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SUMMARY:Towards the Standard Model on Rigid D-Branes - Honecker\, MG (Joha
 nnes Gutenberg-Universitt Mainz)
DTSTART:20120628T151500Z
DTEND:20120628T153000Z
UID:TALK38725@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:D-brane worlds have provided a geometrically intuitive approac
 h for Standard Model (SM) engineering within string theory compactificatio
 ns. While the types and ranks of gauge groups and the chiral matter conten
 t are tackled in a straightforward manner\, it remains on the one hand an 
 open question if the SM can be obtained on rigid D-branes - without contin
 uous gauge symmetry breaking along flat directions and with non-trivial D-
 brane instanton contributions to the effective action - and on the other h
 and if such models are consistent with low-energy data. The T6/Z(2)xZ(6') 
 orbifold with discrete torsion admits a plethora of left-right symmetric `
 local models' without exotic matter in the adjoint\, symmetric or antisymm
 etric representation. However\, `global' completions usually come at the c
 ost of introducing new exotic states in bifundamental representations. It 
 furthermore turns out that USp(2) and SO(2) in place of U(2) symmetries ca
 n at most provide one particle generation. Last but not least\, it turns o
 ut that for any T6/Z(2)xZ(2M) orbifold with discrete torsion and tilted to
 ri\, orientifold invariant stacks of D6-branes carry USp(2N) or SO(2N) gau
 ge groups depending on their relative position to the exotic O6-plane. The
  new classification reduces the number of K-theory constraints. If time pe
 rmits\, I will briefly comment on the drastic change in the pattern of Yuk
 awa couplings on orbifolds compared to the six-torus using a T6/Z6' exampl
 e. As a result\, quark Yukawas can provide large mixings while lepton Yuka
 was are flavour diagonal at leading order. Also the rule of `one massive g
 eneration only' is circumvented.\n\n
LOCATION:Seminar Room 2\, Newton Institute Gatehouse
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