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The cubic surfaces with twenty-seven lines over finite fields
In this thesis, we classify the cubic surfaces with twenty-seven lines in three dimensional projective space over small finite fields. We use the Clebsch map to construct cubic surfaces with twenty-seven lines in PG(3; q) from 6-arcs not on a conic in PG(2; q). We introduce computational and geometrical procedures for the classification of cubic surfaces over the finite field Fq. The performance of the algorithms is illustrated by the example of cubic surfaces over F13, F17 and F19
Markoff Triples and Strong Approximation
We investigate the transitivity properties of the group of morphisms
generated by Vieta involutions on the solutions in congruences to the Markoff
equation as well as to other Markoff type affine cubic surfaces. These are
dictated by the finite orbits of these actions and these can
be determined effectively. The results are applied to give forms of strong
approximation for integer points, and to sieving, on these surface
Hilbert's fourteenth problem over finite fields, and a conjecture on the cone of curves
We give examples over arbitrary fields of rings of invariants that are not
finitely generated. The group involved can be as small as three copies of the
additive group, as in Mukai's examples over the complex numbers. The failure of
finite generation comes from certain elliptic fibrations or abelian surface
fibrations having positive Mordell-Weil rank.
Our work suggests a generalization of the Morrison-Kawamata cone conjecture
from Calabi-Yau varieties to klt Calabi-Yau pairs. We prove the conjecture in
dimension 2 in the case of minimal rational elliptic surfaces.Comment: 26 pages. To appear in Compositio Mathematic
Massless Higher Spins and Holography
We treat free large N superconformal field theories as holographic duals of
higher spin (HS) gauge theories expanded around AdS spacetime with radius R.
The HS gauge theories contain massless and light massive AdS fields. The HS
current correlators are written in a crossing symmetric form including only
exchange of other HS currents. This and other arguments point to the existence
of a consistent truncation to massless HS fields. A survey of massless HS
theories with 32 supersymmetries in D=4,5,7 (where the 7D results are new) is
given and the corresponding composite operators are discussed. In the case of
AdS_4, the cubic couplings of a minimal bosonic massless HS gauge theory are
described. We examine high energy/small tension limits giving rise to massless
HS fields in the Type IIB string on AdS_5 x S^5 and M theory on AdS_{4/7} x
S^{7/4}. We discuss breaking of HS symmetries to the symmetries of ordinary
supergravity, and a particularly natural Higgs mechanism in AdS_5 x S^5 and
AdS_4 x S^7 where the HS symmetry is broken by finite g_{YM}. In AdS_5 x S^5 it
is shown that the supermultiplets of the leading Regge trajectory cross over
into the massless HS spectrum. We propose that g_{YM}=0 corresponds to a
critical string tension of order 1/R^2 and a finite string coupling of order
1/N. In AdS_7 x S^4 we give a rotating membrane solution coupling to the
massless HS currents, and describe these as limits of Wilson surfaces in the
A_{N-1}(2,0) SCFT, expandable in terms of operators with anomalous dimensions
that are asymptotically small for large spin. The minimal energy configurations
have semi-classical energy E=s for all s and the geometry of infinitely
stretched strings with energy and spin density concentrated at the endpoints.Comment: 77 pages, latex, minor corrections to eqs 4.26-30, a refined
discussion of long strings in Sec
Construction of Rational Surfaces Yielding Good Codes
In the present article, we consider Algebraic Geometry codes on some rational
surfaces. The estimate of the minimum distance is translated into a point
counting problem on plane curves. This problem is solved by applying the upper
bound "\`a la Weil" of Aubry and Perret together with the bound of Homma and
Kim for plane curves. The parameters of several codes from rational surfaces
are computed. Among them, the codes defined by the evaluation of forms of
degree 3 on an elliptic quadric are studied. As far as we know, such codes have
never been treated before. Two other rational surfaces are studied and very
good codes are found on them. In particular, a [57,12,34] code over
and a [91,18,53] code over are discovered, these
codes beat the best known codes up to now.Comment: 20 pages, 7 figure
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