An analysis of a minimal vectorlike extension of the Standard Model

We analyze an extension of the Standard Model with an additional SU(2) hypercolor gauge group keeping the Higgs boson as a fundamental field. Vectorlike interactions of new hyperquarks with the intermediate vector bosons are explicitly constructed. We also consider pseudo-Nambu--Goldstone bosons caused by the symmetry breaking SU(4)-> Sp(4). A specific global symmetry of the model with zero hypercharge of the hyperquark doublets ensures the stability of a neutral pseudoscalar field. Some possible manifestations of the lightest states at colliders are also examined.Comment: 16 pages, 1 table, v.2: minor modification, reference is added, formula (62) is correcte

Two-loop kite master integral for a correlator of two composite vertices

We consider the most general two-loop massless correlator $I(n_1,n_2,n_3,n_4,n_5; x,y;D)$ of two composite vertices with the Bjorken fractions $x$ and $y$ for arbitrary indices $\{n_i\}$ and space-time dimension $D$; this correlator is represented by a "kite" diagram. The correlator $I(\{n_i\};x,y;D)$ is the generating function for any scalar Feynman integrals related to this kind of diagrams. We calculate $I(\{n_i\};x,y;D)$ and its Mellin moments in a direct way by evaluating hypergeometric integrals in the $\alpha$ representation. The result for $I(\{n_i\};x,y;D)$ is given in terms of a double hypergeometric series---the Kamp\'{e} de F\'{e}rriet function. In some particular but still quite general cases it reduces to a sum of generalized hypergeometric functions $_3F_2$. The Mellin moments can be expressed through generalized Lauricella functions, which reduce to the Kamp\'{e} de F\'{e}rriet functions in several physically interesting situations. A number of Feynman integrals involved and relations for them are obtained.Comment: 28 pages, 3 figures. v4 corrects misprints in eqs. (3.19), (3.26), and (4.12

Q^2-evolution of nucleon-to-resonance transition form factors in a QCD-inspired vector-meson-dominance model

We adopt the vector-meson-dominance approach to investigate Q^2-evolution of N-R transition form factors (N denotes nucleon and R an excited resonance) in the first and second resonance regions. The developed model is based upon conventional NR\gamma-interaction Lagrangians, introducing three form factors for spin-3/2 resonances and two form factors for spin-1/2 nucleon excitations. Lagrangian form factors are expressed as dispersionlike expansions with four or five poles corresponding to the lowest excitations of the mesons \rho(770) and \omega(782). Correct high-Q^2 form factor behavior predicted by perturbative QCD is due to phenomenological logarithmic renormalization of electromagnetic coupling constants and linear superconvergence relations between the parameters of the meson spectrum. The model is found to be in good agreement with all the experimental data on Q^2-dependence of the transitions N-\Delta(1232), N-N(1440), N-N(1520), N-N(1535). We present fit results and model predictions for high-energy experiments proposed by JLab. Besides, we make special emphasis on the transition to perturbative domain of N-\Delta(1232) form factors.Comment: 22 pages, 22 PS figures, REVTeX 4; v2: +3 refs, minor editorial change

Correlators of vector, tensor, and scalar composite vertices of order O(αs2β0)O(\alpha_s^2\beta_0)

We present analytical results for massless correlators of two vector, tensor, and scalar composite vertices with the Bjorken fractions $x$ and $y$ of order $\alpha_s^2 \beta_0$ of QCD. The structure of these correlators $\Pi^\text{V,T,S}(x,y; p^2)$ and properties of its main elements are discussed in detail. Special attention is paid to verifying the results and comparing them with known particular cases. We apply the correlators to evaluate radiative corrections to the distribution amplitudes of light mesons within the QCD sum rules.Comment: 25 pages, 4 figures; v3: published versio

Renormalon-chain contributions to two-point correlators of nonlocal quark currents

We calculate, within massless QCD, a two-point correlator of nonlocal (composite) vector quark currents with arbitrary-length chains of the simplest fermion loops being inserted into gluon lines. Within the large $n_f$ (or large $\beta_0$) approximation, the correlator defines a perturbative contribution to the leading-twist distribution amplitudes for light mesons. Our results are consistent with a number of special cases in the literature. We consider functionals of the correlator, which are important for the phenomenology, and their properties as function series.Comment: 6 pages, 2 figures. Proceedings of the International Conference on Quantum Field Theory, High-Energy Physics, and Cosmology, Dubna, Russia (July 18-21, 2022); to be published in PEPAN Letter

Factorization effects in a model of unstable particles

The effects of factorization are considered within the framework of the model of unstable particles with a smeared mass. It is shown that two-particle cross section and three-particle decay width can be described by the universal factorized formulae for an unstable particles of an arbitrary spin in an intermediate state. The exact factorization is caused by the specific structure of the model unstable-particle propagators. This result is generalized to complicated scattering and decay-chain processes with unstable particles in intermediate states. We analyze applicability of the method and evaluate its accuracy.Comment: 13 pages, 7 figure