246 research outputs found
Tree-level Graviton Scattering in the Worldline Formalism
We use the worldline formalism to study tree-level scattering processes
involving gravitons. A massless spin 2 particle is described by an
supersymmetric worldline action which is also symmetric. More generally,
supersymmetric worldline actions exhibiting symmetry describe
free spin particles. Recently a BRST approach was used to construct the
on-shell background graviton emission vertex from a graviton worldline.
Nonetheless, an action describing the coupling of higher spin ()
particles with generic background gravity is unknown. In this paper, we found
that in order to reproduce Einstein's general relativity 3-point graviton
vertex, interpreted as the emission of an off-shell graviton from the
worldline, the coupling to background gravity must break the symmetry to
. In addition to this symmetry-breaking feature, we also
found that the coefficient of the worldline action counterterm differs from previous results in the literature. By comparing the linearized
graviton and photon emission vertex operators from different worldlines, we
noticed that they obey a squaring relation. For MHV (Maximal Helicity
Violating) amplitudes, these squaring relations among the linearized vertex
operators directly result in double-copy-like relations between the scattering
amplitudes.Comment: 63 page
Gravitational wave energy-momentum tensor and radiated power in a strongly curved background
Allowing for the possibility of extra dimensions, there are two paradigms:
either the extra dimensions are hidden from observations by being compact and
small as in Kaluza-Klein scenarios, or the extra dimensions are
large/non-compact and undetectable due to a large warping as in the
Randall-Sundrum scenario. In the latter case, the five-dimensional background
has a large curvature, and Isaacson's construction of the gravitational
energy-momentum tensor, which relies on the assumption that the wavelength of
the metric fluctuations is much smaller than the curvature length of the
background spacetime, cannot be used. In this paper, we construct the
gravitational energy-momentum tensor in a strongly curved background such as
Randall-Sundrum. We perform a scalar-vector-tensor decomposition of the metric
fluctuations with respect to the background isometry and construct
the covariantly-conserved gravitational energy-momentum tensor out of the
gauge-invariant metric fluctuations. We give a formula for the power radiated
by gravitational waves and verify it in known cases. In using the
gauge-invariant metric fluctuations to construct the gravitational
energy-momentum tensor we follow previous work done in cosmology. Our framework
has applicability beyond the Randall-Sundrum model.Comment: 50 pages, minor typos fixe
Continuous-wave and Transient Characteristics of Phosphorene Microwave Transistors
Few-layer phosphorene MOSFETs with 0.3-um-long gate and 15-nm-thick Al2O3
gate insulator was found to exhibit a forward-current cutoff frequency of 2 GHz
and a maximum oscillation frequency of 8 GHz after de-embedding for the
parasitic capacitance associated mainly with the relatively large probe pads.
The gate lag and drain lag of the transistor was found to be on the order of 1
us or less, which is consistent with the lack of hysteresis, carrier freeze-out
or persistent photoconductivity in DC characteristics. These results confirm
that the phosphorene MOSFET can be a viable microwave transistor for both
small-signal and large-signal applications.Comment: Accepted for oral presentation at IMS 201
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