59 research outputs found
Fake Conformal Symmetry in Conformal Cosmological Models
We examine the local conformal invariance (Weyl invariance) in tensor-scalar
theories used in recently proposed conformal cosmological models. We show that
the Noether currents associated with Weyl invariance in these theories vanish.
We assert that the corresponding Weyl symmetry does not have any dynamical
role.Comment: References updated, errors corrected, published in Phys. Rev. D. 4
pages, RevTeX, no figure
Topological Mass Generation in Four Dimensions
Schwinger's mechanism for mass generation relies on topological structures of
a 2-dimensional gauge theory. In the same manner, corresponding 4-dimensional
topological entities give rise to topological mass generation in four
dimensions.Comment: 10 pages, 2 figure
Irrational vs. rational charge and statistics in two-dimensional quantum systems
We show that quasiparticle excitations with irrational charge and irrational
exchange statistics exist in tight-biding systems described, in the continuum
approximation, by the Dirac equation in (2+1)-dimensional space and time. These
excitations can be deconfined at zero temperature, but when they are, the
charge re-rationalizes to the value 1/2 and the exchange statistics to that of
"quartons" (half-semions).Comment: 4 pages, 2 figure
Dissipationless conductance in a topological coaxial cable
We present a dynamical mechanism leading to dissipationless conductance, whose quantized value is controllable in a (3+1)-dimensional electronic system. The mechanism is exemplified by a theory of Weyl fermions coupled to a Higgs field, also known as an axion insulator. We show that the insertion of an axial gauge flux can induce vortex lines in the Higgs field, similar to the development of vortices in a superconductor upon the insertion of magnetic flux. We further show that the necessary axial gauge flux can be generated using Rashba spin-orbit coupling or a magnetic field. Vortex lines in the Higgs field are known to bind chiral fermionic modes, each of which serves as a one-way channel for electric charge with conductance e²/h. Combining these elements, we present a physical picture, the “topological coaxial cable,” illustrating how the value of the quantized conductance could be controlled in such an axion insulator.National Science Foundation (U.S.) (DGE-1247312)United States. Department of Energy (DEF-06ER46316
Seeking an Even-Parity Mass Term for 3-D Gauge Theory
Mass-gap calculations in three-dimensional gauge theories are discussed. Also
we present a Chern--Simons-like mass-generating mechanism which preserves
parity and is realized non-perturbatively.Comment: 11 pages, revte
Driven Graphene as a Tunable Semiconductor with Topological Properties
Controlling the properties of materials by driving them out of equilibrium is
an exciting prospect that has only recently begun to be explored. In this
Letter we give a striking theoretical example of such materials design: a
tunable gap in monolayer graphene is generated by exciting a particular
optical phonon. We show that the system reaches a steady state whose transport
properties are the same as if the system had a static electronic gap,
controllable by the driving amplitude. Moreover, the steady state displays
topological phenomena: there are chiral edge currents, which circulate a
fractional charge e/2 per rotation cycle, with the frequency set by the
optical phonon frequency
Materials Design from Nonequilibrium Steady States: Driven Graphene as a Tunable Semiconductor with Topological Properties
Controlling the properties of materials by driving them out of equilibrium is an exciting prospect that has only recently begun to be explored. In this Letter we give a striking theoretical example of such materials design: a tunable gap in monolayer graphene is generated by exciting a particular optical phonon. We show that the system reaches a steady state whose transport properties are the same as if the system had a static electronic gap, controllable by the driving amplitude. Moreover, the steady state displays topological phenomena: there are chiral edge currents, which circulate a fractional charge e/2 per rotation cycle, with the frequency set by the optical phonon frequency
Zero mode in the time-dependent symmetry breaking of theory
We apply the quartic exponential variational approximation to the symmetry
breaking phenomena of scalar field in three and four dimensions. We calculate
effective potential and effective action for the time-dependent system by
separating the zero mode from other non-zero modes of the scalar field and
treating the zero mode quantum mechanically. It is shown that the quantum
mechanical properties of the zero mode play a non-trivial role in the symmetry
breaking of the scalar theory.Comment: 10 pages, 3 figure
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