1. Constructing 5D Orbifold GUTs from Heterotic Strings w/ R.J. Zhang and T. Kobayashi Phys. Lett. B593, 262 (2004) & Nucl. Phys. B704, 3 (2005) w/ A. Wingerter and P. Vaudrevange, in progress Fermilab Theory Seminar Stuart Raby May 25, 2006

2. In 2007, the LHC turns on; hopefully opening up a new age of discovery. String theory is by far the best candidate for a self- consistent quantum theory of gravity. Moreover, it provides a framework for a true theory of everything. Estimates suggest there are more than 10 300 string vacua. The string vacuum fixes the gauge group, the number of families, fermion masses and supersymmetry breaking. Many have searched for phenomenologically acceptable string vacua. Yet we do not know whether even one string vacuum exists which looks like the real world. This talk describes a new search in an old direction -- the weakly coupled heterotic string. Our results are promising; already providing some interesting new models. We are guided in our approach by recent progress in understanding model building in 5 and 6 dimensional orbifold SUSY GUT field theories.

3. Phenomenological Guidelines 1. Preserve gauge coupling unification 2. Low energy SUSY M Z << M G 3. Quarks and leptons in 16 of SO(10) 4. Higgs in 10 5. Preserve GUT relations for 3 rd family Yukawa 6. “Natural” See-Saw scale ~ M G 7. Use intuition from Orbifold GUTs

4. Outline 3 Family Orbifold GUT on M 4 x S 1 /(Z 2 xZ 2 ’) Heterotic string compactified on [T 2 ] 3 /Z 6 + Wilson lines Consider E 6 example

5. Title of talk5

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8. E 6 Orbifold GUT on M 4 x S 1 /(Z 2 xZ 2 ’)

9. E 8 x E 8 Heterotic string in 10D Compactify 6D on (T 2 ) 3 Then mod by Z 6 = (Z 3 x Z 2 ) and Add Wilson lines Z 6 embedded in E 8 x E 8 gauge lattice as shift V 6 : consistent with mod. inv. !

10. First consider (T 2 ) 3 /Z 3 + W 3 [Wilson line in SU 3 torus] Massless modes From Untwisted sector + (G 2, SU 3 ) twisted sector E 6 GUT in 5D

11. Then add Z 2 orbifold + W 2 [in long direction] E6E6 SO(10)SU(4)xSU(2) L xSU(2) R F 3 = (4,2,1), F 3 c = (4 c,1,2), H = (1,2,2) PP’ ( V 2 )( V 2 + W 2 )

12. Two families sit on Z 2 fixed points !! D 4 family symmetry !! Exotics

13. D 4 family symmetry doublet singlet

14. Extra color triplets !! Z 2 twisted sector

15. E 6 Orbifold GUT on M 4 x S 1 /(Z 2 xZ 2 ’)

16.  3 rd family in bulkgauge-Yukawa unification  1 st and 2 nd families on Z 2 fixed points D 4 family symmetry  Higgs for PS symmetry breaking To summarize

17. PS symmetry breaking F and D flat direction breaks PS to SM + gives mass to all SM non-singlets

18. Gauge coupling unification ? 4D GUT 5D Orbifold GUT

19. Gauge coupling unification ++ and -- modes are in overlap of and

20. Weak B.C.s Strong

21. Successe s 3 rd generation and Higgs in bulk -> gauge-Yukawa unif. D 4 family symmetry : family hierarchy + suppress flavor violation Gauge coupling unification

22. D 4 family symmetry

23. So what’s the problem ?  Exotics So what now ? Search for R parity inv. theory Z 3 x Z 2 or Alternate orbifold construct  NO R parity !! BUT Vector-like May be OK ? OK ! IF massive

24. New Search Z 2 x Z 4 orbifold V 2 x V 4 120 inequivalent possibilities W 1 and/or W 2 500,000 possible models Narrow the search Consider eg. MSSM in 4D Why bother with GUTs Demand - 3 ( 3, 2 ) + 6 ( 3*, 1 ) + > 5 ( 1, 2 ) TYPICALLY have Chiral Exotics i.e. Wrong Hypercharge  w/ Wingerter & Vaudrevange

25. Solution - Demand PS or SU(5) intermediate sym. & identify hypercharge ½ ( B – L) + T 3R in PS or Y in SU(5) I. MSSM in 4D w/ 3 families & NO chiral exotics Find PS -> SM - 6 models SU(5) -> SM - 40 models II. Pati – Salam in 4D w/ 3 families, PS Higgs & NO chiral exotics Find ~ 220 models

26. Title of talk26 Z 2 x Z 4 orbifold construction One example : preliminary Part of third family in bulk => heavy top Two light families on (0,1) fixed poiints

27. Spectrum Order S 0 : top mass S 2 : bottom + tau mass  term

28. Conclusions  New 3 family E 6 orbifold GUT  3 rd generation -- gauge-Yukawa unif.  D 4 family symmetry : family hierarchy + suppress flavor violation  Few vector-like exotics  NO R parity  Z 2 x Z 4 & Z 2 x Z 3 search in progress