8,530 research outputs found
Neutrino Majorana Masses from String Theory Instanton Effects
Finding a plausible origin for right-handed neutrino Majorana masses in
semirealistic compactifications of string theory remains one of the most
difficult problems in string phenomenology. We argue that right-handed neutrino
Majorana masses are induced by non-perturbative instanton effects in certain
classes of string compactifications in which the gauge boson has a
St\"uckelberg mass. The induced operators are of the form
where is a closed string modulus whose imaginary part transforms
appropriately under . This mass term may be quite large since this is not
a gauge instanton and is not directly related to SM gauge couplings.
Thus the size of the induced right-handed neutrino masses could be a few orders
of magnitude below the string scale, as phenomenologically required. It is also
argued that this origin for neutrino masses would predict the existence of
R-parity in SUSY versions of the SM. Finally we comment on other
phenomenological applications of similar instanton effects, like the generation
of a -term, or of Yukawa couplings forbidden in perturbation theory.Comment: 40 pages, 4 figures (v2: added references, small corrections)(v3:
minor corrections
Linear Complexity Hexahedral Mesh Generation
We show that any polyhedron forming a topological ball with an even number of
quadrilateral sides can be partitioned into O(n) topological cubes, meeting
face to face. The result generalizes to non-simply-connected polyhedra
satisfying an additional bipartiteness condition. The same techniques can also
be used to reduce the geometric version of the hexahedral mesh generation
problem to a finite case analysis amenable to machine solution.Comment: 12 pages, 17 figures. A preliminary version of this paper appeared at
the 12th ACM Symp. on Computational Geometry. This is the final version, and
will appear in a special issue of Computational Geometry: Theory and
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