arXiv subjects

Ivan Schmidt

Publications and source records attributed to Ivan Schmidt.

At least 109 records · Page 6Linked to original sources

arXiv2013

Light-front quark model consistent with Drell-Yan-West duality and quark counting rules

We propose a phenomenological light-front wave function for hadrons with arbitrary twist-dimension (mesons, baryons and multiquark states), which gives the correct scaling behavior of structure functions (parton distributions) and form factors for pions and nucleons. For other hadronic states the proposed wave function produces form factors consistent with quark counting rules, and gives predictions for structure functions (parton distributions). As an application we build a light-front quark model for nucleons based on the proposed wave function.

hep-ph↗

arXiv2013

Gauge Invariant Descriptions of Gluon Polarizations Revisited

We examine the feasibility of gauge invariant descriptions of the gluon polarization following the proposal that a gauge field can be decomposed into its physical part and its pure gauge part. We show that gauge invariant angular momentum currents can be constructed from summations of gauge variant Noether currents. We present novel expressions of the pure gauge field, which are used to formulate gauge invariant descriptions of the gluon spin and the photon spin. We show that the gauge invariant extension of the Chern-Simons current can describe the spins of the Laguerre-Gauss laser modes. We also discuss the relation of gauge invariant operators and the parton distributions constructed from Dirac variables.

hep-ph↗

arXiv2013

Gauge Invariant Descriptions of Gluon Polarizations

We propose methods to construct gauge invariant decompositions of the nucleon spin, particularly gauge invariant descriptions of the gluon polarization. We show that gauge invariant decompositions of the nucleon spin can be derived naturally from the conserved current of a generalized Lorentz transformation by the Noether theorem. We propose a gauge invariant extension of the Chern-Simons current as a possible description of the gluon spin, and we also examine the problem of gauge dependence of this extended Chern-Simons current.

hep-ph↗

arXiv2013

Single-Spin Asymmetries in Semi-inclusive Deep Inelastic Scattering and Drell-Yan Processes

We examine in detail the diagrammatic mechanisms which provide the change of sign between the single transverse spin asymmetries measured in semi-inclusive deep inelastic scattering (SIDIS) and in the Drell-Yan process (DY). This asymmetry is known to arise due to the transverse spin dependence of the target proton combined with a T-odd complex phase. Using the discrete symmetry properties of transverse spinors, we show that the required complex phase originates in the denominators of rescattering diagrams and their respective cuts. For simplicity, we work in a model where the proton consists of a valence quark and a scalar diquark. We then show that the phases generated in SIDIS and in DY originate from distinctly different cuts in the amplitudes, which at first appears to obscure the relationship between the single-spin asymmetries in the two processes. Nevertheless, further analysis demonstrates that the contributions of these cuts are identical in the leading-twist Bjorken kinematics considered, resulting in the standard sign-flip relation between the Sivers functions in SIDIS and DY. Physically, this fundamental, but yet untested, prediction occurs because the Sivers effect in the Drell-Yan reaction is modified by the initial-state "lensing" interactions of the annihilating antiquark, in contrast to the final-state lensing which produces the Sivers effect in deep inelastic scattering.

hep-ph↗

arXiv2013

Limits on Lepton Flavor Violation from μ-e-conversion

We revisit the status of Lepton Flavor Violating (LFV) μe qq contact interactions from the view point of μ- e -conversion in nuclei. We consider their contribution to this LFV process via the two mechanisms on the hadronic level: direct nucleon and meson exchange ones. In the former case the quarks are embedded directly into the nucleons while in the latter in mesons which then interact with nucleons in a nucleus. We revise and in some cases reevaluate the hadronic parameters relevant for both mechanisms and calculate the contribution of the above mentioned contact interactions in coherent μ- e -conversion in various nuclei. Then we update the existing upper bounds and also derive new ones for the scales of the μe qq contact interactions from the experimental limits on the capture rates of μ- e -conversion. We compare these limits with the ones derived in the literature from other LFV processes and comment on the prospects of LHC searches related to the contact μe qq interactions.

hep-ph↗

arXiv2013

Bethe-Heitler type radiative corrections to deeply virtual neutrinoproduction of mesons

We study the electromagnetic Bethe-Heitler type contribution to neutrino-induced deeply virtual meson production (\nuDVMP). Such O(α_{em})-corrections decrease with Q^{2} in the Bjorken regime less steeply than the standard \nuDVMP handbag contribution. Therefore, they are relatively enhanced at high Q^{2}. The Bethe-Heitler terms give rise to an angular correlation between the lepton and hadron scattering planes with harmonics sensitive to the real and imaginary parts of the DVMP amplitude. These corrections constitute a few percent effect in the kinematics of the forthcoming Minerva experiment at Fermilab and should be taken into account in precision tests of GPD parametrizations. For virtualities Q^{2}~100 GeV^{2} these corrections become on a par with DVMP handbag contributions. A computational code, which can be used for the evaluation of these corrections employing various GPD models is provided.

hep-ph↗

arXiv2013

Nucleon resonances in AdS/QCD

We describe the electroproduction of the N(1440) Roper resonance in soft-wall AdS/QCD. The Roper resonance is identified as the first radially excited state of the nucleon, where higher-Fock states in addition to the three-quark component are included. The main conclusion is that the leading 3q component plays the dominant role in the description of electroproduction properties of this resonance: form factors, helicity amplitudes and charge densities. The obtained results are in good agreement with the recent results of the CLAS Collaboration at JLab.

hep-ph↗

arXiv2013

Chiral Symmetry Breaking and Meson Wave Functions in Soft-Wall AdS/QCD

We consider mesons composed of light and heavy quarks and discuss the construction of the corresponding meson wave functions in soft-wall AdS/QCD. We specifically take care that constraints imposed by chiral symmetry breaking and by the heavy quark limit are fulfilled. The main results are: i) the wave functions of light mesons have a nontrivial dependence on the current quark mass, which gives rise to a mass spectrum consistent with the one including explicit breaking of chiral symmetry; ii) the wave functions of heavy-light mesons generate their correct mass spectrum, the mass splittings of vector and pseudoscalar states, and the correct scaling of leptonic decay constants f(Q \bar q) \sim 1/sqrt(mQ); iii) the wave functions of heavy quarkonia produce their correct mass spectrum and lead to a scaling behaviour of the leptonic decay constants f(Q \bar Q) \sim sqrt(mQ) and f(c \bar b) \sim mc/sqrt(mb) at mc << mb, consistent with potential models and QCD sum rules.

hep-ph↗

arXiv2012

Flavor structure of generalized parton distributions from neutrino experiments

The analysis of deeply virtual meson production is extended to neutrino-production of the pseudo-Goldstone mesons (pions, kaons, eta-mesons) on nucleons, with the flavor content of the recoil baryon either remaining intact, or changing to a hyperon from the SU(3) octet. We rely on the SU(3) relations and express all the cross-sections in terms of the proton generalized parton distributions (GPDs). The corresponding amplitudes are calculated at the leading twist level and in the leading order in α_{s}, using a phenomenological parametrization of GPDs. We provide a computational code, which can be used for evaluation of the cross-sections employing various GPD parametrizations. We conclude that these processes can be studied in the experiment Minerva at FERMILAB, which could supplement the measurements at JLAB and help to extract the GPD flavor structure from data.

hep-ph↗

arXiv2012

Nonperturbative features of the axial current

We study the nonperturbative structure of the axial current and evaluate the two-point light-cone distribution amplitudes (DA) associated with the correlator \int dξexp(-iqξ)<0|\barψ(x)Γψ(y)J_μ^{5}(ξ)|0> within the instanton vacuum model in the leading order in O(1/N_c). Due to the built-in chiral symmetry, four of eight axial DAs are related to that for pions. Knowledge of these nonperturbative objects is important for phenomenological study of high-energy neutrino interactions and semileptonic decays of heavy quarks. We provide a code for evaluation of these DAs and an interpolation formula valid in the region Q^2 < 1 GeV^2.

hep-ph↗

arXiv2012

Phenomenological Constraints to Dimensionality of the Spacetime with Torsion

Using the recent limits established by ATLAS to the contact four-fermion interaction, bounds on the size of the extra dimensions of space-time have been found, by assuming that the contact interactions come through the inclusion of torsion in the higher dimensional theory. For two extra dimensions, the limits are comparable to those in the literature, while for higher dimensional space-time, the volume of the extra dimensions is strongly constrained.

hep-ph↗

arXiv2012

J/Psi production off nuclei: a detour from SPS to LHC

We present a collection of selected phenomena observed in J/Psi production from proton-nucleus and heavy ion collisions at energies, ranging between the SPS and LHC. The emphasis is placed on the related theoretical ideas or techniques, which are either not widely known, or offer an alternative explanation to the observed nuclear effects.

hep-ph↗

arXiv2012

Incurable Adler relation for soft neutrino interactions

The Adler relation (AR), which bridges soft interactions of neutrinos and pions, might look as a manifestation of pion dominance. However neutrino cannot fluctuate to a pion because of lepton current conservation, instead it interacts via much heavier hadronic components. This fact leads to nontrivial relations between interaction amplitudes of different hadronic species, in particular, it links diagonal and off-diagonal diffractive interactions of pions. Absorptive corrections break these relations making the AR impossible to hold universally, i.e. for any target and at any energy. We predict a dramatic breakdown of the AR for coherent neutrino-production of pions on nuclei at all energies.

hep-ph↗

arXiv2012

Nuclear Shadowing in Electro-Weak Interactions

Shadowing is a quantum phenomenon leading to a non-additivity of electroweak cross sections on nucleons bound in a nucleus. It occurs due to destructive interference of amplitudes on different nucleons. Although the current experimental evidence for shadowing is dominated by charged-lepton nucleus scattering, studies of neutrino nucleus scattering have recently begun and revealed unexpected results.

hep-ph↗

arXiv2012

T-odd quark-gluon-quark correlation function in the diquark model

We study the transverse momentum dependent quark-gluon-quark correlation function. Using a spectator diquark model, we calculate the eight time-reversal-odd interaction-dependent twist-3 quark distributions appearing in the decomposition of the transverse momentum dependent quark-gluon-quark correlator. In order to obtain finite results, we assume a dipole form factor for the nucleon-quark-diquark coupling, instead of a point-like coupling. The results are compared with the time-reversal-odd interaction-independent twist-3 TMDs calculated in the same model.

hep-ph↗

arXiv2012

Quenching of high-pT hadrons: Energy Loss vs Color Transparency

High-pT hadrons produced in hard collisions and detected inclusively bear peculiar features: (i) they originate from jets whose initial virtuality and energy are of the same order; (ii) such jets are rare and have a very biased energy sharing among the particles, namely, the detected hadron carries the main fraction of the jet energy. The former feature leads to an extremely intensive gluon radiation and energy dissipation at the early stage of hadronization, either in vacuum or in a medium. As a result, a leading hadron must be produced on a short length scale. Evaluation within a model of perturbative fragmentation confirms the shortness of the production length. This result is at variance with the unjustified assumption of long production length, made within the popular energy loss scenario. Thus we conclude that the main reason of suppression of high-pT hadrons in heavy ion collisions is the controlled by color transparency attenuation of a high-pT dipole propagating through the hot medium. Adjusting a single parameter, the transport coefficient, we describe quite well the data from LHC and RHIC for the suppression factor R_{AA} as function of pT, collision energy and centrality. We observe that the complementary effect of initial state interaction causes a flattening and even fall of R_{AA} at large pT. The azimuthal anisotropy of hadron production, calculated with no further adjustment, also agrees well with data at different energies and centralities.

hep-ph↗

arXiv2012

Nucleon structure including high Fock states in AdS/QCD

We present a detailed analysis of nucleon electromagnetic and axial form factors in a holographic soft-wall model. This approach is based on an action which describes hadrons with broken conformal invariance and incorporates confinement through the presence of a background dilaton field.For Nc=3 we describe the nucleon structure in a superposition of a three valence quark state with high Fock states including an adjustable number of partons (quarks, antiquarks and gluons) via studying the dynamics of 5D fermion fields of different scaling dimension in anti-de Sitter (ADS) space. According to the gauge/gravity duality the 5D fermion fields of different scaling dimension correspond to the Fock state components with a specific number of partons. In the present application we restrict to the contribution of 3, 4 and 5 parton components in the nucleon Fock state. With a minimal number of free parameters (dilaton scale parameter, mixing parameters of partial contributions of Fock states, coupling constants in the effective Lagrangian) we achieve a reasonable agreement with data for the nucleon form factors.

hep-ph↗

arXiv2012

Converting Classical Theories to Quantum Theories by Solutions of the Hamilton-Jacobi Equation

By employing special solutions of the Hamilton-Jacobi equation and tools from lattice theories, we suggest an approach to convert classical theories to quantum theories for mechanics and field theories. Some nontrivial results are obtained for a gauge field and a fermion field. For a topologically massive gauge theory, we can obtain a first order Lagrangian with mass term. For the fermion field, in order to make our approach feasible, we supplement the conventional Lagrangian with a surface term. This surface term can also produce the massive term for the fermion.

hep-th↗