17,166 research outputs found
On organizing principles of Discrete Differential Geometry. Geometry of spheres
Discrete differential geometry aims to develop discrete equivalents of the
geometric notions and methods of classical differential geometry. In this
survey we discuss the following two fundamental Discretization Principles: the
transformation group principle (smooth geometric objects and their
discretizations are invariant with respect to the same transformation group)
and the consistency principle (discretizations of smooth parametrized
geometries can be extended to multidimensional consistent nets). The main
concrete geometric problem discussed in this survey is a discretization of
curvature line parametrized surfaces in Lie geometry. We find a discretization
of curvature line parametrization which unifies the circular and conical nets
by systematically applying the Discretization Principles.Comment: 57 pages, 18 figures; In the second version the terminology is
slightly changed and umbilic points are discusse
The Soft-Collinear Bootstrap: N=4 Yang-Mills Amplitudes at Six and Seven Loops
Infrared divergences in scattering amplitudes arise when a loop momentum
becomes collinear with a massless external momentum . In gauge
theories, it is known that the L-loop logarithm of a planar amplitude has much
softer infrared singularities than the L-loop amplitude itself. We argue that
planar amplitudes in N=4 super-Yang-Mills theory enjoy softer than expected
behavior as already at the level of the integrand. Moreover,
we conjecture that the four-point integrand can be uniquely determined, to any
loop-order, by imposing the correct soft-behavior of the logarithm together
with dual conformal invariance and dihedral symmetry. We use these simple
criteria to determine explicit formulae for the four-point integrand through
seven-loops, finding perfect agreement with previously known results through
five-loops. As an input to this calculation we enumerate all four-point dual
conformally invariant (DCI) integrands through seven-loops, an analysis which
is aided by several graph-theoretic theorems we prove about general DCI
integrands at arbitrary loop-order. The six- and seven-loop amplitudes receive
non-zero contributions from 229 and 1873 individual DCI diagrams respectively.Comment: 27 pages, 48 figures, detailed results including PDF and Mathematica
files available at http://goo.gl/qIKe8 v2: minor corrections v3: figure 7
corrected, Lemma 2 remove
Equivalent String Networks and Uniqueness of BPS States
We analyze string networks in 7-brane configurations in IIB string theory. We
introduce a complex parameter M characterizing equivalence classes of networks
on a fixed 7-brane background and specifying the BPS mass of the network as
M_{BPS} = | M |. We show that M can be calculated without knowing the
particular representative of the BPS state. Based on detailed examination of
backgrounds with three and four 7-branes we argue that equivalent networks may
not be simultaneously BPS, an essential requirement of consistency.Comment: 28 pages, LaTeX, 18 eps figure
Decomposition and Oxidation of the N-Extended Supersymmetric Quantum Mechanics Multiplets
We furnish an algebraic understanding of the inequivalent connectivities
(computed up to ) of the graphs associated to the irreducible
supermultiplets of the N-extended Supersymmetric Quantum Mechanics. We prove
that the inequivalent connectivities of the N=5 and N=9 irreducible
supermultiplets are due to inequivalent decompositions into two sets of N=4
(respectively, N=8) supermultiplets. "Oxido-reduction" diagrams linking the
irreducible supermultiplets of the N=5,6,7,8 supersymmetries are presented. We
briefly discuss these results and their possible applications.Comment: 15 pages, 5 figure
Refining the classification of the irreps of the 1D N-Extended Supersymmetry
The linear finite irreducible representations of the algebra of the 1D
-Extended Supersymmetric Quantum Mechanics are discussed in terms of their
"connectivity" (a symbol encoding information on the graphs associated to the
irreps). The classification of the irreducible representations with the same
fields content and different connectivity is presented up to .Comment: Two extra cases added. Reply to hep-th/0611060v2 comments adde
- …