12,257 research outputs found
The synchrotron foreground and CMB temperature-polarization cross correlation power spectrum from the first year WMAP data
We analyse the temperature-polarization cross-correlation in the Galactic
synchrotron template that we have recently developed, and between the template
and CMB temperature maps derived from WMAP data. Since the polarized
synchrotron template itself uses WMAP data, we can estimate residual
synchrotron contamination in the CMB angular spectrum. While
appears to be contamined by synchrotron, no evidence for
contamination is found in the multipole range which is most relevant for the
fit of the cosmological optical depth.Comment: Accepted for pubblication on MNRAS Lette
Two-dimensional black holes in accelerated frames: quantum aspects
By considering charged black hole solutions of a one parameter family of two
dimensional dilaton gravity theories, one finds the existence of quantum
mechanically stable gravitational kinks with a simple mass to charge relation.
Unlike their Einsteinian counterpart (i.e. extreme Reissner-Nordstr\"om), these
have nonvanishing horizon surface gravity.Comment: 18 pages, harvmac, 2 figure
Zero Energy of Plane-Waves for ELKOs
We consider the ELKO field in interaction through contorsion with its own
spin density, and we investigate the form of the consequent autointeractions;
to do so we take into account the high-density limit and find plane wave
solutions: such plane waves give rise to contorsional autointeractions for
which the Ricci metric curvature vanishes and therefore the energy density is
equal to zero identically. Consequences are discussed.Comment: 7 page
Running coupling in electroweak interactions of leptons from f(R)-gravity with torsion
The f(R)-gravitational theory with torsion is considered for one family of
leptons; it is found that the torsion tensor gives rise to interactions having
the structure of the weak forces while the intrinsic non-linearity of the f(R)
function provides an energy-dependent coupling: in this way, torsional f(R)
gravity naturally generates both structure and strength of the electroweak
interactions among leptons. This implies that the weak interactions among the
lepton fields could be addressed as a geometric effect due to the interactions
among spinors induced by the presence of torsion in the most general f(R)
gravity. Phenomenological considerations are addressed.Comment: 9 pages. arXiv admin note: text overlap with arXiv:1012.5529 by other
author
A modified theory of gravity with torsion and its applications to cosmology and particle physics
In this paper we consider the most general least-order derivative theory of
gravity in which not only curvature but also torsion is explicitly present in
the Lagrangian, and where all independent fields have their own coupling
constant: we will apply this theory to the case of ELKO fields, which is the
acronym of the German \textit{Eigenspinoren des LadungsKonjugationsOperators}
designating eigenspinors of the charge conjugation operator, and thus they are
a Majorana-like special type of spinors; and to the Dirac fields, the most
general type of spinors. We shall see that because torsion has a coupling
constant that is still undetermined, the ELKO and Dirac field equations are
endowed with self-interactions whose coupling constant is undetermined: we
discuss different applications according to the value of the coupling constants
and the different properties that consequently follow. We highlight that in
this approach, the ELKO and Dirac field's self-interactions depend on the
coupling constant as a parameter that may even make these non-linearities
manifest at subatomic scales.Comment: 21 page
Active stabilisation of single drive dual-parallel Mach-Zehnder modulator for single sideband signal generation
Presented is a study on a single-drive dual-parallel Mach-Zehnder modulator implementation as a single sideband suppressed carrier generator. High values of both extinction ratio and sidemode suppression ratio were obtained at different modulation frequencies over the Cband. In addition, a stabilisation loop had been developed to preserve the single sideband generation over time
Direct evidence for efficient ultrafast charge separation in epitaxial WS/graphene heterostructure
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to
investigate ultrafast charge transfer in an epitaxial heterostructure made of
monolayer WS and graphene. This heterostructure combines the benefits of a
direct gap semiconductor with strong spin-orbit coupling and strong
light-matter interaction with those of a semimetal hosting massless carriers
with extremely high mobility and long spin lifetimes. We find that, after
photoexcitation at resonance to the A-exciton in WS, the photoexcited holes
rapidly transfer into the graphene layer while the photoexcited electrons
remain in the WS layer. The resulting charge transfer state is found to
have a lifetime of \,ps. We attribute our findings to differences in
scattering phase space caused by the relative alignment of WS and graphene
bands as revealed by high resolution ARPES. In combination with spin-selective
excitation using circularly polarized light the investigated WS/graphene
heterostructure might provide a new platform for efficient optical spin
injection into graphene.Comment: 28 pages, 14 figure
Direct evidence for efficient ultrafast charge separation in epitaxial WS<sub>2</sub>/graphene heterostructures
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS2 and graphene. This heterostructure combines the benefits of a direct-gap semiconductor with strong spin-orbit coupling and strong light-matter interaction with those of a semimetal hosting massless carriers with extremely high mobility and long spin lifetimes. We find that, after photoexcitation at resonance to the A-exciton in WS2, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS2 layer. The resulting charge-separated transient state is found to have a lifetime of ∼1 ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS2 and graphene bands as revealed by high-resolution ARPES. In combination with spin-selective optical excitation, the investigated WS2/graphene heterostructure might provide a platform for efficient optical spin injection into graphene
Particles and energy fluxes from a CFT perspective
We analyze the creation of particles in two dimensions under the action of
conformal transformations. We focus our attention on Mobius transformations and
compare the usual approach, based on the Bogolubov coefficients, with an
alternative but equivalent viewpoint based on correlation functions. In the
latter approach the absence of particle production under full Mobius
transformations is manifest. Moreover, we give examples, using the
moving-mirror analogy, to illustrate the close relation between the production
of quanta and energy.Comment: Revised version. To appear in Phys.Rev.
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