1,500 research outputs found
Exploiting pattern transformation to tune phononic band gaps in a two-dimensional granular crystal
The band structure of a two-dimensional granular crystal composed of silicone rubber and polytetrafluoroethylene (PTFE) cylinders is investigated numerically. This system was previously shown to undergo a pattern transformation with uniaxial compression by Göncü et al. [Soft Matter 7, 2321 (2011)]. The dispersion relations of the crystal are computed at different levels of deformation to demonstrate the tunability of the band structure, which is strongly affected by the pattern transformation that induces new band gaps. Replacement of PTFE particles with rubber ones reveals that the change of the band structure is essentially governed by pattern transformation rather than particles¿ mechanical properties
Extended Cold Molecular Gas Reservoirs in z~3.4 Submillimeter Galaxies
We report the detection of spatially resolved CO(1-0) emission in the z~3.4
submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the
Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two
previously reported millimeter sources H6 and H7, separated by ~30kpc in
projection. We derive CO(1-0) line luminosities of L'(CO 1-0) = (2.49+/-0.86)
and (5.82+/-1.22) x 10^10 K km/s pc^2 for H6 and H7, and L'(CO 1-0) =
(23.4+/-4.1) x 10^10 K km/s pc^2 for SMM J13120+4242. These are ~1.5-4.5x
higher than what is expected from simple excitation modeling of higher-J CO
lines, suggesting the presence of copious amounts of low-excitation gas. This
is supported by the finding that the CO(1-0) line in SMM J13120+4242, the
system with lowest CO excitation, appears to have a broader profile and more
extended spatial structure than seen in higher-J CO lines (which is less
prominently seen in SMM J09431+4700). Based on L'(CO 1-0) and excitation
modeling, we find M_gas = 2.0-4.3 and 4.7-12.7 x 10^10 Msun for H6 and H7, and
M_gas = 18.7-69.4 x 10^10 Msun for SMM J13120+4242. The observed CO(1-0)
properties are consistent with the picture that SMM J09431+4700 represents an
early-stage, gas-rich major merger, and that SMM J13120+4242 represents such a
system in an advanced stage. This study thus highlights the importance of
spatially and dynamically resolved CO(1-0) observations of SMGs to further
understand the gas physics that drive star formation in these distant galaxies,
which becomes possible only now that the EVLA rises to its full capabilities.Comment: 6 pages, 4 figures, to appear in ApJL (EVLA Special Issue; accepted
May 19, 2011
Determination of the Newtonian Gravitational Constant Using Atom Interferometry
We present a new measurement of the Newtonian gravitational constant G based
on cold atom interferometry. Freely falling samples of laser-cooled rubidium
atoms are used in a gravity gradiometer to probe the field generated by nearby
source masses. In addition to its potential sensitivity, this method is
intriguing as gravity is explored by a quantum system. We report a value of
G=6.667 10^{-11} m^{3} kg^{-1} s^{-2}, estimating a statistical uncertainty of
0.011 10^{-11} m^{3} kg^{-1} s^{-2} and a systematic uncertainty of
0.003 10^{-11} m^{3} kg^{-1} s^{-2}. The long-term stability of the instrument
and the signal-to-noise ratio demonstrated here open interesting perspectives
for pushing the measurement accuracy below the 100 ppm level.Comment: 4 figure
Observations of Dense Molecular Gas in a Quasar Host Galaxy at z=6.42: Further Evidence for a Non-Linear Dense Gas - Star Formation Relation at Early Cosmic Times
We report a sensitive search for the HCN(J=2-1) emission line towards SDSS
J1148+5251 at z=6.42 with the VLA. HCN emission is a star formation indicator,
tracing dense molecular hydrogen gas (n(H2) >= 10^4 cm^-3) within star-forming
molecular clouds. No emission was detected in the deep interferometer maps of
J1148+5251. We derive a limit for the HCN line luminosity of L'(HCN) < 3.3 x
10^9 K km/s pc^2, corresponding to a HCN/CO luminosity ratio of L'(HCN)/L'(CO)
< 0.13. This limit is consistent with a fraction of dense molecular gas in
J1148+5251 within the range of nearby ultraluminous infrared galaxies (ULIRGs;
median value: L'(HCN)/L'(CO) = 0.17 {+0.05/-0.08}) and HCN-detected z>2
galaxies (0.17 {+0.09/-0.08}). The relationship between L'(HCN) and L(FIR) is
considered to be a measure for the efficiency at which stars form out of dense
gas. In the nearby universe, these quantities show a linear correlation, and
thus, a practically constant average ratio. In J1148+5251, we find
L(FIR)/L'(HCN) > 6600. This is significantly higher than the average ratios for
normal nearby spiral galaxies (L(FIR)/L'(HCN) = 580 {+510/-270}) and ULIRGs
(740 {+505/-50}), but consistent with a rising trend as indicated by other z>2
galaxies (predominantly quasars; 1525 {+1300/-475}). It is unlikely that this
rising trend can be accounted for by a contribution of AGN heating to L(FIR)
alone, and may hint at a higher median gas density and/or elevated
star-formation efficiency toward the more luminous high-redshift systems. There
is marginal evidence that the L(FIR)/L'(HCN) ratio in J1148+5251 may even
exceed the rising trend set by other z>2 galaxies; however, only future
facilities with very large collecting areas such as the SKA will offer the
sensitivity required to further investigate this question.Comment: 5 pages, 2 figures, 2 tables, to appear in ApJL (accepted October 24,
2007
Double Scaling Limits in Gauge Theories and Matrix Models
We show that gauge theories with an adjoint chiral multiplet admit a
wide class of large-N double-scaling limits where is taken to infinity in a
way coordinated with a tuning of the bare superpotential. The tuning is such
that the theory is near an Argyres-Douglas-type singularity where a set of
non-local dibaryons becomes massless in conjunction with a set of confining
strings becoming tensionless. The doubly-scaled theory consists of two
decoupled sectors, one whose spectrum and interactions follow the usual large-N
scaling whilst the other has light states of fixed mass in the large-N limit
which subvert the usual large-N scaling and lead to an interacting theory in
the limit. -term properties of this interacting sector can be calculated
using a Dijkgraaf-Vafa matrix model and in this context the double-scaling
limit is precisely the kind investigated in the "old matrix model'' to describe
two-dimensional gravity coupled to conformal field theories. In
particular, the old matrix model double-scaling limit describes a sector of a
gauge theory with a mass gap and light meson-like composite states, the
approximate Goldstone boson of superconformal invariance, with a mass which is
fixed in the double-scaling limit. Consequently, the gravitational -terms in
these cases satisfy the string equation of the KdV hierarchy.Comment: 38 pages, 1 figure, reference adde
Large N gauge theories and topological cigars
We analyze the conjectured duality between a class of double-scaling limits
of a one-matrix model and the topological twist of non-critical superstring
backgrounds that contain the N=2 Kazama-Suzuki SL(2)/U(1) supercoset model. The
untwisted backgrounds are holographically dual to double-scaled Little String
Theories in four dimensions and to the large N double-scaling limit of certain
supersymmetric gauge theories. The matrix model in question is the auxiliary
Dijkgraaf-Vafa matrix model that encodes the F-terms of the above
supersymmetric gauge theories. We evaluate matrix model loop correlators with
the goal of extracting information on the spectrum of operators in the dual
non-critical bosonic string. The twisted coset at level one, the topological
cigar, is known to be equivalent to the c=1 non-critical string at self-dual
radius and to the topological theory on a deformed conifold. The spectrum and
wavefunctions of the operators that can be deduced from the matrix model
double-scaling limit are consistent with these expectations.Comment: 34 page
Holography and Unquenched Quark-Gluon Plasmas
We employ the string/gauge theory correspondence to study properties of
strongly coupled quark-gluon plasmas in thermal gauge theories with a large
number of colors and flavors. In particular, we analyze non-critical string
duals of conformal (S)QCD, as well as ten dimensional wrapped fivebrane duals
of SQCD-like theories. We study general properties of the dual plasmas,
including the drag force exerted on a probe quark and the jet quenching
parameter. We find that these plasma observables depend on the number of colors
and flavors in the ``QCD dual''; in particular, we find that the jet quenching
parameter increases linearly with N_f/N_c at leading order in the probe limit.
In the ten dimensional case we find a non trivial drag coefficient but a
vanishing jet quenching parameter. We comment on the relation of this result
with total screening and argue that the same features are shared by all known
plasmas dual to fivebranes in ten dimensions. We also construct new D5 black
hole solutions with spherical horizon and show that they exhibit the same
features.Comment: 30 pages. v2: Comments in section 2 and references updated, a typo
fixe
A Sensitive Search for [N II]205 μm Emission in a z = 6.4 Quasar Host Galaxy
We present a sensitive search for the 3P1 → 3P0 ground-state fine structure line at 205 μm of ionized nitrogen ([N II]205μm) in one of the highest-redshift quasars (J1148+5251 at z = 6.42) using the IRAM 30 m telescope. The line is not detected at a (3σ) depth of 0.47 Jy km s^−1, corresponding to a [N II]205μm luminosity limit of L[N II] 7) using the Atacama Large Millimeter/submillimeter Array, for which the highly excited rotational transitions of CO will be shifted outside the accessible (sub-)millimeter bands
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