11,347 research outputs found
Dyon Spectrum in CHL Models
We propose a formula for the degeneracy of quarter BPS dyons in a class of
CHL models. The formula uses a modular form of a subgroup of the genus two
modular group Sp(2,Z). Our proposal is S-duality invariant and reproduces
correctly the entropy of a dyonic black hole to first non-leading order for
large values of the charges.Comment: LaTeX file, 38 pages, minor changes in section 3.3(v2), minor changes
in introduction, appendix A and C(v3
Induced Coherence and Stable Soliton Spiraling
We develop a theory of soliton spiraling in a bulk nonlinear medium and
reveal a new physical mechanism: periodic power exchange via induced coherence,
which can lead to stable spiraling and the formation of dynamical two-soliton
states. Our theory not only explains earlier observations, but provides a
number of predictions which are also verified experimentally. Finally, we show
theoretically and experimentally that soliton spiraling can be controled by the
degree of mutual initial coherence.Comment: 4 pages, 5 figure
Counting Dyons in N=8 String Theory
A recently discovered relation between 4D and 5D black holes is used to
derive exact (weighted) BPS black hole degeneracies for 4D N=8 string theory
from the exactly known 5D degeneracies. A direct 4D microscopic derivation in
terms of weighted 4D D-brane bound state degeneracies is sketched and found to
agree.Comment: 10 page
Exact Black Hole Degeneracies and the Topological String
Motivated by the recent conjecture of Ooguri, Strominger and Vafa, we compute
the semi-canonical partition function of BPS black holes in N=4 and N=8 string
theories, to all orders in perturbation theory. Not only are the black hole
partition functions surprisingly simple; they capture the full topological
string amplitudes, as expected from the OSV conjecture. The agreement is not
perfect, however, as there are differences between the black hole and
topological string partition functions even at the perturbative level. We
propose a minimal modification of the OSV conjecture, in which these
differences are understood as a nontrivial measure factor for the topological
string.Comment: 24 page
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Virus-Inspired Membrane Encapsulation of DNA Nanostructures To Achieve In Vivo Stability
DNA nanotechnology enables engineering of molecular-scale devices with exquisite control over geometry and site-specific functionalization. This capability promises compelling advantages in advancing nanomedicine; nevertheless, instability in biological environments and innate immune activation remain as obstacles for in vivo application. Natural particle systems (i.e., viruses) have evolved mechanisms to maintain structural integrity and avoid immune recognition during infection, including encapsulation of their genome and protein capsid shell in a lipid envelope. Here we introduce virus-inspired enveloped DNA nanostructures as a design strategy for biomedical applications. Achieving a high yield of tightly wrapped unilamellar nanostructures, mimicking the morphology of enveloped virus particles, required precise control over the density of attached lipid conjugates and was achieved at 1 per ∼180 nm2. Envelopment of DNA nanostructures in PEGylated lipid bilayers conferred protection against nuclease digestion. Immune activation was decreased 2 orders of magnitude below controls, and pharmacokinetic bioavailability improved by a factor of 17. By establishing a design strategy suitable for biomedical applications, we have provided a platform for the engineering of sophisticated, translation-ready DNA nanodevices
Supersymmetry Breaking, R-Symmetry Breaking and Metastable Vacua
Models of spontaneous supersymmetry breaking generically have an R-symmetry,
which is problematic for obtaining gaugino masses and avoiding light R-axions.
The situation is improved in models of metastable supersymmetry breaking, which
generically have only an approximate R-symmetry. Based on this we argue, with
mild assumptions, that metastable supersymmetry breaking is inevitable. We also
illustrate various general issues regarding spontaneous and explicit R-symmetry
breaking, using simple toy models of supersymmetry breaking.Comment: 23 page
Peer Evaluation of Video Lab Reports in a Blended Introductory Physics Course
The Georgia Tech blended introductory calculus-based mechanics course
emphasizes scientific communication as one of its learning goals, and to that
end, we gave our students a series of four peer-evaluation assignments intended
to develop their abilities to present and evaluate scientific arguments. Within
these assignments, we also assessed students' evaluation abilities by comparing
their evaluations to a set of expert evaluations. We summarize our development
efforts and describe the changes we observed in student evaluation behavior.Comment: 4 pages, 1 table, 2 figures, submitted to Summer 2014 PERC
Proceeding
R-symmetry breaking, runaway directions and global symmetries in O'Raifeartaigh models
We discuss O'Raifeartaigh models with general R-charge assignments,
introduced by Shih to break R-symmetry spontaneously. We argue that most of
these models have runaway directions related to the R-symmetry. In addition, we
study the simplest model with a U(N) global symmetry and show that in a range
of parameters R-symmetry is spontaneously broken in a metastable vacuum.Comment: 16 pages, 1 figur
The Initial State of Students Taking an Introductory Physics MOOC
As part of a larger research project into massively open online courses
(MOOCs), we have investigated student background, as well as student
participation in a physics MOOC with a laboratory component. Students completed
a demographic survey and the Force and Motion Conceptual Evaluation at the
beginning of the course. While the course is still actively running, we have
tracked student participation over the first five weeks of the eleven-week
course.Comment: Accepted to PERC Proceedings 201
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