The leading power asymptotic behaviour of the dimensionally regularized massless on-shell planar triple box diagram in the Regge limit t/s → 0 is analytically evaluated. E-mail: [email protected] Systematical analytical evaluation of two-loop Feynman diagrams with four external lines within dimensional regularization [1] began three years ago. In the pure massless case with all end-poi...

The Feynman–Hellmann theorem is used to show that vector meson energy eigenvalues are monotonically decreasing functions of the reduced masses of their constituent quarks. The experimental meson masses are used to put constraints on the values of quark masses and to predict the masses of some as yet undiscovered mesons. The mass of the B * c meson is predicted to be 6320 ± 10 MeV, and, with les...

We discuss a progress in calculation of Feynman integrals which has been done with help of the differential equation method and demonstrate the results for a class of two-point two-loop diagrams. The idea of the differential equation method (DEM) (see [1,2]): to apply the integration by parts procedure [3] to an internal n-point subgraph of a complicated Feynman diagram and later to represent n...

We study trie dynamics of a single hole in an otherwise half-filled two-dimensional Hubbard model by introducing a nonlocal Bogolyubov transformation in trie antiferromagnetic state. This allows us to rewrite trie Hamiltonian in a form that makes a separation between highenergy processes (involving double-occupancy) and low-energy puysics possible. A diagrammatic scheme is developed tuat allows...

A new kind of cut diagram is introduced to sum Feynman diagrams with non-abelian vertices. Unlike the Cutkosky diagrams which compute the discontinuity of single Feynman diagrams, the nonabelian cut diagrams represent a resummation of both the real and the imaginary parts of Feynman diagrams related by permutations. Several applications of the technique are reported, including a resolution of t...

Recently presented explicit formulae for asymptotic expansions of Feynman diagrams in the Sudakov limit [1] are applied to typical two-loop diagrams. For a diagram with one non-zero mass these formulae provide an algorithm for analytical calculation of all powers and logarithms, i.e. coefficients in the corresponding expansion (Q) ∑ n,j=0 cnjt −n ln t, with t = Q/m and j ≤ 4. Results for the co...

We derive a minimal set of Feynman rules for the loop amplitudes in unitary models of closed strings, whose target space is a simply laced (extended) Dynkin diagram. The string field Feynman graphs are composed of propagators, vertices (including tadpoles) of all topologies, and leg factors for the macroscopic loops. A vertex of given topology factorizes into a fusion coefficient for the matter...

In the last chapter we have shown that the problem of determining the counterterms in φ 4-theory can be reduced completely to the calculation of massless Feynman integrals in momentum space. Among these, the massless propagator-type integrals generated by the technique of infrared rearrangement in Section 12.2 can be calculated most easily by algebraic methods. The result of a successive applic...

In the last chapter we have shown that the problem of determining the counterterms in φ 4-theory can be reduced completely to the calculation of massless Feynman integrals in momentum space. Among these, the massless propagator-type integrals generated by the technique of infrared rearrangement in Section 12.2 can be calculated most easily by algebraic methods. The result of a successive applic...