1,577 research outputs found
The first main theorem on complements: from global to local
The aim of this paper is to clarify and generalize techniques of works
alg-geom/9711024 (see also math.AG/9810097 and math.AG/9901004). Roughly
speaking, we prove that for local Fano contractions the existence of
complements can be reduced to the existence of complements for lower
dimensional projective Fano varieties.Comment: 27 pages, LaTeX2
On birational involutions of
Let be a rationally connected three-dimensional algebraic variety and let
be an element of order two in the group of its birational selfmaps.
Suppose that there exists a non-uniruled divisorial component of the
-fixed point locus. Using the equivariant minimal model program we give a
rough classification of such elements.Comment: 24 pages, late
Gravitational wave background from coalescing compact stars in eccentric orbits
Stochastic gravitational wave background produced by a stationary coalescing
population of binary neutron stars in the Galaxy is calculated. This background
is found to constitute a confusion limit within the LISA frequency band up to a
limiting frequency \NUlim{}\sim 10^{-3} Hz, leaving the frequency window
-- Hz open for the potential detection of cosmological
stochastic gravitational waves and of signals involving massive black holes out
to cosmological distances.Comment: 6 pages, 7 figure
Hard production of a Z boson plus heavy flavor jets at LHC and the intrinsic charm content of a proton
The cross section of associated production of a Z boson with heavy flavor
jets in collisions is calculated using the SHERPA Monte Carlo generator
and the analytical combined QCD approach based on kt-factorization at small x
and conventional collinear QCD at large x. A satisfactory description of the
ATLAS and CMS data on the spectra of Z bosons and c-jets in the whole
rapidity, y, region is shown. Searching for the intrinsic charm (IC)
contribution in these processes, which could be visible at large y > 1.5, we
study observables very sensitive to non-zero IC contributions and less affected
by theoretical QCD scale uncertainties. One of such observables is the
so-called double ratio: the ratio of the differential cross section of Z + c
production in the central region of |y| < 1.5 and in the forward region 1.5 <
|y| < 2.5, divided by the same ratio for Z + b production. These observables
could be more promising for the search of IC at LHC as compared to the
observables considered earlier.Comment: 18 pages, 7 figure
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