1,423 research outputs found
Radio variability of 1st 3-months Fermi blazars at 5 GHz: affected by interstellar scintillation?
Blazars from the first-three-months Fermi-AGN list were observed with the
Urumqi 25m radio telescope at 5GHz in IDV (Intra-Day Variability) mode and
inter-month observation mode. A significant correlation between the flux
density at 5GHz and the gamma-ray intensity for the Fermi-LAT detected blazars
is seen. There is a higher IDV detection rate in Fermi detected blazars than
those reported for other samples. Stronger variability appears at lower
Galactic latitudes; IDV appears to be stronger in weaker sources, indicating
that the variability is affected by interstellar scintillation.Comment: 4 pages, 4 figures, in proceedings of 'Multiwavelength Variability of
Blazars' in Guangzhou Uni. of China, 22-24, Sep. 2010, to appear in JA
On effective actions of BPS branes and their higher derivative corrections
We calculate in detail the disk level S-matrix element of one Ramond-Ramond
field and three gauge field vertex operators in the world volume of BPS branes,
to find four gauge field couplings to all orders of up to on-shell
ambiguity. Then using these infinite couplings we find that the massless pole
of the field theory amplitude is exactly equal to the massless pole S-matrix
element of this amplitude for the case to all orders of .
Finally we show that the infinite massless poles and the contact terms of this
amplitude for the case can be reproduced by the Born-Infeld action and
the Wess-Zumino actions and by their higher derivative corrections.Comment: 26 pages, 2 figures, minor corrections,references added and version
published in JHE
Quantum States and Phases in Driven Open Quantum Systems with Cold Atoms
An open quantum system, whose time evolution is governed by a master
equation, can be driven into a given pure quantum state by an appropriate
design of the system-reservoir coupling. This points out a route towards
preparing many body states and non-equilibrium quantum phases by quantum
reservoir engineering. Here we discuss in detail the example of a \emph{driven
dissipative Bose Einstein Condensate} of bosons and of paired fermions, where
atoms in an optical lattice are coupled to a bath of Bogoliubov excitations via
the atomic current representing \emph{local dissipation}. In the absence of
interactions the lattice gas is driven into a pure state with long range order.
Weak interactions lead to a weakly mixed state, which in 3D can be understood
as a depletion of the condensate, and in 1D and 2D exhibits properties
reminiscent of a Luttinger liquid or a Kosterlitz-Thouless critical phase at
finite temperature, with the role of the ``finite temperature'' played by the
interactions.Comment: 9 pages, 2 figure
Topological Photonics
Topology is revolutionizing photonics, bringing with it new theoretical
discoveries and a wealth of potential applications. This field was inspired by
the discovery of topological insulators, in which interfacial electrons
transport without dissipation even in the presence of impurities. Similarly,
new optical mirrors of different wave-vector space topologies have been
constructed to support new states of light propagating at their interfaces.
These novel waveguides allow light to flow around large imperfections without
back-reflection. The present review explains the underlying principles and
highlights the major findings in photonic crystals, coupled resonators,
metamaterials and quasicrystals.Comment: progress and review of an emerging field, 12 pages, 6 figures and 1
tabl
On open-closed extension of boundary string field theory
We investigate a classical open-closed string field theory whose open string
sector is given by boundary string field theory. The open-closed interaction is
introduced by the overlap of a boundary state with a closed string field. With
the help of the Batalin-Vilkovisky formalism, the closed string sector is
determined to be the HIKKO closed string field theory. We also discuss the
gauge invariance of this theory in both open and closed string sides.Comment: 25 pages, 2 figures, comments and a reference added, typos correcte
Variability of disk emission in pre-main sequence and related stars. II. Variability in the gas and dust emission of the Herbig Fe star SAO 206462
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.We present 13 epochs of near-infrared (0.8-5 μm) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Brα, Brγ, Paβ, Paγ, Paδ, Paepsilon, and the 0.8446 μm line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 × 10–8 M ☉ yr–1 was derived from the Brγ and Paβ lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only ~30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 μm was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on timescales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer timescales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on timescales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer timescales that have been sampled so far.This work was supported by NASA ADP grants NNH06CC28C and NNX09AC73G, Hubble Space Telescope grants HST-GO-10764 and HST-GO-10864, Chilean National TAC grants CNTAC-010A-064
On renormalization group flows and the a-theorem in 6d
We study the extension of the approach to the a-theorem of Komargodski and
Schwimmer to quantum field theories in d=6 spacetime dimensions. The dilaton
effective action is obtained up to 6th order in derivatives. The anomaly flow
a_UV - a_IR is the coefficient of the 6-derivative Euler anomaly term in this
action. It then appears at order p^6 in the low energy limit of n-point
scattering amplitudes of the dilaton for n > 3. The detailed structure with the
correct anomaly coefficient is confirmed by direct calculation in two examples:
(i) the case of explicitly broken conformal symmetry is illustrated by the free
massive scalar field, and (ii) the case of spontaneously broken conformal
symmetry is demonstrated by the (2,0) theory on the Coulomb branch. In the
latter example, the dilaton is a dynamical field so 4-derivative terms in the
action also affect n-point amplitudes at order p^6. The calculation in the
(2,0) theory is done by analyzing an M5-brane probe in AdS_7 x S^4.
Given the confirmation in two distinct models, we attempt to use dispersion
relations to prove that the anomaly flow is positive in general. Unfortunately
the 4-point matrix element of the Euler anomaly is proportional to stu and
vanishes for forward scattering. Thus the optical theorem cannot be applied to
show positivity. Instead the anomaly flow is given by a dispersion sum rule in
which the integrand does not have definite sign. It may be possible to base a
proof of the a-theorem on the analyticity and unitarity properties of the
6-point function, but our preliminary study reveals some difficulties.Comment: 41 pages, 5 figure
Axion searches with the EDELWEISS-II experiment
We present new constraints on the couplings of axions and more generic
axion-like particles using data from the EDELWEISS-II experiment. The EDELWEISS
experiment, located at the Underground Laboratory of Modane, primarily aims at
the direct detection of WIMPs using germanium bolometers. It is also sensitive
to the low-energy electron recoils that would be induced by solar or dark
matter axions. Using a total exposure of up to 448 kg.d, we searched for
axion-induced electron recoils down to 2.5 keV within four scenarios involving
different hypotheses on the origin and couplings of axions. We set a 95% CL
limit on the coupling to photons GeV in
a mass range not fully covered by axion helioscopes. We also constrain the
coupling to electrons, , similar to the more
indirect solar neutrino bound. Finally we place a limit on , where is the
effective axion-nucleon coupling for Fe. Combining these results we
fully exclude the mass range keV for DFSZ axions and
keV for KSVZ axions
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