4,237 research outputs found
Flux Vacua and Branes of the Minimal Superstring
We analyze exactly the simplest minimal superstring theory, using its dual
matrix model. Its target space is one dimensional (the Liouville direction),
and the background fields include a linear dilaton, a possible tachyon
condensate, and RR flux. The theory has both charged and neutral branes, and
these exhibit new and surprising phenomena. The smooth moduli space of charged
branes has different weakly coupled boundaries in which the branes have
different RR charges. This new duality between branes of different charges
shows that the semiclassical notion of localized charge is not precise in the
quantum theory, and that the charges of these branes can fluctuate.
Correspondingly, the RR flux in some parts of target space can also fluctuate
-- only the net flux at infinity is fixed. We substantiate our physical picture
with a detailed semiclassical analysis of the exact answers. Along the way, we
uncover new subtleties in super-Liouville theory.Comment: 46 pages, 3 figures, new identities for the neutral brane, references
added, minor change
Minimal String Theory
We summarize recent progress in the understanding of minimal string theory,
focusing on the worldsheet description of physical operators and D-branes. We
review how a geometric interpretation of minimal string theory emerges
naturally from the study of the D-branes. This simple geometric picture ties
together many otherwise unrelated features of minimal string theory, and it
leads directly to a worldsheet derivation of the dual matrix model.Comment: 10 pages, 4 figures, talk presented by NS at Strings '0
Higgs Mediation with Strong Hidden Sector Dynamics
We present a simple model that achieves GeV in the MSSM with
large -terms and TeV-scale stops through a combination of gauge mediation
and Higgs-messenger interactions. The / and / problems
are both solved by a common mechanism -- partial sequestering from strong
hidden sector dynamics. Using the framework of General Messenger Higgs
Mediation, we explicitly calculate the soft masses in terms of the vacuum
expectation values, operator dimensions and OPE coefficients of the
strongly-coupled hidden sector. Along the way, we also present a general
analysis of the various constraints on sequestered Higgs mediation models. The
phenomenology of such models is similar to gaugino mediation, but with large
-terms. The NLSP is always long-lived and is either the lightest stau or the
Higgsino. The colored states are typically out of reach of the 8 TeV LHC, but
may be accessible at 14 TeV, especially if the NLSP is the lightest stau.Comment: 40 pages, 8 figures, corrected minor typos, updated collider bounds,
version accepted in JHE
Pulling Out All the Tops with Computer Vision and Deep Learning
We apply computer vision with deep learning -- in the form of a convolutional
neural network (CNN) -- to build a highly effective boosted top tagger.
Previous work (the "DeepTop" tagger of Kasieczka et al) has shown that a
CNN-based top tagger can achieve comparable performance to state-of-the-art
conventional top taggers based on high-level inputs. Here, we introduce a
number of improvements to the DeepTop tagger, including architecture, training,
image preprocessing, sample size and color pixels. Our final CNN top tagger
outperforms BDTs based on high-level inputs by a factor of --3 or more
in background rejection, over a wide range of tagging efficiencies and fiducial
jet selections. As reference points, we achieve a QCD background rejection
factor of 500 (60) at 50\% top tagging efficiency for fully-merged (non-merged)
top jets with in the 800--900 GeV (350--450 GeV) range. Our CNN can also
be straightforwardly extended to the classification of other types of jets, and
the lessons learned here may be useful to others designing their own deep NNs
for LHC applications.Comment: 33 pages, 11 figure
Spontaneous R-symmetry Breaking with Multiple Pseudomoduli
We examine generalized O'Raifeartaigh models that feature multiple tree-level
flat directions and only contain fields with R-charges 0 or 2. We show that
spontaneous R-breaking at up to one-loop order is impossible in such theories.
Specifically, we prove that the R-symmetric origin of field space is always a
local minimum of the one-loop Coleman-Weinberg potential, generalizing an
earlier result for the case of a single flat direction. This result has
consequences for phenomenology and helps elucidate the behavior of various
models of dynamical SUSY breaking
General Gauge Mediation
We give a general definition of gauge mediated supersymmetry breaking which
encompasses all the known gauge mediation models. In particular, it includes
both models with messengers as well as direct mediation models. A formalism for
computing the soft terms in the generic model is presented. Such a formalism is
necessary in strongly-coupled direct mediation models where perturbation theory
cannot be used. It allows us to identify features of the entire class of gauge
mediation models and to distinguish them from specific signatures of various
subclasses.Comment: 19 pages, 1 figure, minor change
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