39 research outputs found
Light third-generation squarks from flavour gauge messengers
We study models of gauge-mediated supersymmetry breaking with a gauged
horizontal SU(3)_F symmetry acting on the quark superfields. If SU(3)_F is
broken non-supersymmetrically by F-term vacuum expectation values, the massive
gauge bosons and gauginos become messengers for SUSY breaking mediation. These
gauge messenger fields induce a flavour-dependent, negative contribution to the
soft masses of the squarks at one loop. In combination with the soft terms from
standard gauge mediation, one obtains large and degenerate first- and
second-generation squark masses, while the stops and sbottoms are light. We
discuss the implications of this mechanism for the superparticle spectrum and
for flavour precision observables. We also provide an explicit realization in a
model with simultaneous SUSY and SU(3)_F breaking.Comment: 25 pages, 7 figure
The Flavour of Natural SUSY
An inverted mass hierarchy in the squark sector, as in so-called "natural
supersymmetry", requires non-universal boundary conditions at the mediation
scale of supersymmetry breaking. We propose a formalism to define such boundary
conditions in a basis-independent manner and apply it to generic scenarios
where the third-generation squarks are light, while the first two generation
squarks are heavy and near-degenerate. We show that not only is our formalism
particularly well-suited to study such hierarchical squark mass patterns, but
in addition the resulting soft terms at the TeV scale are manifestly compatible
with the principle of minimal flavour violation, and thus automatically obey
constraints from flavour physics.Comment: 19 pages, 4 figures; v2: matches journal versio
Vacuum stability and supersymmetry at high scales with two Higgs doublets
We investigate the stability of the electroweak vacuum for two-Higgs doublet
models with a supersymmetric UV completion. The supersymmetry breaking scale is
taken to be of the order of the grand unification scale. We first study the
case where all superpartners decouple at this scale. We show that contrary to
the Standard Model with one Higgs doublet, matching to the supersymmetric UV
completion is possible if the low-scale model contains two Higgs doublets. In
this case vacuum stability and experimental constraints point towards low
values of tan(beta) < 2 and pseudoscalar masses of at least about a TeV. If the
higgsino superpartners of the Higgs fields are also kept light, the conclusions
are similar and essentially independent of the higgsino mass. Finally, if all
gauginos are also given electroweak-scale masses (split supersymmetry with two
Higgs doublets), the model cannot be matched to supersymmetry at very high
scales when requiring a 125 GeV Higgs. Light neutral and charged higgsinos
therefore emerge as a promising signature of a supersymmetric UV completion of
the Standard Model at the grand unification scale.Comment: 27 pages, 4 figures; v2: minor changes in references and text,
results unchange
Fluxes, Hierarchies, and Metastable Vacua in Supersymmetric Field Theories
This thesis concerns topics both in low-energy effective field theories from type IIB superstring flux compactifications and in fourdimensional, rigidly supersymmetric gauge theories. We introduce flux compactifications with so-called “warped throat” regions, which lead to large hierarchies of scales in the effective four-dimensional theory. The correspondence between a particular such throat and a five-dimensional Randall-Sundrum-like model is established. We shown how certain string-theoretic features of the compactification, such as moduli stabilization by fluxes or the presence of an unstabilized Kähler modulus, are incorporated in the five-dimensional picture. The KKLT construction for metastable de Sitter vacua is reviewed, as well as some possible modifications involving spontaneous F-term supersymmetry breaking. For KKLT-like models with their hidden sector localized inside a throat, the mediation of supersymmetry breaking to the visible sector is investigated. We review the mechanism of mixed modulus-anomaly mediation, and show that there can be additional equally important gravity-mediated contributions. We finally turn to the ISS model of metastable dynamical supersymmetry breaking in four dimensions, and present a renormalizable extension which generates a large hierarchy naturally. We also recapitulate how the ISS model may be obtained from a type IIB superstring model
Metastable supersymmetry breaking without scales
We construct new examples of models of metastable D=4 N=1 supersymmetry
breaking in which all scales are generated dynamically. Our models rely on
Seiberg duality and on the ISS mechanism of supersymmetry breaking in massive
SQCD. Some of the electric quark superfields arise as composites of a strongly
coupled gauge sector. This allows us to start with a simple cubic
superpotential and an asymptotically free gauge group in the ultraviolet, and
end up with an infrared effective theory which breaks supersymmetry dynamically
in a metastable state.Comment: 6 pages, 1 figure; v2: journal versio
A natural renormalizable model of metastable SUSY breaking
We propose a model of metastable dynamical supersymmetry breaking in which
all scales are generated dynamically. Our construction is a simple variant of
the Intriligator-Seiberg-Shih model, with quark masses induced by
renormalizable couplings to an auxiliary supersymmetric QCD sector. Since all
scales arise from dimensional transmutation, the model has no fundamental
dimensionful parameters. It also does not rely on higher-dimensional operators.Comment: 9 pages; v2: typos correcte
Holographic metastability
We show how supersymmetric QCD in a slice of AdS can naturally acquire
metastable vacua. The formulation closely follows that of Intriligator, Seiberg
and Shih (ISS), with an "electric" sector on the UV brane and a "magnetic"
sector on the IR brane. However the 't Hooft anomaly matching that constrains
the Seiberg duality central to ISS is replaced by anomaly inflow and
cancellation, and the source of strong coupling is the CFT to which the theory
couples rather than the gauge groups. The theory contains an anomaly free
R-symmetry that, when broken by UV effects, leads to an O'Raifeartaigh model on
the IR brane. In contrast to ISS, the R-symmetry breaking in the UV can be
maximal, and yet the R-symmetry breaking in the IR theory remains under strict
control: there is no need for retrofitting of small parameters.Comment: 20 pages, 2 figure
Minicharges and Magnetic Monopoles
Minicharged particles arise naturally in extensions of the Standard Model
with a kinetic mixing term between the ordinary electromagnetic U(1) and an
extra "hidden sector" U(1). In this note we study the compatibility of these
particles with the existence of magnetic monopoles. We find that angular
momentum quantization allows only certain combinations of ordinary and hidden
monopole charge. Using the example where one of the U(1)s originates from a
spontaneously broken SU(2), we demonstrate that exactly the allowed types of
monopoles arise as 't Hooft-Polyakov monopoles.Comment: 9 pages, 1 figur