M. Siddikov

Breakdown of partial conservation of axial current in diffractive neutrino interactions

We test the hypothesis of partially conserved axial current (PCAC) in high energy diffractive neutrino production of pions. Since the pion pole contribution to the Adler relation (AR) is forbidden by conservation of the lepton current, the heavier states, like the a1 pole, ρ-π cut, etc., control the lifetime of the hadronic fluctuations of the neutrino. We evaluate the deviation from the AR in diffractive neutrino-production of pions on proton and nuclear targets. At high energies, when all the relevant time scales considerably exceed the size of the target, the AR explicitly breaks down on an absorptive target, such as a heavy nucleus. In this regime, close to the black disc limit, the off-diagonal diffractive amplitudes vanish, while the diagonal one, π → π, which enters the AR, maximizes and saturates the unitarity bound. At lower energies, in the regime of short lifetime of heavy hadronic fluctuations the AR is restored, i.e. it is not altered by the nuclear effects.

Nonperturbative features of the axial current

Abstract We study the nonperturbative structure of the axial current and evaluate the two-point light-cone distribution amplitudes (DA) associated with the correlator ∫ d ξ e − i q ⋅ ξ 〈 0 | ψ ¯ ( x ) Γ ψ ( y ) J μ 5 ( ξ ) | 0 〉 within the instanton vacuum model in the leading order in O ( 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 .

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 \alpha_{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.

Higher-twist contributions to neutrino-production of pions

In this paper we estimate the size of twist-3 corrections to the deeply virtual meson production in neutrino interactions due to the chiral odd transversity Generalized Parton Distribution (GPD). We conclude that in contrast to pion electroproduction, in neutrino-induced reactions these corrections are small. This happens due to large contribution of unpolarized GPDs H, E to the leading-twist amplitude in neutrinoproduction. We provide a computational code, which can be used for evaluation of the cross-sections accounting for these twist-3 corrections with various GPD models. Our results are particularly relevant for analyses of the pion and kaon production in the Minerva experiment at FERMILAB.

Bethe-Heitler type radiative corrections to deeply virtual neutrino production of mesons

We study the electromagnetic Bethe-Heitler type contribution to neutrino-induced deeply virtual meson production (\nuDVMP). Such O(\alpha_{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.

Diffractive neutrino production of pions on nuclei: Adler relation within the color-dipole description

Effects of coherence in neutrino production of pions off nuclei are studied employing the color-dipole representation and path integral technique. If the nucleus remains intact, the process is controlled by the interplay of two length scales. One is related to the pion mass and is quite long (at low

Neutrino production of single pions: Dipole description

{Q}^{2}

Lorentz-boosted description of a heavy quarkonium

), while the other, associated with heavy axial-vector states, is much shorter. The Adler relation is found to be broken at all energies, but especially strongly at

Semiclassical solution to the BFKL equation with massive gluons

\ensuremath{\nu}\ensuremath{\gtrsim}10\text{ }\text{ }\mathrm{GeV}

Suppression versus enhancement of heavy quarkonia in pA collisions

, where the cross section is suppressed by a factor