2,317 research outputs found
Unidirectional spectral singularities
We propose a class of spectral singularities emerging from the coincidence of two independent singularities with highly directional responses. These spectral singularities result from resonance trapping induced by the interplay between parity-time symmetry and Fano resonances. At these singularities, while the system is reciprocal in terms of a finite transmission, a simultaneous infinite reflection from one side and zero reflection from the opposite side can be realized
A BMS-invariant free scalar model
The BMS (Bondi-van der Burg-Metzner-Sachs) symmetry arises as the asymptotic
symmetry of flat spacetime at null infinity. In particular, the BMS algebra for
three dimensional flat spacetime (BMS) is generated by the super-rotation
generators which form a Virasoro sub-algebra with central charge ,
together with mutually-commuting super-translation generators. The
super-rotation and super-translation generators have non-trivial commutation
relations with another central charge . In this paper, we study a free
scalar theory in two dimensions exhibiting BMS symmetry, which can also be
understood as the ultra-relativistic limit of a free scalar CFT. Upon
canonical quantization on the highest weight vacuum, the central charges are
found to be and . Because of the vanishing central charge
, the theory features novel properties: there exist primary states which
form a multiplet, and the Hilbert space can be organized by an enlarged version
of BMS modules dubbed the staggered modules. We further calculate correlation
functions and the torus partition function, the later of which is also shown
explicitly to be modular invariant.Comment: 59 pages, 5 figures. v2, minor revision: typos correted and some
statement rephrase
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