63 research outputs found
Issues on 3D Noncommutative Electromagnetic Duality
We extend the ordinary 3D electromagnetic duality to the noncommutative (NC)
space-time through a Seiberg-Witten map to second order in the noncommutativity
parameter (theta), defining a new scalar field model. There are similarities
with the 4D NC duality, these are exploited to clarify properties of both
cases. Up to second order in theta, we find that duality interchanges the
2-form theta with its 1-form Hodge dual *theta times the gauge coupling
constant, i.e., theta --> *theta g^2 (similar to the 4D NC electromagnetic
duality). We directly prove that this property is false in the third order
expansion in both 3D and 4D space-times, unless the slowly varying fields limit
is imposed. Outside this limit, starting from the third order expansion, theta
cannot be rescaled to attain an S-duality. In addition to possible applications
on effective models, the 3D space-time is useful for studying general
properties of NC theories. In particular, in this dimension, we deduce an
expression that significantly simplifies the Seiberg-Witten mapped Lagrangian
to all orders in theta.Comment: 15 pages, revtex4. v.2: We added a proof that the terms in (4.9) are
not surface terms, a new paragraph in our conclusion and new references. v.3:
improvements in our introduction and conclusions. v.4: Published version
(PRD): additional comments and reference
Anisotropic Cosmological Constant and the CMB Quadrupole Anomaly
There are evidences that the cosmic microwave background (CMB) large-angle
anomalies imply a departure from statistical isotropy and hence from the
standard cosmological model. We propose a LCDM model extension whose dark
energy component preserves its nondynamical character but wield anisotropic
vacuum pressure. Exact solutions for the cosmological scale factors are
presented, upper bounds for the deformation parameter are evaluated and its
value is estimated considering the elliptical universe proposal to solve the
quadrupole anomaly. This model can be constructed from a Bianchi I cosmology
with cosmological constant from two different ways: i) a straightforward
anisotropic modification of the vacuum pressure consistently with
energy-momentum conservation; ii) a Poisson structure deformation between
canonical momenta such that the dynamics remain invariant under scale factors
rescalings.Comment: 8 pages, 2 columns, 1 figure. v2: figure improved, added comments on
higher eccentricity powers and references. v3: typos corrected, version to
appear in PR
Primordial perturbations and inflation in holographic cosmology
We consider an inflationary scenario in the holographic braneworld with a
cosmological fluid occupying the 3+1 dimensional brane located at the
holographic boundary of an asymptotic ADS bulk. The contribution of the
boundary conformal field can be represented as a modification of Einstein's
equations on the boundary. Using these effective Einstein equations we
calculate the cosmological perturbations and derive the corresponding power
spectra assuming a general -essence type of inflaton. We find that the
braneworld scenario affects the scalar power spectrum only in the speed of
sound dependence on the slow-roll parameters whereas there is no change in the
tensor power spectrum. This implies that the changes in the spectral indices
appear at the second order in the slow-roll parameter expansion.Comment: v2: 19 pages, 1 figure. Appendices and references added. Accepted in
PR
Voltage-Controlled High-Bandwidth Terahertz Oscillators Based On Antiferromagnets
Producing compact voltage-controlled frequency generators and sensors
operating in the terahertz (THz) regime represents a major technological
challenge. Here, we show that noncollinear antiferromagnets (NCAFM) with kagome
structure host gapless self-oscillations whose frequencies are tunable from 0
Hz to the THz regime via electrically induced spin-orbit torques (SOTs). The
auto-oscillations' initiation, bandwidth, and amplitude are investigated by
deriving an effective theory, which captures the reactive and dissipative SOTs.
We find that the dynamics strongly depends on the ground state's chirality,
with one chirality having gapped excitations, whereas the opposite chirality
provides gapless self-oscillations. Our results reveal that NCAFMs offer unique
THz functional components, which could play a significant role in filling the
THz technology gap.Comment: 6 pages, 2 figure
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