26,508 research outputs found

### $\Delta\pi N$ 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

- âŠ