Cutting: what school counselors should know about students who self-injure

Includes bibliographical references

Search for a heavy magnetic monopole at the Fermilab Tevatron and CERN LHC

If a heavy Dirac monopole exists, the light to light scattering below the monopole production threshold is enhanced due to the strong coupling of monopoles to photons. This effect could be observable in the collision of virtual photons at proton colliders. At the Tevatron it will be seen as pair production of photons with energies 200--400 GeV and roughly compensated transverse momenta 100--400 GeV/c. This effect could be seen at monopole masses about 1--2.5 TeV at the upgraded Tevatron and 7.4--19 TeV at LHC depending on monopole spin.Comment: 11 pages, 2 figures, Latex(Revtex), small changes in estimates of Sect.III and in Fig.2 due to corrected form factor scale of eq. (19), title made more precis

Studying the infrared region in Landau gauge QCD

We report on the progress we made in studying the infrared behavior of the ghost and gluon dressing functions in Landau gauge. Related to this we also investigate a running coupling given in terms of those functions and compare our results to those coming from the Dyson-Schwinger approach. We present first numerical results for the SU(3) ghost-ghost-gluon vertex renormalization constant. In addition the spectrum of low-lying eigenvalues and eigenfunctions of the Faddeev-Popov operator is determined. The saturation of the ghost propagator in terms of those eigenvalues and eigenmodes is discussed at lower momenta.Comment: 6 pages, 4 figures, talk presented at Lattice 2005 (Topology and Confinement

New method for calculating helicity amplitudes of jet-like QED processes for high-energy colliders II. Processes with lepton pair production

As continuation of our previous paper we further develop our new method for calculating helicity amplitudes of jet-like QED processes described by tree diagrams, applying it to lepton pair production. This method consists in replacing spinor structures for real and weakly virtual intermediate leptons by simple transition vertices. New vertices are introduced for the pair production case, and previous bremsstrahlung vertices are generalized to include virtual photons inside the considered jet. We present a diagrammatic approach that allows to write down in an efficient way the leading helicity amplitudes, at tree level. The obtained compact amplitudes are particularly suitable for numerical calculations in jet-like kinematics. Several examples with up to four particles in a jet are discussed in detail.Comment: 11 pages, 11 figures, Latex, Springer-Latex macros include

The influence of Gribov copies on the gluon and ghost propagator

The dependence of the gluon and ghost propagator in pure SU(3) gauge theory on the choice of Gribov copies in Landau gauge is studied. Simulations were performed on several lattice sizes at $\beta$=5.8, 6.0 and 6.2. In the infrared region the ghost propagator turns out to depend on the choice, while the impact on the gluon propagator is not resolvable. Also the eigenvalue distribution of the Faddeev-Popov operator is sensitive to Gribov copies.Comment: Talk presented at Quark Confinement and the Hadron Spectrum VI, Villasimius, Sardinia, Italy, September 21-25, 2004, 3 pages, 2 figure

New method for calculating helicity amplitudes of jet--like QED processes for high--energy colliders I. Bremsstrahlung processes

Inelastic QED processes, the cross sections of which do not drop with increasing energy, play an important role at high-energy colliders. Such reactions have the form of two-jet processes with the exchange of a virtual photon in the t-channel. We consider them in the region of small scattering angles $m/E \lesssim \theta \ll 1$, which yields the dominant contribution to their total cross sections. A new effective method is presented and applied to QED processes with emission of real photons to calculate the helicity amplitudes of these processes. Its basic idea is similar to the well-known equivalent-lepton method. Compact analytical expressions for those amplitudes up to $e^8$ are derived omitting only terms of the order of $m^2/E^2, \theta^2$, $\theta m/E$ and higher order. The helicity amplitudes are presented in a compact form in which large compensating terms are already cancelled. Some common properties for all jet-like processes are found and we discuss their origin.Comment: 17 pages, LATEX (svjour style files included