ΔπN\Delta\pi N coupling constant in light cone QCD sum rules

We employ the light cone QCD sum rules to calculate $\Delta\pi N$ coupling constant by studying the two point correlation function between the vacuum and the pion state. Our result is consistent with the traditional QCD sum rules calculations and it is in agreement with the experimental value.Comment: 8 pages, latex, 2 figure

Three Generations on the Quintic Quotient

A three-generation SU(5) GUT, that is 3x(10+5bar) and a single 5-5bar pair, is constructed by compactification of the E_8 heterotic string. The base manifold is the Z_5 x Z_5-quotient of the quintic, and the vector bundle is the quotient of a positive monad. The group action on the monad and its bundle-valued cohomology is discussed in detail, including topological restrictions on the existence of equivariant structures. This model and a single Z_5 quotient are the complete list of three generation quotients of positive monads on the quintic.Comment: 19 pages, LaTeX. v2: section on anomaly cancellation adde

The 24-Cell and Calabi-Yau Threefolds with Hodge Numbers (1,1)

Calabi-Yau threefolds with h^11(X)=h^21(X)=1 are constructed as free quotients of a hypersurface in the ambient toric variety defined by the 24-cell. Their fundamental groups are SL(2,3), a semidirect product of Z_3 and Z_8, and Z_3 x Q_8.Comment: 22 pages, 3 figures, 3 table

The Exact MSSM Spectrum from String Theory

We show the existence of realistic vacua in string theory whose observable sector has exactly the matter content of the MSSM. This is achieved by compactifying the E_8 x E_8 heterotic superstring on a smooth Calabi-Yau threefold with an SU(4) gauge instanton and a Z_3 x Z_3 Wilson line. Specifically, the observable sector is N=1 supersymmetric with gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}, three families of quarks and leptons, each family with a right-handed neutrino, and one Higgs-Higgs conjugate pair. Importantly, there are no extra vector-like pairs and no exotic matter in the zero mode spectrum. There are, in addition, 6 geometric moduli and 13 gauge instanton moduli in the observable sector. The holomorphic SU(4) vector bundle of the observable sector is slope-stable.Comment: 15 pages, LaTeX; v2: Hidden sector is unstable, symbol typesetting error corrected, clarifications and references added; v3: New discussion of hidden secto

Nucleons on the light-cone: Theory and phenomenology of baryon distribution amplitudes

This is a short review of the theory and phenomenology of baryon distribution amplitudes, including recent applications to the studies of nucleon form factors at intermediate momentum transfers using the light-cone sum rule approach.Comment: 16 pages, talk at CAQCD2006, Minneapoli

Ultraviolet dominance of power corrections in QCD?

I explain current theoretical ideas on higher-twist (hadronization) corrections to physical observables in QCD.Comment: 7 pages, LATEX, no figures; Presented at 5th International Conference on Physics Beyond the Standard Model, Balholm, Norway, 29 Apr - 4May 199

Deep Inelastic Scattering Beyond Perturbation Theory

I discuss possibilities to observe the instanton-induced contributions to deep inelastic scattering which correspond to nonperturbative exponential corrections to the coefficient functions in front of parton distributions of the leading twist.Comment: Talk given at the Leipzig workshop on High Energy Physics, Kyffhaeuser, September 20-24,1993, LATEX, 12 pages, 3 figures included as uu-encoded file, MPI-Ph/93-7

Electroproduction of Resonances at Large Momentum Transfers

Measurements of transition form factors for the electro-excitation of nucleon resonances in the Q^2=5-14 GeV^2 region can provide one with the information on quark wave functions at small transverse separations. In particular a comparison of form factors for the states of opposite parity can give insight in the mechanisms of chiral symmetry breaking. I discuss perspectives of the theoretical description of such reactions using a combination of lattice calculations and light-cone sum rulesComment: 10 pages, 5 figures. Contribution to the Proceedings of the 4th Workshop on Exclusive Reactions at High Momentum Transfer, May 18-21, 2010 Thomas Jefferson National Accelerator Facility Newport News, Virginia US