790 research outputs found
Calculable Dynamical Supersymmetry Breaking on Deformed Moduli Spaces
We consider models of dynamical supersymmetry breaking in which the
extremization of a tree-level superpotential conflicts with a quantum
constraint. We show that in such models the low-energy effective theory near
the origin of moduli space is an O'Raifeartaigh model, and the sign of the
mass-squared for the pseudo-flat direction at the origin is calculable. We
analyze vector-like models with gauge groups SU(N) and Sp(2N) with and without
global symmetries. In all cases there is a stable minimum at the origin with an
unbroken U(1)_R symmetry.Comment: 8 pages, LaTeX2e, no figure
A Critical Cosmological Constant from Millimeter Extra Dimensions
We consider `brane universe' scenarios with standard-model fields localized
on a 3-brane in 6 spacetime dimensions. We show that if the spacetime is
rotationally symmetric about the brane, local quantities in the bulk are
insensitive to the couplings on the brane. This potentially allows
compactifications where the effective 4-dimensional cosmological constant is
independent of the couplings on the 3-brane. We consider several possible
singularity-free compactification mechanisms, and find that they do not
maintain this property. We also find solutions with naked spacetime
singularities, and we speculate that new short-distance physics can become
important near the singularities and allow a compactification with the desired
properties. The picture that emerges is that standard-model loop contributions
to the effective 4-dimensional cosmological constant can be cut off at
distances shorter than the compactification scale. At shorter distance scales,
renormalization effects due to standard-model fields renormalize the 3-brane
tension, which changes a deficit angle in the transverse space without
affecting local quantities in the bulk. For a compactification scale of order
10^{-2} mm, this gives a standard-model contribution to the cosmological
constant in the range favored by cosmology.Comment: 15 pages, LaTeX2e. Major revisions; see abstrac
Realistic Anomaly-mediated Supersymmetry Breaking
We consider supersymmetry breaking communicated entirely by the
superconformal anomaly in supergravity. This scenario is naturally realized if
supersymmetry is broken in a hidden sector whose couplings to the observable
sector are suppressed by more than powers of the Planck scale, as occurs if
supersymmetry is broken in a parallel universe living in extra dimensions. This
scenario is extremely predictive: soft supersymmetry breaking couplings are
completely determined by anomalous dimensions in the effective theory at the
weak scale. Gaugino and scalar masses are naturally of the same order, and
flavor-changing neutral currents are automatically suppressed. The most glaring
problem with this scenario is that slepton masses are negative in the minimal
supersymmetric standard model. We point out that this problem can be simply
solved by coupling extra Higgs doublets to the leptons. Lepton flavor-changing
neutral currents can be naturally avoided by approximate symmetries. We also
describe more speculative solutions involving compositeness near the weak
scale. We then turn to electroweak symmetry breaking. Adding an explicit \mu
term gives a value for B\mu that is too large by a factor of order 100. We
construct a realistic model in which the \mu term arises from the vacuum
expectation value of a singlet field, so all weak-scale masses are directly
related to m_{3/2}. We show that fully realistic electroweak symmetry breaking
can occur in this model with moderate fine-tuning.Comment: 32 pages, LaTeX2e, 3 eps figure
Gaugino Mediated Supersymmetry Breaking
We consider supersymmetric theories where the standard-model quark and lepton
fields are localized on a "3-brane" in extra dimensions, while the gauge and
Higgs fields propagate in the bulk. If supersymmetry is broken on another
3-brane, supersymmetry breaking is communicated to gauge and Higgs fields by
direct higher-dimension interactions, and to quark and lepton fields via
standard-model loops. We show that this gives rise to a realistic and
predictive model for supersymmetry breaking. The size of the extra dimensions
is required to be of order 10-100 times larger than fundamental scale (e.g. the
string scale). The spectrum is similar to (but distinguishable from) the
predictions of "no-scale" models. Flavor-changing neutral currents are
naturally suppressed. The \mu term can be generated by the Giudice-Masiero
mechanism. The supersymmetric CP problem is naturally solved if CP violation
occurs only on the observable sector 3-brane. These are the simplest models in
the literature that solve all supersymmetric naturalness problems.Comment: Refs. added. 12 pages, 1 figur
Ghosts and Tachyons in the Fifth Dimension
We present several solutions for the five dimensional gravity models in the
presence of bulk ghosts and tachyons to argue that these "troublesome" fields
can be a useful model-building tool. The ghost-like signature of the kinetic
term for a bulk scalar creates a minimum in the scale factor, removing the
necessity for a negative tension brane in models with the compactified fifth
dimension. It is shown that the model with the positive tension branes and a
ghost field in the bulk leads to the radion stabilization. The bulk scalar with
the variable sign kinetic term can be used to model both positive and negative
tension branes of a finite width in the compact dimension. Finally, we present
several ghost and tachyon field configurations in the bulk that lead to the
localization of gravity in four dimensions, including one solution with the
Gaussian profile for the metric, g_{\mu\nu}(y)=\eta_{\mu\nu}\exp{-\alpha y^2},
which leads to a stronger localization of gravity than the Randall-Sundrum
model.Comment: New references adde
On the one-loop Kahler potential in five-dimensional brane-world supergravity
We present an on-shell formulation of 5d gauged supergravity coupled to
chiral matter multiplets localized at the orbifold fixed points. The brane
action is constructed via the Noether method. In such set-up we compute
one-loop corrections to the Kahler potential of the effective 4d supergravity
and compare the result with previous computations based on the off-shell
formalism. The results agree at lowest order in brane sources, however at
higher order there are differences. We explain this discrepancy by an ambiguity
in resolving singularities associated with the presence of infinitely thin
branes.Comment: 20 page
Supersymmetry and Electroweak Breaking in the Interval
Hypermultiplets are considered in the five-dimensional interval where all
fields are continuous and the boundary conditions are dynamically obtained from
the action principle. The orbifold boundary conditions are obtained as
particular cases. We can interpret the Scherk-Schwarz supersymmetry breaking as
a misalignment of boundary conditions while a new source of supersymmetry
breaking corresponding to a mismatch of different boundary parameters is
identified. The latter can be viewed as coming from boundary supersymmetry
breaking masses for hyperscalars and the nature of the corresponding
supersymmetry breaking parameter is analyzed. For some regions of the parameter
space where supersymmetry is broken (either by Scherk-Schwarz boundary
conditions or by boundary hyperscalar masses) electroweak symmetry breaking can
be triggered at the tree level.Comment: 28 pages, 5 figure
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