Electroweak Baryogenesis in the MSSM

We review the baryogenesis scenario in the MSSM at the perturbative level and, in particular, the impact of two-loop corrections on the strength of the phase transition and the amount of generated baryon asymmetry. We confirm the baryogenesis window, where m_H is less than 115GeV, for m_Q less than a few GeV, and the right-handed stop mass is constrained in the region between 100GeV and the top mass. This scenario will be tested at LEP and Tevatron colliders.Comment: Latex2.09, 12 pages, uses sprocl.sty, 10 figures; some references adde

Large radii and string unification

We study strong coupling effects in four-dimensional heterotic string models where supersymmetry is spontaneously broken with large internal dimensions, consistently with perturbative unification of gauge couplings. These effects give rise to thresholds associated to the dual theories: type I superstring or M-theory. In the case of one large dimension, we find that these thresholds appear close to the field-theoretical unification scale $\sim 10^{16}$ GeV, offering an appealing scenario for unification of gravitational and gauge interactions. We also identify the inverse size of the eleventh dimension of M-theory with the energy at which four-fermion effective operators become important.Comment: 12 pages, LateX, no figures. Version to appear in Physics Letters B. One reference adde

Higgs-gauge unification without tadpoles

In orbifold gauge theories localized tadpoles can be radiatively generated at the fixed points where U(1) subgroups are conserved. If the Standard Model Higgs fields are identified with internal components of the bulk gauge fields (Higgs-gauge unification) in the presence of these tadpoles the Higgs mass becomes sensitive to the UV cutoff and electroweak symmetry breaking is spoiled. We find the general conditions, based on symmetry arguments, for the absence/presence of localized tadpoles in models with an arbitrary number of dimensions D. We show that in the class of orbifold compactifications based on T^{D-4}/Z_N (D even, N>2) tadpoles are always allowed, while on T^{D-4}/\mathbb Z_2 (arbitrary D) with fermions in arbitrary representations of the bulk gauge group tadpoles can only appear in D=6 dimensions. We explicitly check this with one- and two-loops calculationsComment: 19 pages, 3 figures, axodraw.sty. v2: version to appear in Nucl. Phys.

Tadpoles and Symmetries in Higgs-Gauge Unification Theories

In theories with extra dimensions the Standard Model Higgs fields can be identified with internal components of bulk gauge fields (Higgs-gauge unification). The bulk gauge symmetry protects the Higgs mass from quadratic divergences, but at the fixed points localized tadpoles can be radiatively generated if U(1) subgroups are conserved, making the Higgs mass UV sensitive. We show that a global symmetry, remnant of the internal rotation group after orbifold projection, can prevent the generation of such tadpoles. In particular we consider the classes of orbifold compactifications T^d/Z_N (d even, N>2) and T^d/Z_2 (arbitrary d) and show that in the first case tadpoles are always allowed, while in the second they can appear only for d=2 (six dimensions).Comment: 10 pages, based on talks given by M.Q. at String Phenomenology 2004, University of Michigan, Ann Arbor, August 1-6, 2004 and 10th International Symposium on Particles, Strings and Cosmology (PASCOS'04 and Nath Fest), Northeastern University, Boston, August 16-22, 200

What is the upper limit on the lightest supersymmetric Higgs mass?

In this talk the question of what is the upper bound on the lightest supersymmetric Higgs mass, m_h is addressed. This question is relevant since experimental lower bounds on m_h might implement, in the near future, exclusion of supersymmetry. By imposing (perturbative) unification of the gauge couplings at some high scale \simgt 10^{17} GeV, we have found that for a top-quark mass M_t=175 GeV, and depending on the supersymmetric parameters, this bound can be as high as 205 GeV.Comment: 7 pages, 4 figures, Work presented at PASCOS-98, March 22-29 199

Electroweak and Flavor Physics in Extensions of the Standard Model with Large Extra Dimensions

We study the implications of extra dimensions of size $R\sim 1/TeV$ on electroweak and flavor physics due to the presence of Kaluza-Klein excitations of the SM gauge-bosons. We consider several scenarios with the SM fermions either living in the bulk or being localized at different points of an extra dimension. Global fits to electroweak observables provide lower bounds on 1/R, which are generically in the 2-5 TeV range. We find, however, certain models where the fit to electroweak observables is better than in the SM, because of an improvement in the prediction to the weak charge Q_W. We also consider the case of softly-broken supersymmetric theories and we find new non-decoupling effects that put new constraints on 1/R. If quarks of different families live in different points of the extra dimension, we find that the Kaluza-Klein modes of the SM gluons generate (at tree level) dangerous flavor and CP-violating interactions. The lower bounds on 1/R can increase in this case up to 5000 TeV, disfavoring these scenarios in the context of TeV-strings.Comment: 21 pages, 3 figures, Late

Bulk and brane radiative effects in gauge theories on orbifolds

We have computed one-loop bulk and brane mass renormalization effects in a five-dimensional gauge theory compactified on the M_4 \times S^1/Z_2 orbifold, where an arbitrary gauge group G is broken by the orbifold action to its subgroup H. The space-time components of the gauge boson zero modes along the H generators span the gauge theory on the orbifold fixed point branes while the zero modes of the higher-dimensional components of the gauge bosons along the G/H generators play the role of Higgs fields with respect to the gauge group H. No quadratic divergences in the mass renormalization of the gauge and Higgs fields are found either in the bulk or on the branes. All brane effects for the Higgs field masses vanish (only wave function renormalization effects survive) while bulk effects are finite and can trigger, depending on the fermionic content of the theory, spontaneous Hosotani breaking of the brane gauge group H. For the gauge fields we do find logarithmic divergences corresponding to mass renormalization of their heavy Kaluza-Klein modes. Two-loop brane effects for Higgs field masses are expected from wave function renormalization brane effects inserted into finite bulk mass corrections.Comment: 31 pages, uses axodraw.sty and mcite.st