4,727 research outputs found
Viscosity of gauge theory plasma with a chemical potential from AdS/CFT correspondence
We compute the strong coupling limit of the shear viscosity for the N=4
super-Yang-Mill theory with a chemical potential. We use the five-dimensional
Reissner-Nordstrom-anti-deSitter black hole, so the chemical potential is the
one for the R-charges U(1)_R^3. We compute the quasinormal frequencies of the
gravitational and electromagnetic vector perturbations in the background
numerically. This enables one to explicitly locate the diffusion pole for the
shear viscosity. The ratio of the shear viscosity eta to the entropy density s
is eta/s=1/(4pi) within numerical errors, which is the same result as the one
without chemical potential.Comment: 11 pages, 5 figures, ReVTeX4; v2: minor improvements; v3:
explanations added and improved; v4: version to appear in PR
Radiation from an accelerated quark via AdS/CFT
In this paper we investigate radiation by an accelerated quark in a strongly
coupled gauge theory via AdS/CFT correspondence. According to AdS/CFT
dictionary, we can read off energy density or energy flux of the radiation from
asymptotic gravitational field in AdS bulk sourced by an accelerated string
trailing behind the quark. In the case of an oscillating quark with frequency
, we show that the time averaged energy density is asymptotically
isotropic and it falls off as with
distance from the source. In a toy model of a scattered quark by an
external field, we simply estimate Poynting vector by the bremsstrahlung
radiation and show that the energy flux is anisotropic outgoing radiation.
Based on these investigations, we discuss the properties of strongly coupled
gauge theory radiation in comparison with electromagnetic radiation.Comment: 16 pages, no figures, accepted for publication in Phys. Rev.
On two pieces of folklore in the AdS/CFT duality
In the AdS/CFT duality, it is often said that a local symmetry in a bulk
theory corresponds to a global symmetry in the corresponding boundary theory,
but the global symmetry can become local when one couples with an external
source. As a result, the GKP-Witten relation gives a response function instead
of a Green function. We explore this point in details using the example of
holographic superconductors. We point out that these points play a crucial role
to interpret the holographic London equation properly.Comment: 11 pages, ReVTeX4.1; v2: added discussio
Dynamic critical phenomena in the AdS/CFT duality
In critical phenomena, singular behaviors arise not only for thermodynamic
quantities but also for transport coefficients. We study this dynamic critical
phenomenon in the AdS/CFT duality. We consider black holes with a single
R-charge in various dimensions and compute the R-charge diffusion in the linear
perturbations. In this case, the black holes belong to model B according to the
classification of Hohenberg and Halperin.Comment: 17 pages, ReVTeX4; v2: added references and discussio
Strange filamentary structures ("fireballs") around a merger galaxy in the Coma cluster of galaxies
We found an unusual complex of narrow blue filaments, bright blue knots, and
H-alpha emitting filaments and clouds, which morphologically resembled a
complex of ``fireballs,'' extending up to 80 kpc south from an E+A galaxy RB199
in the Coma cluster. The galaxy has a highly disturbed morphology indicative of
a galaxy--galaxy merger remnant. The narrow blue filaments extend in straight
shapes toward the south from the galaxy, and several bright blue knots are
located at the southern ends of the filaments. The Rc band absolute magnitudes,
half light radii and estimated masses of the bright knots are -12 - -13 mag,
200 - 300 pc and 10^6-7 Msolar, respectively. Long, narrow H-alpha emitting
filaments are connected at the south edge of the knots. The average color of
the fireballs is B - Rc = 0.5, which is bluer than RB199 (B - R = 0.99),
suggesting that most of the stars in the fireballs were formed within several
times 10^8 yr. The narrow blue filaments exhibit almost no H-alpha emission.
Strong H-alpha and UV emission appear in the bright knots. These
characteristics indicate that star formation recently ceased in the blue
filaments and now continues in the bright knots. The gas stripped by some
mechanism from the disk of RB199 may be traveling in the intergalactic space,
forming stars left along its trajectory. The most plausible fireball formation
mechanism is ram pressure stripping by high-speed collision between the galaxy
and the hot intra-cluster medium. The fireballs may be a snapshot of diffuse
intra-cluster population formation, or halo star population formation in a
cluster galaxy.Comment: 13 pages, 14 figures, submitted to Ap
Screening length and the direction of plasma winds
We study the screening length of a heavy quark-antiquark pair in strongly
coupled gauge theory plasmas flowing at velocity v following a proposal by Liu,
Rajagopal, and Wiedemann. We analyze the screening length as the direction of
the plasma winds vary. To leading order in v, this angle-dependence can be
studied analytically for many theories by extending our previous formalism. We
show that the screening length is locally a minimum (maximum) when the pair is
perpendicular (parallel) to the plasma winds, which has been observed for the
N=4 plasma. Also, we compare AdS/CFT results with weak coupling ones, and we
discuss the subleading dependence on v for the Dp-brane.Comment: 20 pages, 4 figures, JHEP3; v2: discussion added and modifie
Carbon in Spiral Galaxies from Hubble Space Telescope Spectroscopy
We present measurements of the gas-phase C/O abundance ratio in six H II
regions in the spiral galaxies M101 and NGC 2403, based on ultraviolet
spectroscopy using the Faint Object Spectrograph on the Hubble Space Telescope.
The C/O ratios increase systematically with O/H in both galaxies, from log C/O
approximately -0.8 at log O/H = -4.0 to log C/O approx. -0.1 at log O/H = -3.4.
C/N shows no correlation with O/H. The rate of increase of C/O is somewhat
uncertain because of uncertainty as to the appropriate UV reddening law, and
uncertainty in the metallicity dependence on grain depletions. However, the
trend of increasing C/O with O/H is clear, confirming and extending the trend
in C/O indicated previously from observations of irregular galaxies. Our data
indicate that the radial gradients in C/H across spiral galaxies are steeper
than the gradients in O/H. Comparing the data to chemical evolution models for
spiral galaxies shows that models in which the massive star yields do not vary
with metallicity predict radial C/O gradients that are much flatter than the
observed gradients. The most likely hypothesis at present is that stellar winds
in massive stars have an important effect on the yields and thus on the
evolution of carbon and oxygen abundances. C/O and N/O abundance ratios in the
outer disks of spirals determined to date are very similar to those in dwarf
irregular galaxies. This implies that the outer disks of spirals have average
stellar population ages much younger than the inner disks.Comment: 38 pages, 9 postscript figures, uses aaspp4.sty. Accepted for
publication in The Astrophysical Journa
Indirect and direct energy gaps in the Kondo semiconductor YbB12
Optical conductivity [] of the Kondo semiconductor YbB
has been measured over wide ranges of temperature (=8690 K) and photon
energy ( 1.3 meV). The data reveal the
entire crossover of YbB from a metallic electronic structure at high
into a semiconducting one at low . Associated with the gap development in
, a clear onset is newly found at =15 meV for 20 K. The onset energy is identified as the gap width of YbB
appearing in . This gap in \sigma(\omega)\sigma(\omega)$ is interpreted as arising from the direct gap. The
absorption coefficient around the onset and the mIR peak indeed show
characteristic energy dependences expected for indirect and direct optical
transitions in conventional semiconductors.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp
Optical Conductivity and Electronic Structure of CeRu4Sb12 under High Pressure
Optical conductivity [s(w)] of Ce-filled skutterudite CeRu4Sb12 has been
measured at high pressure to 8 GPa and at low temperature, to probe the
pressure evolution of its electronic structures. At ambient pressure, a
mid-infrared peak at 0.1 eV was formed in s(w) at low temperature, and the
spectral weight below 0.1 eV was strongly suppressed, due to a hybridization of
the f electron and conduction electron states. With increasing external
pressure, the mid-infrared peak shifts to higher energy, and the spectral
weight below the peak was further depleted. The obtained spectral data are
analyzed in comparison with band calculation result and other reported physical
properties. It is shown that the electronic structure of CeRu4Sb12 becomes
similar to that of a narrow-gap semiconductor under external pressure.Comment: 8 pages, 9 figure
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