Electroweak symmetry breaking in TeV-scale string models
  We propose a scenario of the electroweak symmetry breaking by one-loop radiative corrections in a class of string models with D3-branes at non-supersymmetric orbifold singularities with the string scale in TeV region. As a test example, we consider a simple model based on a D3-brane at locally C^3/Z_6 orbifold singularity, and the electroweak Higgs doublet fields are identified with the massless bosonic modes of the open string on that D3-brane. They have Yukawa couplings with three generations of left-handed quarks and right-handed up-type quarks which are identified with the massless fermionic modes of the open string on the D3-brane. We calculate the one-loop correction to the Higgs mass due to the non-supersymmetric string spectrum and interactions, and qualitatively suggest that the negative mass squared can be generated. The problems which must be solved to proceed quantitative calculations are pointed out. 
Noriaki Kitazawa