1. The Higgs Reduction Mechanism in Free Fermionic Models Elisa Manno (with A. Faraggi and C.Timirgaziu) Eur. Phys. J. C (2007) University of Liverpool UKBSM Workshop, 29-30 March 2007

2. Outline Motivations Motivations Free Fermionic Models (FFM) Free Fermionic Models (FFM) Yukawa selection mechanism Yukawa selection mechanism Higgs doublet-triplet splitting Higgs doublet-triplet splitting Model with reduced Higgs spectrum Model with reduced Higgs spectrum Conclusions Conclusions

3. Motivations In the free fermionic formulation we have realistic models Existence of 3 chiral generations Observable gauge group : SU(3)xSU(2)xU(1) n N=1 Supersymmetry Standard SO(10) embedding for the weak hypercharge Stability of the proton … Heterotic string vacuaMSSM states Heterotic string vacua with solely MSSM states are derived.

4. The Free Fermionic Models Field content ( light-cone gauge ) {   12  1,..6 y 1,..6  1,..6  y 1,..6  1,..6  1,..5  1,2,3  1,..8 } left sector (susy) right sector A model is constructed by specifying phases picked up the phases picked up by the WS fermions along non-contractible loops f → e –i  (f)π f modular invariance The phases are consistent with modular invariance

5. basis vectors The phases are given in terms of basis vectors b = {  (   12 ),  (  1 ),  (  2 ),..} For a given basis B = {b 1,..b n } the Hilbert space the Hilbert space  =  m i b i, m i = 1,..N bi -1 is obtained by acting on the vacuum with bosonic and fermionic operators The physical spectrum is obtained by applying the GSO projections If B = {1,S,b 1,b 2,b 3 } + opportune choice of , ,  b.c. basis vectors we have 4D models with N=1 Susy + 3 chiral generations, one from each b i, i=1,2,3.

6. Yukawa selection mechanism The Yukawa selection mechanism is given by the vector  responsible of the breaking SO(10) → SU(5) x U(1) The b.c. basis vectors in  fix the Yukawa couplings Quh, LNh Qdh, Leh Each sector b i gives rise to an up-like or down-like cubic level Yukawa coupl.  i = |  L -  R | =0,1 down-quark type Yukawa coupl. up-quark type Yukawa coupl.

7. Higgs doublet-triplet splitting The NS sector gives 3 multiplets of Higgs states in the 10 of SO(10) each of them associated with one of the twisted sectors b i. Higgs electroweak doublets h i, h i  i,i+1 (  4,5 )*  i Higgs colour triplets D i, D i  i,i+1 (  4,5 )*  i The doublet-triplet splitting mechanism results from the b. c. in  which break SO(10) → SO(6) x SO(4)  i =|  L –  R | = 0,1 h i projected out h i remains in the spectrum

8. We look for models such that… No Higgs triplets ; one Higgs doublet  3 (  ) = 1 Up-quark type Yukawa couplings selected  3 (  ) = 1 No chiral fractionally charged exotics

9. Model with reduced Higgs spectrum SO(10) breaking Hidden gauge group breaking b 1 sector b 2 sector b 3 sector

10. Model with reduced Higgs spectrum keep h 1 keep D 2 keep h 3 Project out the untwisted vectorial repr.   = 1 (up-quark type Yukawa coupling is selected)

11. Conclusions Free Fermionic Models produce some of the most realistic string models to date. The presence of 3 pairs of Higgs doublets is generally reduced by the analysis of supersymmetric flat directions. An alternative option for the reduction of the Higgs states is given by an opportune choice of free fermion boundary conditions at the string scale. The previous mechanism also provides a reduction of the moduli space.