31 research outputs found
Quantum Symmetries and Marginal Deformations
We study the symmetries of the N=1 exactly marginal deformations of N=4 Super
Yang-Mills theory. For generic values of the parameters, these deformations are
known to break the SU(3) part of the R-symmetry group down to a discrete
subgroup. However, a closer look from the perspective of quantum groups reveals
that the Lagrangian is in fact invariant under a certain Hopf algebra which is
a non-standard quantum deformation of the algebra of functions on SU(3). Our
discussion is motivated by the desire to better understand why these theories
have significant differences from N=4 SYM regarding the planar integrability
(or rather lack thereof) of the spin chains encoding their spectrum. However,
our construction works at the level of the classical Lagrangian, without
relying on the language of spin chains. Our approach might eventually provide a
better understanding of the finiteness properties of these theories as well as
help in the construction of their AdS/CFT duals.Comment: 1+40 pages. v2: minor clarifications and references added. v3: Added
an appendix, fixed minor typo
Defects, Decay, and Dissipated States
The worldsheet renormalization group approach to tachyon condensation in string theory is reviewed. The open string case is summarized with examples, and closed string tachyon condensation on nonsupersymmetric orbifolds is examined in detail. The idea that the renormalization group dissipates the localized states associated to the defect is explored
Comb-Based Radio-Frequency Photonic Filters with Rapid Tunability and High Selectivity
Photonic technologies have received considerable attention for enhancement of
radio-frequency (RF) electrical systems, including high-frequency analog signal
transmission, control of phased arrays, analog-to-digital conversion, and
signal processing. Although the potential of radio-frequency photonics for
implementation of tunable electrical filters over broad RF bandwidths has been
much discussed, realization of programmable filters with highly selective
filter lineshapes and rapid reconfigurability has faced significant challenges.
A new approach for RF photonic filters based on frequency combs offers a
potential route to simultaneous high stopband attenuation, fast tunability, and
bandwidth reconfiguration. In one configuration tuning of the RF passband
frequency is demonstrated with unprecedented (~40 ns) speed by controlling the
optical delay between combs. In a second, fixed filter configuration, cascaded
four-wave mixing simultaneously broadens and smoothes comb spectra, resulting
in Gaussian RF filter lineshapes exhibiting extremely high (>60 dB) main lobe
to sidelobe suppression ratio and (>70 dB) stopband attenuation.Comment: Updated the submission with the most recent version of the pape
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