2,500 research outputs found
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 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 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
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