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B. L. Ioffe

Publications and source records attributed to B. L. Ioffe.

66 records · Page 4Linked to original sources
arXiv1996

On the Forward Scattering Amplitude of the Virtual Longitudinal Photon at Zero Energy

The theorem is proved, determining the forward scatterring amplitude of virtual longitudinal photon at zero energy on any hadronic target in the limit of small photon virtualities $Q^2$. The theorem is strict, based only on Lorenz and gauge invariance. No assumptions about the strong interaction, besides the gap in the mass spectrum, are used. Two terms in the expansion over $Q^2$ are calculated. The estimation is given up to what $Q^2$ the elastic term can represent the whole amplitude of longitudinal virtual photon-proton scattering.

hep-ph↗
arXiv1996

Meson Masses in Nuclear Matter

Mass shifts $Δm$ of particles in nuclear matter relative to their vacuum values are considered. A general formula relating $Δm(E)$ ($E$ is the particle energy) to the real part of the forward particle-nucleon scattering amplitude ${\rm Re} f(E)$ is presented and its applicability domain is formulated. The $ρ$-meson mass shift in nuclear matter is calculated at $2\la E_ρ\la 7$ GeV for transversally and longitudinally polarized $ρ$-mesons with the results: $Δm_ρ^T \sim 50$ MeV and $Δm_ρ^L \sim 10$ MeV at normal nuclear density.

hep-ph↗
arXiv1996

The structure functions of longitudinal virtual photon at low virtualities

The structure functions of longitudinal virtual photon at low virtualities are calculated in the framework of chiral pertubation theory(ChPT) in the zero and first order of ChPT. It is assumed that the virtuality of target longitudinal photon is much less than the virtuality of the hard projectile photon and both are less than the characteristic ChPT scale.

hep-ph↗
arXiv1995

Nucleon Spin Structure. Sum Rules

Contents: 1. The sum rules or $Γ_{p,n}$.Theoretical status. 2. Calculations of matrix elements over the polarized nucleon by the QCD sum rule approach. 3. Twist-4 corrections to $Γ_{p,n}$ from QCD sum rules. 4. Gerasimov, Drell-Hearn (GDH) sum rules. The estimate of higher twist corrections to $Γ_{p,n}$ using interpolation between $Γ_{p,n}$ and GDH sum rules. 5. Comparison with experiment. 6. The calculations of polarized structure functions by the QCD sum rule method. 7. Calculation of the chirality violating structure function $h_1(x)$ by QCD sum rules. 8. Conclusions.

hep-ph↗
arXiv1995

Sum Rules for Nucleon Spin Structure Functions

The uncertainties in the perturbative and higher twist corrections to the sum rules for $Γ_{p,n}$ are analyzed. The theoretical predictions for $Γ_{p,n}$ are compared with the whole set of experimental data and the restrictions on theoretical uncertainties was obtained. Suggestions for future experiments are given.

hep-ph↗
arXiv1995

Gluon Distributions in Real and Virtual Photon and the Photon Structure Function

Gluon distributions in real and virtual photons are calculated using evolution equations in the NLO approximation. The quark distributions in the photon determined on the basis of the QCD sum rule approach in ref.[1] are taken as an input. It is shown that gluon distribution in the photon can be reliably determined up to $x = 0.03 ÷0.05$ much lower than the corresponding values in the case of quark distributions.Two variants of the calculations are considered: (1) it is assumed that there are no intrinsic gluons in the photon at some low normalization point $Q^2 = Q^2_0 \sim 1 GeV^2$; (2) it is assumed that gluonic content of the photon at low $Q^2_0$ is described by gluonic content of vector mesons $ρ, ω, φ$. The gluon distributions in these two variants appear to be different. This fact permits one to clarify the origin of nonperturbative gluonic content of the photon by comparing the results with experiment. Structure functions $F_2(x)$ for real and virual photon are calculated and it is shown that in the region $x \geq 0.2$ where QCD approach is valid, there is a good agreement with experiment.

hep-ph↗
arXiv1995

the Three-Point Vertex of Hadron Interaction with External Fields in QCD Sum Rules

The calculation method of the hadron interaction vertex with constant external fields in QCD sum rules is discussed. The representation of the polarization operator in terms of physical states contributions is considered and the most suitable form of this representation is suggested. The estimates of uncertainties in the previous calculations of hadron interaction vertices with external fields are given.

hep-ph↗
arXiv1994

The Nucleon Spin Problem

C o n t e n t s 1. Introduction. 2. General Relations. 3. Small $x$ Domain -- Regge Behaviour. 4. The Parton Model. 5. Sum Rules in the Parton Model. 6. QCD Corrections to Sum Rules. 7. Nucleon Axial Coupling Constants. 8. The Experimental Data on $g_1(x)$ and Their Interpretation. 9. Suggestions for Future Experiments. 10. The Structure Function $g_2(x)$. 11. Chirality Violating Structure Function $h_1(x)$. 12. Conclusions.

hep-ph↗
arXiv1994

Next-to-leading-order temperature corrections to correlators in QCD

Corrections of order $T^4$ to vector and axial current correlators in QCD at a finite temperature $T<T_c$ are obtained using dispersion relations for the amplitudes of deep inelastic scattering on pions. Their relation with the operator product expansion is presented. An interpretation of the results in terms of $T$-dependent meson masses is given: masses of $ρ$ and $a_1$ start to move with temperature in order $T^4$.

hep-ph↗
arXiv1993

On the current correlators in QCD at finite temperature

Current correlators in QCD at a finite temperature $T$ are considered from the viewpoint of operator product expansion. It is stressed that at low $T$ the heat bath must be represented by hadronic, and not quark-gluon states. A possibility to express the results in terms of $T$-dependent resonance masses is discussed. It is demonstrated that in order $T^2$ the masses do not move and the only phenomenon which occurs is a parity and isospin mixing.

hep-ph↗
arXiv1993

Estimates of $m_d - m_u$ and $\langle\bar{d}d\rangle - \langle\bar{u}u\rangle$ from QCD sum rules for $D$ and $D^{\ast}$ isospin mass differences

The recent experimental data on $D^{+}-D^{0}$ and $D^{\ast\, +}-D^{\ast\,0}$ mass differences are used as inputs in the QCD sum rules to obtain new estimates on the mass difference of light quarks and on the difference of their condensates: $m_d -m_u =3\pm 1\, MeV$, $\langle\bar{d}d\rangle -\langle\bar{u}u\rangle = -(2.5\pm 1)\cdot 10^{-3}\langle\bar{u}u\rangle$ (at a standard normalization point, $μ= 0.5\, GeV$).

hep-ph↗