order coefficient functions for matrix elements of twist-3 vector and axial-vector quark string operators and their LO evolution equations are presented.
We computed twist-4 part of the photon spin-flip amplitude in deeply virtual Compton scattering on a nucleon in the Wandzura-Wilczek approximation. We found a factorizable contribution, which arises from photon scattering on quarks with non-zero angular momentum along the collision axis. As the genuine twist-2 amplitude arises at the NLO, for moderate virtualities of the hard photon, $Q^2 \le 10$ GeV$^2$, kinematical twist-4 correction can give numerically important contribution to the photon helicity-flip amplitude.
A genuinely non-perturbative evaluation of higher-twist contributions to the structure functions of the nucleon, with all mixing effects and renormalon ambiguities taken care of, is presented. Higher-twist corrections turn out to be significant at moderate values of $q^2$.
We show a novel charge structure of baryons in electromagnetic field due to the chiral anomaly. A key connection is to treat baryons as solitons of mesons. We use Skyrmions to calculate the charge distributions in a single nucleon and find an additional charge. We also perform calculations of charge distribution for classical multi-baryons with B=2, 3,...,8 and 17; they show amusing charge distributions.
We discuss the question in the title employing manifestly covariant Baryon Chiral Perturbation Theory and recent high-statistics lattice results published in [1].
The overlap of the nucleons in nuclei plays an important role in understanding the nuclear dependence of deep inelastic scattering data. It is shown that the nuclear modification of the higher twist scale can be essentially determined by the overlapping volume per nucleon and this effect gives a large contribution to nuclear shadowing for small $x$ and low $Q^2$. In this kinematical region there is also a moderate enhancement of the longitudinal structure function in nuclei.
We calculate the phase shifts in the pion-nucleon scattering using the heavy baryon formalism. We consider phase shifts for the pion energy range of 140 to $200 $ MeV. We employ two different methods for calculating the phase shifts - the first using the full third order calculation of the pion-nucleon scattering amplitude and the second by including the resonances $Δ$ and $N^*$ as explicit degrees of freedom in the Lagrangian. We compare the results of the two methods with phase shifts extracted from fits to the pion-nucleon scattering data. We find good to fair agreement between the calculat…
We study heavy baryons with an exotic flavor quantum number formed by a heavy meson and a nucleon (Dbar-N and B-N) through a long range one pion exchange interaction. The bound state found previously in the (I,JP) =(0,1/2-) channel survives when short range interaction is included. In addition, we find a resonant state with (I,JP)=(0,3/2-) as a Feshbach resonance predominated by a heavy vector meson and a nucleon (Dbar*-N and B*-N). We find that these exotic states exist for the charm and heavier flavor region.
Using the framework of QCD sum rules we predict the twist-3 contribution to the second moment of the polarized nucleon structure function $g_2(x)$. As the relevant local operator depends explicitely on the gluon field, we employ a recently studied interpolating nucleon current which contains three quark field and one gluon field operator. Despite the fact that our calculation is based on the analysis of a completely different correlation function, our estimates are consitent with those of Balitsky, Braun and Kolesnichenko who used a three-quark current.
The decomposition of the nucleon spin into that of quarks and gluons is related to twist-two GPDs according to Ji sum rule. Further decomposition into the helicity and the orbital angular momentum inevitably requires twist-three GPDs. In this paper we derive exact relations between twist-three GPDs and the canonical orbital angular momentum density of quarks and gluons, and check their consistency with the spin sum rule. Our work demonstrates that the complete decomposition of the nucleon spin fits well with the framework of perturbative QCD.
Within the collective coordinate approach to chiral soliton models we suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave-functions while the charge operators have no (or only small) symmetry breaking components. In this framework we study the $g_A/g_V$ ratios for hyperon beta-decay as well as the various quark flavor components of the axial charge of the nucleon and the $Λ$-hyperon.
We compute the nucleon matrix elements of QCD operators of twist 3 and 4 in the instanton vacuum. We consider the operators determining 1/Q^2-power corrections to the Bjorken, Ellis-Jaffe and Gross-Llewellyn-Smith sum rules. The nucleon is described as a soliton of the effective chiral theory derived from instantons in the 1/N_c-expansion. QCD operators involving the gluon field are systematically represented by effective operators in the effective chiral theory. We find that twist-3 matrix elements are suppressed relative to twist-4 by a power of the packing fraction of the instanton medium. …
The positivity of the integrand of certain Euclidean space functional integrals implies that the free energy per unit volume for QCD with a baryon chemical potential $μ_B$ (and zero isospin chemical potential) is greater than the free energy with isospin chemical potential $μ_I = (2 μ_B)/N_c$ (and zero baryon chemical potential). This relation implies a bound on the nucleon mass: there exists a particle X in QCD such that $M_N \ge (N_c m_X)/(2 I_X)$ where $m_X$ is the mass and of the particle and $I_X$ is its isospin.
We report a theoretical study of the axial Nucleon to Delta(1232) ($N\toΔ$) transition form factors up to one-loop order in relativistic baryon chiral perturbation theory. We adopt a formalism in which the $Δ$ couplings obey the spin-3/2 gauge symmetry and, therefore, decouple the unphysical spin-1/2 fields. We compare the results with phenomenological form factors obtained from neutrino bubble chamber data and in quark models.
We extend our previous analysis of the unitarized pion-nucleon scattering amplitude including up to fourth order terms in Heavy Baryon Chiral Perturbation Theory. We pay special attention to the stability of the generated Delta(1232 resonance, the convergence problems and the power counting of the chiral parameters.
Owing to the Kubo relation, the shear viscosities of pionic and nucleonic components have been evaluated from their corresponding retarded correlators of viscous stress tensor in the static limit, which become non-divergent only for the non-zero thermal widths of the constituent particles. In the real-time thermal field theory, the pion and nucleon thermal widths have respectively been obtained from the pion self-energy for different meson, baryon loops and the nucleon self-energy for different pion-baryon loops. We have found a non-monotonic momentum distributions of pion and nucleon thermal …
In a recent analysis of the world data on polarized DIS, Blumlein and Bottcher conclude that there is no evidence for higher twist contributions, in contrast to the claim of the LSS group, who find evidence for significant higher twist effects. We explain the origin of the apparent contradiction between these results.
Most of model considerations of the hidden nucleon strangeness, as well as some preliminary experimental evidence, led to the expectations of relatively sizeable strange vector form factors of the proton. For example, it seemed that the contribution of the fluctuating strange quark-antiquark pairs accounts for as much as one tenth of the proton's magnetic moment. By the same token, baryon models which failed to produce the "vector strangeness" of the nucleon seemed disfavored. Recently, however, more accurate measurements and more sophisticated data analysis, as well as lattice simulations, re…
The effects of the spin-orbit and the tensor parts of the instanton-induced interaction on the excited nonstrange baryons up to $N$=2 and on the two-nucleon systems are investigated. The spin-orbit force from the instanton-induced interaction cancels most of that from the one-gluon exchange in the excited baryons while the spin-orbit force in the nucleon systems remains strong after the inclusion of the instanton-induced interaction. The model including the spin-orbit and the tensor terms of the instanton-induced interaction as well as the one-gluon exchange is found to reproduce successfully …
I discuss the latest progress in calculating baryon-baryon interactions with lattice QCD. The latest results from the NPLQCD collaboration for nucleon-nucleon scattering along with preliminary calculations of hyperon-nucleon scattering are presented.
The spin-dependent twist-3 and 4 nucleon matrix elements d^(2) and f^(2) describing power corrections to the Bjorken and Ellis-Jaffe sum rules are computed in the instanton vacuum. A systematic expansion in the small packing fraction of the instanton medium, rho / R << 1, is performed. We find that the twist-3 matrix element d^(2) is suppressed [of order (rho / R)^4], while the twist-4 matrix element f^(2) is of order unity. Numerically, d^(2) << f^(2). The small value of d^(2) \sim 10^{-3} obtained from instantons is consistent with the recent E143 measurements of the structure function g_2, …
We develope the holographic mean field theory approach in a bottom-up holographic QCD model including baryons and scalar mesons in addition to vector mesons and pions. We study the effect of parity doubling structure of baryons at non-zero density to the equation of state between the chemical potential and the baryon number density. We first show that we can adjust the amount of nucleon mass coming from the chiral symmetry breaking by changing the boundary value of the five-dimensional baryon fields. Then, introducing the mean field for the baryon fields, we calculate the equation of state bet…
We show that the two complementary pictures of large $N_c$ baryons - the single-quark orbital excitation about a symmetric core and the meson-nucleon resonance -- are compatible for $\ell$ = 3 SU(4) baryons. The proof is based on a simple Hamiltonian including operators up to order $\mathcal{O}(N^0_c)$ used previously in the literature for $\ell$ = 1.
We consider 3 types of processes pertinent to the phenomenology of an H di-baryon: conversion of two $Λ$'s in a doubly-strange hypernucleus to an H, decay of the H to two baryons, and -- if the H is light enough -- conversion of two nucleons in a nucleus to an H. We compute the spatial wavefunction overlap using the Isgur-Karl and Bethe-Goldstone wavefunctions, and treat the weak interactions phenomenologically. The observation of $Λ$ decays from doubly-strange hypernuclei puts a constraint on the H wavefunction which is plausibly satisfied. In this case the H is very long-lived as we calculat…
In the real-time thermal field theory, the standard expression of shear viscosity for the nucleonic constituents is derived from the two point function of nucleonic viscous stress tensors at finite temperature and density. The finite thermal width or Landau damping is traditionally included in the nucleon propagators. This thermal width is calculated from the in-medium self-energy of nucleon for different possible pion-baryon loops. The dynamical part of nucleon-pion-baryon interactions are taken care by the effective Lagrangian densities of standard hadronic model. The shear viscosity to entr…
We review the description of nucleon structure functions in the instanton vacuum. This includes the calculation of the twist-2 parton distributions at a low normalization point as well as higher-twist matrix elements. The instanton vacuum with its inherent small parameter, the packing fraction of the instanton medium, $\barρ/ R$, provides a consistent picture of the non-perturbative gluon degrees of freedom at the scale $\barρ^{-1} \simeq 600 MeV$. The twist-2 quark and antiquark distributions are of order unity, while the twist-2 gluon distribution is of order $(\barρ/ R)^4$. Twist-4 matrix e…
In this talk, we report on two recent studies of relativistic nucleon-nucleon and hyperon-nucleon interactions in covariant chiral perturbation theory, where they are constructed up to leading order. The relevant unknown low energy constants are fixed by fitting to the nucleon-nucleon and hyperon-nucleon scattering data. It is shown that these interactions can describe the scattering data with a quality similar to their next-to-leading order non-relativistic counterparts. These studies show that it is technically feasible to construct relativist baryon-baryon interactions, and in addition, aft…
We discuss the status of current dynamical lattice QCD simulations in connection to the emerging results on the strange and charmed baryon spectrum, excited states of the nucleon and the investigation of the structure of scalar mesons.
We have constructed a heavy baryon effective field theory with photon as an external field in accordance with the symmetry requirements similar to the heavy quark effective field theory. By treating the heavy baryon and anti-baryon equally on the same footing in the effective field theory, we have calculated the spin polarisabilities $γ_i, i=1...4$ of the nucleon at third order and at fourth-order of the spin-dependent Compton scattering. At leading order (LO), our results agree with the corresponding results of the heavy baryon chiral perturbation theory, at the next-to-leading order(NLO) the…
We review the recent baryon chiral perturbation theory results for the nucleon polarisabilities that describe the different regimes of nucleon Compton scattering --- real, virtual, and doubly virtual. We stress the importance of the empirical verification of the theory in the context of the calculation of the inelastic nucleon structure corrections, such as the two-photon exchange contributions. We also discuss the recently obtained constraints that relate the different regimes of nucleon Compton scattering and can provide additional information on the nucleon structure.
The covariant parton model is generalized to describe quark correlators in a systematic way. Previous results are reproduced for the T-even leading-twist transverse momentum dependent parton distribution functions (TMDs), and for the first time all T-even twist-3 TMDs are evaluated in this model. We apply the approach to evaluate the fully unintegrated quark correlator which allows us to understand the model-specific relations between different TMDs. We verify the consistency of the approach, present numerical results and compare to available TMD parametrizations.
Baryon-number-violating nucleon decays in SMEFT extended with a light scalar
State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究所核物理与技术国家重点实验室）；Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Nuclear Science（广东省基础研究中心物质结构与基本相互作用卓越中心广东省核科学重点实验室）；Sydney Consortium for Particle Physics and Cosmology, School of Physics, The University of New South Wales（新南威尔士大学物理学院悉尼粒子物理与宇宙学联盟）
