5,972 research outputs found
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
Quiver varieties and a noncommutative P²
To any finite group Γ ⊂ SL₂(ℂ) and each element t in the center of the group algebra
Of Γ we associate a category, Coh(ℙ²_(Γ, τ),ℙ¹). It is defined as a suitable quotient of the
category of graded modules over (a graded version of) the deformed preprojective algebra
introduced by Crawley-Boevey and Holland. The category Coh(ℙ²_(Γ, τ),ℙ¹) should be thought
of as the category of coherent sheaves on a ‘noncommutative projective space’, ℙ²_(Γ, τ), equipped
with a framing at ℙ¹, the line at infinity. Our first result establishes an isomorphism between
the moduli space of torsion free objects of Coh(ℙ²_(Γ, τ),ℙ¹) and the Nakajima quiver variety arising
from G via the McKay correspondence. We apply the above isomorphism to deduce a generalization
of the Crawley-Boevey and Holland conjecture, saying that the moduli space of ‘rank 1’
projective modules over the deformed preprojective algebra is isomorphic to a particular quiver
variety. This reduces, for Γ = {1}, to the recently obtained parametrisation of the isomorphism
classes of right ideals in the first Weyl algebra, A₁, by points of the Calogero–
Moser space, due to Cannings and Holland and Berest and Wilson. Our approach is algebraic
and is based on a monadic description of torsion free sheaves on ℙ²_(Γ, τ). It is totally different
from the one used by Berest and Wilson, involving τ-functions
A new method for calculating jet-like QED processes
We consider inelastic QED processes, the cross sections of which do not drop
with increasing energy. 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 <= theta << 1, which yield the dominant
contribution to their cross sections. A new effective method is presented to
calculate the corresponding helicity amplitudes. Its basic idea consists in
replacing spinor structures for real and weakly virtual intermediate leptons by
simple transition vertices for real leptons. The obtained compact amplitudes
are particularly suitable for numerical calculations in jet-like kinematics.Comment: 6 pages, 2 figures, Contribution presented by V.G. Serbo at PHOTON
2003, Frascati, Ital
Semiempirical methods for computing turbulent flows
Two semiempirical theories which provide a basis for determining the turbulent friction and heat exchange near a wall are presented: (1) the Prandtl-Karman theory, and (2) the theory utilizing an equation for the energy of turbulent pulsations. A comparison is made between exact numerical methods and approximate integral methods for computing the turbulent boundary layers in the presence of pressure, blowing, or suction gradients. Using the turbulent flow around a plate as an example, it is shown that, when computing turbulent flows with external turbulence, it is preferable to construct a turbulence model based on the equation for energy of turbulent pulsations
Charge asymmetry of pions in the process
The study of the charge asymmetry of produced particles allows to investigate
the interference of different production mechanisms and to determine new
features of the corresponding amplitudes. In the process the two-pion system is produced via two mechanisms: two-photon
(C-even state) and bremsstrahlung (C-odd state) production. We study the charge
asymmetry of pions in a differential in the pion momenta cross section
originating from an interference between these two mechanisms. At low effective
mass of dipions this asymmetry is directly related to the s- and p-phases of
elastic scattering. At higher energies it can give new information
about the meson family, meson, etc. The asymmetry is
expressed via the pion form factor and helicity amplitudes for
the subprocess as where we have calculated analytically the coefficients
for the region giving the main contribution to the effect. Several
distributions of pions are presented performing a numerical analysis in a model
with point-like pions. In the region near the dipion threshold the asymmetry is
of the order of 1%. We show that with suitable cuts the signal to background
ratio can be increased up to about 10%.Comment: 16 pages, 10 figures, LaTeX, style files for EPJC include
Pair Production at the Photon Linear Collider
scattering at the Photon Linear Collider is
considered. Explicit formulas for helicity amplitudes due to boson loops
are presented. It is shown that the pair production will be easily
observable at PLC and separation of the loop contribution will be possible
at c.m. energy of 300~GeV or higher.Comment: 9 pages of standard LaTeX + 3 PostScript figures (uuencoded and
compressed
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